Source file src/pkg/cmd/link/internal/arm/asm.go

     1	// Inferno utils/5l/asm.c
     2	// https://bitbucket.org/inferno-os/inferno-os/src/default/utils/5l/asm.c
     3	//
     4	//	Copyright © 1994-1999 Lucent Technologies Inc.  All rights reserved.
     5	//	Portions Copyright © 1995-1997 C H Forsyth (forsyth@terzarima.net)
     6	//	Portions Copyright © 1997-1999 Vita Nuova Limited
     7	//	Portions Copyright © 2000-2007 Vita Nuova Holdings Limited (www.vitanuova.com)
     8	//	Portions Copyright © 2004,2006 Bruce Ellis
     9	//	Portions Copyright © 2005-2007 C H Forsyth (forsyth@terzarima.net)
    10	//	Revisions Copyright © 2000-2007 Lucent Technologies Inc. and others
    11	//	Portions Copyright © 2009 The Go Authors. All rights reserved.
    12	//
    13	// Permission is hereby granted, free of charge, to any person obtaining a copy
    14	// of this software and associated documentation files (the "Software"), to deal
    15	// in the Software without restriction, including without limitation the rights
    16	// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
    17	// copies of the Software, and to permit persons to whom the Software is
    18	// furnished to do so, subject to the following conditions:
    19	//
    20	// The above copyright notice and this permission notice shall be included in
    21	// all copies or substantial portions of the Software.
    22	//
    23	// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    24	// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    25	// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
    26	// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    27	// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
    28	// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
    29	// THE SOFTWARE.
    30	
    31	package arm
    32	
    33	import (
    34		"cmd/internal/objabi"
    35		"cmd/internal/sys"
    36		"cmd/link/internal/ld"
    37		"cmd/link/internal/sym"
    38		"debug/elf"
    39		"fmt"
    40		"log"
    41	)
    42	
    43	// This assembler:
    44	//
    45	//         .align 2
    46	// local.dso_init:
    47	//         ldr r0, .Lmoduledata
    48	// .Lloadfrom:
    49	//         ldr r0, [r0]
    50	//         b runtime.addmoduledata@plt
    51	// .align 2
    52	// .Lmoduledata:
    53	//         .word local.moduledata(GOT_PREL) + (. - (.Lloadfrom + 4))
    54	// assembles to:
    55	//
    56	// 00000000 <local.dso_init>:
    57	//    0:        e59f0004        ldr     r0, [pc, #4]    ; c <local.dso_init+0xc>
    58	//    4:        e5900000        ldr     r0, [r0]
    59	//    8:        eafffffe        b       0 <runtime.addmoduledata>
    60	//                      8: R_ARM_JUMP24 runtime.addmoduledata
    61	//    c:        00000004        .word   0x00000004
    62	//                      c: R_ARM_GOT_PREL       local.moduledata
    63	
    64	func gentext(ctxt *ld.Link) {
    65		if !ctxt.DynlinkingGo() {
    66			return
    67		}
    68		addmoduledata := ctxt.Syms.Lookup("runtime.addmoduledata", 0)
    69		if addmoduledata.Type == sym.STEXT && ctxt.BuildMode != ld.BuildModePlugin {
    70			// we're linking a module containing the runtime -> no need for
    71			// an init function
    72			return
    73		}
    74		addmoduledata.Attr |= sym.AttrReachable
    75		initfunc := ctxt.Syms.Lookup("go.link.addmoduledata", 0)
    76		initfunc.Type = sym.STEXT
    77		initfunc.Attr |= sym.AttrLocal
    78		initfunc.Attr |= sym.AttrReachable
    79		o := func(op uint32) {
    80			initfunc.AddUint32(ctxt.Arch, op)
    81		}
    82		o(0xe59f0004)
    83		o(0xe08f0000)
    84	
    85		o(0xeafffffe)
    86		rel := initfunc.AddRel()
    87		rel.Off = 8
    88		rel.Siz = 4
    89		rel.Sym = ctxt.Syms.Lookup("runtime.addmoduledata", 0)
    90		rel.Type = objabi.R_CALLARM
    91		rel.Add = 0xeafffffe // vomit
    92	
    93		o(0x00000000)
    94		rel = initfunc.AddRel()
    95		rel.Off = 12
    96		rel.Siz = 4
    97		rel.Sym = ctxt.Moduledata
    98		rel.Type = objabi.R_PCREL
    99		rel.Add = 4
   100	
   101		if ctxt.BuildMode == ld.BuildModePlugin {
   102			ctxt.Textp = append(ctxt.Textp, addmoduledata)
   103		}
   104		ctxt.Textp = append(ctxt.Textp, initfunc)
   105		initarray_entry := ctxt.Syms.Lookup("go.link.addmoduledatainit", 0)
   106		initarray_entry.Attr |= sym.AttrReachable
   107		initarray_entry.Attr |= sym.AttrLocal
   108		initarray_entry.Type = sym.SINITARR
   109		initarray_entry.AddAddr(ctxt.Arch, initfunc)
   110	}
   111	
   112	// Preserve highest 8 bits of a, and do addition to lower 24-bit
   113	// of a and b; used to adjust ARM branch instruction's target
   114	func braddoff(a int32, b int32) int32 {
   115		return int32((uint32(a))&0xff000000 | 0x00ffffff&uint32(a+b))
   116	}
   117	
   118	func adddynrel(ctxt *ld.Link, s *sym.Symbol, r *sym.Reloc) bool {
   119		targ := r.Sym
   120	
   121		switch r.Type {
   122		default:
   123			if r.Type >= objabi.ElfRelocOffset {
   124				ld.Errorf(s, "unexpected relocation type %d (%s)", r.Type, sym.RelocName(ctxt.Arch, r.Type))
   125				return false
   126			}
   127	
   128			// Handle relocations found in ELF object files.
