linux-kernel - RE: "struct perf_sample

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Message-ID: <f768c4e8085b45889971d623aeded560@AcuMS.aculab.com>
Date:   Mon, 8 Mar 2021 10:01:20 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Peter Zijlstra' <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
CC:     Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        "Namhyung Kim" <namhyung@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: RE: "struct perf_sample_data" alignment

...
> What I remember is that since perf_sample_data is fairly large,
> unconditionally initializing the whole thing is *slow* (and
> -fauto-var-init=zero will hurt here).

That will hurt everywhere.
I can also imagine it hiding bugs and making people
shrink on-stack arrays to the point where they either overrun
or cause an unexpected error or string truncation.

Initialising to zero is a bad choice if the aim is to
avoid leaking stack.

	David

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