Source file src/pkg/cmd/cgo/out.go

     1	// Copyright 2009 The Go Authors. All rights reserved.
     2	// Use of this source code is governed by a BSD-style
     3	// license that can be found in the LICENSE file.
     4	
     5	package main
     6	
     7	import (
     8		"bytes"
     9		"debug/elf"
    10		"debug/macho"
    11		"debug/pe"
    12		"fmt"
    13		"go/ast"
    14		"go/printer"
    15		"go/token"
    16		"internal/xcoff"
    17		"io"
    18		"io/ioutil"
    19		"os"
    20		"os/exec"
    21		"path/filepath"
    22		"regexp"
    23		"sort"
    24		"strings"
    25	)
    26	
    27	var (
    28		conf         = printer.Config{Mode: printer.SourcePos, Tabwidth: 8}
    29		noSourceConf = printer.Config{Tabwidth: 8}
    30	)
    31	
    32	// writeDefs creates output files to be compiled by gc and gcc.
    33	func (p *Package) writeDefs() {
    34		var fgo2, fc io.Writer
    35		f := creat(*objDir + "_cgo_gotypes.go")
    36		defer f.Close()
    37		fgo2 = f
    38		if *gccgo {
    39			f := creat(*objDir + "_cgo_defun.c")
    40			defer f.Close()
    41			fc = f
    42		}
    43		fm := creat(*objDir + "_cgo_main.c")
    44	
    45		var gccgoInit bytes.Buffer
    46	
    47		fflg := creat(*objDir + "_cgo_flags")
    48		for k, v := range p.CgoFlags {
    49			fmt.Fprintf(fflg, "_CGO_%s=%s\n", k, strings.Join(v, " "))
    50			if k == "LDFLAGS" && !*gccgo {
    51				for _, arg := range v {
    52					fmt.Fprintf(fgo2, "//go:cgo_ldflag %q\n", arg)
    53				}
    54			}
    55		}
    56		fflg.Close()
    57	
    58		// Write C main file for using gcc to resolve imports.
    59		fmt.Fprintf(fm, "int main() { return 0; }\n")
    60		if *importRuntimeCgo {
    61			fmt.Fprintf(fm, "void crosscall2(void(*fn)(void*, int, __SIZE_TYPE__), void *a, int c, __SIZE_TYPE__ ctxt) { }\n")
    62			fmt.Fprintf(fm, "__SIZE_TYPE__ _cgo_wait_runtime_init_done(void) { return 0; }\n")
    63			fmt.Fprintf(fm, "void _cgo_release_context(__SIZE_TYPE__ ctxt) { }\n")
    64			fmt.Fprintf(fm, "char* _cgo_topofstack(void) { return (char*)0; }\n")
    65		} else {
    66			// If we're not importing runtime/cgo, we *are* runtime/cgo,
    67			// which provides these functions. We just need a prototype.
    68			fmt.Fprintf(fm, "void crosscall2(void(*fn)(void*, int, __SIZE_TYPE__), void *a, int c, __SIZE_TYPE__ ctxt);\n")
    69			fmt.Fprintf(fm, "__SIZE_TYPE__ _cgo_wait_runtime_init_done(void);\n")
    70			fmt.Fprintf(fm, "void _cgo_release_context(__SIZE_TYPE__);\n")
    71		}
    72		fmt.Fprintf(fm, "void _cgo_allocate(void *a, int c) { }\n")
    73		fmt.Fprintf(fm, "void _cgo_panic(void *a, int c) { }\n")
    74		fmt.Fprintf(fm, "void _cgo_reginit(void) { }\n")
    75	
    76		// Write second Go output: definitions of _C_xxx.
    77		// In a separate file so that the import of "unsafe" does not
    78		// pollute the original file.
    79		fmt.Fprintf(fgo2, "// Code generated by cmd/cgo; DO NOT EDIT.\n\n")
    80		fmt.Fprintf(fgo2, "package %s\n\n", p.PackageName)
    81		fmt.Fprintf(fgo2, "import \"unsafe\"\n\n")
    82		if !*gccgo && *importRuntimeCgo {
    83			fmt.Fprintf(fgo2, "import _ \"runtime/cgo\"\n\n")
    84		}
    85		if *importSyscall {
    86			fmt.Fprintf(fgo2, "import \"syscall\"\n\n")
    87			fmt.Fprintf(fgo2, "var _ syscall.Errno\n")
    88		}
    89		fmt.Fprintf(fgo2, "func _Cgo_ptr(ptr unsafe.Pointer) unsafe.Pointer { return ptr }\n\n")
    90	
    91		if !*gccgo {
    92			fmt.Fprintf(fgo2, "//go:linkname _Cgo_always_false runtime.cgoAlwaysFalse\n")
    93			fmt.Fprintf(fgo2, "var _Cgo_always_false bool\n")
    94			fmt.Fprintf(fgo2, "//go:linkname _Cgo_use runtime.cgoUse\n")
    95			fmt.Fprintf(fgo2, "func _Cgo_use(interface{})\n")
    96		}
    97	
    98		typedefNames := make([]string, 0, len(typedef))
    99		for name := range typedef {
   100			typedefNames = append(typedefNames, name)
   101		}
   102		sort.Strings(typedefNames)
   103		for _, name := range typedefNames {
   104			def := typedef[name]
   105			fmt.Fprintf(fgo2, "type %s ", name)
   106			// We don't have source info for these types, so write them out without source info.
   107			// Otherwise types would look like:
   108			//
   109			// type _Ctype_struct_cb struct {
   110			// //line :1
   111			//        on_test *[0]byte
   112			// //line :1
   113			// }
   114			//
   115			// Which is not useful. Moreover we never override source info,
   116			// so subsequent source code uses the same source info.
   117			// Moreover, empty file name makes compile emit no source debug info at all.
   118			var buf bytes.Buffer
   119			noSourceConf.Fprint(&buf, fset, def.Go)
   120			if bytes.HasPrefix(buf.Bytes(), []byte("_Ctype_")) {
   121				// This typedef is of the form `typedef a b` and should be an alias.
   122				fmt.Fprintf(fgo2, "= ")
   123			}
   124			fmt.Fprintf(fgo2, "%s", buf.Bytes())
   125			fmt.Fprintf(fgo2, "\n\n")
   126		}
   127		if *gccgo {
   128			fmt.Fprintf(fgo2, "type _Ctype_void byte\n")
   129		} else {
   130			fmt.Fprintf(fgo2, "type _Ctype_void [0]byte\n")
   131		}
   132	
   133		if *gccgo {
   134			fmt.Fprint(fgo2, gccgoGoProlog)
   135			fmt.Fprint(fc, p.cPrologGccgo())
   136		} else {
   137			fmt.Fprint(fgo2, goProlog)
   138		}
   139	
   140		if fc != nil {
   141			fmt.Fprintf(fc, "#line 1 \"cgo-generated-wrappers\"\n")
   142		}
   143		if fm != nil {
   144			fmt.Fprintf(fm, "#line 1 \"cgo-generated-wrappers\"\n")
   145		}
   146	
   147		gccgoSymbolPrefix := p.gccgoSymbolPrefix()
   148	
   149		cVars := make(map[string]bool)
   150		for _, key := range nameKeys(p.Name) {
   151			n := p.Name[key]
   152			if !n.IsVar() {
   153				continue
   154			}
   155	
   156			if !cVars[n.C] {
   157				if *gccgo {
   158					fmt.Fprintf(fc, "extern byte *%s;\n", n.C)
   159				} else {
   160					fmt.Fprintf(fm, "extern char %s[];\n", n.C)
   161					fmt.Fprintf(fm, "void *_cgohack_%s = %s;\n\n", n.C, n.C)
   162					fmt.Fprintf(fgo2, "//go:linkname __cgo_%s %s\n", n.C, n.C)
   163					fmt.Fprintf(fgo2, "//go:cgo_import_static %s\n", n.C)
   164					fmt.Fprintf(fgo2, "var __cgo_%s byte\n", n.C)
   165				}
   166				cVars[n.C] = true
   167			}
   168	
   169			var node ast.Node
   170			if n.Kind == "var" {
   171				node = &ast.StarExpr{X: n.Type.Go}
   172			} else if n.Kind == "fpvar" {
   173				node = n.Type.Go
   174			} else {
   175				panic(fmt.Errorf("invalid var kind %q", n.Kind))
   176			}
   177			if *gccgo {
   178				fmt.Fprintf(fc, `extern void *%s __asm__("%s.%s");`, n.Mangle, gccgoSymbolPrefix, n.Mangle)
   179				fmt.Fprintf(&gccgoInit, "\t%s = &%s;\n", n.Mangle, n.C)
   180				fmt.Fprintf(fc, "\n")
   181			}
   182	
   183			fmt.Fprintf(fgo2, "var %s ", n.Mangle)
   184			conf.Fprint(fgo2, fset, node)
   185			if !*gccgo {
   186				fmt.Fprintf(fgo2, " = (")
   187				conf.Fprint(fgo2, fset, node)
   188				fmt.Fprintf(fgo2, ")(unsafe.Pointer(&__cgo_%s))", n.C)
   189			}
   190			fmt.Fprintf(fgo2, "\n")
   191		}
   192		if *gccgo {
   193			fmt.Fprintf(fc, "\n")
   194		}
   195	
   196		for _, key := range nameKeys(p.Name) {
   197			n := p.Name[key]
   198			if n.Const != "" {
   199				fmt.Fprintf(fgo2, "const %s = %s\n", n.Mangle, n.Const)
   200			}
   201		}
   202		fmt.Fprintf(fgo2, "\n")
   203	
   204		callsMalloc := false
   205		for _, key := range nameKeys(p.Name) {
   206			n := p.Name[key]
   207			if n.FuncType != nil {
   208				p.writeDefsFunc(fgo2, n, &callsMalloc)
   209			}
   210		}
   211	
   212		fgcc := creat(*objDir + "_cgo_export.c")
   213		fgcch := creat(*objDir + "_cgo_export.h")
   214		if *gccgo {
   215			p.writeGccgoExports(fgo2, fm, fgcc, fgcch)
   216		} else {
   217			p.writeExports(fgo2, fm, fgcc, fgcch)
   218		}
   219	
   220		if callsMalloc && !*gccgo {
   221			fmt.Fprint(fgo2, strings.Replace(cMallocDefGo, "PREFIX", cPrefix, -1))
   222			fmt.Fprint(fgcc, strings.Replace(strings.Replace(cMallocDefC, "PREFIX", cPrefix, -1), "PACKED", p.packedAttribute(), -1))
   223		}
   224	
   225		if err := fgcc.Close(); err != nil {
   226			fatalf("%s", err)
   227		}
   228		if err := fgcch.Close(); err != nil {
   229			fatalf("%s", err)
   230		}
   231	
   232		if *exportHeader != "" && len(p.ExpFunc) > 0 {
   233			fexp := creat(*exportHeader)
   234			fgcch, err := os.Open(*objDir + "_cgo_export.h")
   235			if err != nil {
   236				fatalf("%s", err)
   237			}
   238			_, err = io.Copy(fexp, fgcch)
   239			if err != nil {
   240				fatalf("%s", err)
   241			}
   242			if err = fexp.Close(); err != nil {
   243				fatalf("%s", err)
   244			}
   245		}
   246	
   247		init := gccgoInit.String()
   248		if init != "" {
   249			// The init function does nothing but simple
   250			// assignments, so it won't use much stack space, so
   251			// it's OK to not split the stack. Splitting the stack
   252			// can run into a bug in clang (as of 2018-11-09):
   253			// this is a leaf function, and when clang sees a leaf
   254			// function it won't emit the split stack prologue for
   255			// the function. However, if this function refers to a
   256			// non-split-stack function, which will happen if the
   257			// cgo code refers to a C function not compiled with
   258			// -fsplit-stack, then the linker will think that it
   259			// needs to adjust the split stack prologue, but there
   260			// won't be one. Marking the function explicitly
   261			// no_split_stack works around this problem by telling
   262			// the linker that it's OK if there is no split stack
   263			// prologue.
