The `FIXTURE(args)` macro defines an empty `struct _test_data_args`, leading to `sizeof(struct _test_data_args)` evaluating to 0. This caused a build error due to a compiler warning on a `memset` call with a zero size argument.
Adding a dummy member to the struct ensures its size is non-zero, resolving the build issue.
Signed-off-by: Wake Liu wakel@google.com --- tools/testing/selftests/futex/functional/futex_requeue_pi.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/tools/testing/selftests/futex/functional/futex_requeue_pi.c b/tools/testing/selftests/futex/functional/futex_requeue_pi.c index f299d75848cd..000fec468835 100644 --- a/tools/testing/selftests/futex/functional/futex_requeue_pi.c +++ b/tools/testing/selftests/futex/functional/futex_requeue_pi.c @@ -52,6 +52,7 @@ struct thread_arg {
FIXTURE(args) { + char dummy; };
FIXTURE_SETUP(args)
Hi Wake,
Em 19/11/2025 00:00, Wake Liu escreveu:
The `FIXTURE(args)` macro defines an empty `struct _test_data_args`, leading to `sizeof(struct _test_data_args)` evaluating to 0. This caused a build error due to a compiler warning on a `memset` call with a zero size argument.
Do you mind sharing your compiler options? I can't reproduce this warning here. I also noted that a few other selftests have this pattern of defining an empty FIXTURE(), do they also produce warnings?
On Wed, Nov 19 2025 at 11:00, Wake Liu wrote:
The `FIXTURE(args)` macro defines an empty `struct _test_data_args`, leading to `sizeof(struct _test_data_args)` evaluating to 0. This caused a build error due to a compiler warning on a `memset` call with a zero size argument.
Where is that memset? The only possibly related one I can find in the kselftest harness is:
if (sizeof(foo) > 0) memset(foo, 0, sizeof(foo));
If your compiler complains about that, then you need to fix your compiler and not perfectly correct code.
You again fail to provide enough information to understand what you are trying to "fix" including the compiler version and related built options.
Thanks,
tglx
When building kselftests with a toolchain that enables source fortification (e.g., Android's build environment, which uses -D_FORTIFY_SOURCE=3), a build failure occurs in tests that use an empty FIXTURE().
The root cause is that an empty fixture struct results in `sizeof(self_private)` evaluating to 0. The compiler's fortification checks then detect the `memset()` call with a compile-time constant size of 0, issuing a `-Wuser-defined-warnings` which is promoted to an error by `-Werror`.
An initial attempt to guard the call with `if (sizeof(self_private) > 0)` was insufficient. The compiler's static analysis is aggressive enough to flag the `memset(..., 0)` pattern before evaluating the conditional, thus still triggering the error.
To resolve this robustly, this change introduces a `static inline` helper function, `__kselftest_memset_safe()`. This function wraps the size check and the `memset()` call. By replacing the direct `memset()` in the `__TEST_F_IMPL` macro with a call to this helper, we create an abstraction boundary. This prevents the compiler's static analyzer from "seeing" the problematic pattern at the macro expansion site, resolving the build failure.
