Golang与C交互时崩溃问题排查

Golang与C交互时崩溃问题排查 下面的代码使用 C 操作符 &xx->out 来访问嵌入结构体的第一个条目，而 GO 使用 &xx.out 来完成相同的任务 → 问题在于 GO 会评估 xx，而 C 不会。如果你查看汇编代码：Compiler Explorer，C 编译器将 &xx->out 翻译成一个简单的指针转换，没有任何开销，而 GO 似乎忽略了这一事实。

以下 C 代码运行正常：

#include <stdlib.h>
#include <stdio.h>

struct base {
    int b;
};

struct A {
    struct base obj;
    int a;
};

void method_base (struct base* hdl, int val) {
    if (hdl == NULL) {
      fprintf(stderr,"sorry.\n");
    } else {
      hdl->b = val;
      fprintf(stderr,"set: hdl->b = %d\n", hdl->b);
    }
}

int main(int argc, char** argv) {

    fprintf(stderr,"init: aO = calloc\n");
    struct A * aO = (struct A*) calloc(1,sizeof(*aO));
    fprintf(stderr,"init: bO = NULL\n");
    struct A * bO = NULL;

    fprintf(stderr,"step: cast aO\n");
    method_base((struct base*) aO, 1);
    fprintf(stderr,"step: ref aO\n");
    method_base(&aO->obj, 2);
    fprintf(stderr,"step: cast bO\n");
    method_base((struct base*) bO, 3);
    fprintf(stderr,"step: ref bO\n");
    method_base(&bO->obj, 4);
    fprintf(stderr,"step: end.\n");
}

输出：

init: aO = calloc init: bO = NULL step: cast aO set: hdl->b = 1 step: ref aO set: hdl->b = 2 step: cast bO sorry. step: ref bO sorry. step: end.

以下 GO 代码崩溃

package main

// #include <stdlib.h>
// #include <stdio.h>
// struct base {
//     int b;
// };
// struct A {
//     struct base obj;
//     int a;
// };
// void method_base (struct base* hdl, int val) {
//     if (hdl == NULL) {
//       fprintf(stderr,"sorry.\n");
//     } else {
//       hdl->b = val;
//       fprintf(stderr,"set: hdl->b = %d\n", hdl->b);
//     }
// }
import "C"
import "fmt"
import "unsafe"
import "os"

func main() {

    fmt.Fprintf(os.Stderr,"init: aO = calloc\n");
    aO := (*C.struct_A)(C.calloc(1,C.sizeof_struct_A));
    fmt.Fprintf(os.Stderr,"init: bO = NULL\n");
    bO := (*C.struct_A)(C.NULL);

    fmt.Fprintf(os.Stderr,"step: cast aO\n");
    C.method_base((*C.struct_base)(unsafe.Pointer(aO)), 1);
    fmt.Fprintf(os.Stderr,"step: ref aO\n");
    C.method_base(&aO.obj, 2);
    fmt.Fprintf(os.Stderr,"step: cast bO\n");
    C.method_base((*C.struct_base)(unsafe.Pointer(bO)), 3);
    fmt.Fprintf(os.Stderr,"step: ref bO\n");
    C.method_base(&bO.obj, 4);
    fmt.Fprintf(os.Stderr,"step: end.\n");
}

输出：

init: aO = calloc init: bO = NULL step: cast aO set: hdl->b = 1 step: ref aO set: hdl->b = 2 step: cast bO sorry. step: ref bO panic: runtime error: invalid memory address or nil pointer dereference [signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x48fbb4]

goroutine 1 [running]: main.main() …/main.go:39 +0x224