   264			fmt.Fprintln(fc, "static void init(void) __attribute__ ((constructor, no_split_stack));")
   265			fmt.Fprintln(fc, "static void init(void) {")
   266			fmt.Fprint(fc, init)
   267			fmt.Fprintln(fc, "}")
   268		}
   269	}
   270	
   271	// elfImportedSymbols is like elf.File.ImportedSymbols, but it
   272	// includes weak symbols.
   273	//
   274	// A bug in some versions of LLD (at least LLD 8) cause it to emit
   275	// several pthreads symbols as weak, but we need to import those. See
   276	// issue #31912 or https://bugs.llvm.org/show_bug.cgi?id=42442.
   277	//
   278	// When doing external linking, we hand everything off to the external
   279	// linker, which will create its own dynamic symbol tables. For
   280	// internal linking, this may turn weak imports into strong imports,
   281	// which could cause dynamic linking to fail if a symbol really isn't
   282	// defined. However, the standard library depends on everything it
   283	// imports, and this is the primary use of dynamic symbol tables with
   284	// internal linking.
   285	func elfImportedSymbols(f *elf.File) []elf.ImportedSymbol {
   286		syms, _ := f.DynamicSymbols()
   287		var imports []elf.ImportedSymbol
   288		for _, s := range syms {
   289			if (elf.ST_BIND(s.Info) == elf.STB_GLOBAL || elf.ST_BIND(s.Info) == elf.STB_WEAK) && s.Section == elf.SHN_UNDEF {
   290				imports = append(imports, elf.ImportedSymbol{
   291					Name:    s.Name,
   292					Library: s.Library,
   293					Version: s.Version,
   294				})
   295			}
   296		}
   297		return imports
   298	}
   299	
   300	func dynimport(obj string) {
   301		stdout := os.Stdout
   302		if *dynout != "" {
   303			f, err := os.Create(*dynout)
   304			if err != nil {
   305				fatalf("%s", err)
   306			}
   307			stdout = f
   308		}
   309	
   310		fmt.Fprintf(stdout, "package %s\n", *dynpackage)
   311	
   312		if f, err := elf.Open(obj); err == nil {
   313			if *dynlinker {
   314				// Emit the cgo_dynamic_linker line.
   315				if sec := f.Section(".interp"); sec != nil {
   316					if data, err := sec.Data(); err == nil && len(data) > 1 {
   317						// skip trailing \0 in data
   318						fmt.Fprintf(stdout, "//go:cgo_dynamic_linker %q\n", string(data[:len(data)-1]))
   319					}
   320				}
   321			}
   322			sym := elfImportedSymbols(f)
   323			for _, s := range sym {
   324				targ := s.Name
   325				if s.Version != "" {
   326					targ += "#" + s.Version
   327				}
   328				fmt.Fprintf(stdout, "//go:cgo_import_dynamic %s %s %q\n", s.Name, targ, s.Library)
   329			}
   330			lib, _ := f.ImportedLibraries()
   331			for _, l := range lib {
   332				fmt.Fprintf(stdout, "//go:cgo_import_dynamic _ _ %q\n", l)
   333			}
   334			return
   335		}
   336	
   337		if f, err := macho.Open(obj); err == nil {
   338			sym, _ := f.ImportedSymbols()
   339			for _, s := range sym {
   340				if len(s) > 0 && s[0] == '_' {
   341					s = s[1:]
   342				}
   343				fmt.Fprintf(stdout, "//go:cgo_import_dynamic %s %s %q\n", s, s, "")
   344			}
   345			lib, _ := f.ImportedLibraries()
   346			for _, l := range lib {
   347				fmt.Fprintf(stdout, "//go:cgo_import_dynamic _ _ %q\n", l)
   348			}
   349			return
   350		}
   351	
   352		if f, err := pe.Open(obj); err == nil {
   353			sym, _ := f.ImportedSymbols()
   354			for _, s := range sym {
   355				ss := strings.Split(s, ":")
   356				name := strings.Split(ss[0], "@")[0]
   357				fmt.Fprintf(stdout, "//go:cgo_import_dynamic %s %s %q\n", name, ss[0], strings.ToLower(ss[1]))
   358			}
   359			return
   360		}
   361	
   362		if f, err := xcoff.Open(obj); err == nil {
   363			sym, err := f.ImportedSymbols()
   364			if err != nil {
   365				fatalf("cannot load imported symbols from XCOFF file %s: %v", obj, err)
   366			}
   367			for _, s := range sym {
   368				if s.Name == "runtime_rt0_go" || s.Name == "_rt0_ppc64_aix_lib" {
   369					// These symbols are imported by runtime/cgo but
   370					// must not be added to _cgo_import.go as there are
   371					// Go symbols.
   372					continue
   373				}
   374				fmt.Fprintf(stdout, "//go:cgo_import_dynamic %s %s %q\n", s.Name, s.Name, s.Library)
   375			}
   376			lib, err := f.ImportedLibraries()
   377			if err != nil {
   378				fatalf("cannot load imported libraries from XCOFF file %s: %v", obj, err)
   379			}
   380			for _, l := range lib {
   381				fmt.Fprintf(stdout, "//go:cgo_import_dynamic _ _ %q\n", l)
   382			}
   383			return
   384		}
   385	
   386		fatalf("cannot parse %s as ELF, Mach-O, PE or XCOFF", obj)
   387	}
   388	
   389	// Construct a gcc struct matching the gc argument frame.
   390	// Assumes that in gcc, char is 1 byte, short 2 bytes, int 4 bytes, long long 8 bytes.
   391	// These assumptions are checked by the gccProlog.
   392	// Also assumes that gc convention is to word-align the
   393	// input and output parameters.
   394	func (p *Package) structType(n *Name) (string, int64) {
   395		var buf bytes.Buffer
   396		fmt.Fprint(&buf, "struct {\n")
   397		off := int64(0)
   398		for i, t := range n.FuncType.Params {
   399			if off%t.Align != 0 {
   400				pad := t.Align - off%t.Align
   401				fmt.Fprintf(&buf, "\t\tchar __pad%d[%d];\n", off, pad)
   402				off += pad
   403			}
   404			c := t.Typedef
   405			if c == "" {
   406				c = t.C.String()
   407			}
   408			fmt.Fprintf(&buf, "\t\t%s p%d;\n", c, i)
   409			off += t.Size
   410		}
   411		if off%p.PtrSize != 0 {
   412			pad := p.PtrSize - off%p.PtrSize
   413			fmt.Fprintf(&buf, "\t\tchar __pad%d[%d];\n", off, pad)
   414			off += pad
   415		}
   416		if t := n.FuncType.Result; t != nil {
   417			if off%t.Align != 0 {
   418				pad := t.Align - off%t.Align
   419				fmt.Fprintf(&buf, "\t\tchar __pad%d[%d];\n", off, pad)
   420				off += pad
   421			}
   422			fmt.Fprintf(&buf, "\t\t%s r;\n", t.C)
   423			off += t.Size
   424		}
   425		if off%p.PtrSize != 0 {
   426			pad := p.PtrSize - off%p.PtrSize
   427			fmt.Fprintf(&buf, "\t\tchar __pad%d[%d];\n", off, pad)
   428			off += pad
   429		}
   430		if off == 0 {
   431			fmt.Fprintf(&buf, "\t\tchar unused;\n") // avoid empty struct
   432		}
   433		fmt.Fprintf(&buf, "\t}")
   434		return buf.String(), off
   435	}
   436	
   437	func (p *Package) writeDefsFunc(fgo2 io.Writer, n *Name, callsMalloc *bool) {
   438		name := n.Go
   439		gtype := n.FuncType.Go
   440		void := gtype.Results == nil || len(gtype.Results.List) == 0
   441		if n.AddError {
   442			// Add "error" to return type list.
   443			// Type list is known to be 0 or 1 element - it's a C function.
   444			err := &ast.Field{Type: ast.NewIdent("error")}
   445			l := gtype.Results.List
   446			if len(l) == 0 {
   447				l = []*ast.Field{err}
   448			} else {
   449				l = []*ast.Field{l[0], err}
   450			}
   451			t := new(ast.FuncType)
   452			*t = *gtype
   453			t.Results = &ast.FieldList{List: l}
   454			gtype = t
   455		}
   456	
   457		// Go func declaration.
   458		d := &ast.FuncDecl{
   459			Name: ast.NewIdent(n.Mangle),
   460			Type: gtype,
   461		}
   462	
   463		// Builtins defined in the C prolog.
   464		inProlog := builtinDefs[name] != ""
   465		cname := fmt.Sprintf("_cgo%s%s", cPrefix, n.Mangle)
   466		paramnames := []string(nil)
   467		if d.Type.Params != nil {
   468			for i, param := range d.Type.Params.List {
   469				paramName := fmt.Sprintf("p%d", i)
   470				param.Names = []*ast.Ident{ast.NewIdent(paramName)}
   471				paramnames = append(paramnames, paramName)
   472			}
   473		}
   474	
   475		if *gccgo {
   476			// Gccgo style hooks.
   477			fmt.Fprint(fgo2, "\n")
   478			conf.Fprint(fgo2, fset, d)
   479			fmt.Fprint(fgo2, " {\n")
   480			if !inProlog {
   481				fmt.Fprint(fgo2, "\tdefer syscall.CgocallDone()\n")
   482				fmt.Fprint(fgo2, "\tsyscall.Cgocall()\n")
   483			}
   484			if n.AddError {
   485				fmt.Fprint(fgo2, "\tsyscall.SetErrno(0)\n")
   486			}
   487			fmt.Fprint(fgo2, "\t")
   488			if !void {
   489				fmt.Fprint(fgo2, "r := ")
   490			}
   491			fmt.Fprintf(fgo2, "%s(%s)\n", cname, strings.Join(paramnames, ", "))
   492	
   493			if n.AddError {
   494				fmt.Fprint(fgo2, "\te := syscall.GetErrno()\n")
   495				fmt.Fprint(fgo2, "\tif e != 0 {\n")
   496				fmt.Fprint(fgo2, "\t\treturn ")
   497				if !void {
   498					fmt.Fprint(fgo2, "r, ")
   499				}
   500				fmt.Fprint(fgo2, "e\n")
   501				fmt.Fprint(fgo2, "\t}\n")
   502				fmt.Fprint(fgo2, "\treturn ")
   503				if !void {
   504					fmt.Fprint(fgo2, "r, ")
   505				}
   506				fmt.Fprint(fgo2, "nil\n")
   507			} else if !void {
   508				fmt.Fprint(fgo2, "\treturn r\n")
   509			}
   510	
   511			fmt.Fprint(fgo2, "}\n")
   512	
   513			// declare the C function.
