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Re: [RFC v2 06/20] sysdeps/futex: Use futex_time64 if avaliable
On Jun 25 2019, Florian Weimer <fweimer@redhat.com> wrote:
> * Alistair Francis:
>
>> +/* __NR_futex isn't defined on all archs (RV32) so use __NR_futex_time64 */
>> +#ifdef __NR_futex_time64
>> +# define lll_futex_syscall(nargs, futexp, op, ...) \
>> + ({ \
>> + INTERNAL_SYSCALL_DECL (__err); \
>> + long int __ret = INTERNAL_SYSCALL (futex_time64, __err, nargs, futexp, op, \
>> + __VA_ARGS__); \
>> + (__glibc_unlikely (INTERNAL_SYSCALL_ERROR_P (__ret, __err)) \
>> + ? -INTERNAL_SYSCALL_ERRNO (__ret, __err) : 0); \
>> + })
>> +#else
>> +# define lll_futex_syscall(nargs, futexp, op, ...) \
>> + ({ \
>> + INTERNAL_SYSCALL_DECL (__err); \
>> + long int __ret = INTERNAL_SYSCALL (futex, __err, nargs, futexp, op, \
>> + __VA_ARGS__); \
>> + (__glibc_unlikely (INTERNAL_SYSCALL_ERROR_P (__ret, __err)) \
>> + ? -INTERNAL_SYSCALL_ERRNO (__ret, __err) : 0); \
>> + })
>> +#endif
>
> I don't think a compile-time check in generic code is correct here. It
> will cause binaries to fail to run on older kernels which do not have
> the system call. This is obviously not a concern for 32-bit RISC-V, but
> it is not acceptable for i386, for example.
>
> I still think you should define __NR_futex in RV32 <sysdep.h>.
For existing 32-bit archs there needs to be a runtime check (if both
__NR_futex and __NR_futex_time64 are defined).
Andreas.
--
Andreas Schwab, SUSE Labs, schwab@suse.de
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