Source file src/plugin/plugin_dlopen.go

     1	// Copyright 2016 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	// +build linux,cgo darwin,cgo
     6	
     7	package plugin
     8	
     9	/*
    10	#cgo linux LDFLAGS: -ldl
    11	#include <dlfcn.h>
    12	#include <limits.h>
    13	#include <stdlib.h>
    14	#include <stdint.h>
    15	
    16	#include <stdio.h>
    17	
    18	static uintptr_t pluginOpen(const char* path, char** err) {
    19		void* h = dlopen(path, RTLD_NOW|RTLD_GLOBAL);
    20		if (h == NULL) {
    21			*err = (char*)dlerror();
    22		}
    23		return (uintptr_t)h;
    24	}
    25	
    26	static void* pluginLookup(uintptr_t h, const char* name, char** err) {
    27		void* r = dlsym((void*)h, name);
    28		if (r == NULL) {
    29			*err = (char*)dlerror();
    30		}
    31		return r;
    32	}
    33	*/
    34	import "C"
    35	
    36	import (
    37		"errors"
    38		"sync"
    39		"unsafe"
    40	)
    41	
    42	func open(name string) (*Plugin, error) {
    43		cPath := make([]byte, C.PATH_MAX+1)
    44		cRelName := make([]byte, len(name)+1)
    45		copy(cRelName, name)
    46		if C.realpath(
    47			(*C.char)(unsafe.Pointer(&cRelName[0])),
    48			(*C.char)(unsafe.Pointer(&cPath[0]))) == nil {
    49			return nil, errors.New(`plugin.Open("` + name + `"): realpath failed`)
    50		}
    51	
    52		filepath := C.GoString((*C.char)(unsafe.Pointer(&cPath[0])))
    53	
    54		pluginsMu.Lock()
    55		if p := plugins[filepath]; p != nil {
    56			pluginsMu.Unlock()
    57			if p.err != "" {
    58				return nil, errors.New(`plugin.Open("` + name + `"): ` + p.err + ` (previous failure)`)
    59			}
    60			<-p.loaded
    61			return p, nil
    62		}
    63		var cErr *C.char
    64		h := C.pluginOpen((*C.char)(unsafe.Pointer(&cPath[0])), &cErr)
    65		if h == 0 {
    66			pluginsMu.Unlock()
    67			return nil, errors.New(`plugin.Open("` + name + `"): ` + C.GoString(cErr))
    68		}
    69		// TODO(crawshaw): look for plugin note, confirm it is a Go plugin
    70		// and it was built with the correct toolchain.
    71		if len(name) > 3 && name[len(name)-3:] == ".so" {
    72			name = name[:len(name)-3]
    73		}
    74		if plugins == nil {
    75			plugins = make(map[string]*Plugin)
    76		}
    77		pluginpath, syms, errstr := lastmoduleinit()
    78		if errstr != "" {
    79			plugins[filepath] = &Plugin{
    80				pluginpath: pluginpath,
    81				err:        errstr,
    82			}
    83			pluginsMu.Unlock()
    84			return nil, errors.New(`plugin.Open("` + name + `"): ` + errstr)
    85		}
    86		// This function can be called from the init function of a plugin.
    87		// Drop a placeholder in the map so subsequent opens can wait on it.
    88		p := &Plugin{
    89			pluginpath: pluginpath,
    90			loaded:     make(chan struct{}),
    91		}
    92		plugins[filepath] = p
    93		pluginsMu.Unlock()
    94	
    95		initStr := make([]byte, len(pluginpath)+len("..inittask")+1) // +1 for terminating NUL
    96		copy(initStr, pluginpath)
    97		copy(initStr[len(pluginpath):], "..inittask")
    98	
    99		initTask := C.pluginLookup(h, (*C.char)(unsafe.Pointer(&initStr[0])), &cErr)
   100		if initTask != nil {
   101			doInit(initTask)
   102		}
   103	
   104		// Fill out the value of each plugin symbol.
   105		updatedSyms := map[string]interface{}{}
   106		for symName, sym := range syms {
   107			isFunc := symName[0] == '.'
   108			if isFunc {
   109				delete(syms, symName)
   110				symName = symName[1:]
   111			}
   112	
   113			fullName := pluginpath + "." + symName
   114			cname := make([]byte, len(fullName)+1)
   115			copy(cname, fullName)
   116	
   117			p := C.pluginLookup(h, (*C.char)(unsafe.Pointer(&cname[0])), &cErr)
   118			if p == nil {
   119				return nil, errors.New(`plugin.Open("` + name + `"): could not find symbol ` + symName + `: ` + C.GoString(cErr))
   120			}
   121			valp := (*[2]unsafe.Pointer)(unsafe.Pointer(&sym))
   122			if isFunc {
   123				(*valp)[1] = unsafe.Pointer(&p)
   124			} else {
   125				(*valp)[1] = p
   126			}
   127			// we can't add to syms during iteration as we'll end up processing
   128			// some symbols twice with the inability to tell if the symbol is a function
   129			updatedSyms[symName] = sym
   130		}
   131		p.syms = updatedSyms
   132	
   133		close(p.loaded)
   134		return p, nil
   135	}
   136	
   137	func lookup(p *Plugin, symName string) (Symbol, error) {
   138		if s := p.syms[symName]; s != nil {
   139			return s, nil
   140		}
   141		return nil, errors.New("plugin: symbol " + symName + " not found in plugin " + p.pluginpath)
   142	}
   143	
   144	var (
   145		pluginsMu sync.Mutex
   146		plugins   map[string]*Plugin
   147	)
   148	
   149	// lastmoduleinit is defined in package runtime
   150	func lastmoduleinit() (pluginpath string, syms map[string]interface{}, errstr string)
   151	
   152	// doInit is defined in package runtime
   153	//go:linkname doInit runtime.doInit
   154	func doInit(t unsafe.Pointer) // t should be a *runtime.initTask
   155	

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