RE: [PATCH] Linux: Switch back to assembly syscall wrapper for prctl (bug 29770)

[Simon Chopin <simon.chopin@canonical.com>]

Hi Florian,

On ven. 02 févr. 2024 22:30:25, Florian Weimer wrote:
> Commit ff026950e280bc3e9487b41b460fb31bc5b57721 ("Add a C wrapper for
> prctl [BZ #25896]") replaced the assembler wrapper with a C function.
> However, the C variadic function implementation has a different ABI
> on powerpc64le-linux-gnu.  Switch back to the assembler implementation
> on most targets and only keep the C implementation for x86-64 x32.
>
> Also add the __prctl_time64 alias from commit
> b39ffab860cd743a82c91946619f1b8158b0b65e ("Linux: Add time64 alias for
> prctl") to sysdeps/unix/sysv/linux/syscalls.list; it was not yet
> present in commit ff026950e280bc3e9487b41b460fb31bc5b57721.
>
> This restores the old ABI on powerpc64le-linux-gnu, thus fixing
> bug 29770.

Codewise it all looks good to me, but I have a perhaps dumb question:
at this point, aren't we breaking ABI again? Presumably, binaries have
been compiled against the varargs ABI, which AFAICT has been shipped in
RHEL 9 and Ubuntu 22.04 among others, which have been out for a while
now.

>
> Notes:
>
> This is just a repost of my previous patch.  I still think it is the
> right thing to do.  We now have a second case where the varargs
> implementation causes stack corruption on powerpc64le-linux-gnu.  This
> time it's the libasan interceptor for prctl:
>
>   libasan uses incorrect prctl prototype
>   <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113728>
>
> Thanks,
> Florian
>
> ---
>  sysdeps/unix/sysv/linux/syscalls.list            | 1 +
>  sysdeps/unix/sysv/linux/{ => x86_64/x32}/prctl.c | 5 +----
>  2 files changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/sysdeps/unix/sysv/linux/syscalls.list b/sysdeps/unix/sysv/linux/syscalls.list
> index 73e941ef89..9ac42c3436 100644
> --- a/sysdeps/unix/sysv/linux/syscalls.list
> +++ b/sysdeps/unix/sysv/linux/syscalls.list
> @@ -46,6 +46,7 @@ open_tree	EXTRA	open_tree	i:isU	open_tree
>  pipe2		-	pipe2		i:fi	__pipe2		pipe2
>  pidfd_open	EXTRA	pidfd_open	i:iU	pidfd_open
>  pidfd_getfd	EXTRA	pidfd_getfd	i:iiU	pidfd_getfd
> +prctl		EXTRA	prctl		i:iiiii	__prctl		prctl __prctl_time64
>  pivot_root	EXTRA	pivot_root	i:ss	pivot_root
>  pidfd_send_signal	EXTRA	pidfd_send_signal	i:iiPU	pidfd_send_signal
>  process_madvise EXTRA   process_madvise i:iPniU process_madvise
> diff --git a/sysdeps/unix/sysv/linux/prctl.c b/sysdeps/unix/sysv/linux/x86_64/x32/prctl.c
> similarity index 93%
> rename from sysdeps/unix/sysv/linux/prctl.c
> rename to sysdeps/unix/sysv/linux/x86_64/x32/prctl.c
> index 52d234ea0d..4bf1b479a0 100644
> --- a/sysdeps/unix/sysv/linux/prctl.c
> +++ b/sysdeps/unix/sysv/linux/x86_64/x32/prctl.c
> @@ -1,4 +1,4 @@
> -/* prctl - Linux specific syscall.
> +/* prctl - Linux specific syscall.  x86-64 x32 version.
>     Copyright (C) 2020-2024 Free Software Foundation, Inc.
>     This file is part of the GNU C Library.
>
> @@ -40,6 +40,3 @@ __prctl (int option, ...)
>
>  libc_hidden_def (__prctl)
>  weak_alias (__prctl, prctl)
> -#if __TIMESIZE != 64
> -weak_alias (__prctl, __prctl_time64)
> -#endif
>
> base-commit: 7c8df0b9441e34928f2d7d70531e3d55e016c32e
>