Date: Thu, 18 Feb 2016 13:33:34 -0500 From: Rich Felker <dalias@...c.org> To: musl@...ts.openwall.com Subject: Re: dynlink.c: bug in reclaim_gaps leading to segfault in __libc_exit_fini On Thu, Feb 18, 2016 at 07:05:13PM +0100, Szabolcs Nagy wrote: > * Szabolcs Nagy <nsz@...t70.net> [2016-02-17 11:19:17 +0100]: > > * Timo Teras <timo.teras@....fi> [2016-02-17 09:03:27 +0200]: > > > Well - musl really should introduce __donatemem or similar for this > > > purpose, and not overload the standard free() function. This would make > > > the valgrind warning go away. > > > > to please valgrind the options are > > > > 1) have an internal free which valgrind does not know > > about, but public free calls it, so all public calls > > of free would go through an extra indirection. > > > > 2) have a copy of the internal logic of free under a > > different name, which means maintenance work and > > code size increase. > > > > 3) or have a suppression file. > > > > i think 3) is a reasonable solution. > > i looked at this again: i think moving most of reclaim() > function into src/malloc makes sense, so all malloc > internal knowledge is at one place (even if dynlink.c > is the only user of this code). > > but i don't see an easy way to do the reclaim without > calling free (so the valgrind problem is not solved, > only code maintenance gets better) I think it could be done by making free a wrapper with zero cost. See how free starts out with: if (!p) return; This could instead be: if (p) return do_free(p); /* end of function */ and the return statement is just a conditional tail-call jump, same cost as the conditional branch in the current code. This would also fix malloc-internal calls to free (which might confuse valgrind?) and eliminate the useless branch to test for null pointer when free is called internally from malloc/realloc. Rich
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