[PATCH] selftests/futex: fix futex_wait() for 32bit ARM

[PATCH] selftests/futex: fix futex_wait() for 32bit ARM

[Dan Carpenter]

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@linaro.org>
Tested-by: Anders Roxell <anders.roxell@linaro.org>
---
 tools/testing/selftests/futex/functional/Makefile |  2 +-
 tools/testing/selftests/futex/include/futextest.h | 11 +++++++++++
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/futex/functional/Makefile b/tools/testing/selftests/futex/functional/Makefile
index 8cfb87f7f7c5..ddfa61d857b9 100644
--- a/tools/testing/selftests/futex/functional/Makefile
+++ b/tools/testing/selftests/futex/functional/Makefile
@@ -1,6 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0
 INCLUDES := -I../include -I../../ $(KHDR_INCLUDES)
-CFLAGS := $(CFLAGS) -g -O2 -Wall -pthread $(INCLUDES) $(KHDR_INCLUDES)
+CFLAGS := $(CFLAGS) -g -O2 -Wall -pthread -D_FILE_OFFSET_BITS=64 -D_TIME_BITS=64 $(INCLUDES) $(KHDR_INCLUDES)
 LDLIBS := -lpthread -lrt -lnuma
 
 LOCAL_HDRS := \
diff --git a/tools/testing/selftests/futex/include/futextest.h b/tools/testing/selftests/futex/include/futextest.h
index 7a5fd1d5355e..3d48e9789d9f 100644
--- a/tools/testing/selftests/futex/include/futextest.h
+++ b/tools/testing/selftests/futex/include/futextest.h
@@ -58,6 +58,17 @@ typedef volatile u_int32_t futex_t;
 #define SYS_futex SYS_futex_time64
 #endif
 
+/*
+ * On 32bit systems if we use "-D_FILE_OFFSET_BITS=64 -D_TIME_BITS=64" or if
+ * we are using a newer compiler then the size of the timestamps will be 64bit,
+ * however, the SYS_futex will still point to the 32bit futex system call.
+ */
+#if __SIZEOF_POINTER__ == 4 && defined(SYS_futex_time64) && \
+	defined(_TIME_BITS) && _TIME_BITS == 64
+# undef SYS_futex
+# define SYS_futex SYS_futex_time64
+#endif
+
 /**
  * futex() - SYS_futex syscall wrapper
  * @uaddr:	address of first futex
-- 
2.47.2

Re: [PATCH] selftests/futex: fix futex_wait() for 32bit ARM

[Sebastian Andrzej Siewior]

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@linaro.org>
> Tested-by: Anders Roxell <anders.roxell@linaro.org>

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

Sebastian