linux-kernel - Re: [PATCH 1/2] selftests/x86/fsgsbase: Indirect output through a wrapper function

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Date:   Mon, 11 Feb 2019 09:45:43 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Mark Brown <broonie@...nel.org>
Cc:     Shuah Khan <shuah@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...capital.net>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH 1/2] selftests/x86/fsgsbase: Indirect output through a
 wrapper function


* Mark Brown <broonie@...nel.org> wrote:

> In preparation for a change to make this test run repeatedly which
> would generate huge amounts of output as is indirect all the printf()
> calls in the program through a wrapper and add a quiet flag which can
> be used to suppress the output.  This is fairly quick and dirty, I'm not
> 100% sure what would be idiomatic here.
> 
> Signed-off-by: Mark Brown <broonie@...nel.org>
> ---
>  tools/testing/selftests/x86/fsgsbase.c | 52 ++++++++++++++++----------
>  1 file changed, 32 insertions(+), 20 deletions(-)

So this really loses useful output when there is a failure. After this 
patch I get:

  dagon:~/tip/tools/testing/selftests/x86> ./fsgsbase_64 -vv
  [FAIL] 24 errors detected in 1 tries

Not very helpful, and no real command-line way to see the failures.

While previously it would tell me what's going on:

 dagon:~/tip/tools/testing/selftests/x86> ./fsgsbase_64  | grep FAIL
 [FAIL]	GS/BASE changed from 0x1/0x1 to 0x1/0x0
 [FAIL]	GS/BASE changed from 0x2/0x1 to 0x2/0x0
 [FAIL]	GS/BASE changed from 0x3/0x1 to 0x3/0x0
 [FAIL]	GS/BASE changed from 0x1/0x1 to 0x1/0x0
 [FAIL]	GS/BASE changed from 0x2/0x1 to 0x2/0x0
 [FAIL]	GS/BASE changed from 0x3/0x1 to 0x3/0x0
 [FAIL]	GS/BASE changed from 0x1/0x1 to 0x1/0x0
 [FAIL]	GS/BASE changed from 0x2/0x1 to 0x2/0x0
 [FAIL]	GS/BASE changed from 0x3/0x1 to 0x3/0x0
 [FAIL]	GS/BASE changed from 0x1/0x1 to 0x1/0x0
 [FAIL]	GS/BASE changed from 0x2/0x1 to 0x2/0x0
 [FAIL]	GS/BASE changed from 0x3/0x1 to 0x3/0x0
 [FAIL]	GS/BASE changed from 0x1/0x200000000 to 0x1/0x0
 [FAIL]	GS/BASE changed from 0x2/0x200000000 to 0x2/0x0
 [FAIL]	GS/BASE changed from 0x3/0x200000000 to 0x3/0x0
 [FAIL]	GS/BASE changed from 0x1/0x200000000 to 0x1/0x0
 [FAIL]	GS/BASE changed from 0x2/0x200000000 to 0x2/0x0
 [FAIL]	GS/BASE changed from 0x3/0x200000000 to 0x3/0x0
 [FAIL]	GS/BASE changed from 0x1/0x200000000 to 0x1/0x0
 [FAIL]	GS/BASE changed from 0x2/0x200000000 to 0x2/0x0
 [FAIL]	GS/BASE changed from 0x3/0x200000000 to 0x3/0x0
 [FAIL]	GS/BASE changed from 0x1/0x200000000 to 0x1/0x0
 [FAIL]	GS/BASE changed from 0x2/0x200000000 to 0x2/0x0
 [FAIL]	GS/BASE changed from 0x3/0x200000000 to 0x3/0x0

So I believe at least failure messages need to be preserved.

Thanks,

	Ingo