This is the mail archive of the
libc-alpha@sourceware.org
mailing list for the glibc project.
Re: [PATCH 03/15] sparc: Use Linux kABI for syscall return
On 11/02/2020 16:24, Florian Weimer wrote:
> * Adhemerval Zanella:
>
>> On 11/02/2020 08:15, Florian Weimer wrote:
>>> * Adhemerval Zanella:
>>>
>>>> + if (__glibc_unlikely (__g1 != 0)) \
>>>
>>> This change is inconsistent with the other updates, which use __g1 ==
>>> -1. Is this deliberate?
>>>
>>> Thanks,
>>> Florian
>>>
>>
>> In fact __SYSCALL_STRING already sets the 'o0' to a negative value if
>> the 'xcc' condition is set (indicating that the syscall has failed).
>> The 'g1' check is superfluous, it will be always true since 'g1' will
>> be either 0 or 1.
>>
>> And both the set and check of 'g1' result is also superfluous, since 'o0'
>> will already hold all the required information.
>>
>> Below is an updated patch, checked on sparc64-linux-gnu and
>> sparcv9-linux-gnu.
>
> I see, nice additional cleanup.
>
>> It changes the sparc internal_syscall* macros to return a negative
>> value instead the 'g1' register value on 'err' macro argument.
> ^ of ^ in the?
>
>
Ack.
>> The __SYSCALL_STRING macro is also changed to no set the 'g1'
> ^ not
>> value, since 'o1' already holds all the required information
>> to check if syscall has failed.
>>
>> The macro INTERNAL_SYSCALL_DECL is no longer required, and the
>> INTERNAL_SYSCALL_ERROR_P follows the other Linux kABIS. The
> ^ macro? ^ kABIs
Ack.
> (or drop the “the“ on the preceding line)
>
>> redefinition of INTERNAL_VSYSCALL_CALL is also no longer
>> required.
>>
>> Checked on sparc64-linux-gnu and sparcv9-linux-gnu. It fixes
>> the sporadic issues on sparc32 where clock_nanosleep does not
>> act as cancellation entrypoint.
>
> I double-checked this against the kernel sources, and entry.S has
> this:
>
> ret_sys_call:
> ld [%curptr + TI_FLAGS], %l6
> cmp %o0, -ERESTART_RESTARTBLOCK
> ld [%sp + STACKFRAME_SZ + PT_PSR], %g3
> set PSR_C, %g2
> bgeu 1f
>
> But ERESTART_RESTARTBLOCK is not 4095, so glibc with this change will
> now treat certain internal kernel error codes as errors, while they
> were previously reported as success. This looks like a kernel bug, in
> that ERESTART_RESTARTBLOCK was not updated when more error codes were
> added. On the other hand, these error codes should never leak into
> userspace.
My understanding is such errors should not be visible by the application,
as indicated by include/linux/errno.h comment. And it seems to be the
case for sparc, at least on:
arch/sparc/kernel/signal_64.c
477 static void do_signal(struct pt_regs *regs, unsigned long orig_i0)
[...]
514 restart_syscall = 0;
515 if (pt_regs_is_syscall(regs) &&
516 (regs->tstate & (TSTATE_XCARRY | TSTATE_ICARRY))) {
517 restart_syscall = 1;
518 orig_i0 = regs->u_regs[UREG_G6];
519 }
520
521 if (has_handler) {
522 if (restart_syscall)
523 syscall_restart(orig_i0, regs, &ksig.ka.sa);
524 signal_setup_done(setup_rt_frame(&ksig, regs), &ksig, 0);
525 } else {
526 if (restart_syscall) {
527 switch (regs->u_regs[UREG_I0]) {
528 case ERESTARTNOHAND:
529 case ERESTARTSYS:
530 case ERESTARTNOINTR:
531 /* replay the system call when we are done */
532 regs->u_regs[UREG_I0] = orig_i0;
533 regs->tpc -= 4;
534 regs->tnpc -= 4;
535 pt_regs_clear_syscall(regs);
536 /* fall through */
537 case ERESTART_RESTARTBLOCK:
538 regs->u_regs[UREG_G1] = __NR_restart_syscall;
539 regs->tpc -= 4;
540 regs->tnpc -= 4;
541 pt_regs_clear_syscall(regs);
542 }
543 }
544
If signal has a handler, syscall_restart will either set EINTR or
previous 'o0' value. Otherwise if syscall should be restarted,
either it will be trying again (line 538) or previous error code
would be set.
>
> To me, your patch looks good.
>