On Mon, Jan 18, 2021 at 5:34 PM Emiliano Ingrassia
[off-list ref] wrote:

in a simple user space app which calls futex (I changed do_futex with
SYS_futex):

#include <stdlib.h>
#include <stdint.h>
#include <unistd.h>
#include <sys/syscall.h>
#include <linux/futex.h>
#include <sys/time.h>

#ifdef __NR_futex
#define SYS_futex (sizeof(time_t) == sizeof(__kernel_long_t)) ? \
                                           __NR_futex : __NR_futex_time64
#else
#define SYS_futex __NR_futex
#endif

Note that SYS_futex will clash with a libc defined macro of the same name,
so better avoid that.

I guess you also need a third path

#ifndef __NR_futex /* using time64/__kernel_timespec */
...
#elif !defined(__NR_futex64) /* using __kernel_old_timespec */
...
#else /* libc dependent */
...
#endif

static int
futex(uint32_t *uaddr, int futex_op, uint32_t val,
      const struct timespec *timeout, uint32_t *uaddr2, uint32_t val3)
{
        return syscall(SYS_futex, uaddr, futex_op, val, timeout, uaddr2, val3);
}

int main(void)
{
        return futex(NULL, FUTEX_WAKE, 0, NULL, NULL, 0);
}

But what I get is:

error: ‘__NR_futex’ undeclared (first use in this function)
   12 | #define SYS_futex __NR_futex


The problem is that if __NR_futex is not defined it will not work anyway.

Right, sorry about that, see above.

So the only viable solution to correctly compile and use perf on riscv
32 bit is the implementation of time32 syscall for that architecture?

You only need a time32 syscall if your libc defines the time32
version of 'struct timespec'.

And this is true for all 32 bit applications that want to call futex
syscall with a non NULL timer parameter, right?

Also the ones that pass a NULL parameter, as the kernel does
not necessarily implement both.

         Arnd