Build Context: Compiler: Android (14488419, +pgo, +bolt, +lto, +mlgo, based on r584948) clang version 22.0.0 (https://android.googlesource.com/toolchain/llvm-project 2d65e4108033380e6fe8e08b1f1826cd2bfb0c99) Relevant Options: -O2 -Wall -Werror -D_FORTIFY_SOURCE=3 -target i686-linux-android10000
Test: m kselftest_futex_futex_requeue_pi
Change-Id: If4fdfe6ffcbe9736fbd8f66b2453e8cbbb95e25e Signed-off-by: Wake Liu wakel@google.com --- tools/testing/selftests/kselftest_harness.h | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/tools/testing/selftests/kselftest_harness.h b/tools/testing/selftests/kselftest_harness.h index 3f66e862e83eb..159cd6729af33 100644 --- a/tools/testing/selftests/kselftest_harness.h +++ b/tools/testing/selftests/kselftest_harness.h @@ -70,6 +70,12 @@
#include "kselftest.h"
+static inline void __kselftest_memset_safe(void *s, int c, size_t n) +{ + if (n > 0) + memset(s, c, n); +} + #define TEST_TIMEOUT_DEFAULT 30
/* Utilities exposed to the test definitions */ @@ -416,7 +422,7 @@ self = mmap(NULL, sizeof(*self), PROT_READ | PROT_WRITE, \ MAP_SHARED | MAP_ANONYMOUS, -1, 0); \ } else { \ - memset(&self_private, 0, sizeof(self_private)); \ + __kselftest_memset_safe(&self_private, 0, sizeof(self_private)); \ self = &self_private; \ } \ } \
On 12/24/25 01:41, Wake Liu wrote:
When building kselftests with a toolchain that enables source fortification (e.g., Android's build environment, which uses -D_FORTIFY_SOURCE=3), a build failure occurs in tests that use an empty FIXTURE().
The root cause is that an empty fixture struct results in `sizeof(self_private)` evaluating to 0. The compiler's fortification checks then detect the `memset()` call with a compile-time constant size of 0, issuing a `-Wuser-defined-warnings` which is promoted to an error by `-Werror`.
An initial attempt to guard the call with `if (sizeof(self_private) > 0)` was insufficient. The compiler's static analysis is aggressive enough to flag the `memset(..., 0)` pattern before evaluating the conditional, thus still triggering the error.
To resolve this robustly, this change introduces a `static inline` helper function, `__kselftest_memset_safe()`. This function wraps the size check and the `memset()` call. By replacing the direct `memset()` in the `__TEST_F_IMPL` macro with a call to this helper, we create an abstraction boundary. This prevents the compiler's static analyzer from "seeing" the problematic pattern at the macro expansion site, resolving the build failure.
Build Context: Compiler: Android (14488419, +pgo, +bolt, +lto, +mlgo, based on r584948) clang version 22.0.0 (https://android.googlesource.com/toolchain/llvm-project 2d65e4108033380e6fe8e08b1f1826cd2bfb0c99) Relevant Options: -O2 -Wall -Werror -D_FORTIFY_SOURCE=3 -target i686-linux-android10000
Test: m kselftest_futex_futex_requeue_pi
Change-Id: If4fdfe6ffcbe9736fbd8f66b2453e8cbbb95e25e
I removed this before applying. In the future remove these before sending the patch - running checkpatch.pl prompts you to remove it.
Signed-off-by: Wake Liu wakel@google.com
tools/testing/selftests/kselftest_harness.h | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/tools/testing/selftests/kselftest_harness.h b/tools/testing/selftests/kselftest_harness.h index 3f66e862e83eb..159cd6729af33 100644 --- a/tools/testing/selftests/kselftest_harness.h +++ b/tools/testing/selftests/kselftest_harness.h @@ -70,6 +70,12 @@ #include "kselftest.h" +static inline void __kselftest_memset_safe(void *s, int c, size_t n) +{
- if (n > 0)
memset(s, c, n);+}
- #define TEST_TIMEOUT_DEFAULT 30
/* Utilities exposed to the test definitions */ @@ -416,7 +422,7 @@ self = mmap(NULL, sizeof(*self), PROT_READ | PROT_WRITE, \ MAP_SHARED | MAP_ANONYMOUS, -1, 0); \ } else { \
memset(&self_private, 0, sizeof(self_private)); \
__kselftest_memset_safe(&self_private, 0, sizeof(self_private)); \ self = &self_private; \ } \
Applied to linux-kselftest fixes branch for next rc.
thanks, -- Shuah
linux-kselftest-mirror@lists.linaro.org
-
André Almeida -
Shuah Khan -
Thomas Gleixner -
Wake Liu