Re: [PATCH v2 2/2] perf bench: Add support for 32-bit systems with 64-bit time_t
From: Arnd Bergmann <arnd@arndb.de>
Date: 2021-09-10 07:18:03
Also in:
linux-riscv, lkml
On Fri, Sep 10, 2021 at 6:31 AM Alistair Francis [off-list ref] wrote:
quoted hunk ↗ jump to hunk
From: Alistair Francis <redacted> Some 32-bit architectures (such are 32-bit RISC-V) only have a 64-bit time_t and as such don't have the SYS_futex syscall. This patch will allow us to use the SYS_futex_time64 syscall on those platforms. Signed-off-by: Alistair Francis <redacted> --- tools/perf/bench/futex.h | 43 +++++++++++++++++++++++++++++++++++++++- 1 file changed, 42 insertions(+), 1 deletion(-)diff --git a/tools/perf/bench/futex.h b/tools/perf/bench/futex.h index f80a4759ee79b..09c5596726c60 100644 --- a/tools/perf/bench/futex.h +++ b/tools/perf/bench/futex.h@@ -27,6 +27,12 @@ struct bench_futex_parameters { unsigned int nrequeue; }; +/* A version of 'struct timespec' with 32-bit time_t and nanoseconds. */ +struct __timespec32 { + __kernel_long_t tv_sec; + __kernel_long_t tv_nsec; +};
Why not use the existing __kernel_old_timespec structure definition from the header?
+#if defined(SYS_futex)
+ if (sizeof(*timeout) == sizeof(struct __timespec32))
+ return syscall(SYS_futex, uaddr, op | opflags, val, timeout, uaddr2, val3);
+
+ if (timeout && timeout->tv_sec == (long)timeout->tv_sec) {
+ struct __timespec32 ts32;
+
+ ts32.tv_sec = (__kernel_long_t) timeout->tv_sec;
+ ts32.tv_nsec = (__kernel_long_t) timeout->tv_nsec;
+
+ return syscall(SYS_futex, uaddr, op | opflags, val, ts32, uaddr2, val3);
+ } else if (!timeout) {
+ return syscall(SYS_futex, uaddr, op | opflags, val, NULL, uaddr2, val3);
+ }
+#endif
+
+ errno = ENOSYS;
+ return -1;
Similarly, I think just using the kernel's constants like __NR_futex instead of
SYS_futex would be more appropriate here, this way you know if futex_time64
is available and don't have to do the emulation for running the binary
on pre-5.1
kernels. Perf already uses __NR_perf_event_open, __NR_getcpu, and
__NR_setns instead of the SYS_* versions.
Arnd