linux-kernel - Re: [PATCH] ia64: fix ptrace(PTRACE

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Message-ID: <20180211185134.76ccfd45@sf>
Date:   Sun, 11 Feb 2018 18:51:34 +0000
From:   Sergei Trofimovich <slyfox@...too.org>
To:     "Luck, Tony" <tony.luck@...el.com>
Cc:     Fenghua Yu <fenghua.yu@...el.com>, linux-ia64@...r.kernel.org,
        linux-kernel@...r.kernel.org, stanton_arch@...l.com
Subject: Re: [PATCH] ia64: fix ptrace(PTRACE_GETREGS) (unbreaks strace, gdb)

On Fri, 2 Feb 2018 23:02:20 +0000
Sergei Trofimovich <slyfox@...too.org> wrote:

> On Fri, 2 Feb 2018 14:22:32 -0800
> "Luck, Tony" <tony.luck@...el.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).

Another report on the positive patch effect:

rx2600 boots successfully with this patch (did not without, my guess is due to
early access fault at bad address): https://bugs.gentoo.org/579278#c13

Tested-by: stanton_arch@...l.com

-- 

  Sergei