   514			fmt.Fprintf(fgo2, "//extern %s\n", cname)
   515			d.Name = ast.NewIdent(cname)
   516			if n.AddError {
   517				l := d.Type.Results.List
   518				d.Type.Results.List = l[:len(l)-1]
   519			}
   520			conf.Fprint(fgo2, fset, d)
   521			fmt.Fprint(fgo2, "\n")
   522	
   523			return
   524		}
   525	
   526		if inProlog {
   527			fmt.Fprint(fgo2, builtinDefs[name])
   528			if strings.Contains(builtinDefs[name], "_cgo_cmalloc") {
   529				*callsMalloc = true
   530			}
   531			return
   532		}
   533	
   534		// Wrapper calls into gcc, passing a pointer to the argument frame.
   535		fmt.Fprintf(fgo2, "//go:cgo_import_static %s\n", cname)
   536		fmt.Fprintf(fgo2, "//go:linkname __cgofn_%s %s\n", cname, cname)
   537		fmt.Fprintf(fgo2, "var __cgofn_%s byte\n", cname)
   538		fmt.Fprintf(fgo2, "var %s = unsafe.Pointer(&__cgofn_%s)\n", cname, cname)
   539	
   540		nret := 0
   541		if !void {
   542			d.Type.Results.List[0].Names = []*ast.Ident{ast.NewIdent("r1")}
   543			nret = 1
   544		}
   545		if n.AddError {
   546			d.Type.Results.List[nret].Names = []*ast.Ident{ast.NewIdent("r2")}
   547		}
   548	
   549		fmt.Fprint(fgo2, "\n")
   550		fmt.Fprint(fgo2, "//go:cgo_unsafe_args\n")
   551		conf.Fprint(fgo2, fset, d)
   552		fmt.Fprint(fgo2, " {\n")
   553	
   554		// NOTE: Using uintptr to hide from escape analysis.
   555		arg := "0"
   556		if len(paramnames) > 0 {
   557			arg = "uintptr(unsafe.Pointer(&p0))"
   558		} else if !void {
   559			arg = "uintptr(unsafe.Pointer(&r1))"
   560		}
   561	
   562		prefix := ""
   563		if n.AddError {
   564			prefix = "errno := "
   565		}
   566		fmt.Fprintf(fgo2, "\t%s_cgo_runtime_cgocall(%s, %s)\n", prefix, cname, arg)
   567		if n.AddError {
   568			fmt.Fprintf(fgo2, "\tif errno != 0 { r2 = syscall.Errno(errno) }\n")
   569		}
   570		fmt.Fprintf(fgo2, "\tif _Cgo_always_false {\n")
   571		if d.Type.Params != nil {
   572			for i := range d.Type.Params.List {
   573				fmt.Fprintf(fgo2, "\t\t_Cgo_use(p%d)\n", i)
   574			}
   575		}
   576		fmt.Fprintf(fgo2, "\t}\n")
   577		fmt.Fprintf(fgo2, "\treturn\n")
   578		fmt.Fprintf(fgo2, "}\n")
   579	}
   580	
   581	// writeOutput creates stubs for a specific source file to be compiled by gc
   582	func (p *Package) writeOutput(f *File, srcfile string) {
   583		base := srcfile
   584		if strings.HasSuffix(base, ".go") {
   585			base = base[0 : len(base)-3]
   586		}
   587		base = filepath.Base(base)
   588		fgo1 := creat(*objDir + base + ".cgo1.go")
   589		fgcc := creat(*objDir + base + ".cgo2.c")
   590	
   591		p.GoFiles = append(p.GoFiles, base+".cgo1.go")
   592		p.GccFiles = append(p.GccFiles, base+".cgo2.c")
   593	
   594		// Write Go output: Go input with rewrites of C.xxx to _C_xxx.
   595		fmt.Fprintf(fgo1, "// Code generated by cmd/cgo; DO NOT EDIT.\n\n")
   596		fmt.Fprintf(fgo1, "//line %s:1:1\n", srcfile)
   597		fgo1.Write(f.Edit.Bytes())
   598	
   599		// While we process the vars and funcs, also write gcc output.
   600		// Gcc output starts with the preamble.
   601		fmt.Fprintf(fgcc, "%s\n", builtinProlog)
   602		fmt.Fprintf(fgcc, "%s\n", f.Preamble)
   603		fmt.Fprintf(fgcc, "%s\n", gccProlog)
   604		fmt.Fprintf(fgcc, "%s\n", tsanProlog)
   605		fmt.Fprintf(fgcc, "%s\n", msanProlog)
   606	
   607		for _, key := range nameKeys(f.Name) {
   608			n := f.Name[key]
   609			if n.FuncType != nil {
   610				p.writeOutputFunc(fgcc, n)
   611			}
   612		}
   613	
   614		fgo1.Close()
   615		fgcc.Close()
   616	}
   617	
   618	// fixGo converts the internal Name.Go field into the name we should show
   619	// to users in error messages. There's only one for now: on input we rewrite
   620	// C.malloc into C._CMalloc, so change it back here.
   621	func fixGo(name string) string {
   622		if name == "_CMalloc" {
   623			return "malloc"
   624		}
   625		return name
   626	}
   627	
   628	var isBuiltin = map[string]bool{
   629		"_Cfunc_CString":   true,
   630		"_Cfunc_CBytes":    true,
   631		"_Cfunc_GoString":  true,
   632		"_Cfunc_GoStringN": true,
   633		"_Cfunc_GoBytes":   true,
   634		"_Cfunc__CMalloc":  true,
   635	}
   636	
   637	func (p *Package) writeOutputFunc(fgcc *os.File, n *Name) {
   638		name := n.Mangle
   639		if isBuiltin[name] || p.Written[name] {
   640			// The builtins are already defined in the C prolog, and we don't
   641			// want to duplicate function definitions we've already done.
   642			return
   643		}
   644		p.Written[name] = true
   645	
   646		if *gccgo {
   647			p.writeGccgoOutputFunc(fgcc, n)
   648			return
   649		}
   650	
   651		ctype, _ := p.structType(n)
   652	
   653		// Gcc wrapper unpacks the C argument struct
   654		// and calls the actual C function.
   655		fmt.Fprintf(fgcc, "CGO_NO_SANITIZE_THREAD\n")
   656		if n.AddError {
   657			fmt.Fprintf(fgcc, "int\n")
   658		} else {
   659			fmt.Fprintf(fgcc, "void\n")
   660		}
   661		fmt.Fprintf(fgcc, "_cgo%s%s(void *v)\n", cPrefix, n.Mangle)
   662		fmt.Fprintf(fgcc, "{\n")
   663		if n.AddError {
   664			fmt.Fprintf(fgcc, "\tint _cgo_errno;\n")
   665		}
   666		// We're trying to write a gcc struct that matches gc's layout.
   667		// Use packed attribute to force no padding in this struct in case
   668		// gcc has different packing requirements.
   669		fmt.Fprintf(fgcc, "\t%s %v *_cgo_a = v;\n", ctype, p.packedAttribute())
   670		if n.FuncType.Result != nil {
   671			// Save the stack top for use below.
   672			fmt.Fprintf(fgcc, "\tchar *_cgo_stktop = _cgo_topofstack();\n")
   673		}
   674		tr := n.FuncType.Result
   675		if tr != nil {
   676			fmt.Fprintf(fgcc, "\t__typeof__(_cgo_a->r) _cgo_r;\n")
   677		}
   678		fmt.Fprintf(fgcc, "\t_cgo_tsan_acquire();\n")
   679		if n.AddError {
   680			fmt.Fprintf(fgcc, "\terrno = 0;\n")
   681		}
   682		fmt.Fprintf(fgcc, "\t")
   683		if tr != nil {
   684			fmt.Fprintf(fgcc, "_cgo_r = ")
   685			if c := tr.C.String(); c[len(c)-1] == '*' {
   686				fmt.Fprint(fgcc, "(__typeof__(_cgo_a->r)) ")
   687			}
   688		}
   689		if n.Kind == "macro" {
   690			fmt.Fprintf(fgcc, "%s;\n", n.C)
   691		} else {
   692			fmt.Fprintf(fgcc, "%s(", n.C)
   693			for i := range n.FuncType.Params {
   694				if i > 0 {
   695					fmt.Fprintf(fgcc, ", ")
   696				}
   697				fmt.Fprintf(fgcc, "_cgo_a->p%d", i)
   698			}
   699			fmt.Fprintf(fgcc, ");\n")
   700		}
   701		if n.AddError {
   702			fmt.Fprintf(fgcc, "\t_cgo_errno = errno;\n")
   703		}
   704		fmt.Fprintf(fgcc, "\t_cgo_tsan_release();\n")
   705		if n.FuncType.Result != nil {
   706			// The cgo call may have caused a stack copy (via a callback).
   707			// Adjust the return value pointer appropriately.
   708			fmt.Fprintf(fgcc, "\t_cgo_a = (void*)((char*)_cgo_a + (_cgo_topofstack() - _cgo_stktop));\n")
   709			// Save the return value.
   710			fmt.Fprintf(fgcc, "\t_cgo_a->r = _cgo_r;\n")
   711			// The return value is on the Go stack. If we are using msan,
   712			// and if the C value is partially or completely uninitialized,
   713			// the assignment will mark the Go stack as uninitialized.
   714			// The Go compiler does not update msan for changes to the
   715			// stack. It is possible that the stack will remain
   716			// uninitialized, and then later be used in a way that is
   717			// visible to msan, possibly leading to a false positive.
   718			// Mark the stack space as written, to avoid this problem.
   719			// See issue 26209.
   720			fmt.Fprintf(fgcc, "\t_cgo_msan_write(&_cgo_a->r, sizeof(_cgo_a->r));\n")
   721		}
   722		if n.AddError {
   723			fmt.Fprintf(fgcc, "\treturn _cgo_errno;\n")
   724		}
   725		fmt.Fprintf(fgcc, "}\n")
   726		fmt.Fprintf(fgcc, "\n")
   727	}
   728	
   729	// Write out a wrapper for a function when using gccgo. This is a
   730	// simple wrapper that just calls the real function. We only need a
   731	// wrapper to support static functions in the prologue--without a
   732	// wrapper, we can't refer to the function, since the reference is in
   733	// a different file.
   734	func (p *Package) writeGccgoOutputFunc(fgcc *os.File, n *Name) {
   735		fmt.Fprintf(fgcc, "CGO_NO_SANITIZE_THREAD\n")
   736		if t := n.FuncType.Result; t != nil {
   737			fmt.Fprintf(fgcc, "%s\n", t.C.String())
   738		} else {
   739			fmt.Fprintf(fgcc, "void\n")
   740		}
   741		fmt.Fprintf(fgcc, "_cgo%s%s(", cPrefix, n.Mangle)
   742		for i, t := range n.FuncType.Params {
   743			if i > 0 {
   744				fmt.Fprintf(fgcc, ", ")
   745			}
   746			c := t.Typedef
   747			if c == "" {
   748				c = t.C.String()
   749			}
   750			fmt.Fprintf(fgcc, "%s p%d", c, i)
   751		}
   752		fmt.Fprintf(fgcc, ")\n")
   753		fmt.Fprintf(fgcc, "{\n")
   754		if t := n.FuncType.Result; t != nil {
   755			fmt.Fprintf(fgcc, "\t%s _cgo_r;\n", t.C.String())
   756		}
   757		fmt.Fprintf(fgcc, "\t_cgo_tsan_acquire();\n")
   758		fmt.Fprintf(fgcc, "\t")
   759		if t := n.FuncType.Result; t != nil {
   760			fmt.Fprintf(fgcc, "_cgo_r = ")
   761			// Cast to void* to avoid warnings due to omitted qualifiers.
