perf bench futex: Define SYS_futex on 32-bit arches with 64-bit time_t

The kernel does not provide sys_futex() on 32-bit architectures that lack a 32-bit time representation, such as riscv32. Consequently glibc does not define SYS_futex there, only SYS_futex_time64, and perf bench's futex benchmarks fail to build:

bench/futex.h: In function 'futex_syscall':
bench/futex.h:77:18: error: 'SYS_futex' undeclared (first use in this function)

Define SYS_futex as SYS_futex_time64 when only the latter is available. The guard and its comment are taken verbatim from tools/testing/selftests/futex/include/futextest.h, where they were added by commit 04850819c65c ("selftests/futex: Define SYS_futex on 32-bit architectures with 64-bit time_t"), keeping the two futex userspace headers in sync.

No timespec conversion helper is needed on top of this. glibc lays out struct timespec on 32-bit architectures with 64-bit time_t as { int64 tv_sec; int32 tv_nsec; 32-bit pad }, which is compatible with struct __kernel_timespec, and every futex_wait()/futex_lock_pi()/ futex_wait_requeue_pi() call site in perf bench passes a NULL timeout anyway, so no timespec ever crosses the syscall boundary here.

Note that an earlier and more ambitious attempt at this was commit c1ff12dac465 ("perf bench futex: Add support for 32-bit systems with 64-bit time_t"), reverted by
commit ba4026b09d83 ("Revert "perf bench futex: Add support for 32-bit systems with 64-bit time_t"") because it included linux/time_types.h, which is unavailable on older distributions. This change deliberately avoids that dependency and adds only the one guard needed to fix compilation.

Signed-off-by Nylon Chen <[email protected]>

---
 tools/perf/bench/futex.h | 11 +++++++++++
 1 file changed, 11 insertions(+)

tools/perf/bench/futex.h +11 -0

index fcb72d682cf8..6df8837b365b 100644
@@ -14,6 +14,17 @@
 #include <sys/types.h>
 #include <linux/futex.h>
 
+/*
+ * SYS_futex is expected from system C library, in glibc some 32-bit
+ * architectures (e.g. RV32) are using 64-bit time_t, therefore it doesn't have
+ * SYS_futex defined but just SYS_futex_time64. Define SYS_futex as
+ * SYS_futex_time64 in this situation to ensure the compilation and the
+ * compatibility.
+ */
+#if !defined(SYS_futex) && defined(SYS_futex_time64)
+#define SYS_futex SYS_futex_time64
+#endif
+
 struct bench_futex_parameters {
        bool silent;
        bool fshared;

base-commit: 66498c75b4f8017f62d720d9b59675bdf3abce91 --
2.43.7

Quoted 32 lines · Nylon Chen

The kernel does not provide sys_futex() on 32-bit architectures that lack a 32-bit time representation, such as riscv32. Consequently glibc does not define SYS_futex there, only SYS_futex_time64, and perf bench's futex benchmarks fail to build:

bench/futex.h: In function 'futex_syscall':
bench/futex.h:77:18: error: 'SYS_futex' undeclared (first use in this function)

Define SYS_futex as SYS_futex_time64 when only the latter is available. The guard and its comment are taken verbatim from tools/testing/selftests/futex/include/futextest.h, where they were added by commit 04850819c65c ("selftests/futex: Define SYS_futex on 32-bit architectures with 64-bit time_t"), keeping the two futex userspace headers in sync.

No timespec conversion helper is needed on top of this. glibc lays out struct timespec on 32-bit architectures with 64-bit time_t as { int64 tv_sec; int32 tv_nsec; 32-bit pad }, which is compatible with struct __kernel_timespec, and every futex_wait()/futex_lock_pi()/ futex_wait_requeue_pi() call site in perf bench passes a NULL timeout anyway, so no timespec ever crosses the syscall boundary here.

Note that an earlier and more ambitious attempt at this was commit c1ff12dac465 ("perf bench futex: Add support for 32-bit systems with 64-bit time_t"), reverted by
commit ba4026b09d83 ("Revert "perf bench futex: Add support for 32-bit systems with 64-bit time_t"") because it included linux/time_types.h, which is unavailable on older distributions. This change deliberately avoids that dependency and adds only the one guard needed to fix compilation.

Quoted 1 line

Signed-off-by Nylon Chen <[email protected]>

Reviewed-by Ian Rogers <[email protected]>