   129		case objabi.ElfRelocOffset + objabi.RelocType(elf.R_ARM_PLT32):
   130			r.Type = objabi.R_CALLARM
   131	
   132			if targ.Type == sym.SDYNIMPORT {
   133				addpltsym(ctxt, targ)
   134				r.Sym = ctxt.Syms.Lookup(".plt", 0)
   135				r.Add = int64(braddoff(int32(r.Add), targ.Plt()/4))
   136			}
   137	
   138			return true
   139	
   140		case objabi.ElfRelocOffset + objabi.RelocType(elf.R_ARM_THM_PC22): // R_ARM_THM_CALL
   141			ld.Exitf("R_ARM_THM_CALL, are you using -marm?")
   142			return false
   143	
   144		case objabi.ElfRelocOffset + objabi.RelocType(elf.R_ARM_GOT32): // R_ARM_GOT_BREL
   145			if targ.Type != sym.SDYNIMPORT {
   146				addgotsyminternal(ctxt, targ)
   147			} else {
   148				addgotsym(ctxt, targ)
   149			}
   150	
   151			r.Type = objabi.R_CONST // write r->add during relocsym
   152			r.Sym = nil
   153			r.Add += int64(targ.Got())
   154			return true
   155	
   156		case objabi.ElfRelocOffset + objabi.RelocType(elf.R_ARM_GOT_PREL): // GOT(nil) + A - nil
   157			if targ.Type != sym.SDYNIMPORT {
   158				addgotsyminternal(ctxt, targ)
   159			} else {
   160				addgotsym(ctxt, targ)
   161			}
   162	
   163			r.Type = objabi.R_PCREL
   164			r.Sym = ctxt.Syms.Lookup(".got", 0)
   165			r.Add += int64(targ.Got()) + 4
   166			return true
   167	
   168		case objabi.ElfRelocOffset + objabi.RelocType(elf.R_ARM_GOTOFF): // R_ARM_GOTOFF32
   169			r.Type = objabi.R_GOTOFF
   170	
   171			return true
   172	
   173		case objabi.ElfRelocOffset + objabi.RelocType(elf.R_ARM_GOTPC): // R_ARM_BASE_PREL
   174			r.Type = objabi.R_PCREL
   175	
   176			r.Sym = ctxt.Syms.Lookup(".got", 0)
   177			r.Add += 4
   178			return true
   179	
   180		case objabi.ElfRelocOffset + objabi.RelocType(elf.R_ARM_CALL):
   181			r.Type = objabi.R_CALLARM
   182			if targ.Type == sym.SDYNIMPORT {
   183				addpltsym(ctxt, targ)
   184				r.Sym = ctxt.Syms.Lookup(".plt", 0)
   185				r.Add = int64(braddoff(int32(r.Add), targ.Plt()/4))
   186			}
   187	
   188			return true
   189	
   190		case objabi.ElfRelocOffset + objabi.RelocType(elf.R_ARM_REL32): // R_ARM_REL32
   191			r.Type = objabi.R_PCREL
   192	
   193			r.Add += 4
   194			return true
   195	
   196		case objabi.ElfRelocOffset + objabi.RelocType(elf.R_ARM_ABS32):
   197			if targ.Type == sym.SDYNIMPORT {
   198				ld.Errorf(s, "unexpected R_ARM_ABS32 relocation for dynamic symbol %s", targ.Name)
   199			}
   200			r.Type = objabi.R_ADDR
   201			return true
   202	
   203			// we can just ignore this, because we are targeting ARM V5+ anyway
   204		case objabi.ElfRelocOffset + objabi.RelocType(elf.R_ARM_V4BX):
   205			if r.Sym != nil {
   206				// R_ARM_V4BX is ABS relocation, so this symbol is a dummy symbol, ignore it
   207				r.Sym.Type = 0
   208			}
   209	
   210			r.Sym = nil
   211			return true
   212	
   213		case objabi.ElfRelocOffset + objabi.RelocType(elf.R_ARM_PC24),
   214			objabi.ElfRelocOffset + objabi.RelocType(elf.R_ARM_JUMP24):
   215			r.Type = objabi.R_CALLARM
   216			if targ.Type == sym.SDYNIMPORT {
   217				addpltsym(ctxt, targ)
   218				r.Sym = ctxt.Syms.Lookup(".plt", 0)
   219				r.Add = int64(braddoff(int32(r.Add), targ.Plt()/4))
   220			}
   221	
   222			return true
   223		}
   224	
   225		// Handle references to ELF symbols from our own object files.
   226		if targ.Type != sym.SDYNIMPORT {
   227			return true
   228		}
   229	
   230		switch r.Type {
   231		case objabi.R_CALLARM:
   232			if ctxt.LinkMode == ld.LinkExternal {
   233				// External linker will do this relocation.