   762			if c := t.C.String(); c[len(c)-1] == '*' {
   763				fmt.Fprintf(fgcc, "(void*)")
   764			}
   765		}
   766		if n.Kind == "macro" {
   767			fmt.Fprintf(fgcc, "%s;\n", n.C)
   768		} else {
   769			fmt.Fprintf(fgcc, "%s(", n.C)
   770			for i := range n.FuncType.Params {
   771				if i > 0 {
   772					fmt.Fprintf(fgcc, ", ")
   773				}
   774				fmt.Fprintf(fgcc, "p%d", i)
   775			}
   776			fmt.Fprintf(fgcc, ");\n")
   777		}
   778		fmt.Fprintf(fgcc, "\t_cgo_tsan_release();\n")
   779		if t := n.FuncType.Result; t != nil {
   780			fmt.Fprintf(fgcc, "\treturn ")
   781			// Cast to void* to avoid warnings due to omitted qualifiers
   782			// and explicit incompatible struct types.
   783			if c := t.C.String(); c[len(c)-1] == '*' {
   784				fmt.Fprintf(fgcc, "(void*)")
   785			}
   786			fmt.Fprintf(fgcc, "_cgo_r;\n")
   787		}
   788		fmt.Fprintf(fgcc, "}\n")
   789		fmt.Fprintf(fgcc, "\n")
   790	}
   791	
   792	// packedAttribute returns host compiler struct attribute that will be
   793	// used to match gc's struct layout. For example, on 386 Windows,
   794	// gcc wants to 8-align int64s, but gc does not.
   795	// Use __gcc_struct__ to work around https://gcc.gnu.org/PR52991 on x86,
   796	// and https://golang.org/issue/5603.
   797	func (p *Package) packedAttribute() string {
   798		s := "__attribute__((__packed__"
   799		if !p.GccIsClang && (goarch == "amd64" || goarch == "386") {
   800			s += ", __gcc_struct__"
   801		}
   802		return s + "))"
   803	}
   804	
   805	// Write out the various stubs we need to support functions exported
   806	// from Go so that they are callable from C.
   807	func (p *Package) writeExports(fgo2, fm, fgcc, fgcch io.Writer) {
   808		p.writeExportHeader(fgcch)
   809	
   810		fmt.Fprintf(fgcc, "/* Code generated by cmd/cgo; DO NOT EDIT. */\n\n")
   811		fmt.Fprintf(fgcc, "#include <stdlib.h>\n")
   812		fmt.Fprintf(fgcc, "#include \"_cgo_export.h\"\n\n")
   813	
   814		// We use packed structs, but they are always aligned.
   815		// The pragmas and address-of-packed-member are only recognized as
   816		// warning groups in clang 4.0+, so ignore unknown pragmas first.
   817		fmt.Fprintf(fgcc, "#pragma GCC diagnostic ignored \"-Wunknown-pragmas\"\n")
   818		fmt.Fprintf(fgcc, "#pragma GCC diagnostic ignored \"-Wpragmas\"\n")
   819		fmt.Fprintf(fgcc, "#pragma GCC diagnostic ignored \"-Waddress-of-packed-member\"\n")
   820	
   821		fmt.Fprintf(fgcc, "extern void crosscall2(void (*fn)(void *, int, __SIZE_TYPE__), void *, int, __SIZE_TYPE__);\n")
   822		fmt.Fprintf(fgcc, "extern __SIZE_TYPE__ _cgo_wait_runtime_init_done(void);\n")
   823		fmt.Fprintf(fgcc, "extern void _cgo_release_context(__SIZE_TYPE__);\n\n")
   824		fmt.Fprintf(fgcc, "extern char* _cgo_topofstack(void);")
   825		fmt.Fprintf(fgcc, "%s\n", tsanProlog)
   826		fmt.Fprintf(fgcc, "%s\n", msanProlog)
   827	
   828		for _, exp := range p.ExpFunc {
   829			fn := exp.Func
   830	
   831			// Construct a gcc struct matching the gc argument and
   832			// result frame. The gcc struct will be compiled with
   833			// __attribute__((packed)) so all padding must be accounted
   834			// for explicitly.
   835			ctype := "struct {\n"
   836			off := int64(0)
   837			npad := 0
   838			if fn.Recv != nil {
   839				t := p.cgoType(fn.Recv.List[0].Type)
   840				ctype += fmt.Sprintf("\t\t%s recv;\n", t.C)
   841				off += t.Size
   842			}
   843			fntype := fn.Type
   844			forFieldList(fntype.Params,
   845				func(i int, aname string, atype ast.Expr) {
   846					t := p.cgoType(atype)
   847					if off%t.Align != 0 {
   848						pad := t.Align - off%t.Align
   849						ctype += fmt.Sprintf("\t\tchar __pad%d[%d];\n", npad, pad)
   850						off += pad
   851						npad++
   852					}
   853					ctype += fmt.Sprintf("\t\t%s p%d;\n", t.C, i)
   854					off += t.Size
   855				})
   856			if off%p.PtrSize != 0 {
   857				pad := p.PtrSize - off%p.PtrSize
   858				ctype += fmt.Sprintf("\t\tchar __pad%d[%d];\n", npad, pad)
   859				off += pad
   860				npad++
   861			}
   862			forFieldList(fntype.Results,
   863				func(i int, aname string, atype ast.Expr) {
   864					t := p.cgoType(atype)
   865					if off%t.Align != 0 {
   866						pad := t.Align - off%t.Align
   867						ctype += fmt.Sprintf("\t\tchar __pad%d[%d];\n", npad, pad)
   868						off += pad
   869						npad++
   870					}
   871					ctype += fmt.Sprintf("\t\t%s r%d;\n", t.C, i)
   872					off += t.Size
   873				})
   874			if off%p.PtrSize != 0 {
   875				pad := p.PtrSize - off%p.PtrSize
   876				ctype += fmt.Sprintf("\t\tchar __pad%d[%d];\n", npad, pad)
   877				off += pad
   878				npad++
   879			}
   880			if ctype == "struct {\n" {
   881				ctype += "\t\tchar unused;\n" // avoid empty struct
   882			}
   883			ctype += "\t}"
   884	
   885			// Get the return type of the wrapper function
   886			// compiled by gcc.
   887			gccResult := ""
   888			if fntype.Results == nil || len(fntype.Results.List) == 0 {
   889				gccResult = "void"
   890			} else if len(fntype.Results.List) == 1 && len(fntype.Results.List[0].Names) <= 1 {
   891				gccResult = p.cgoType(fntype.Results.List[0].Type).C.String()
   892			} else {
   893				fmt.Fprintf(fgcch, "\n/* Return type for %s */\n", exp.ExpName)
   894				fmt.Fprintf(fgcch, "struct %s_return {\n", exp.ExpName)
   895				forFieldList(fntype.Results,
   896					func(i int, aname string, atype ast.Expr) {
   897						fmt.Fprintf(fgcch, "\t%s r%d;", p.cgoType(atype).C, i)
   898						if len(aname) > 0 {
   899							fmt.Fprintf(fgcch, " /* %s */", aname)
   900						}
   901						fmt.Fprint(fgcch, "\n")
   902					})
   903				fmt.Fprintf(fgcch, "};\n")
   904				gccResult = "struct " + exp.ExpName + "_return"
   905			}
   906	
   907			// Build the wrapper function compiled by gcc.
   908			s := fmt.Sprintf("%s %s(", gccResult, exp.ExpName)
   909			if fn.Recv != nil {
   910				s += p.cgoType(fn.Recv.List[0].Type).C.String()
   911				s += " recv"
   912			}
   913			forFieldList(fntype.Params,
   914				func(i int, aname string, atype ast.Expr) {
   915					if i > 0 || fn.Recv != nil {
   916						s += ", "
   917					}
   918					s += fmt.Sprintf("%s p%d", p.cgoType(atype).C, i)
   919				})
   920			s += ")"
   921	
   922			if len(exp.Doc) > 0 {
   923				fmt.Fprintf(fgcch, "\n%s", exp.Doc)
   924			}
   925			fmt.Fprintf(fgcch, "\nextern %s;\n", s)
   926	
   927			fmt.Fprintf(fgcc, "extern void _cgoexp%s_%s(void *, int, __SIZE_TYPE__);\n", cPrefix, exp.ExpName)
   928			fmt.Fprintf(fgcc, "\nCGO_NO_SANITIZE_THREAD")
   929			fmt.Fprintf(fgcc, "\n%s\n", s)
   930			fmt.Fprintf(fgcc, "{\n")
   931			fmt.Fprintf(fgcc, "\t__SIZE_TYPE__ _cgo_ctxt = _cgo_wait_runtime_init_done();\n")
   932			fmt.Fprintf(fgcc, "\t%s %v a;\n", ctype, p.packedAttribute())
   933			if gccResult != "void" && (len(fntype.Results.List) > 1 || len(fntype.Results.List[0].Names) > 1) {
   934				fmt.Fprintf(fgcc, "\t%s r;\n", gccResult)
   935			}
   936			if fn.Recv != nil {
   937				fmt.Fprintf(fgcc, "\ta.recv = recv;\n")
   938			}
   939			forFieldList(fntype.Params,
   940				func(i int, aname string, atype ast.Expr) {
   941					fmt.Fprintf(fgcc, "\ta.p%d = p%d;\n", i, i)
   942				})
   943			fmt.Fprintf(fgcc, "\t_cgo_tsan_release();\n")
   944			fmt.Fprintf(fgcc, "\tcrosscall2(_cgoexp%s_%s, &a, %d, _cgo_ctxt);\n", cPrefix, exp.ExpName, off)
   945			fmt.Fprintf(fgcc, "\t_cgo_tsan_acquire();\n")
   946			fmt.Fprintf(fgcc, "\t_cgo_release_context(_cgo_ctxt);\n")
   947			if gccResult != "void" {
   948				if len(fntype.Results.List) == 1 && len(fntype.Results.List[0].Names) <= 1 {
   949					fmt.Fprintf(fgcc, "\treturn a.r0;\n")
   950				} else {
   951					forFieldList(fntype.Results,
   952						func(i int, aname string, atype ast.Expr) {
   953							fmt.Fprintf(fgcc, "\tr.r%d = a.r%d;\n", i, i)
   954						})
   955					fmt.Fprintf(fgcc, "\treturn r;\n")
   956				}
   957			}
   958			fmt.Fprintf(fgcc, "}\n")
   959	
   960			// Build the wrapper function compiled by cmd/compile.
   961			goname := "_cgoexpwrap" + cPrefix + "_"
   962			if fn.Recv != nil {
   963				goname += fn.Recv.List[0].Names[0].Name + "_"
   964			}
   965			goname += exp.Func.Name.Name
   966			fmt.Fprintf(fgo2, "//go:cgo_export_dynamic %s\n", exp.ExpName)
   967			fmt.Fprintf(fgo2, "//go:linkname _cgoexp%s_%s _cgoexp%s_%s\n", cPrefix, exp.ExpName, cPrefix, exp.ExpName)
   968			fmt.Fprintf(fgo2, "//go:cgo_export_static _cgoexp%s_%s\n", cPrefix, exp.ExpName)
   969			fmt.Fprintf(fgo2, "//go:nosplit\n") // no split stack, so no use of m or g
   970			fmt.Fprintf(fgo2, "//go:norace\n")  // must not have race detector calls inserted
   971			fmt.Fprintf(fgo2, "func _cgoexp%s_%s(a unsafe.Pointer, n int32, ctxt uintptr) {\n", cPrefix, exp.ExpName)
   972			fmt.Fprintf(fgo2, "\tfn := %s\n", goname)
   973			// The indirect here is converting from a Go function pointer to a C function pointer.
