在 cgo、golang 中使用 free 时获得双重释放或损坏（退出）

Question

我正在尝试理解和学习 cgo，作为其中的一部分，我编写了一个使用C.stat.

import (

    "fmt"

    "unsafe"

    "os"

)

//#include <sys/stat.h>

//#include <stdlib.h>

import "C"

func CheckPerm(filename string) {

    statt := C.stat //stat struct from C

    path := C.CString(filename)

    st := *(*C.struct_stat)(unsafe.Pointer(statt)) //Casting unsafe pointer to C.struct_stat

    defer C.free(unsafe.Pointer(path)) //free

    defer C.free(unsafe.Pointer(statt))

    C.stat(path, &st)

    if st.st_mode & C.S_IRGRP > 0 || st.st_mode & C.S_IWGRP > 0 || st.st_mode & C.S_IXGRP > 0 || st.st_mode & C.S_IROTH > 0 || st.st_mode & C.S_IWOTH > 0 || st.st_mode & C.S_IXOTH > 0 {

        fmt.Println("file permission too broad, make it non-readable to groups and others.")

        os.Exit(1)

    }

    fmt.Println("File permission looks fine")

}

将文件路径传递给函数后，它会出错说

*** Error in `/tmp/Build go-sync.go and run77go': double free or corruption (out): 0x0000000000609480 ***

SIGABRT: abort

PC=0x7fe4302f3267 m=0

signal arrived during cgo execution

goroutine 1 [syscall, locked to thread]:

runtime.cgocall(0x401930, 0xc820097808, 0xc800000000)

/usr/lib/go/src/runtime/cgocall.go:120 +0x11b fp=0xc8200977d8 sp=0xc8200977a8

gosyncmodules._Cfunc_free(0x609480)

==========snip============

由于最后一行粘贴在这里gosyncmodules._Cfunc_free(0x609480)，我删除了defer C.free(unsafe.Pointer(statt))它，现在它工作正常。

• 为什么当我尝试释放创建的结构时会抛出错误，而它可用于释放路径变量？

• 如果不是在这种情况下，类似的情况会导致内存泄漏吗？

Answer 1

来自https://golang.org/cmd/cgo/#hdr-Go_references_to_C：// Go string to C string// The C string is allocated in the C heap using malloc.// It is the caller's responsibility to arrange for it to be// freed, such as by calling C.free (be sure to include stdlib.h// if C.free is needed).func C.CString(string) *C.char你的path := C.CString(filename)制作一个副本，你必须释放它，而它statt是一个普通的 Go 内存管理变量。