linux-kernel - Re: [PATCH 0/2] kselftest: Support nolibc

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Date:   Thu, 6 Apr 2023 16:20:29 +0200
From:   Willy Tarreau <w@....eu>
To:     Mark Brown <broonie@...nel.org>
Cc:     Shuah Khan <shuah@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] kselftest: Support nolibc

Hi Mark,

On Thu, Apr 06, 2023 at 02:56:28PM +0100, Mark Brown wrote:
> At present the kselftest header can't be used with nolibc since it makes
> use of vprintf() which is not available in nolibc and seems like it would
> be inappropriate to implement given the minimal system requirements and
> environment intended for nolibc.

In fact we already have vfprintf(), and printf() is based on it, so
wouldn't it just be a matter of adding vprintf() that calls vfprintf()
for your case ? Maybe just something like this :

  static int vprintf(const char *fmt, va_list args)
  {
	return vfprintf(stdout, fmt, args);
  }

It's possible I'm missing something, but it's also possible you didn't
find vfprintf() which is why I prefer to raise my hand ;-)

> This has resulted in some open coded
> kselftests which use nolibc to test features that are supposed to be
> controlled via libc and therefore better exercised in an environment with
> no libc.

Yeah that's ugly. In nolibc-test we now have two build targets so that
we can more easily verify the compatibility between the default libc and
nolibc, so my recommendation would be to stick to a common subset of both
libcs, but not to rely on nolibc-specific stuff that could make tests
harder to debug.

Regards,
Willy