   974			fmt.Fprintf(fgo2, "\t_cgo_runtime_cgocallback(**(**unsafe.Pointer)(unsafe.Pointer(&fn)), a, uintptr(n), ctxt);\n")
   975			fmt.Fprintf(fgo2, "}\n")
   976	
   977			fmt.Fprintf(fm, "int _cgoexp%s_%s;\n", cPrefix, exp.ExpName)
   978	
   979			// This code uses printer.Fprint, not conf.Fprint,
   980			// because we don't want //line comments in the middle
   981			// of the function types.
   982			fmt.Fprintf(fgo2, "\n")
   983			fmt.Fprintf(fgo2, "func %s(", goname)
   984			comma := false
   985			if fn.Recv != nil {
   986				fmt.Fprintf(fgo2, "recv ")
   987				printer.Fprint(fgo2, fset, fn.Recv.List[0].Type)
   988				comma = true
   989			}
   990			forFieldList(fntype.Params,
   991				func(i int, aname string, atype ast.Expr) {
   992					if comma {
   993						fmt.Fprintf(fgo2, ", ")
   994					}
   995					fmt.Fprintf(fgo2, "p%d ", i)
   996					printer.Fprint(fgo2, fset, atype)
   997					comma = true
   998				})
   999			fmt.Fprintf(fgo2, ")")
  1000			if gccResult != "void" {
  1001				fmt.Fprint(fgo2, " (")
  1002				forFieldList(fntype.Results,
  1003					func(i int, aname string, atype ast.Expr) {
  1004						if i > 0 {
  1005							fmt.Fprint(fgo2, ", ")
  1006						}
  1007						fmt.Fprintf(fgo2, "r%d ", i)
  1008						printer.Fprint(fgo2, fset, atype)
  1009					})
  1010				fmt.Fprint(fgo2, ")")
  1011			}
  1012			fmt.Fprint(fgo2, " {\n")
  1013			if gccResult == "void" {
  1014				fmt.Fprint(fgo2, "\t")
  1015			} else {
  1016				// Verify that any results don't contain any
  1017				// Go pointers.
  1018				addedDefer := false
  1019				forFieldList(fntype.Results,
  1020					func(i int, aname string, atype ast.Expr) {
  1021						if !p.hasPointer(nil, atype, false) {
  1022							return
  1023						}
  1024						if !addedDefer {
  1025							fmt.Fprint(fgo2, "\tdefer func() {\n")
  1026							addedDefer = true
  1027						}
  1028						fmt.Fprintf(fgo2, "\t\t_cgoCheckResult(r%d)\n", i)
  1029					})
  1030				if addedDefer {
  1031					fmt.Fprint(fgo2, "\t}()\n")
  1032				}
  1033				fmt.Fprint(fgo2, "\treturn ")
  1034			}
  1035			if fn.Recv != nil {
  1036				fmt.Fprintf(fgo2, "recv.")
  1037			}
  1038			fmt.Fprintf(fgo2, "%s(", exp.Func.Name)
  1039			forFieldList(fntype.Params,
  1040				func(i int, aname string, atype ast.Expr) {
  1041					if i > 0 {
  1042						fmt.Fprint(fgo2, ", ")
  1043					}
  1044					fmt.Fprintf(fgo2, "p%d", i)
  1045				})
  1046			fmt.Fprint(fgo2, ")\n")
  1047			fmt.Fprint(fgo2, "}\n")
  1048		}
  1049	
  1050		fmt.Fprintf(fgcch, "%s", gccExportHeaderEpilog)
  1051	}
  1052	
  1053	// Write out the C header allowing C code to call exported gccgo functions.
  1054	func (p *Package) writeGccgoExports(fgo2, fm, fgcc, fgcch io.Writer) {
  1055		gccgoSymbolPrefix := p.gccgoSymbolPrefix()
  1056	
  1057		p.writeExportHeader(fgcch)
  1058	
  1059		fmt.Fprintf(fgcc, "/* Code generated by cmd/cgo; DO NOT EDIT. */\n\n")
  1060		fmt.Fprintf(fgcc, "#include \"_cgo_export.h\"\n")
  1061	
  1062		fmt.Fprintf(fgcc, "%s\n", gccgoExportFileProlog)
  1063		fmt.Fprintf(fgcc, "%s\n", tsanProlog)
  1064		fmt.Fprintf(fgcc, "%s\n", msanProlog)
  1065	
  1066		for _, exp := range p.ExpFunc {
  1067			fn := exp.Func
  1068			fntype := fn.Type
  1069	
  1070			cdeclBuf := new(bytes.Buffer)
  1071			resultCount := 0
  1072			forFieldList(fntype.Results,
  1073				func(i int, aname string, atype ast.Expr) { resultCount++ })
  1074			switch resultCount {
  1075			case 0:
  1076				fmt.Fprintf(cdeclBuf, "void")
  1077			case 1:
  1078				forFieldList(fntype.Results,
  1079					func(i int, aname string, atype ast.Expr) {
  1080						t := p.cgoType(atype)
  1081						fmt.Fprintf(cdeclBuf, "%s", t.C)
  1082					})
  1083			default:
  1084				// Declare a result struct.
  1085				fmt.Fprintf(fgcch, "\n/* Return type for %s */\n", exp.ExpName)
  1086				fmt.Fprintf(fgcch, "struct %s_return {\n", exp.ExpName)
  1087				forFieldList(fntype.Results,
  1088					func(i int, aname string, atype ast.Expr) {
  1089						t := p.cgoType(atype)
  1090						fmt.Fprintf(fgcch, "\t%s r%d;", t.C, i)
  1091						if len(aname) > 0 {
  1092							fmt.Fprintf(fgcch, " /* %s */", aname)
  1093						}
  1094						fmt.Fprint(fgcch, "\n")
  1095					})
  1096				fmt.Fprintf(fgcch, "};\n")
  1097				fmt.Fprintf(cdeclBuf, "struct %s_return", exp.ExpName)
  1098			}
  1099	
  1100			cRet := cdeclBuf.String()
  1101	
  1102			cdeclBuf = new(bytes.Buffer)
  1103			fmt.Fprintf(cdeclBuf, "(")
  1104			if fn.Recv != nil {
  1105				fmt.Fprintf(cdeclBuf, "%s recv", p.cgoType(fn.Recv.List[0].Type).C.String())
  1106			}
  1107			// Function parameters.
  1108			forFieldList(fntype.Params,
  1109				func(i int, aname string, atype ast.Expr) {
  1110					if i > 0 || fn.Recv != nil {
  1111						fmt.Fprintf(cdeclBuf, ", ")
  1112					}
  1113					t := p.cgoType(atype)
  1114					fmt.Fprintf(cdeclBuf, "%s p%d", t.C, i)
  1115				})
  1116			fmt.Fprintf(cdeclBuf, ")")
  1117			cParams := cdeclBuf.String()
  1118	
  1119			if len(exp.Doc) > 0 {
  1120				fmt.Fprintf(fgcch, "\n%s", exp.Doc)
  1121			}
  1122	
  1123			fmt.Fprintf(fgcch, "extern %s %s%s;\n", cRet, exp.ExpName, cParams)
  1124	
  1125			// We need to use a name that will be exported by the
  1126			// Go code; otherwise gccgo will make it static and we
  1127			// will not be able to link against it from the C
  1128			// code.
  1129			goName := "Cgoexp_" + exp.ExpName
  1130			fmt.Fprintf(fgcc, `extern %s %s %s __asm__("%s.%s");`, cRet, goName, cParams, gccgoSymbolPrefix, goName)
  1131			fmt.Fprint(fgcc, "\n")
  1132	
  1133			fmt.Fprint(fgcc, "\nCGO_NO_SANITIZE_THREAD\n")
  1134			fmt.Fprintf(fgcc, "%s %s %s {\n", cRet, exp.ExpName, cParams)
  1135			if resultCount > 0 {
  1136				fmt.Fprintf(fgcc, "\t%s r;\n", cRet)
  1137			}
  1138			fmt.Fprintf(fgcc, "\tif(_cgo_wait_runtime_init_done)\n")
  1139			fmt.Fprintf(fgcc, "\t\t_cgo_wait_runtime_init_done();\n")
  1140			fmt.Fprintf(fgcc, "\t_cgo_tsan_release();\n")
  1141			fmt.Fprint(fgcc, "\t")
  1142			if resultCount > 0 {
  1143				fmt.Fprint(fgcc, "r = ")
  1144			}
  1145			fmt.Fprintf(fgcc, "%s(", goName)
  1146			if fn.Recv != nil {
  1147				fmt.Fprint(fgcc, "recv")
  1148			}
  1149			forFieldList(fntype.Params,
  1150				func(i int, aname string, atype ast.Expr) {
  1151					if i > 0 || fn.Recv != nil {
  1152						fmt.Fprintf(fgcc, ", ")
  1153					}
  1154					fmt.Fprintf(fgcc, "p%d", i)
  1155				})
  1156			fmt.Fprint(fgcc, ");\n")
  1157			fmt.Fprintf(fgcc, "\t_cgo_tsan_acquire();\n")
  1158			if resultCount > 0 {
  1159				fmt.Fprint(fgcc, "\treturn r;\n")
  1160			}
  1161			fmt.Fprint(fgcc, "}\n")
  1162	
  1163			// Dummy declaration for _cgo_main.c
  1164			fmt.Fprintf(fm, `char %s[1] __asm__("%s.%s");`, goName, gccgoSymbolPrefix, goName)
  1165			fmt.Fprint(fm, "\n")
  1166	
  1167			// For gccgo we use a wrapper function in Go, in order
  1168			// to call CgocallBack and CgocallBackDone.
  1169	
  1170			// This code uses printer.Fprint, not conf.Fprint,
  1171			// because we don't want //line comments in the middle
  1172			// of the function types.
  1173			fmt.Fprint(fgo2, "\n")
  1174			fmt.Fprintf(fgo2, "func %s(", goName)
  1175			if fn.Recv != nil {
  1176				fmt.Fprint(fgo2, "recv ")
  1177				printer.Fprint(fgo2, fset, fn.Recv.List[0].Type)
  1178			}
  1179			forFieldList(fntype.Params,
  1180				func(i int, aname string, atype ast.Expr) {
  1181					if i > 0 || fn.Recv != nil {
  1182						fmt.Fprintf(fgo2, ", ")
  1183					}
  1184					fmt.Fprintf(fgo2, "p%d ", i)
  1185					printer.Fprint(fgo2, fset, atype)
  1186				})
  1187			fmt.Fprintf(fgo2, ")")
  1188			if resultCount > 0 {
  1189				fmt.Fprintf(fgo2, " (")
  1190				forFieldList(fntype.Results,
  1191					func(i int, aname string, atype ast.Expr) {
  1192						if i > 0 {
  1193							fmt.Fprint(fgo2, ", ")
  1194						}
  1195						printer.Fprint(fgo2, fset, atype)
  1196					})
  1197				fmt.Fprint(fgo2, ")")
  1198			}
  1199			fmt.Fprint(fgo2, " {\n")
  1200			fmt.Fprint(fgo2, "\tsyscall.CgocallBack()\n")
  1201			fmt.Fprint(fgo2, "\tdefer syscall.CgocallBackDone()\n")
  1202			fmt.Fprint(fgo2, "\t")
  1203			if resultCount > 0 {
  1204				fmt.Fprint(fgo2, "return ")
  1205			}
  1206			if fn.Recv != nil {
  1207				fmt.Fprint(fgo2, "recv.")