   234				return true
   235			}
   236			addpltsym(ctxt, targ)
   237			r.Sym = ctxt.Syms.Lookup(".plt", 0)
   238			r.Add = int64(targ.Plt())
   239			return true
   240	
   241		case objabi.R_ADDR:
   242			if s.Type != sym.SDATA {
   243				break
   244			}
   245			if ctxt.IsELF {
   246				ld.Adddynsym(ctxt, targ)
   247				rel := ctxt.Syms.Lookup(".rel", 0)
   248				rel.AddAddrPlus(ctxt.Arch, s, int64(r.Off))
   249				rel.AddUint32(ctxt.Arch, ld.ELF32_R_INFO(uint32(targ.Dynid), uint32(elf.R_ARM_GLOB_DAT))) // we need a nil + A dynamic reloc
   250				r.Type = objabi.R_CONST                                                                   // write r->add during relocsym
   251				r.Sym = nil
   252				return true
   253			}
   254		}
   255	
   256		return false
   257	}
   258	
   259	func elfreloc1(ctxt *ld.Link, r *sym.Reloc, sectoff int64) bool {
   260		ctxt.Out.Write32(uint32(sectoff))
   261	
   262		elfsym := r.Xsym.ElfsymForReloc()
   263		switch r.Type {
   264		default:
   265			return false
   266		case objabi.R_ADDR:
   267			if r.Siz == 4 {
   268				ctxt.Out.Write32(uint32(elf.R_ARM_ABS32) | uint32(elfsym)<<8)
   269			} else {
   270				return false
   271			}
   272		case objabi.R_PCREL:
   273			if r.Siz == 4 {
   274				ctxt.Out.Write32(uint32(elf.R_ARM_REL32) | uint32(elfsym)<<8)
   275			} else {
   276				return false
   277			}
   278		case objabi.R_CALLARM:
   279			if r.Siz == 4 {
   280				if r.Add&0xff000000 == 0xeb000000 { // BL
   281					ctxt.Out.Write32(uint32(elf.R_ARM_CALL) | uint32(elfsym)<<8)
   282				} else {
   283					ctxt.Out.Write32(uint32(elf.R_ARM_JUMP24) | uint32(elfsym)<<8)
   284				}
   285			} else {
   286				return false
   287			}
   288		case objabi.R_TLS_LE:
   289			ctxt.Out.Write32(uint32(elf.R_ARM_TLS_LE32) | uint32(elfsym)<<8)
   290		case objabi.R_TLS_IE:
   291			ctxt.Out.Write32(uint32(elf.R_ARM_TLS_IE32) | uint32(elfsym)<<8)
   292		case objabi.R_GOTPCREL:
   293			if r.Siz == 4 {
   294				ctxt.Out.Write32(uint32(elf.R_ARM_GOT_PREL) | uint32(elfsym)<<8)
   295			} else {
   296				return false
   297			}
   298		}
   299	
   300		return true
   301	}
   302	
   303	func elfsetupplt(ctxt *ld.Link) {
   304		plt := ctxt.Syms.Lookup(".plt", 0)
   305		got := ctxt.Syms.Lookup(".got.plt", 0)
   306		if plt.Size == 0 {
   307			// str lr, [sp, #-4]!
   308			plt.AddUint32(ctxt.Arch, 0xe52de004)
   309	
   310			// ldr lr, [pc, #4]
   311			plt.AddUint32(ctxt.Arch, 0xe59fe004)
   312	
   313			// add lr, pc, lr
   314			plt.AddUint32(ctxt.Arch, 0xe08fe00e)
   315	
   316			// ldr pc, [lr, #8]!
   317			plt.AddUint32(ctxt.Arch, 0xe5bef008)
   318	
   319			// .word &GLOBAL_OFFSET_TABLE[0] - .
   320			plt.AddPCRelPlus(ctxt.Arch, got, 4)
   321	
   322			// the first .plt entry requires 3 .plt.got entries
   323			got.AddUint32(ctxt.Arch, 0)
   324	
   325			got.AddUint32(ctxt.Arch, 0)
   326			got.AddUint32(ctxt.Arch, 0)
   327		}
   328	}
   329	
   330	func machoreloc1(arch *sys.Arch, out *ld.OutBuf, s *sym.Symbol, r *sym.Reloc, sectoff int64) bool {
   331		var v uint32
   332	
   333		rs := r.Xsym
   334	
   335		if r.Type == objabi.R_PCREL {
   336			if rs.Type == sym.SHOSTOBJ {
   337				ld.Errorf(s, "pc-relative relocation of external symbol is not supported")
   338				return false
   339			}
   340			if r.Siz != 4 {
   341				return false
   342			}
   343	
   344			// emit a pair of "scattered" relocations that
   345			// resolve to the difference of section addresses of
   346			// the symbol and the instruction
   347			// this value is added to the field being relocated
   348			o1 := uint32(sectoff)
   349			o1 |= 1 << 31 // scattered bit
   350			o1 |= ld.MACHO_ARM_RELOC_SECTDIFF << 24
   351			o1 |= 2 << 28 // size = 4
   352	
   353			o2 := uint32(0)
   354			o2 |= 1 << 31 // scattered bit
   355			o2 |= ld.MACHO_ARM_RELOC_PAIR << 24
   356			o2 |= 2 << 28 // size = 4
   357	
   358			out.Write32(o1)
   359			out.Write32(uint32(ld.Symaddr(rs)))
   360			out.Write32(o2)
