c - An alternative for the deprecated __malloc_hook functionality of glibc -

i writing memory profiler c , intercepting calls malloc, realloc , free functions via malloc_hooks. unfortunately, these deprecated because of poor behaviour in multithreaded environments. not find document describing alternative best practice solution achieve same thing, can enlighten me?

i've read simple #define malloc(s) malloc_hook(s) trick, not work system setup have in mind, because intrusive original code base suitable use in profiling / tracing tool. having manually change original application code killer decent profiler. optimally, solution looking should enabled or disabled linking optional shared library. example, current setup uses function declared __attribute__ ((constructor)) install intercepting malloc hooks.

thanks

after trying things, managed figure out how this.

first of all, in glibc, malloc defined weak symbol, means can overwritten application or shared library. hence, ld_preload not needed. instead, implemented following function in shared library:

void* malloc (size_t size) {   [ ... ] } 

which gets called application instead of glibcs malloc.

now, equivalent __malloc_hooks functionality, couple of things still missing.

1.) caller address

in addition original parameters malloc, glibcs __malloc_hooks provide address of calling function, return address of malloc return to. achieve same thing, can use __builtin_return_address function available in gcc. have not looked other compilers, because limited gcc anyway, if happen know how such thing portably, please drop me comment :)

our malloc function looks this:

void* malloc (size_t size) {   void *caller = __builtin_return_address(0);   [ ... ] } 

2.) accessing glibcs malloc within hook

as limited glibc in application, chose use __libc_malloc access original malloc implementation. alternatively, dlsym(rtld_next, "malloc") can used, @ possible pitfall function uses calloc on first call, possibly resulting in infinite loop leading segfault.

complete malloc hook

my complete hooking function looks this:

extern void *__libc_malloc(size_t size);  int malloc_hook_active = 0;  void* malloc (size_t size) {   void *caller = __builtin_return_address(0);   if (malloc_hook_active)     return my_malloc_hook(size, caller);   return __libc_malloc(size); } 

where my_malloc_hook looks this:

void* my_malloc_hook (size_t size, void *caller) {   void *result;    // deactivate hooks logging   malloc_hook_active = 0;    result = malloc(size);    // logging   [ ... ]    // reactivate hooks   malloc_hook_active = 1;    return result; } 

of course, hooks calloc, realloc , free work similarly.

dynamic , static linking

with these functions, dynamic linking works out of box. linking .so file containing malloc hook implementation result of calls malloc application , library calls routed through hook. static linking problematic though. have not yet wrapped head around completely, in static linking malloc not weak symbol, resulting in multiple definition error @ link time.

if need static linking whatever reason, example translating function addresses in 3rd party libraries code lines via debug symbols, can link these 3rd party libs statically while still linking malloc hooks dynamically, avoiding multiple definition problem. have not yet found better workaround this, if know one,feel free leave me comment.

here short example:

gcc -o test test.c -lmalloc_hook_library -wl,-bstatic -l3rdparty -wl,-bdynamic 

3rdparty linked statically, while malloc_hook_library linked dynamically, resulting in expected behaviour, , addresses of functions in 3rdparty translatable via debug symbols in test. pretty neat, huh?

conlusion

the techniques above describe non-deprecated, pretty equivalent approach __malloc_hooks, couple of mean limitations:

__builtin_caller_address works gcc

__libc_malloc works glibc

dlsym(rtld_next, [...]) gnu extension in glibc

the linker flags -wl,-bstatic , -wl,-bdynamic specific gnu binutils.

in other words, solution utterly non-portable , alternative solutions have added if hooks library ported non-gnu operating system.