  1208			}
  1209			fmt.Fprintf(fgo2, "%s(", exp.Func.Name)
  1210			forFieldList(fntype.Params,
  1211				func(i int, aname string, atype ast.Expr) {
  1212					if i > 0 {
  1213						fmt.Fprint(fgo2, ", ")
  1214					}
  1215					fmt.Fprintf(fgo2, "p%d", i)
  1216				})
  1217			fmt.Fprint(fgo2, ")\n")
  1218			fmt.Fprint(fgo2, "}\n")
  1219		}
  1220	
  1221		fmt.Fprintf(fgcch, "%s", gccExportHeaderEpilog)
  1222	}
  1223	
  1224	// writeExportHeader writes out the start of the _cgo_export.h file.
  1225	func (p *Package) writeExportHeader(fgcch io.Writer) {
  1226		fmt.Fprintf(fgcch, "/* Code generated by cmd/cgo; DO NOT EDIT. */\n\n")
  1227		pkg := *importPath
  1228		if pkg == "" {
  1229			pkg = p.PackagePath
  1230		}
  1231		fmt.Fprintf(fgcch, "/* package %s */\n\n", pkg)
  1232		fmt.Fprintf(fgcch, "%s\n", builtinExportProlog)
  1233	
  1234		// Remove absolute paths from #line comments in the preamble.
  1235		// They aren't useful for people using the header file,
  1236		// and they mean that the header files change based on the
  1237		// exact location of GOPATH.
  1238		re := regexp.MustCompile(`(?m)^(#line\s+[0-9]+\s+")[^"]*[/\\]([^"]*")`)
  1239		preamble := re.ReplaceAllString(p.Preamble, "$1$2")
  1240	
  1241		fmt.Fprintf(fgcch, "/* Start of preamble from import \"C\" comments.  */\n\n")
  1242		fmt.Fprintf(fgcch, "%s\n", preamble)
  1243		fmt.Fprintf(fgcch, "\n/* End of preamble from import \"C\" comments.  */\n\n")
  1244	
  1245		fmt.Fprintf(fgcch, "%s\n", p.gccExportHeaderProlog())
  1246	}
  1247	
  1248	// gccgoUsesNewMangling reports whether gccgo uses the new collision-free
  1249	// packagepath mangling scheme (see determineGccgoManglingScheme for more
  1250	// info).
  1251	func gccgoUsesNewMangling() bool {
  1252		if !gccgoMangleCheckDone {
  1253			gccgoNewmanglingInEffect = determineGccgoManglingScheme()
  1254			gccgoMangleCheckDone = true
  1255		}
  1256		return gccgoNewmanglingInEffect
  1257	}
  1258	
  1259	const mangleCheckCode = `
  1260	package läufer
  1261	func Run(x int) int {
  1262	  return 1
  1263	}
  1264	`
  1265	
  1266	// determineGccgoManglingScheme performs a runtime test to see which
  1267	// flavor of packagepath mangling gccgo is using. Older versions of
  1268	// gccgo use a simple mangling scheme where there can be collisions
  1269	// between packages whose paths are different but mangle to the same
  1270	// string. More recent versions of gccgo use a new mangler that avoids
  1271	// these collisions. Return value is whether gccgo uses the new mangling.
  1272	func determineGccgoManglingScheme() bool {
  1273	
  1274		// Emit a small Go file for gccgo to compile.
  1275		filepat := "*_gccgo_manglecheck.go"
  1276		var f *os.File
  1277		var err error
  1278		if f, err = ioutil.TempFile(*objDir, filepat); err != nil {
  1279			fatalf("%v", err)
  1280		}
  1281		gofilename := f.Name()
  1282		defer os.Remove(gofilename)
  1283	
  1284		if err = ioutil.WriteFile(gofilename, []byte(mangleCheckCode), 0666); err != nil {
  1285			fatalf("%v", err)
  1286		}
  1287	
  1288		// Compile with gccgo, capturing generated assembly.
  1289		gccgocmd := os.Getenv("GCCGO")
  1290		if gccgocmd == "" {
  1291			gpath, gerr := exec.LookPath("gccgo")
  1292			if gerr != nil {
  1293				fatalf("unable to locate gccgo: %v", gerr)
  1294			}
  1295			gccgocmd = gpath
  1296		}
  1297		cmd := exec.Command(gccgocmd, "-S", "-o", "-", gofilename)
  1298		buf, cerr := cmd.CombinedOutput()
  1299		if cerr != nil {
  1300			fatalf("%s", cerr)
  1301		}
  1302	
  1303		// New mangling: expect go.l..u00e4ufer.Run
  1304		// Old mangling: expect go.l__ufer.Run
  1305		return regexp.MustCompile(`go\.l\.\.u00e4ufer\.Run`).Match(buf)
  1306	}
  1307	
  1308	// gccgoPkgpathToSymbolNew converts a package path to a gccgo-style
  1309	// package symbol.
  1310	func gccgoPkgpathToSymbolNew(ppath string) string {
  1311		bsl := []byte{}
  1312		changed := false
  1313		for _, c := range []byte(ppath) {
  1314			switch {
  1315			case 'A' <= c && c <= 'Z', 'a' <= c && c <= 'z',
  1316				'0' <= c && c <= '9', c == '_', c == '.':
  1317				bsl = append(bsl, c)
  1318			default:
  1319				changed = true
  1320				encbytes := []byte(fmt.Sprintf("..z%02x", c))
  1321				bsl = append(bsl, encbytes...)
  1322			}
  1323		}
  1324		if !changed {
  1325			return ppath
  1326		}
  1327		return string(bsl)
  1328	}
  1329	
  1330	// gccgoPkgpathToSymbolOld converts a package path to a gccgo-style
  1331	// package symbol using the older mangling scheme.
  1332	func gccgoPkgpathToSymbolOld(ppath string) string {
  1333		clean := func(r rune) rune {
  1334			switch {
  1335			case 'A' <= r && r <= 'Z', 'a' <= r && r <= 'z',
  1336				'0' <= r && r <= '9':
  1337				return r
  1338			}
  1339			return '_'
  1340		}
  1341		return strings.Map(clean, ppath)
  1342	}
  1343	
  1344	// gccgoPkgpathToSymbol converts a package path to a mangled packagepath
  1345	// symbol.
  1346	func gccgoPkgpathToSymbol(ppath string) string {
  1347		if gccgoUsesNewMangling() {
  1348			return gccgoPkgpathToSymbolNew(ppath)
  1349		} else {
  1350			return gccgoPkgpathToSymbolOld(ppath)
  1351		}
  1352	}
  1353	
  1354	// Return the package prefix when using gccgo.
  1355	func (p *Package) gccgoSymbolPrefix() string {
  1356		if !*gccgo {
  1357			return ""
  1358		}
  1359	
  1360		if *gccgopkgpath != "" {
  1361			return gccgoPkgpathToSymbol(*gccgopkgpath)
  1362		}
  1363		if *gccgoprefix == "" && p.PackageName == "main" {
  1364			return "main"
  1365		}
  1366		prefix := gccgoPkgpathToSymbol(*gccgoprefix)
  1367		if prefix == "" {
  1368			prefix = "go"
  1369		}
  1370		return prefix + "." + p.PackageName
  1371	}
  1372	
  1373	// Call a function for each entry in an ast.FieldList, passing the
  1374	// index into the list, the name if any, and the type.
  1375	func forFieldList(fl *ast.FieldList, fn func(int, string, ast.Expr)) {
  1376		if fl == nil {
  1377			return
  1378		}
  1379		i := 0
  1380		for _, r := range fl.List {
  1381			if r.Names == nil {
  1382				fn(i, "", r.Type)
  1383				i++
  1384			} else {
  1385				for _, n := range r.Names {
  1386					fn(i, n.Name, r.Type)
  1387					i++
  1388				}
  1389			}
  1390		}
  1391	}
  1392	
  1393	func c(repr string, args ...interface{}) *TypeRepr {
  1394		return &TypeRepr{repr, args}
  1395	}
  1396	
  1397	// Map predeclared Go types to Type.
  1398	var goTypes = map[string]*Type{
  1399		"bool":       {Size: 1, Align: 1, C: c("GoUint8")},
  1400		"byte":       {Size: 1, Align: 1, C: c("GoUint8")},
  1401		"int":        {Size: 0, Align: 0, C: c("GoInt")},
  1402		"uint":       {Size: 0, Align: 0, C: c("GoUint")},
  1403		"rune":       {Size: 4, Align: 4, C: c("GoInt32")},
  1404		"int8":       {Size: 1, Align: 1, C: c("GoInt8")},
  1405		"uint8":      {Size: 1, Align: 1, C: c("GoUint8")},
  1406		"int16":      {Size: 2, Align: 2, C: c("GoInt16")},
  1407		"uint16":     {Size: 2, Align: 2, C: c("GoUint16")},
  1408		"int32":      {Size: 4, Align: 4, C: c("GoInt32")},
  1409		"uint32":     {Size: 4, Align: 4, C: c("GoUint32")},
  1410		"int64":      {Size: 8, Align: 8, C: c("GoInt64")},
  1411		"uint64":     {Size: 8, Align: 8, C: c("GoUint64")},
  1412		"float32":    {Size: 4, Align: 4, C: c("GoFloat32")},
  1413		"float64":    {Size: 8, Align: 8, C: c("GoFloat64")},
  1414		"complex64":  {Size: 8, Align: 4, C: c("GoComplex64")},
  1415		"complex128": {Size: 16, Align: 8, C: c("GoComplex128")},
  1416	}
  1417	
  1418	// Map an ast type to a Type.
  1419	func (p *Package) cgoType(e ast.Expr) *Type {
  1420		switch t := e.(type) {
  1421		case *ast.StarExpr:
  1422			x := p.cgoType(t.X)
  1423			return &Type{Size: p.PtrSize, Align: p.PtrSize, C: c("%s*", x.C)}
  1424		case *ast.ArrayType:
  1425			if t.Len == nil {
  1426				// Slice: pointer, len, cap.
  1427				return &Type{Size: p.PtrSize * 3, Align: p.PtrSize, C: c("GoSlice")}
  1428			}
  1429			// Non-slice array types are not supported.
  1430		case *ast.StructType:
  1431			// Not supported.
  1432		case *ast.FuncType:
  1433			return &Type{Size: p.PtrSize, Align: p.PtrSize, C: c("void*")}
  1434		case *ast.InterfaceType:
  1435			return &Type{Size: 2 * p.PtrSize, Align: p.PtrSize, C: c("GoInterface")}
  1436		case *ast.MapType:
  1437			return &Type{Size: p.PtrSize, Align: p.PtrSize, C: c("GoMap")}
  1438		case *ast.ChanType:
  1439			return &Type{Size: p.PtrSize, Align: p.PtrSize, C: c("GoChan")}
  1440		case *ast.Ident:
  1441			// Look up the type in the top level declarations.
  1442			// TODO: Handle types defined within a function.