   361			out.Write32(uint32(s.Value + int64(r.Off)))
   362			return true
   363		}
   364	
   365		if rs.Type == sym.SHOSTOBJ || r.Type == objabi.R_CALLARM {
   366			if rs.Dynid < 0 {
   367				ld.Errorf(s, "reloc %d (%s) to non-macho symbol %s type=%d (%s)", r.Type, sym.RelocName(arch, r.Type), rs.Name, rs.Type, rs.Type)
   368				return false
   369			}
   370	
   371			v = uint32(rs.Dynid)
   372			v |= 1 << 27 // external relocation
   373		} else {
   374			v = uint32(rs.Sect.Extnum)
   375			if v == 0 {
   376				ld.Errorf(s, "reloc %d (%s) to symbol %s in non-macho section %s type=%d (%s)", r.Type, sym.RelocName(arch, r.Type), rs.Name, rs.Sect.Name, rs.Type, rs.Type)
   377				return false
   378			}
   379		}
   380	
   381		switch r.Type {
   382		default:
   383			return false
   384	
   385		case objabi.R_ADDR:
   386			v |= ld.MACHO_GENERIC_RELOC_VANILLA << 28
   387	
   388		case objabi.R_CALLARM:
   389			v |= 1 << 24 // pc-relative bit
   390			v |= ld.MACHO_ARM_RELOC_BR24 << 28
   391		}
   392	
   393		switch r.Siz {
   394		default:
   395			return false
   396		case 1:
   397			v |= 0 << 25
   398	
   399		case 2:
   400			v |= 1 << 25
   401	
   402		case 4:
   403			v |= 2 << 25
   404	
   405		case 8:
   406			v |= 3 << 25
   407		}
   408	
   409		out.Write32(uint32(sectoff))
   410		out.Write32(v)
   411		return true
   412	}
   413	
   414	func pereloc1(arch *sys.Arch, out *ld.OutBuf, s *sym.Symbol, r *sym.Reloc, sectoff int64) bool {
   415		rs := r.Xsym
   416	
   417		if rs.Dynid < 0 {
   418			ld.Errorf(s, "reloc %d (%s) to non-coff symbol %s type=%d (%s)", r.Type, sym.RelocName(arch, r.Type), rs.Name, rs.Type, rs.Type)
   419			return false
   420		}
   421	
   422		out.Write32(uint32(sectoff))
   423		out.Write32(uint32(rs.Dynid))
   424	
   425		var v uint32
   426		switch r.Type {
   427		default:
   428			// unsupported relocation type
   429			return false
   430	
   431		case objabi.R_DWARFSECREF:
   432			v = ld.IMAGE_REL_ARM_SECREL
   433	
   434		case objabi.R_ADDR:
   435			v = ld.IMAGE_REL_ARM_ADDR32
   436		}
   437	
   438		out.Write16(uint16(v))
   439	
   440		return true
   441	}
   442	
   443	// sign extend a 24-bit integer
   444	func signext24(x int64) int32 {
   445		return (int32(x) << 8) >> 8
   446	}
   447	
   448	// encode an immediate in ARM's imm12 format. copied from ../../../internal/obj/arm/asm5.go
   449	func immrot(v uint32) uint32 {
   450		for i := 0; i < 16; i++ {
   451			if v&^0xff == 0 {
   452				return uint32(i<<8) | v | 1<<25
   453			}
   454			v = v<<2 | v>>30
   455		}
   456		return 0
   457	}
   458	
   459	// Convert the direct jump relocation r to refer to a trampoline if the target is too far
   460	func trampoline(ctxt *ld.Link, r *sym.Reloc, s *sym.Symbol) {
   461		switch r.Type {
   462		case objabi.R_CALLARM:
   463			// r.Add is the instruction
   464			// low 24-bit encodes the target address
   465			t := (ld.Symaddr(r.Sym) + int64(signext24(r.Add&0xffffff)*4) - (s.Value + int64(r.Off))) / 4
   466			if t > 0x7fffff || t < -0x800000 || (*ld.FlagDebugTramp > 1 && s.File != r.Sym.File) {
   467				// direct call too far, need to insert trampoline.
   468				// look up existing trampolines first. if we found one within the range
   469				// of direct call, we can reuse it. otherwise create a new one.
   470				offset := (signext24(r.Add&0xffffff) + 2) * 4
   471				var tramp *sym.Symbol
   472				for i := 0; ; i++ {
   473					name := r.Sym.Name + fmt.Sprintf("%+d-tramp%d", offset, i)
   474					tramp = ctxt.Syms.Lookup(name, int(r.Sym.Version))
   475					if tramp.Type == sym.SDYNIMPORT {
   476						// don't reuse trampoline defined in other module
   477						continue
   478					}
   479					if tramp.Value == 0 {
   480						// either the trampoline does not exist -- we need to create one,
   481						// or found one the address which is not assigned -- this will be
   482						// laid down immediately after the current function. use this one.
