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

[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.

Signed-off-by: Nylon Chen <nylon.chen@xxxxxxxxxx>
---
 tools/perf/bench/futex.h | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/tools/perf/bench/futex.h b/tools/perf/bench/futex.h
index fcb72d682cf8..6df8837b365b 100644
--- a/tools/perf/bench/futex.h
+++ b/tools/perf/bench/futex.h
@@ -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