linux-kernel - Re: [PATCH] selftests/futex: fix futex

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Message-ID: <20250827105854.DwmcsKlC@linutronix.de>
Date: Wed, 27 Aug 2025 12:58:54 +0200
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Dan Carpenter <dan.carpenter@...aro.org>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Darren Hart <dvhart@...radead.org>,
	Davidlohr Bueso <dave@...olabs.net>,
	André Almeida <andrealmeid@...lia.com>,
	Shuah Khan <shuah@...nel.org>,
	Cynthia Huang <cynthia@...estech.com>,
	Ben Zong-You Xie <ben717@...estech.com>,
	Muhammad Usama Anjum <usama.anjum@...labora.com>,
	linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH] selftests/futex: fix futex_wait() for 32bit ARM

On 2025-08-26 17:25:11 [+0300], Dan Carpenter wrote:
> On 32bit ARM systems gcc-12 will use 32bit timestamps while gcc-13 and
> later will use 64bit timestamps.  The problem is that SYS_futex will
> continue pointing at the 32bit system call.  This makes the futex_wait
> test fail like this:
> 
> waiter failed errno 110
> not ok 1 futex_wake private returned: 0 Success
> waiter failed errno 110
> not ok 2 futex_wake shared (page anon) returned: 0 Success
> waiter failed errno 110
> not ok 3 futex_wake shared (file backed) returned: 0 Success
> 
> Instead of compiling differently depending on the gcc version, use the
> -D_FILE_OFFSET_BITS=64 -D_TIME_BITS=64 options to ensure that we are
> building with 64bit timestamps.  Then use ifdefs to make SYS_futex point
> to the 64bit system call.
> 
> Signed-off-by: Dan Carpenter <dan.carpenter@...aro.org>
> Tested-by: Anders Roxell <anders.roxell@...aro.org>

It appears glibc uses the 64bit syscall by default. So that is fine.

Sebastian