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Re: [PATCH] Remove unnecessary IFUNC dispatch for __memset_chk.
- From: Zack Weinberg <zackw at panix dot com>
- To: OndÅej BÃlka <neleai at seznam dot cz>
- Cc: "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: Mon, 10 Aug 2015 19:41:49 -0400
- Subject: Re: [PATCH] Remove unnecessary IFUNC dispatch for __memset_chk.
- Authentication-results: sourceware.org; auth=none
- 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>
On Mon, Aug 10, 2015 at 5:12 PM, OndÅej BÃlka <neleai@seznam.cz> wrote:
> On Sun, Aug 09, 2015 at 11:09:20PM -0400, Mike Frysinger wrote:
>> On 09 Aug 2015 14:24, Zack Weinberg wrote:
>> > Is an IFUNC's variant-selecting function called only once per process,
>> > or every time?
>>
>> it's once-per-process. if it were every time, it'd defeat the point of the
>> optimization.
>
> No, its once per each shared library.
I don't see how that can possibly be right. Doesn't each shared
library provide the one true PLT entry for each function it exports?
If not, how can we be obeying the C standard's rules about function
pointer equality?
...
> thats completely flawed analysis
...
I would like to believe you about this, because I would have liked not
to have to patch 66 files for explicit_bzero, but I don't; not because
I disbelieve any of your concrete claims - they all sound *plausible*
- but because your attitude does not admit the possibility that you
might be wrong. Every time there's a question of string function
performance, lately, you insist that your analysis of the situation is
right and everyone else's is wrong, and if challenged you insist that
the other person's analysis and/or benchmarks are invalid. This is
self-defeating -- the more you do it, the less anyone will listen to
you, even if in some situation you do happen to be right.
zw