   483						break
   484					}
   485	
   486					t = (ld.Symaddr(tramp) - 8 - (s.Value + int64(r.Off))) / 4
   487					if t >= -0x800000 && t < 0x7fffff {
   488						// found an existing trampoline that is not too far
   489						// we can just use it
   490						break
   491					}
   492				}
   493				if tramp.Type == 0 {
   494					// trampoline does not exist, create one
   495					ctxt.AddTramp(tramp)
   496					if ctxt.DynlinkingGo() {
   497						if immrot(uint32(offset)) == 0 {
   498							ld.Errorf(s, "odd offset in dynlink direct call: %v+%d", r.Sym, offset)
   499						}
   500						gentrampdyn(ctxt.Arch, tramp, r.Sym, int64(offset))
   501					} else if ctxt.BuildMode == ld.BuildModeCArchive || ctxt.BuildMode == ld.BuildModeCShared || ctxt.BuildMode == ld.BuildModePIE {
   502						gentramppic(ctxt.Arch, tramp, r.Sym, int64(offset))
   503					} else {
   504						gentramp(ctxt.Arch, ctxt.LinkMode, tramp, r.Sym, int64(offset))
   505					}
   506				}
   507				// modify reloc to point to tramp, which will be resolved later
   508				r.Sym = tramp
   509				r.Add = r.Add&0xff000000 | 0xfffffe // clear the offset embedded in the instruction
   510				r.Done = false
   511			}
   512		default:
   513			ld.Errorf(s, "trampoline called with non-jump reloc: %d (%s)", r.Type, sym.RelocName(ctxt.Arch, r.Type))
   514		}
   515	}
   516	
   517	// generate a trampoline to target+offset
   518	func gentramp(arch *sys.Arch, linkmode ld.LinkMode, tramp, target *sym.Symbol, offset int64) {
   519		tramp.Size = 12 // 3 instructions
   520		tramp.P = make([]byte, tramp.Size)
   521		t := ld.Symaddr(target) + offset
   522		o1 := uint32(0xe5900000 | 11<<12 | 15<<16) // MOVW (R15), R11 // R15 is actual pc + 8
   523		o2 := uint32(0xe12fff10 | 11)              // JMP  (R11)
   524		o3 := uint32(t)                            // WORD $target
   525		arch.ByteOrder.PutUint32(tramp.P, o1)
   526		arch.ByteOrder.PutUint32(tramp.P[4:], o2)
   527		arch.ByteOrder.PutUint32(tramp.P[8:], o3)
   528	
   529		if linkmode == ld.LinkExternal {
   530			r := tramp.AddRel()
   531			r.Off = 8
   532			r.Type = objabi.R_ADDR
   533			r.Siz = 4
   534			r.Sym = target
   535			r.Add = offset
   536		}
   537	}
   538	
   539	// generate a trampoline to target+offset in position independent code
   540	func gentramppic(arch *sys.Arch, tramp, target *sym.Symbol, offset int64) {
   541		tramp.Size = 16 // 4 instructions
   542		tramp.P = make([]byte, tramp.Size)
   543		o1 := uint32(0xe5900000 | 11<<12 | 15<<16 | 4)  // MOVW 4(R15), R11 // R15 is actual pc + 8
   544		o2 := uint32(0xe0800000 | 11<<12 | 15<<16 | 11) // ADD R15, R11, R11
   545		o3 := uint32(0xe12fff10 | 11)                   // JMP  (R11)
   546		o4 := uint32(0)                                 // WORD $(target-pc) // filled in with relocation
   547		arch.ByteOrder.PutUint32(tramp.P, o1)
   548		arch.ByteOrder.PutUint32(tramp.P[4:], o2)
   549		arch.ByteOrder.PutUint32(tramp.P[8:], o3)
   550		arch.ByteOrder.PutUint32(tramp.P[12:], o4)
   551	
   552		r := tramp.AddRel()
   553		r.Off = 12
   554		r.Type = objabi.R_PCREL
   555		r.Siz = 4
   556		r.Sym = target
   557		r.Add = offset + 4
   558	}
   559	
   560	// generate a trampoline to target+offset in dynlink mode (using GOT)
   561	func gentrampdyn(arch *sys.Arch, tramp, target *sym.Symbol, offset int64) {
   562		tramp.Size = 20                                 // 5 instructions
   563		o1 := uint32(0xe5900000 | 11<<12 | 15<<16 | 8)  // MOVW 8(R15), R11 // R15 is actual pc + 8
   564		o2 := uint32(0xe0800000 | 11<<12 | 15<<16 | 11) // ADD R15, R11, R11
   565		o3 := uint32(0xe5900000 | 11<<12 | 11<<16)      // MOVW (R11), R11
   566		o4 := uint32(0xe12fff10 | 11)                   // JMP  (R11)
   567		o5 := uint32(0)                                 // WORD $target@GOT // filled in with relocation
   568		o6 := uint32(0)
   569		if offset != 0 {
   570			// insert an instruction to add offset
   571			tramp.Size = 24 // 6 instructions
   572			o6 = o5
   573			o5 = o4
   574			o4 = 0xe2800000 | 11<<12 | 11<<16 | immrot(uint32(offset)) // ADD $offset, R11, R11
   575			o1 = uint32(0xe5900000 | 11<<12 | 15<<16 | 12)             // MOVW 12(R15), R11
   576		}
   577		tramp.P = make([]byte, tramp.Size)
   578		arch.ByteOrder.PutUint32(tramp.P, o1)
   579		arch.ByteOrder.PutUint32(tramp.P[4:], o2)
   580		arch.ByteOrder.PutUint32(tramp.P[8:], o3)
   581		arch.ByteOrder.PutUint32(tramp.P[12:], o4)
   582		arch.ByteOrder.PutUint32(tramp.P[16:], o5)
   583		if offset != 0 {
   584			arch.ByteOrder.PutUint32(tramp.P[20:], o6)
   585		}
   586	
   587		r := tramp.AddRel()
   588		r.Off = 16
   589		r.Type = objabi.R_GOTPCREL
   590		r.Siz = 4
   591		r.Sym = target
   592		r.Add = 8
   593		if offset != 0 {
   594			// increase reloc offset by 4 as we inserted an ADD instruction
   595			r.Off = 20
   596			r.Add = 12
   597		}
   598	}
   599	
   600	func archreloc(ctxt *ld.Link, r *sym.Reloc, s *sym.Symbol, val int64) (int64, bool) {
   601		if ctxt.LinkMode == ld.LinkExternal {
   602			switch r.Type {
   603			case objabi.R_CALLARM:
   604				r.Done = false
   605	
   606				// set up addend for eventual relocation via outer symbol.
