我正在尝试使用 LD_PRELOAD 机制插入对 pthread_cond_broadcast 的调用。我插入的 pthread_cond_broadcast 函数只是调用了原始的 pthread_cond_broadcast。但是,对于一个同时调用 pthread_cond_wait 和 pthread_cond_broadcast 的非常简单的 pthread 代码,我要么在 glibc 中出现段错误(对于 glibc 2.11.1),要么程序挂起(对于 glibc 2.15)。有什么线索吗?
插入代码(编译为共享库):
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <dlfcn.h>
static int (*orig_pthread_cond_broadcast)(pthread_cond_t *cond) = NULL;
__attribute__((constructor))
static void start() {
orig_pthread_cond_broadcast =
(int (*)()) dlsym(RTLD_NEXT, "pthread_cond_broadcast");
if (orig_pthread_cond_broadcast == NULL) {
printf("pthread_cond_broadcast not found!!!\n");
exit(1);
}
}
__attribute__((__visibility__("default")))
int pthread_cond_broadcast(pthread_cond_t *cond) {
return orig_pthread_cond_broadcast(cond);
}
简单的 pthread 程序:
#include <stdio.h>
#include <pthread.h>
#include <unistd.h>
pthread_mutex_t cond_mutex;
pthread_cond_t cond_var;
int condition;
void *thread0_work(void *arg) {
pthread_mutex_lock(&cond_mutex);
printf("Signal\n");
condition = 1;
pthread_cond_broadcast(&cond_var);
pthread_mutex_unlock(&cond_mutex);
return NULL;
}
void *thread1_work(void *arg) {
pthread_mutex_lock(&cond_mutex);
while (condition == 0) {
printf("Wait\n");
pthread_cond_wait(&cond_var, &cond_mutex);
printf("Done waiting\n");
}
pthread_mutex_unlock(&cond_mutex);
return NULL;
}
int main() {
pthread_t thread1;
pthread_mutex_init(&cond_mutex, NULL);
pthread_cond_init(&cond_var, NULL);
pthread_create(&thread1, NULL, thread1_work, NULL);
// Slowdown this thread, so the thread 1 does pthread_cond_wait.
usleep(1000);
thread0_work(NULL);
pthread_join(thread1, NULL);
return 0;
}
编辑:
对于 glibc 2.11.1,gdb bt 给出:
(gdb) set environment LD_PRELOAD=./libintercept.so
(gdb) run
Starting program: /home/seguljac/intercept/main
[Thread debugging using libthread_db enabled]
[New Thread 0x7ffff7436700 (LWP 19165)]
Wait
Signal
Before pthread_cond_broadcast
Program received signal SIGSEGV, Segmentation fault.
0x00007ffff79ca0e7 in pthread_cond_broadcast@@GLIBC_2.3.2 () from /lib/libpthread.so.0
(gdb) bt
#0 0x00007ffff79ca0e7 in pthread_cond_broadcast@@GLIBC_2.3.2 () from /lib/libpthread.so.0
#1 0x00007ffff7bdb769 in pthread_cond_broadcast () from ./libintercept.so
#2 0x00000000004008e8 in thread0_work ()
#3 0x00000000004009a4 in main ()
编辑2:
(已解决)正如 R.. 所建议的那样(谢谢!),问题是在我的平台上 pthread_cond_broadcast 是一个版本符号,而 dlsym 给出了错误的版本。这个博客非常详细地解释了这种情况:http: //blog.fesnel.com/blog/2009/08/25/preloading-with-multiple-symbol-versions/