From: David Edelsohn <dje.gcc@gmail.com>
To: Richard Biener <richard.guenther@gmail.com>
Cc: Richard Biener <rguenther@suse.de>,
GCC Patches <gcc-patches@gcc.gnu.org>
Subject: Re: genmatch infinite loop during bootstrap on AIX
Date: Thu, 30 Oct 2014 14:29:00 -0000 [thread overview]
Message-ID: <CAGWvnynDX6VqPWPjeK83Goxdtm5UmR=pz0xD2Rj-pc+S2gjyvQ@mail.gmail.com> (raw)
In-Reply-To: <CAFiYyc178vbTAjWH49N=hLTMZEAs81vs=TBHP-Y3Cnkv0X4qeQ@mail.gmail.com>
On Thu, Oct 30, 2014 at 4:51 AM, Richard Biener
<richard.guenther@gmail.com> wrote:
> On Wed, Oct 29, 2014 at 6:13 PM, David Edelsohn <dje.gcc@gmail.com> wrote:
>> On Wed, Oct 29, 2014 at 9:24 AM, Richard Biener
>> <richard.guenther@gmail.com> wrote:
>>
>>> Because only genmatch calls functions from libstdc++. Btw, why
>>> would genmatch miscompile an empty function or the call to it?
>>
>> I tried bootstrapping with libstdc++ built without the AIX ld "-G"
>> flag and that is succeeding.
>>
>> "-G" produces a shared object for use with SVR4-style runtime linking,
>> so this version of libstdc++ no longer allows runtime function
>> interposition, e.g., operator new, although it is not used frequently.
>> Something about the GCC-produced tail calls is interacting badly with
>> that feature.
>>
>> Note that this makes GCC bootstrap on AIX very fragile at the moment
>> because it depends on how libstdc++ was built in previous releases. I
>> can bootstrap with GCC 4.6.3 and 4.8.1 but not with 4.7.3, 4.8.0, nor
>> 4.9.0. A problematic libstdc++ from earlier releases causes genmatch
>> to loop in stage 1.
>
> I see. A bootstrap with IPA ICF disabled did not succeed but runs into
> the same issue in stage2. So I wonder if the issue is latent for much
> longer and genmatch just exposes it now.
>
> I'll see if I can remove the use of std::map from genmatch as a
> workaround.
I assume that this is a pervasive issue in the interaction between GCC
optimizations and AIX -G linker option. Something expects the second
call to point to a different implementation. I don't know if the
address in the TOC (GOT) is wrong or something expects the second call
to use a different TOC, but there is a circular reference.
I am going to apply a patch to GCC to not build libstdc++ with -G. I
also will apply it to GCC 4.9 branch. I was hoping that it could be
included in GCC 4.9.2, but I needed to test it thoroughly and Jakub
beat me with the release.
- David
next prev parent reply other threads:[~2014-10-30 14:15 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-24 23:37 David Edelsohn
2014-10-25 8:08 ` Richard Biener
2014-10-25 14:05 ` David Edelsohn
2014-10-25 15:16 ` David Edelsohn
2014-10-25 17:40 ` David Edelsohn
[not found] ` <CAGWvnynWYR5FYctJTa2GGvwGo3asvkU23Y-7Om8pLqCT3w-52A@mail.gmail.com>
2014-10-26 6:40 ` David Edelsohn
2014-10-26 10:37 ` Richard Biener
2014-10-27 1:36 ` David Edelsohn
2014-10-27 7:48 ` Richard Biener
2014-10-27 14:32 ` David Edelsohn
2014-10-27 14:56 ` David Edelsohn
2014-10-27 19:28 ` David Edelsohn
2014-10-27 20:13 ` Richard Biener
2014-10-27 23:36 ` David Edelsohn
2014-10-28 8:43 ` Richard Biener
2014-10-29 12:54 ` Richard Biener
2014-10-29 13:23 ` David Edelsohn
2014-10-29 13:31 ` Richard Biener
2014-10-29 17:31 ` David Edelsohn
2014-10-30 8:54 ` Richard Biener
2014-10-30 14:29 ` David Edelsohn [this message]
2014-10-31 8:54 ` Richard Biener
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