   607				rs := r.Sym
   608	
   609				r.Xadd = int64(signext24(r.Add & 0xffffff))
   610				r.Xadd *= 4
   611				for rs.Outer != nil {
   612					r.Xadd += ld.Symaddr(rs) - ld.Symaddr(rs.Outer)
   613					rs = rs.Outer
   614				}
   615	
   616				if rs.Type != sym.SHOSTOBJ && rs.Type != sym.SDYNIMPORT && rs.Sect == nil {
   617					ld.Errorf(s, "missing section for %s", rs.Name)
   618				}
   619				r.Xsym = rs
   620	
   621				// ld64 for arm seems to want the symbol table to contain offset
   622				// into the section rather than pseudo virtual address that contains
   623				// the section load address.
   624				// we need to compensate that by removing the instruction's address
   625				// from addend.
   626				if ctxt.HeadType == objabi.Hdarwin {
   627					r.Xadd -= ld.Symaddr(s) + int64(r.Off)
   628				}
   629	
   630				if r.Xadd/4 > 0x7fffff || r.Xadd/4 < -0x800000 {
   631					ld.Errorf(s, "direct call too far %d", r.Xadd/4)
   632				}
   633	
   634				return int64(braddoff(int32(0xff000000&uint32(r.Add)), int32(0xffffff&uint32(r.Xadd/4)))), true
   635			}
   636	
   637			return -1, false
   638		}
   639	
   640		switch r.Type {
   641		case objabi.R_CONST:
   642			return r.Add, true
   643		case objabi.R_GOTOFF:
   644			return ld.Symaddr(r.Sym) + r.Add - ld.Symaddr(ctxt.Syms.Lookup(".got", 0)), true
   645	
   646		// The following three arch specific relocations are only for generation of
   647		// Linux/ARM ELF's PLT entry (3 assembler instruction)
   648		case objabi.R_PLT0: // add ip, pc, #0xXX00000
   649			if ld.Symaddr(ctxt.Syms.Lookup(".got.plt", 0)) < ld.Symaddr(ctxt.Syms.Lookup(".plt", 0)) {
   650				ld.Errorf(s, ".got.plt should be placed after .plt section.")
   651			}
   652			return 0xe28fc600 + (0xff & (int64(uint32(ld.Symaddr(r.Sym)-(ld.Symaddr(ctxt.Syms.Lookup(".plt", 0))+int64(r.Off))+r.Add)) >> 20)), true
   653		case objabi.R_PLT1: // add ip, ip, #0xYY000
   654			return 0xe28cca00 + (0xff & (int64(uint32(ld.Symaddr(r.Sym)-(ld.Symaddr(ctxt.Syms.Lookup(".plt", 0))+int64(r.Off))+r.Add+4)) >> 12)), true
   655		case objabi.R_PLT2: // ldr pc, [ip, #0xZZZ]!
   656			return 0xe5bcf000 + (0xfff & int64(uint32(ld.Symaddr(r.Sym)-(ld.Symaddr(ctxt.Syms.Lookup(".plt", 0))+int64(r.Off))+r.Add+8))), true
   657		case objabi.R_CALLARM: // bl XXXXXX or b YYYYYY
   658			// r.Add is the instruction
   659			// low 24-bit encodes the target address
   660			t := (ld.Symaddr(r.Sym) + int64(signext24(r.Add&0xffffff)*4) - (s.Value + int64(r.Off))) / 4
   661			if t > 0x7fffff || t < -0x800000 {
   662				ld.Errorf(s, "direct call too far: %s %x", r.Sym.Name, t)
   663			}
   664			return int64(braddoff(int32(0xff000000&uint32(r.Add)), int32(0xffffff&t))), true
   665		}
   666	
   667		return val, false
   668	}
   669	
   670	func archrelocvariant(ctxt *ld.Link, r *sym.Reloc, s *sym.Symbol, t int64) int64 {
   671		log.Fatalf("unexpected relocation variant")
   672		return t
   673	}
   674	
   675	func addpltreloc(ctxt *ld.Link, plt *sym.Symbol, got *sym.Symbol, s *sym.Symbol, typ objabi.RelocType) {
   676		r := plt.AddRel()
   677		r.Sym = got
   678		r.Off = int32(plt.Size)
   679		r.Siz = 4
   680		r.Type = typ
   681		r.Add = int64(s.Got()) - 8
   682	
   683		plt.Attr |= sym.AttrReachable
   684		plt.Size += 4
   685		plt.Grow(plt.Size)
   686	}
   687	
   688	func addpltsym(ctxt *ld.Link, s *sym.Symbol) {
   689		if s.Plt() >= 0 {
   690			return
   691		}
   692	
   693		ld.Adddynsym(ctxt, s)
   694	
   695		if ctxt.IsELF {
   696			plt := ctxt.Syms.Lookup(".plt", 0)
   697			got := ctxt.Syms.Lookup(".got.plt", 0)
   698			rel := ctxt.Syms.Lookup(".rel.plt", 0)
   699			if plt.Size == 0 {
   700				elfsetupplt(ctxt)
   701			}
   702	
   703			// .got entry
   704			s.SetGot(int32(got.Size))
   705	
   706			// In theory, all GOT should point to the first PLT entry,
   707			// Linux/ARM's dynamic linker will do that for us, but FreeBSD/ARM's
   708			// dynamic linker won't, so we'd better do it ourselves.
