perf tools build broken for RISCV 32 bit

[Arnd Bergmann]

On Wed, Jan 20, 2021 at 3:44 PM Emiliano Ingrassia
<ingrassia at epigenesys.com> wrote:
> On Tue, Jan 19, 2021 at 08:47:59PM +0100, Arnd Bergmann wrote:
> > On Tue, Jan 19, 2021 at 5:53 PM Emiliano Ingrassia
> >
> > I didn't think that COMPAT_32BIT_TIME was even allowed on rv32,
> > but it seems there is a bug in Kconfig, it should be disabled for any
> > architecture that does not set __ARCH_WANT_TIME32_SYSCALLS,
> > but this should not affect the problem at hand.
>
> Ok, will you submit a patch for this bug?

Sure, will do.
>
> Here is the example futex app corrected w.r.t. all the previous
> considerations:
>
> |#include <features.h>
> |#if (defined __GLIBC__) && (__GLIBC__ >= 2 && __GLIBC_MINOR__ >= 32)
> |#include <asm/unistd.h>
> |#include <bits/timesize.h>
> |# ifndef __NR_futex
> |#  if defined (__NR_futex_time64) && (__TIMESIZE == 64)
> |#   define __NR_futex  __NR_futex_time64
> |#  endif
> |# endif
> |#endif

This is broken on musl (which does not define __GLIBC__), on kernels
running with CONFIG_COMPAT_32BIT_TIME disabled (which may
define __NR_futex, but always returns -ENOSYS), and on any future glibc
with 64-bit time_t on anything other all existing architectures (which
define __NR_futex but expect an incompatible argument). It may also
be broken on rv32 if we end up adding support for futex() in the future,
as has been discussed as a possible workaround.

> > rv32 is in the unfortunate position of being the first one that has a glibc
> > port, so it hits a lot of problems that other architectures do not.
> > If the applications get fixed properly, then at least they will also
> > work with musl-1.2 and a (will work-in-progress) glibc that will
> > eventually allow building with 64-bit time_t.
>
> Ok, so in case of perf we probably should limit the needed patch to
> riscv 32 bit architecture, unless we want to solve the problem for all
> 32 bit architecture with time_t 64 bit support.

No, whatever you do should be written to work on all 32-bit
architectures. It would be crazy to add a special case for one
architecture when it's easier to fix it properly.

What was wrong with the helper function I suggested?

       Arnd