linux-kernel - Re: [PATCH] Only add -fno-var-tracking-assignments workaround for old GCC versions.

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Message-ID: <20201014151701.vl3gh5e5teb2hqj7@two.firstfloor.org>
Date:   Wed, 14 Oct 2020 08:17:01 -0700
From:   Andi Kleen <andi@...stfloor.org>
To:     Mark Wielaard <mark@...mp.org>
Cc:     linux-kernel@...r.kernel.org,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        linux-kbuild@...r.kernel.org, Ian Rogers <irogers@...gle.com>,
        linux-toolchains@...r.kernel.org, Andi Kleen <andi@...stfloor.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Segher Boessenkool <segher@...nel.crashing.org>,
        Florian Weimer <fw@...eb.enyo.de>
Subject: Re: [PATCH] Only add -fno-var-tracking-assignments workaround for
 old GCC versions.

On Wed, Oct 14, 2020 at 01:01:32PM +0200, Mark Wielaard wrote:
> Some old GCC versions between 4.5.0 and 4.9.1 might miscompile code
> with -fvar-tracking-assingments (which is enabled by default with -g -O2).
> commit 2062afb4f added -fno-var-tracking-assignments unconditionally to
> work around this. But newer versions of GCC no longer have this bug, so
> only add it for versions of GCC before 5.0.

Add

... This allows various tools such as a perf probe or gdb debuggers
or systemtap to resolve variable locations using dwarf locations in 
more code.
> 
> Signed-off-by: Mark Wielaard <mark@...mp.org>
> Acked-by: Ian Rogers <irogers@...gle.com>
> Cc: linux-toolchains@...r.kernel.org
> Cc: Andi Kleen <andi@...stfloor.org>
> Cc: Nick Desaulniers <ndesaulniers@...gle.com>
> Cc: Segher Boessenkool <segher@...nel.crashing.org>
> Cc: Florian Weimer <fw@...eb.enyo.de>

Reviewed-by: Andi Kleen <ak@...ux.intel.com>

-Andi