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

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Date:   Fri, 2 Feb 2018 14:22:32 -0800
From:   "Luck, Tony" <tony.luck@...el.com>
To:     Sergei Trofimovich <slyfox@...too.org>
Cc:     Fenghua Yu <fenghua.yu@...el.com>, linux-ia64@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ia64: fix ptrace(PTRACE_GETREGS) (unbreaks strace, gdb)

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