Re: [PATCH v2] Add public function syscall_no_errno

[Askar Safin <safinaskar@zohomail.com>]

 ---- On Mon, 12 Feb 2024 21:25:27 +0400  Zack Weinberg  wrote --- 
 > 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) ?

Yes.

 > here's the assembly dump of
 > getuid() on x86-64:

Even "incorrect" getuid implementation will work correctly on x86_64,
because uids are 32 bit on Linux. Whole this problem matters for 32-bit
architectures, not 64-bit ones.

 > 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.

getuid is defined in ./sysdeps/unix/sysv/linux/i386/syscalls.list (and similar
files). In 4th column we see "E". This means that getuid never fails and we
should pass raw syscall result to userspace.

"E" gets processed here:
https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/make-syscalls.sh;h=4f6c3490a20bc3eb34f11f1e7aab0ddec7e82e5d;hb=155bb9d036646138348fee0ac045de601811e0c5#l169

Then here:
https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/make-syscalls.sh;h=4f6c3490a20bc3eb34f11f1e7aab0ddec7e82e5d;hb=155bb9d036646138348fee0ac045de601811e0c5#l273

--
Askar Safin
https://types.pl/@safinaskar