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Date:   Fri, 2 Feb 2018 23:02:20 +0000
From:   Sergei Trofimovich <slyfox@gentoo.org>
To:     "Luck, Tony" <tony.luck@intel.com>
Cc:     Fenghua Yu <fenghua.yu@intel.com>, linux-ia64@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] ia64: fix ptrace(PTRACE_GETREGS) (unbreaks strace, gdb)
Message-ID: <20180202230220.13b74e8c@sf>
In-Reply-To: <20180202222231.23favlxecnxcencr@agluck-desk>
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        <20180202222231.23favlxecnxcencr@agluck-desk>
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On Fri, 2 Feb 2018 14:22:32 -0800
"Luck, Tony" <tony.luck@intel.com> wrote:

> On Fri, Feb 02, 2018 at 10:12:24PM +0000, Sergei Trofimovich wrote:
> > The strace breakage looks like that:
> > ./strace: get_regs: get_regs_error: Input/output error
> > 
> > It happens because ia64 needs to load unwind tables
> > to read certain registers. Unwind tables fail to load
> > due to GCC quirk on the following code:
> > 
> >     extern char __end_unwind[];
> >     const struct unw_table_entry *end = (struct unw_table_entry *)table_end;
> >     table->end = segment_base + end[-1].end_offset;
> > 
> > GCC does not generate correct code for this single memory
> > reference after constant propagation (see https://gcc.gnu.org/PR84184).  
> 
> I'm not seeing this ... probably because I build with
> a pre-historic 4.3.4 version of gcc.
> 
> Do you know which version(s) are affected? I'm not looking
> for an exhaustive list, just the one on which you found this
> would be good.
> 
> -Tony

Original bug https://bugs.gentoo.org/518130 claims regression appeared
around gcc-4.5. Locally am seeing the problem with gcc-6.4.0, gcc-7.2.0 and
gcc-8 (HEAD).

-- 

  Sergei