c-不同的行为取决于体系结构

Question

我似乎在libc中遇到了一个可能的错误。我有以下代码：

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <unistd.h>
struct bla
{
int a,b,c,d;
};
pthread_t tid;
void print (const char *s, const struct bla *fp);
void * thr_fn1 ( void * arg);
int main()
{
struct bla *bla_main;
pthread_create (&tid,NULL,thr_fn1,NULL);
pthread_join (tid, (void *)  &bla_main);
print ("Old thread: n",bla_main);
return 0;
}
void print (const char *s, const struct bla *bla_print)
{
printf ("%sn",s);
printf ("Struct address: %pn",bla_print);
printf ("fp.a = %dn",bla_print->a);
printf ("fp.b = %dn",bla_print->b);
printf ("fp.c = %dn",bla_print->c);
printf ("fp.d = %dn",bla_print->d);
}
void * thr_fn1 ( void * arg)
{
struct bla *bla_thr;
bla_thr=  malloc(1);
bla_thr->a=1;
bla_thr->b=2;
bla_thr->c=3;
bla_thr->d=4;
print ("Thread 1:n",bla_thr);
pthread_exit ((void *) bla_thr);
}

编译是使用gcc -Wall -pthread file.c完成的，它不会产生错误/警告。但是，当我尝试在我的Raspberry Pi(32位)上运行它时，我会得到以下输出：

[alex@ArchPi code]$ ./a.out 
Thread 1:
Struct address: 0xb6500468
fp.a = 1
fp.b = 2
fp.c = 3
fp.d = 4
a.out: malloc.c:2365: sysmalloc: Assertion `(old_top == (((mbinptr) (((char *) &((av)->bins[((1) - 1) * 2])) - __builtin_offsetof (struct malloc_chunk, fd)))) && old_size == 0) || ((unsigned long) (old_size) >= (unsigned long)((((__builtin_offsetof (struct malloc_chunk, fd_nextsize))+((2 * (sizeof(size_t))) - 1)) & ~((2 * (sizeof(size_t))) - 1))) && ((old_top)->size & 0x1) && ((unsigned long)old_end & pagemask) == 0)' failed.
Aborted (core dumped)
[alex@ArchPi code]$ file a.out 
a.out: ELF 32-bit LSB executable, ARM, EABI5 version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.27, BuildID[sha1]=33e5d87872f0b40924a709fe266d47f9f011a06c, not stripped

我注意到，当我尝试在英特尔处理器上运行它时，也会发生同样的事情，使用-m32选项作为编译步骤，以生成32位可执行文件。

alex@debian:~/code$ ./a.out 
Thread 1:
Struct address: 0x804e098
fp.a = 1
fp.b = 2
fp.c = 3
fp.d = 4
a.out: malloc.c:3096: sYSMALLOc: Assertion `(old_top == (((mbinptr) (((char *) &((av)->bins[((1) - 1) * 2])) - __builtin_offsetof (struct malloc_chunk, fd)))) && old_size == 0) || ((unsigned long) (old_size) >= (unsigned long)((((__builtin_offsetof (struct malloc_chunk, fd_nextsize))+((2 * (sizeof(size_t))) - 1)) & ~((2 * (sizeof(size_t))) - 1))) && ((old_top)->size & 0x1) && ((unsigned long)old_end & pagemask) == 0)' failed.
Aborted

alex@debian:~/code$ file a.out 
a.out: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.26, BuildID[sha1]=0x9966b205f3f6cd3d3a544ea010608e11346f6f9a, not stripped

但是，在英特尔上运行程序的64位可执行文件时不会发生这种情况。

alex@debian:~/code$ ./a.out 
Thread 1:
Struct address: 0xb42130
fp.a = 1
fp.b = 2
fp.c = 3
fp.d = 4
Old thread: 
Struct address: 0xb42130
fp.a = 1
fp.b = 2
fp.c = 3
fp.d = 4
alex@debian:~/code$ file a.out 
a.out: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.26, BuildID[sha1]=0x4bb04ef61287bfe750a37427bb41b8b1578d74e1, not stripped

那么，这是libc/malloc()中的错误，还是我做错了什么？如果你需要更多的细节，请告诉我。

感谢

Answer 1

您正在为4个ints分配1个字节：

bla_thr=  malloc(1);
bla_thr->a=1;
bla_thr->b=2;
bla_thr->c=3;
bla_thr->d=4;

这会调用未定义的行为，因此任何事情都可能发生。错误在您的代码中，而不是libc中。如果您使用分配足够的空间

bla_thr = malloc(sizeof *bla_thr); // == sizeof(struct bla);

它应该起作用。以后别忘了free()的记忆！