  1443			for _, d := range p.Decl {
  1444				gd, ok := d.(*ast.GenDecl)
  1445				if !ok || gd.Tok != token.TYPE {
  1446					continue
  1447				}
  1448				for _, spec := range gd.Specs {
  1449					ts, ok := spec.(*ast.TypeSpec)
  1450					if !ok {
  1451						continue
  1452					}
  1453					if ts.Name.Name == t.Name {
  1454						return p.cgoType(ts.Type)
  1455					}
  1456				}
  1457			}
  1458			if def := typedef[t.Name]; def != nil {
  1459				return def
  1460			}
  1461			if t.Name == "uintptr" {
  1462				return &Type{Size: p.PtrSize, Align: p.PtrSize, C: c("GoUintptr")}
  1463			}
  1464			if t.Name == "string" {
  1465				// The string data is 1 pointer + 1 (pointer-sized) int.
  1466				return &Type{Size: 2 * p.PtrSize, Align: p.PtrSize, C: c("GoString")}
  1467			}
  1468			if t.Name == "error" {
  1469				return &Type{Size: 2 * p.PtrSize, Align: p.PtrSize, C: c("GoInterface")}
  1470			}
  1471			if r, ok := goTypes[t.Name]; ok {
  1472				if r.Size == 0 { // int or uint
  1473					rr := new(Type)
  1474					*rr = *r
  1475					rr.Size = p.IntSize
  1476					rr.Align = p.IntSize
  1477					r = rr
  1478				}
  1479				if r.Align > p.PtrSize {
  1480					r.Align = p.PtrSize
  1481				}
  1482				return r
  1483			}
  1484			error_(e.Pos(), "unrecognized Go type %s", t.Name)
  1485			return &Type{Size: 4, Align: 4, C: c("int")}
  1486		case *ast.SelectorExpr:
  1487			id, ok := t.X.(*ast.Ident)
  1488			if ok && id.Name == "unsafe" && t.Sel.Name == "Pointer" {
  1489				return &Type{Size: p.PtrSize, Align: p.PtrSize, C: c("void*")}
  1490			}
  1491		}
  1492		error_(e.Pos(), "Go type not supported in export: %s", gofmt(e))
  1493		return &Type{Size: 4, Align: 4, C: c("int")}
  1494	}
  1495	
  1496	const gccProlog = `
  1497	#line 1 "cgo-gcc-prolog"
  1498	/*
  1499	  If x and y are not equal, the type will be invalid
  1500	  (have a negative array count) and an inscrutable error will come
  1501	  out of the compiler and hopefully mention "name".
  1502	*/
  1503	#define __cgo_compile_assert_eq(x, y, name) typedef char name[(x-y)*(x-y)*-2+1];
  1504	
  1505	/* Check at compile time that the sizes we use match our expectations. */
  1506	#define __cgo_size_assert(t, n) __cgo_compile_assert_eq(sizeof(t), n, _cgo_sizeof_##t##_is_not_##n)
  1507	
  1508	__cgo_size_assert(char, 1)
  1509	__cgo_size_assert(short, 2)
  1510	__cgo_size_assert(int, 4)
  1511	typedef long long __cgo_long_long;
  1512	__cgo_size_assert(__cgo_long_long, 8)
  1513	__cgo_size_assert(float, 4)
  1514	__cgo_size_assert(double, 8)
  1515	
  1516	extern char* _cgo_topofstack(void);
  1517	
  1518	/*
  1519	  We use packed structs, but they are always aligned.
  1520	  The pragmas and address-of-packed-member are only recognized as warning
  1521	  groups in clang 4.0+, so ignore unknown pragmas first.
  1522	*/
  1523	#pragma GCC diagnostic ignored "-Wunknown-pragmas"
  1524	#pragma GCC diagnostic ignored "-Wpragmas"
  1525	#pragma GCC diagnostic ignored "-Waddress-of-packed-member"
  1526	
  1527	#include <errno.h>
  1528	#include <string.h>
  1529	`
  1530	
  1531	// Prologue defining TSAN functions in C.
  1532	const noTsanProlog = `
  1533	#define CGO_NO_SANITIZE_THREAD
  1534	#define _cgo_tsan_acquire()
  1535	#define _cgo_tsan_release()
  1536	`
  1537	
  1538	// This must match the TSAN code in runtime/cgo/libcgo.h.
  1539	// This is used when the code is built with the C/C++ Thread SANitizer,
  1540	// which is not the same as the Go race detector.
  1541	// __tsan_acquire tells TSAN that we are acquiring a lock on a variable,
  1542	// in this case _cgo_sync. __tsan_release releases the lock.
  1543	// (There is no actual lock, we are just telling TSAN that there is.)
  1544	//
  1545	// When we call from Go to C we call _cgo_tsan_acquire.
  1546	// When the C function returns we call _cgo_tsan_release.
  1547	// Similarly, when C calls back into Go we call _cgo_tsan_release
  1548	// and then call _cgo_tsan_acquire when we return to C.
  1549	// These calls tell TSAN that there is a serialization point at the C call.
  1550	//
  1551	// This is necessary because TSAN, which is a C/C++ tool, can not see
  1552	// the synchronization in the Go code. Without these calls, when
  1553	// multiple goroutines call into C code, TSAN does not understand
  1554	// that the calls are properly synchronized on the Go side.
  1555	//
  1556	// To be clear, if the calls are not properly synchronized on the Go side,
  1557	// we will be hiding races. But when using TSAN on mixed Go C/C++ code
  1558	// it is more important to avoid false positives, which reduce confidence
  1559	// in the tool, than to avoid false negatives.
  1560	const yesTsanProlog = `
  1561	#line 1 "cgo-tsan-prolog"
  1562	#define CGO_NO_SANITIZE_THREAD __attribute__ ((no_sanitize_thread))
  1563	
  1564	long long _cgo_sync __attribute__ ((common));
  1565	
  1566	extern void __tsan_acquire(void*);
  1567	extern void __tsan_release(void*);
  1568	
  1569	__attribute__ ((unused))
  1570	static void _cgo_tsan_acquire() {
  1571		__tsan_acquire(&_cgo_sync);
  1572	}
  1573	
  1574	__attribute__ ((unused))
  1575	static void _cgo_tsan_release() {
  1576		__tsan_release(&_cgo_sync);
  1577	}
  1578	`
  1579	
  1580	// Set to yesTsanProlog if we see -fsanitize=thread in the flags for gcc.
  1581	var tsanProlog = noTsanProlog
  1582	
  1583	// noMsanProlog is a prologue defining an MSAN function in C.
  1584	// This is used when not compiling with -fsanitize=memory.
  1585	const noMsanProlog = `
  1586	#define _cgo_msan_write(addr, sz)
  1587	`
  1588	
  1589	// yesMsanProlog is a prologue defining an MSAN function in C.
  1590	// This is used when compiling with -fsanitize=memory.
  1591	// See the comment above where _cgo_msan_write is called.
  1592	const yesMsanProlog = `
  1593	extern void __msan_unpoison(const volatile void *, size_t);
  1594	
  1595	#define _cgo_msan_write(addr, sz) __msan_unpoison((addr), (sz))
  1596	`
  1597	
  1598	// msanProlog is set to yesMsanProlog if we see -fsanitize=memory in the flags
  1599	// for the C compiler.
  1600	var msanProlog = noMsanProlog
  1601	
  1602	const builtinProlog = `
  1603	#line 1 "cgo-builtin-prolog"
  1604	#include <stddef.h> /* for ptrdiff_t and size_t below */
  1605	
  1606	/* Define intgo when compiling with GCC.  */
  1607	typedef ptrdiff_t intgo;
  1608	
  1609	#define GO_CGO_GOSTRING_TYPEDEF
  1610	typedef struct { const char *p; intgo n; } _GoString_;
  1611	typedef struct { char *p; intgo n; intgo c; } _GoBytes_;
  1612	_GoString_ GoString(char *p);
  1613	_GoString_ GoStringN(char *p, int l);
  1614	_GoBytes_ GoBytes(void *p, int n);
  1615	char *CString(_GoString_);
  1616	void *CBytes(_GoBytes_);
  1617	void *_CMalloc(size_t);
  1618	
  1619	__attribute__ ((unused))
  1620	static size_t _GoStringLen(_GoString_ s) { return (size_t)s.n; }
  1621	
  1622	__attribute__ ((unused))
  1623	static const char *_GoStringPtr(_GoString_ s) { return s.p; }
  1624	`
  1625	
  1626	const goProlog = `
  1627	//go:linkname _cgo_runtime_cgocall runtime.cgocall
  1628	func _cgo_runtime_cgocall(unsafe.Pointer, uintptr) int32
  1629	
  1630	//go:linkname _cgo_runtime_cgocallback runtime.cgocallback
  1631	func _cgo_runtime_cgocallback(unsafe.Pointer, unsafe.Pointer, uintptr, uintptr)
  1632	
  1633	//go:linkname _cgoCheckPointer runtime.cgoCheckPointer
  1634	func _cgoCheckPointer(interface{}, ...interface{})
  1635	
  1636	//go:linkname _cgoCheckResult runtime.cgoCheckResult
  1637	func _cgoCheckResult(interface{})
  1638	`
  1639	
  1640	const gccgoGoProlog = `
  1641	func _cgoCheckPointer(interface{}, ...interface{})
  1642	
  1643	func _cgoCheckResult(interface{})
  1644	`
  1645	
  1646	const goStringDef = `
  1647	//go:linkname _cgo_runtime_gostring runtime.gostring
  1648	func _cgo_runtime_gostring(*_Ctype_char) string
  1649	
  1650	func _Cfunc_GoString(p *_Ctype_char) string {
  1651		return _cgo_runtime_gostring(p)
  1652	}
  1653	`
  1654	
  1655	const goStringNDef = `
  1656	//go:linkname _cgo_runtime_gostringn runtime.gostringn
  1657	func _cgo_runtime_gostringn(*_Ctype_char, int) string
  1658	
  1659	func _Cfunc_GoStringN(p *_Ctype_char, l _Ctype_int) string {
  1660		return _cgo_runtime_gostringn(p, int(l))
  1661	}
  1662	`
  1663	
  1664	const goBytesDef = `
  1665	//go:linkname _cgo_runtime_gobytes runtime.gobytes
  1666	func _cgo_runtime_gobytes(unsafe.Pointer, int) []byte
  1667	
  1668	func _Cfunc_GoBytes(p unsafe.Pointer, l _Ctype_int) []byte {
  1669		return _cgo_runtime_gobytes(p, int(l))
  1670	}
  1671	`
  1672	
  1673	const cStringDef = `
  1674	func _Cfunc_CString(s string) *_Ctype_char {
  1675		p := _cgo_cmalloc(uint64(len(s)+1))
  1676		pp := (*[1<<30]byte)(p)
  1677		copy(pp[:], s)
  1678		pp[len(s)] = 0
  1679		return (*_Ctype_char)(p)
  1680	}
  1681	`
  1682	
  1683	const cBytesDef = `
  1684	func _Cfunc_CBytes(b []byte) unsafe.Pointer {
  1685		p := _cgo_cmalloc(uint64(len(b)))
  1686		pp := (*[1<<30]byte)(p)
  1687		copy(pp[:], b)
  1688		return p
  1689	}
  1690	`
  1691	
  1692	const cMallocDef = `
  1693	func _Cfunc__CMalloc(n _Ctype_size_t) unsafe.Pointer {
  1694		return _cgo_cmalloc(uint64(n))
  1695	}
  1696	`
  1697	
  1698	var builtinDefs = map[string]string{
  1699		"GoString":  goStringDef,
  1700		"GoStringN": goStringNDef,
  1701		"GoBytes":   goBytesDef,
  1702		"CString":   cStringDef,
  1703		"CBytes":    cBytesDef,
  1704		"_CMalloc":  cMallocDef,
  1705	}
  1706	
  1707	// Definitions for C.malloc in Go and in C. We define it ourselves
  1708	// since we call it from functions we define, such as C.CString.
