使用LD_PRELOAD修复对malloc的递归调用

Question

I am using LD_PRELOAD to log malloc calls from an application and map out the virtual address space however malloc is used internally by fopen/printf. Is there a way I can fix this issue?

I know about glibc's hooks but I want to avoid changing the source code of the application.

Answer 1

My issue was caused by the fact that malloc is used internally by glibc so when I use LD_PRELOAD to override malloc any attempt to log caused malloc to be called resulting in a recursive call to malloc itself

Solution: call original malloc whenever the TLS needs memory allocation providing code:

 static __thread int no_hook; static void *(*real_malloc)(size_t) = NULL; static void __attribute__((constructor))init(void) { real_malloc = (void * (*)(size_t))dlsym(RTLD_NEXT, "malloc"); } void * malloc(size_t len) { void* ret; void* caller; if (no_hook) { return (*real_malloc)(len); } no_hook = 1; caller = (void*)(long) __builtin_return_address(0); printf("malloc call %zu from %lu\\n", len, (long)caller); ret = (*real_malloc)(len); // fprintf(logfp, ") -> %pn", ret); no_hook = 0; return ret; }