cc is IBMs "vac.C 5.0.2.6   C for AIX Compiler" on AIX 5.2.

This is from /usr/include/stdlib.h (_ALL_SOURCE is defined):

#if defined(_ALL_SOURCE) && defined(_LINUX_SOURCE_COMPAT)
#ifdef  _NO_PROTO
extern void *__linux_malloc();
extern void *__linux_realloc();
extern void *__linux_calloc();
extern void *__linux_valloc();
#else
extern void *__linux_malloc(size_t);
extern void *__linux_realloc(void *, size_t);
extern void *__linux_calloc(size_t, size_t);
extern void *__linux_valloc(size_t);
#endif
#define malloc __linux_malloc
#define calloc __linux_calloc
#define realloc __linux_realloc
#define valloc __linux_valloc
#endif  /* _LINUX_SOURCE_COMPAT */

I couldn't find anything about __linux_malloc() but the following
documents that it is not suitable for 64 Bit:

# cat malloc_broken.c
#include <stdlib.h>
main()
{
    char *p = malloc(10);
    printf("%p\n",p);
    p[0] =0;
}

# cc -q32 -D_LINUX_SOURCE_COMPAT malloc_broken.c
# ./a.out
200004f8
# cc -q64 -D_LINUX_SOURCE_COMPAT malloc_broken.c
# ./a.out
100005f0
Segmentation fault (core dumped)
# cc -q64 malloc_broken.c
# ./a.out
1100005f0

The 64-bit Pointer is truncated to 32 bit!