c - 为什么链接到 FastCGI 库会导致段错误？

Question

我有一个程序正在使用名为“wjelement”的库，每当我尝试将此库与 FastCGI 一起使用时，我都会遇到段错误。我在下面做了一个简化的测试用例。如果我在没有 fcgi_stdio.h 的情况下编译代码并且不链接库，代码工作正常，如果我添加 fastcgi header 并链接它，我会得到一个段错误，即使我不使用任何快速 cgi 调用。

在我的 FastCGI 代码中，反之亦然，如果我删除 WJelement 代码，程序的其余部分工作正常。

我不确定我是否需要责怪我的程序、FastCGI 库或 WJElement 库...

#include <stdio.h>
#include <fcgi_stdio.h>
#include <wjreader.h>

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

    FILE *my_schema_file;
    my_schema_file = fopen("test_schema.json", "rb");

    if (my_schema_file == NULL) {
        printf("Failed to open test schema file\n");
        return 1;
    } else {
        printf("Opened test schema file\n");
    }

    WJReader my_schema_reader;
    my_schema_reader = WJROpenFILEDocument(my_schema_file, NULL, 0);

    if (my_schema_reader  == NULL) {
        printf("Failed to open test schema reader\n");
        return 1;
    } else {
        printf("Opened test schema reader\n");
    }

    return 0;
}

GDB 回溯:

Program received signal SIGSEGV, Segmentation fault.
0x0000003e19e6c85f in __GI__IO_fread (buf=0x6023c4, size=1, count=2731, fp=0x602250) at iofread.c:41
41    _IO_acquire_lock (fp);
(gdb) backtrace
#0  0x0000003e19e6c85f in __GI__IO_fread (buf=0x6023c4, size=1, count=2731, fp=0x602250) at iofread.c:41
#1  0x00007ffff7dde5d9 in WJRFileCallback () from /lib/libwjreader.so.0
#2  0x00007ffff7dde037 in WJRFillBuffer () from /lib/libwjreader.so.0
#3  0x00007ffff7dde4e9 in _WJROpenDocument () from /lib/libwjreader.so.0
#4  0x000000000040081f in main (argc=1, argv=0x7fffffffdeb8) at test.c:20

Answer 1

在这里找到答案:http://www.fastcgi.com/devkit/doc/fcgi-devel-kit.htm

If your application passes FILE * to functions implemented in libraries for which you do not have source code, then you'll need to include the headers for these libraries before you include fcgi_stdio.h

然后我必须使用 FCGI_ToFILE(FCGI_FILE *); 从 FCGI_FILE * 转换为 FILE *;

#include <stdio.h>
#include <wjreader.h>
#include <fcgi_stdio.h>

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

    FILE *my_schema_file;
    my_schema_file = fopen("test_schema.json", "rb");

    if (my_schema_file == NULL) {
        printf("Failed to open test schema file\n");
        return 1;
    } else {
        printf("Opened test schema file\n");
    }

    WJReader my_schema_reader;
    my_schema_reader = WJROpenFILEDocument(FCGI_ToFILE(my_schema_file), NULL, 0);

    if (my_schema_reader  == NULL) {
        printf("Failed to open test schema reader\n");
        return 1;
    } else {
        printf("Opened test schema reader\n");
    }

    return 0;
}