linux-kernel - Re: Additional debug info to aid cacheline analysis

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Date:   Sat, 10 Oct 2020 22:58:36 +0200
From:   Mark Wielaard <mark@...mp.org>
To:     Andi Kleen <andi@...stfloor.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Stephane Eranian <eranian@...gle.com>,
        linux-toolchains@...r.kernel.org,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        "Phillips, Kim" <kim.phillips@....com>,
        Mark Rutland <mark.rutland@....com>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: Additional debug info to aid cacheline analysis

On Thu, Oct 08, 2020 at 02:23:00PM -0700, Andi Kleen wrote:
> > Basically you simply want to remove this line in the top-level
> > Makefile:
> > 
> > DEBUG_CFLAGS    := $(call cc-option, -fno-var-tracking-assignments)
> 
> It looks like this was needed as a workaround for a gcc bug that was there
> from 4.5 to 4.9.
> 
> So I guess could disable it for 5.0+ only. 

Yes, that would work. I don't know what the lowest supported GCC
version is, but technically it was definitely fixed in 4.10.0, 4.8.4
and 4.9.2. And various distros would probably have backported the
fix. But checking for 5.0+ would certainly give you a good version.

How about the attached?

Cheers,

Mark
View attachment "0001-Only-add-fno-var-tracking-assignments-workaround-for.patch" of type "text/x-diff" (1285 bytes)