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Re: [PATCH] Remove unnecessary IFUNC dispatch for __memset_chk.
- From: Alexander Monakov <amonakov at ispras dot ru>
- To: Ondřej Bílka <neleai at seznam dot cz>
- Cc: Zack Weinberg <zackw at panix dot com>, "H.J. Lu" <hjl dot tools at gmail dot com>, Andreas Schwab <schwab at linux-m68k dot org>, GNU C Library <libc-alpha at sourceware dot org>
- Date: Tue, 11 Aug 2015 13:10:36 +0300 (MSK)
- Subject: Re: [PATCH] Remove unnecessary IFUNC dispatch for __memset_chk.
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- References: <20150809013434 dot 0B16814B9A at panix1 dot panix dot com> <m28u9lotfk dot fsf at linux-m68k dot org> <55C76FCD dot 5020607 at panix dot com> <CAMe9rOoAWjRma_mG_FazVh3FGOyiGJ=g82=bsfGqa-COnt5p1g at mail dot gmail dot com> <55C78525 dot 40402 at panix dot com> <CAMe9rOrKg8nzB67+OCXz5n1u7ZLnJncpX7J6KkEXqe0Bra843w at mail dot gmail dot com> <55C79AD8 dot 3070301 at panix dot com> <20150810030920 dot GE23550 at vapier> <20150810211200 dot GA17734 at domone> <CAKCAbMia4RCA7X0YHYeXC6eAGCxzDqhWrMiGS4NxA-cDxFioVw at mail dot gmail dot com> <20150811080451 dot GA6280 at domone>
On Tue, 11 Aug 2015, OndÅej BÃlka wrote:
> > If not, how can we be obeying the C standard's rules about function
> > pointer equality?
> >
> Simple, we return null. Following causes segmentation fault.
>
> gcc -fPIC -shared x.c -o libx.so
> void foo (int x) __attribute__ ((ifunc ("resolve_foo")));
>
> int foo_impl(int x)
> {
> return 42;
> }
> int bar()
> {
> foo(5);
> void (*f)(int) = foo;
> f(42);
> }
>
>
> static void (*resolve_foo (void)) (void)
> {
> // printf("ifunc\n");
> return foo_impl; // we'll just always select this routine
> }
> gcc main.c -L. -lx
> void bar();
> int main()
> {
> bar();
> }
This testcase does not segfault on glibc 2.20. Perhaps old glibc that you're
running did not process data relocations to ifunc symbols (as opposed to
jump_slot relocations). But anyway I don't see how the testcase is related to
what Zack was asking.
Alexander