[Bug 252307] dlopen (without RTLD_GLOBAL) overrides weak symbols in libc

[bugzilla-noreply at freebsd.org]

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=252307

--- Comment #2 from Alex S <iwtcex at gmail.com> ---
> OTOH for malloc(3) related functions, I suspect the decision was deliberate
to make it possible to interpose system implementation with any other user
provided with LD_PRELOAD.

Well, I tested (before filling the bug) whether this works in general and, as
expected, it doesn't:

% cat weak_sym_override_test2.c 
#include <assert.h>
#include <dlfcn.h>
#include <stdlib.h>
#include <stdio.h>

#if defined(ORIG)
void __attribute__((weak)) test() {
  printf("original\n");
}
void wrapper() {
  test();
}
#elif defined(OVERRIDE)
void test() {
  printf("override\n");
}
#else
extern void wrapper();
int main() {
  assert(dlopen("override.so", RTLD_NOW) != NULL);
  wrapper();
  return 0;
}
#endif

% cc -shared -fPIC -DORIG weak_sym_override_test2.c -o orig.so
% cc -shared -fPIC -DOVERRIDE weak_sym_override_test2.c -o override.so
% cc weak_sym_override_test2.c orig.so -Wl,-rpath,. -o test
% ./test 
original

Did I miss some compilation flags or something? How do I deliberately get this
effect?

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