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Re: [PATCH] PR32219, weak hidden reference segfault [PING^2]
- From: Chung-Lin Tang <cltang at codesourcery dot com>
- To: Mike Stump <mrs at mrs dot kithrup dot com>
- Cc: Diego Novillo <dnovillo at google dot com>, Bernhard Reutner-Fischer <rep dot dot dot nop at gmail dot com>, gcc-patches <gcc-patches at gcc dot gnu dot org>, Nathan Sidwell <nathan_sidwell at mentor dot com>, <rdsandiford at googlemail dot com>, Richard GÃnther <rguenther at suse dot de>, Jeff Law <law at redhat dot com>
- Date: Mon, 5 Aug 2013 22:15:30 +0800
- Subject: Re: [PATCH] PR32219, weak hidden reference segfault [PING^2]
- References: <518B71DA dot 1030302 at codesourcery dot com> <878v3nt91c dot fsf at talisman dot default> <51935F65 dot 4000803 at codesourcery dot com> <87hai4a1ce dot fsf at sandifor-thinkpad dot stglab dot manchester dot uk dot ibm dot com> <51A85B99 dot 1040102 at codesourcery dot com> <CAC1BbcRkA52ytKsSD3xm2GdgVhSQ+s3vfT3a=gvdCheGZ0LvhQ at mail dot gmail dot com> <51C2A8B4 dot 9020302 at codesourcery dot com> <51E26AA1 dot 7070808 at codesourcery dot com> <CAD_=9DRF6aD=5Rm=V4F3jMYuGV46YCD4LEqZfvHXGDCKvbjgrQ at mail dot gmail dot com> <51FE6FDC dot 2090500 at codesourcery dot com> <83D3619B-170E-412A-AC78-96DA20AAE671 at mrs dot kithrup dot com>
On 13/8/5 10:06 PM, Mike Stump wrote:
> On Aug 4, 2013, at 8:14 AM, Chung-Lin Tang <cltang@codesourcery.com> wrote:
>> On 13/7/15 1:43 AM, Diego Novillo wrote:
>>> Could you please repost the patch with its description? This thread
>>> is sufficiently old and noisy that I'm not even sure what the patch
>>> does nor why.
>>
>> Taking the same example in my first post:
>>
>> Under -fPIC, the code in rtlanal.c:nonzero_address_p() does not properly
>> recognize the "PIC-reg + <constant>" form of load as a weak symbol; it
>> returns 'true' immediately after seeing the pic-reg indexing, and does
>> not test the wrapped symbol for DECL_WEAK.
>
> So, I can't help but think that others would say that looking into an unspec is by nature, the wrong way to do it, unless that code is in the port.
>
> I think the followup from Bernhard points to a better solution, though the wording in the comment was objectionable. Merely say that the symbol, if weak and not defined, is then not local.
When I last tested that patch which moves the DECL_WEAK check, the
testcases for C++ TLS wrappers fail. I don't remember the fine details,
but effectively it filters out the TLS wrappers from being treated
locally, causing them to be called through @PLT, and regressing on some
tests specifically checking for that...
The UNSPEC interpretation here is fairly restricted, FWIW. Earlier talk
on this thread also mentioned that maybe specific RTL constructs for
reasoning about PIC addresses should be introduced, rather than common
idiomatic pattern, though that may be a long shot for now.
Chung-Lin