  1709	// Also, we have historically ensured that C.malloc does not return
  1710	// nil even for an allocation of 0.
  1711	
  1712	const cMallocDefGo = `
  1713	//go:cgo_import_static _cgoPREFIX_Cfunc__Cmalloc
  1714	//go:linkname __cgofn__cgoPREFIX_Cfunc__Cmalloc _cgoPREFIX_Cfunc__Cmalloc
  1715	var __cgofn__cgoPREFIX_Cfunc__Cmalloc byte
  1716	var _cgoPREFIX_Cfunc__Cmalloc = unsafe.Pointer(&__cgofn__cgoPREFIX_Cfunc__Cmalloc)
  1717	
  1718	//go:linkname runtime_throw runtime.throw
  1719	func runtime_throw(string)
  1720	
  1721	//go:cgo_unsafe_args
  1722	func _cgo_cmalloc(p0 uint64) (r1 unsafe.Pointer) {
  1723		_cgo_runtime_cgocall(_cgoPREFIX_Cfunc__Cmalloc, uintptr(unsafe.Pointer(&p0)))
  1724		if r1 == nil {
  1725			runtime_throw("runtime: C malloc failed")
  1726		}
  1727		return
  1728	}
  1729	`
  1730	
  1731	// cMallocDefC defines the C version of C.malloc for the gc compiler.
  1732	// It is defined here because C.CString and friends need a definition.
  1733	// We define it by hand, rather than simply inventing a reference to
  1734	// C.malloc, because <stdlib.h> may not have been included.
  1735	// This is approximately what writeOutputFunc would generate, but
  1736	// skips the cgo_topofstack code (which is only needed if the C code
  1737	// calls back into Go). This also avoids returning nil for an
  1738	// allocation of 0 bytes.
  1739	const cMallocDefC = `
  1740	CGO_NO_SANITIZE_THREAD
  1741	void _cgoPREFIX_Cfunc__Cmalloc(void *v) {
  1742		struct {
  1743			unsigned long long p0;
  1744			void *r1;
  1745		} PACKED *a = v;
  1746		void *ret;
  1747		_cgo_tsan_acquire();
  1748		ret = malloc(a->p0);
  1749		if (ret == 0 && a->p0 == 0) {
  1750			ret = malloc(1);
  1751		}
  1752		a->r1 = ret;
  1753		_cgo_tsan_release();
  1754	}
  1755	`
  1756	
  1757	func (p *Package) cPrologGccgo() string {
  1758		return strings.Replace(strings.Replace(cPrologGccgo, "PREFIX", cPrefix, -1),
  1759			"GCCGOSYMBOLPREF", p.gccgoSymbolPrefix(), -1)
  1760	}
  1761	
  1762	const cPrologGccgo = `
  1763	#line 1 "cgo-c-prolog-gccgo"
  1764	#include <stdint.h>
  1765	#include <stdlib.h>
  1766	#include <string.h>
  1767	
  1768	typedef unsigned char byte;
  1769	typedef intptr_t intgo;
  1770	
  1771	struct __go_string {
  1772		const unsigned char *__data;
  1773		intgo __length;
  1774	};
  1775	
  1776	typedef struct __go_open_array {
  1777		void* __values;
  1778		intgo __count;
  1779		intgo __capacity;
  1780	} Slice;
  1781	
  1782	struct __go_string __go_byte_array_to_string(const void* p, intgo len);
  1783	struct __go_open_array __go_string_to_byte_array (struct __go_string str);
  1784	
  1785	const char *_cgoPREFIX_Cfunc_CString(struct __go_string s) {
  1786		char *p = malloc(s.__length+1);
  1787		memmove(p, s.__data, s.__length);
  1788		p[s.__length] = 0;
  1789		return p;
  1790	}
  1791	
  1792	void *_cgoPREFIX_Cfunc_CBytes(struct __go_open_array b) {
  1793		char *p = malloc(b.__count);
  1794		memmove(p, b.__values, b.__count);
  1795		return p;
  1796	}
  1797	
  1798	struct __go_string _cgoPREFIX_Cfunc_GoString(char *p) {
  1799		intgo len = (p != NULL) ? strlen(p) : 0;
  1800		return __go_byte_array_to_string(p, len);
  1801	}
  1802	
  1803	struct __go_string _cgoPREFIX_Cfunc_GoStringN(char *p, int32_t n) {
  1804		return __go_byte_array_to_string(p, n);
  1805	}
  1806	
  1807	Slice _cgoPREFIX_Cfunc_GoBytes(char *p, int32_t n) {
  1808		struct __go_string s = { (const unsigned char *)p, n };
  1809		return __go_string_to_byte_array(s);
  1810	}
  1811	
  1812	extern void runtime_throw(const char *);
  1813	void *_cgoPREFIX_Cfunc__CMalloc(size_t n) {
  1814	        void *p = malloc(n);
  1815	        if(p == NULL && n == 0)
  1816	                p = malloc(1);
  1817	        if(p == NULL)
  1818	                runtime_throw("runtime: C malloc failed");
  1819	        return p;
  1820	}
  1821	
  1822	struct __go_type_descriptor;
  1823	typedef struct __go_empty_interface {
  1824		const struct __go_type_descriptor *__type_descriptor;
  1825		void *__object;
  1826	} Eface;
  1827	
  1828	extern void runtimeCgoCheckPointer(Eface, Slice)
  1829		__asm__("runtime.cgoCheckPointer")
  1830		__attribute__((weak));
  1831	
  1832	extern void localCgoCheckPointer(Eface, Slice)
  1833		__asm__("GCCGOSYMBOLPREF._cgoCheckPointer");
  1834	
  1835	void localCgoCheckPointer(Eface ptr, Slice args) {
  1836		if(runtimeCgoCheckPointer) {
  1837			runtimeCgoCheckPointer(ptr, args);
  1838		}
  1839	}
  1840	
  1841	extern void runtimeCgoCheckResult(Eface)
  1842		__asm__("runtime.cgoCheckResult")
  1843		__attribute__((weak));
  1844	
  1845	extern void localCgoCheckResult(Eface)
  1846		__asm__("GCCGOSYMBOLPREF._cgoCheckResult");
  1847	
  1848	void localCgoCheckResult(Eface val) {
  1849		if(runtimeCgoCheckResult) {
  1850			runtimeCgoCheckResult(val);
  1851		}
  1852	}
  1853	`
  1854	
  1855	// builtinExportProlog is a shorter version of builtinProlog,
  1856	// to be put into the _cgo_export.h file.
  1857	// For historical reasons we can't use builtinProlog in _cgo_export.h,
  1858	// because _cgo_export.h defines GoString as a struct while builtinProlog
  1859	// defines it as a function. We don't change this to avoid unnecessarily
  1860	// breaking existing code.
  1861	// The test of GO_CGO_GOSTRING_TYPEDEF avoids a duplicate definition
  1862	// error if a Go file with a cgo comment #include's the export header
  1863	// generated by a different package.
  1864	const builtinExportProlog = `
  1865	#line 1 "cgo-builtin-export-prolog"
  1866	
  1867	#include <stddef.h> /* for ptrdiff_t below */
  1868	
  1869	#ifndef GO_CGO_EXPORT_PROLOGUE_H
  1870	#define GO_CGO_EXPORT_PROLOGUE_H
  1871	
  1872	#ifndef GO_CGO_GOSTRING_TYPEDEF
  1873	typedef struct { const char *p; ptrdiff_t n; } _GoString_;
  1874	#endif
  1875	
  1876	#endif
  1877	`
  1878	
  1879	func (p *Package) gccExportHeaderProlog() string {
  1880		return strings.Replace(gccExportHeaderProlog, "GOINTBITS", fmt.Sprint(8*p.IntSize), -1)
  1881	}
  1882	
  1883	// gccExportHeaderProlog is written to the exported header, after the
  1884	// import "C" comment preamble but before the generated declarations
  1885	// of exported functions. This permits the generated declarations to
  1886	// use the type names that appear in goTypes, above.
  1887	//
  1888	// The test of GO_CGO_GOSTRING_TYPEDEF avoids a duplicate definition
  1889	// error if a Go file with a cgo comment #include's the export header
  1890	// generated by a different package. Unfortunately GoString means two
  1891	// different things: in this prolog it means a C name for the Go type,
  1892	// while in the prolog written into the start of the C code generated
  1893	// from a cgo-using Go file it means the C.GoString function. There is
  1894	// no way to resolve this conflict, but it also doesn't make much
  1895	// difference, as Go code never wants to refer to the latter meaning.
  1896	const gccExportHeaderProlog = `
  1897	/* Start of boilerplate cgo prologue.  */
  1898	#line 1 "cgo-gcc-export-header-prolog"
  1899	
  1900	#ifndef GO_CGO_PROLOGUE_H
  1901	#define GO_CGO_PROLOGUE_H
  1902	
  1903	typedef signed char GoInt8;
  1904	typedef unsigned char GoUint8;
  1905	typedef short GoInt16;
  1906	typedef unsigned short GoUint16;
  1907	typedef int GoInt32;
  1908	typedef unsigned int GoUint32;
  1909	typedef long long GoInt64;
  1910	typedef unsigned long long GoUint64;
  1911	typedef GoIntGOINTBITS GoInt;
  1912	typedef GoUintGOINTBITS GoUint;
  1913	typedef __SIZE_TYPE__ GoUintptr;
  1914	typedef float GoFloat32;
  1915	typedef double GoFloat64;
  1916	typedef float _Complex GoComplex64;
  1917	typedef double _Complex GoComplex128;
  1918	
  1919	/*
  1920	  static assertion to make sure the file is being used on architecture
  1921	  at least with matching size of GoInt.
  1922	*/
  1923	typedef char _check_for_GOINTBITS_bit_pointer_matching_GoInt[sizeof(void*)==GOINTBITS/8 ? 1:-1];
  1924	
  1925	#ifndef GO_CGO_GOSTRING_TYPEDEF
  1926	typedef _GoString_ GoString;
  1927	#endif
  1928	typedef void *GoMap;
  1929	typedef void *GoChan;
  1930	typedef struct { void *t; void *v; } GoInterface;
  1931	typedef struct { void *data; GoInt len; GoInt cap; } GoSlice;
  1932	
  1933	#endif
  1934	
  1935	/* End of boilerplate cgo prologue.  */
  1936	
  1937	#ifdef __cplusplus
  1938	extern "C" {
  1939	#endif
  1940	`
  1941	
  1942	// gccExportHeaderEpilog goes at the end of the generated header file.
  1943	const gccExportHeaderEpilog = `
  1944	#ifdef __cplusplus
  1945	}
  1946	#endif
  1947	`
  1948	
  1949	// gccgoExportFileProlog is written to the _cgo_export.c file when
  1950	// using gccgo.
  1951	// We use weak declarations, and test the addresses, so that this code
  1952	// works with older versions of gccgo.
  1953	const gccgoExportFileProlog = `
  1954	#line 1 "cgo-gccgo-export-file-prolog"
  1955	extern _Bool runtime_iscgo __attribute__ ((weak));
  1956	
  1957	static void GoInit(void) __attribute__ ((constructor));
  1958	static void GoInit(void) {
  1959		if(&runtime_iscgo)
  1960			runtime_iscgo = 1;
  1961	}
  1962	
  1963	extern __SIZE_TYPE__ _cgo_wait_runtime_init_done(void) __attribute__ ((weak));
  1964	`
  1965	

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