On Mon, 4 Aug 2025 at 12:12, Denys Vlasenko <[email protected]> wrote: > > On Mon, Aug 4, 2025 at 11:43 AM Roberto A. Foglietta > <[email protected]> wrote: > > > I reproduced it. It's overzealous optimization. gcc just doesn't store > > > the pointer into *to_free, > > > because it can see that in all callers of the static function where > > > the store is done, the address > > > points to a local (on-stack) variable, therefore this variable is not > > > visible to any other thread, > > > and also the store can't alias with any global variables. And we are > > > in a NORETURN function, > > > so gcc can see the entire execution path until the program "ends" > > > So, the store looks "dead" to gcc and it eliminates it. > > > > > > I discovered this when an added debugging statement took the address > > > of the variable and passed > > > it to a printf. The conclusion that the store is "dead" become invalid > > > and the leak disappeared > > > (gcc no longer eliminated the store). > > > > Therefore a free() instead of a printf() that calls such a pointer > > variable, solves both the problems at once: free it, and call it into > > the scope avoiding the gcc over-optimisation. Right? ;-) > > The free is called in the parent, after vforked child execs or exits. >
That is another process which made CoW of the stack of the previous. Why then does the child termination leaks memory? Because gcc over optimisation impacts also in kernel ability to remove such a pointer immediately at exit() child process? Hence this approach is correct, isn't it? + #if ENABLE_FEATURE_CLEAN_UP + free (ptr_to_globals); + #endif By the way, as long as it is a workaround, it has its own dignity and function as well. A TODO comment will make permanent the temporary, as usual for human habits. Best regards, R- _______________________________________________ busybox mailing list [email protected] https://lists.busybox.net/mailman/listinfo/busybox
