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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 := (*C.char)(C.malloc(C.PATH_MAX + 1))
    44		defer C.free(unsafe.Pointer(cPath))
    45	
    46		cRelName := C.CString(name)
    47		defer C.free(unsafe.Pointer(cRelName))
    48		if C.realpath(cRelName, cPath) == nil {
    49			return nil, errors.New("plugin.Open(" + name + "): realpath failed")
    50		}
    51	
    52		filepath := C.GoString(cPath)
    53	
    54		pluginsMu.Lock()
    55		if p := plugins[filepath]; p != nil {
    56			pluginsMu.Unlock()
    57			<-p.loaded
    58			return p, nil
    59		}
    60		var cErr *C.char
    61		h := C.pluginOpen(cPath, &cErr)
    62		if h == 0 {
    63			pluginsMu.Unlock()
    64			return nil, errors.New("plugin.Open: " + C.GoString(cErr))
    65		}
    66		// TODO(crawshaw): look for plugin note, confirm it is a Go plugin
    67		// and it was built with the correct toolchain.
    68		if len(name) > 3 && name[len(name)-3:] == ".so" {
    69			name = name[:len(name)-3]
    70		}
    71	
    72		pluginpath, syms, mismatchpkg := lastmoduleinit()
    73		if mismatchpkg != "" {
    74			pluginsMu.Unlock()
    75			return nil, errors.New("plugin.Open: plugin was built with a different version of package " + mismatchpkg)
    76		}
    77		if plugins == nil {
    78			plugins = make(map[string]*Plugin)
    79		}
    80		// This function can be called from the init function of a plugin.
    81		// Drop a placeholder in the map so subsequent opens can wait on it.
    82		p := &Plugin{
    83			pluginpath: pluginpath,
    84			loaded:     make(chan struct{}),
    85			syms:       syms,
    86		}
    87		plugins[filepath] = p
    88		pluginsMu.Unlock()
    89	
    90		initStr := C.CString(pluginpath + ".init")
    91		initFuncPC := C.pluginLookup(h, initStr, &cErr)
    92		C.free(unsafe.Pointer(initStr))
    93		if initFuncPC != nil {
    94			initFuncP := &initFuncPC
    95			initFunc := *(*func())(unsafe.Pointer(&initFuncP))
    96			initFunc()
    97		}
    98	
    99		// Fill out the value of each plugin symbol.
   100		for symName, sym := range syms {
   101			isFunc := symName[0] == '.'
   102			if isFunc {
   103				delete(syms, symName)
   104				symName = symName[1:]
   105			}
   106	
   107			cname := C.CString(pluginpath + "." + symName)
   108			p := C.pluginLookup(h, cname, &cErr)
   109			C.free(unsafe.Pointer(cname))
   110			if p == nil {
   111				return nil, errors.New("plugin.Open: could not find symbol " + symName + ": " + C.GoString(cErr))
   112			}
   113			valp := (*[2]unsafe.Pointer)(unsafe.Pointer(&sym))
   114			if isFunc {
   115				(*valp)[1] = unsafe.Pointer(&p)
   116			} else {
   117				(*valp)[1] = p
   118			}
   119			syms[symName] = sym
   120		}
   121		close(p.loaded)
   122		return p, nil
   123	}
   124	
   125	func lookup(p *Plugin, symName string) (Symbol, error) {
   126		if s := p.syms[symName]; s != nil {
   127			return s, nil
   128		}
   129		return nil, errors.New("plugin: symbol " + symName + " not found in plugin " + p.pluginpath)
   130	}
   131	
   132	var (
   133		pluginsMu sync.Mutex
   134		plugins   map[string]*Plugin
   135	)
   136	
   137	// lastmoduleinit is defined in package runtime
   138	func lastmoduleinit() (pluginpath string, syms map[string]interface{}, mismatchpkg string)
   139	

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