Re: [PATCH v2] Add public function syscall_no_errno

["Zack Weinberg" <zack@owlfolio.org>]

On Mon, Feb 12, 2024, at 11:16 AM, Askar Safin wrote:
> ---- On Mon, 12 Feb 2024 18:44:31 +0400  Rich Felker  wrote ---
>  > Yes, there are a very small number of such syscalls -- getuid and
>  > getgid are the only relevant ones AFAICT -- but the author of this
>  > proposal is missing the point
>
> Okay, I declare defeat

I have a question for you: Do glibc's existing getuid() and getgid()
functions correctly handle IDs in the [-4095, -1] range (perhaps better
described as the [4294963201, 4294967295] range) ?  It appears to me
from binary code inspection that they do -- here's the assembly dump of
getuid() on x86-64:

(gdb) disas getuid
Dump of assembler code for function __GI_getuid:
   0x00000000000cf940 <+0>:	mov    $0x66,%eax
   0x00000000000cf945 <+5>:	syscall
   0x00000000000cf947 <+7>:	ret
End of assembler dump.

But I am not having any luck figuring out what bit of glibc's *source*
code tells the syscall stub generator not to emit the code to check for
error returns for these syscalls, so it's plausible to me that there is
a bug in here somewhere, possibly only on lesser-used architectures.  If
you know of a case where we get this wrong, please tell us about it so
we can fix it.

zw