   709			got.AddAddrPlus(ctxt.Arch, plt, 0)
   710	
   711			// .plt entry, this depends on the .got entry
   712			s.SetPlt(int32(plt.Size))
   713	
   714			addpltreloc(ctxt, plt, got, s, objabi.R_PLT0) // add lr, pc, #0xXX00000
   715			addpltreloc(ctxt, plt, got, s, objabi.R_PLT1) // add lr, lr, #0xYY000
   716			addpltreloc(ctxt, plt, got, s, objabi.R_PLT2) // ldr pc, [lr, #0xZZZ]!
   717	
   718			// rel
   719			rel.AddAddrPlus(ctxt.Arch, got, int64(s.Got()))
   720	
   721			rel.AddUint32(ctxt.Arch, ld.ELF32_R_INFO(uint32(s.Dynid), uint32(elf.R_ARM_JUMP_SLOT)))
   722		} else {
   723			ld.Errorf(s, "addpltsym: unsupported binary format")
   724		}
   725	}
   726	
   727	func addgotsyminternal(ctxt *ld.Link, s *sym.Symbol) {
   728		if s.Got() >= 0 {
   729			return
   730		}
   731	
   732		got := ctxt.Syms.Lookup(".got", 0)
   733		s.SetGot(int32(got.Size))
   734	
   735		got.AddAddrPlus(ctxt.Arch, s, 0)
   736	
   737		if ctxt.IsELF {
   738		} else {
   739			ld.Errorf(s, "addgotsyminternal: unsupported binary format")
   740		}
   741	}
   742	
   743	func addgotsym(ctxt *ld.Link, s *sym.Symbol) {
   744		if s.Got() >= 0 {
   745			return
   746		}
   747	
   748		ld.Adddynsym(ctxt, s)
   749		got := ctxt.Syms.Lookup(".got", 0)
   750		s.SetGot(int32(got.Size))
   751		got.AddUint32(ctxt.Arch, 0)
   752	
   753		if ctxt.IsELF {
   754			rel := ctxt.Syms.Lookup(".rel", 0)
   755			rel.AddAddrPlus(ctxt.Arch, got, int64(s.Got()))
   756			rel.AddUint32(ctxt.Arch, ld.ELF32_R_INFO(uint32(s.Dynid), uint32(elf.R_ARM_GLOB_DAT)))
   757		} else {
   758			ld.Errorf(s, "addgotsym: unsupported binary format")
   759		}
   760	}
   761	
   762	func asmb(ctxt *ld.Link) {
   763		if ctxt.Debugvlog != 0 {
   764			ctxt.Logf("%5.2f asmb\n", ld.Cputime())
   765		}
   766	
   767		if ctxt.IsELF {
   768			ld.Asmbelfsetup()
   769		}
   770	
   771		sect := ld.Segtext.Sections[0]
   772		ctxt.Out.SeekSet(int64(sect.Vaddr - ld.Segtext.Vaddr + ld.Segtext.Fileoff))
   773		ld.Codeblk(ctxt, int64(sect.Vaddr), int64(sect.Length))
   774		for _, sect = range ld.Segtext.Sections[1:] {
   775			ctxt.Out.SeekSet(int64(sect.Vaddr - ld.Segtext.Vaddr + ld.Segtext.Fileoff))
   776			ld.Datblk(ctxt, int64(sect.Vaddr), int64(sect.Length))
   777		}
   778	
   779		if ld.Segrodata.Filelen > 0 {
   780			if ctxt.Debugvlog != 0 {
   781				ctxt.Logf("%5.2f rodatblk\n", ld.Cputime())
   782			}
   783			ctxt.Out.SeekSet(int64(ld.Segrodata.Fileoff))
   784			ld.Datblk(ctxt, int64(ld.Segrodata.Vaddr), int64(ld.Segrodata.Filelen))
   785		}
   786		if ld.Segrelrodata.Filelen > 0 {
   787			if ctxt.Debugvlog != 0 {
   788				ctxt.Logf("%5.2f relrodatblk\n", ld.Cputime())
   789			}
   790			ctxt.Out.SeekSet(int64(ld.Segrelrodata.Fileoff))
   791			ld.Datblk(ctxt, int64(ld.Segrelrodata.Vaddr), int64(ld.Segrelrodata.Filelen))
   792		}
   793	
   794		if ctxt.Debugvlog != 0 {
   795			ctxt.Logf("%5.2f datblk\n", ld.Cputime())
   796		}
   797	
   798		ctxt.Out.SeekSet(int64(ld.Segdata.Fileoff))
   799		ld.Datblk(ctxt, int64(ld.Segdata.Vaddr), int64(ld.Segdata.Filelen))
   800	
   801		ctxt.Out.SeekSet(int64(ld.Segdwarf.Fileoff))
   802		ld.Dwarfblk(ctxt, int64(ld.Segdwarf.Vaddr), int64(ld.Segdwarf.Filelen))
   803	}
   804	
   805	func asmb2(ctxt *ld.Link) {
   806		machlink := uint32(0)
   807		if ctxt.HeadType == objabi.Hdarwin {
   808			machlink = uint32(ld.Domacholink(ctxt))
   809		}
   810	
   811		/* output symbol table */
   812		ld.Symsize = 0
   813	
   814		ld.Lcsize = 0
   815		symo := uint32(0)
   816		if !*ld.FlagS {
   817			// TODO: rationalize
   818			if ctxt.Debugvlog != 0 {
   819				ctxt.Logf("%5.2f sym\n", ld.Cputime())
   820			}
   821			switch ctxt.HeadType {
   822			default:
   823				if ctxt.IsELF {
   824					symo = uint32(ld.Segdwarf.Fileoff + ld.Segdwarf.Filelen)
   825					symo = uint32(ld.Rnd(int64(symo), int64(*ld.FlagRound)))
   826				}
   827	
   828			case objabi.Hplan9:
   829				symo = uint32(ld.Segdata.Fileoff + ld.Segdata.Filelen)
   830	
   831			case objabi.Hdarwin:
   832				symo = uint32(ld.Segdwarf.Fileoff + uint64(ld.Rnd(int64(ld.Segdwarf.Filelen), int64(*ld.FlagRound))) + uint64(machlink))
   833	
   834			case objabi.Hwindows:
   835				symo = uint32(ld.Segdwarf.Fileoff + ld.Segdwarf.Filelen)
   836				symo = uint32(ld.Rnd(int64(symo), ld.PEFILEALIGN))
   837			}
   838	
   839			ctxt.Out.SeekSet(int64(symo))
   840			switch ctxt.HeadType {
   841			default:
   842				if ctxt.IsELF {
   843					if ctxt.Debugvlog != 0 {
   844						ctxt.Logf("%5.2f elfsym\n", ld.Cputime())
   845					}
   846					ld.Asmelfsym(ctxt)
   847					ctxt.Out.Flush()
   848					ctxt.Out.Write(ld.Elfstrdat)
   849	
   850					if ctxt.LinkMode == ld.LinkExternal {
   851						ld.Elfemitreloc(ctxt)
   852					}
   853				}
   854	
   855			case objabi.Hplan9:
   856				ld.Asmplan9sym(ctxt)
   857				ctxt.Out.Flush()
   858	
   859				sym := ctxt.Syms.Lookup("pclntab", 0)
   860				if sym != nil {
   861					ld.Lcsize = int32(len(sym.P))
   862					ctxt.Out.Write(sym.P)
   863					ctxt.Out.Flush()
   864				}
   865	
   866			case objabi.Hwindows:
   867				if ctxt.Debugvlog != 0 {
   868					ctxt.Logf("%5.2f dwarf\n", ld.Cputime())
   869				}
   870	
   871			case objabi.Hdarwin:
   872				if ctxt.LinkMode == ld.LinkExternal {
   873					ld.Machoemitreloc(ctxt)
   874				}
   875			}
   876		}
   877	
   878		if ctxt.Debugvlog != 0 {
   879			ctxt.Logf("%5.2f header\n", ld.Cputime())
   880		}
   881		ctxt.Out.SeekSet(0)
   882		switch ctxt.HeadType {
   883		default:
   884		case objabi.Hplan9: /* plan 9 */
   885			ctxt.Out.Write32b(0x647)                      /* magic */
   886			ctxt.Out.Write32b(uint32(ld.Segtext.Filelen)) /* sizes */
   887			ctxt.Out.Write32b(uint32(ld.Segdata.Filelen))
   888			ctxt.Out.Write32b(uint32(ld.Segdata.Length - ld.Segdata.Filelen))
   889			ctxt.Out.Write32b(uint32(ld.Symsize))          /* nsyms */
   890			ctxt.Out.Write32b(uint32(ld.Entryvalue(ctxt))) /* va of entry */
   891			ctxt.Out.Write32b(0)
   892			ctxt.Out.Write32b(uint32(ld.Lcsize))
   893	
   894		case objabi.Hlinux,
   895			objabi.Hfreebsd,
   896			objabi.Hnetbsd,
   897			objabi.Hopenbsd,
   898			objabi.Hnacl:
   899			ld.Asmbelf(ctxt, int64(symo))
   900	
   901		case objabi.Hdarwin:
   902			ld.Asmbmacho(ctxt)
   903	
   904		case objabi.Hwindows:
   905			ld.Asmbpe(ctxt)
   906		}
   907	
   908		ctxt.Out.Flush()
   909		if *ld.FlagC {
   910			fmt.Printf("textsize=%d\n", ld.Segtext.Filelen)
   911			fmt.Printf("datsize=%d\n", ld.Segdata.Filelen)
   912			fmt.Printf("bsssize=%d\n", ld.Segdata.Length-ld.Segdata.Filelen)
   913			fmt.Printf("symsize=%d\n", ld.Symsize)
   914			fmt.Printf("lcsize=%d\n", ld.Lcsize)
   915			fmt.Printf("total=%d\n", ld.Segtext.Filelen+ld.Segdata.Length+uint64(ld.Symsize)+uint64(ld.Lcsize))
   916		}
   917	}
   918	

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