linux-kernel - Re: [PATCH] x86/syscalls: shrink entry/syscall

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Date: Wed, 3 Jan 2024 08:50:19 -0800
From: Nick Desaulniers <ndesaulniers@...gle.com>
To: Al Viro <viro@...iv.linux.org.uk>
Cc: Tanzir Hasan <tanzirh@...gle.com>, Andy Lutomirski <luto@...nel.org>, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, 
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org, 
	Nick Desaulniers <nnn@...gle.com>
Subject: Re: [PATCH] x86/syscalls: shrink entry/syscall_32.i via IWYU

On Wed, Dec 27, 2023 at 4:45 PM Al Viro <viro@...iv.linux.org.uk> wrote:
>
> On Wed, Dec 27, 2023 at 11:34:44PM +0000, Al Viro wrote:
>
> > That's _it_.  The same goes for syscall_64.c and syscall_x32.c.
> > Oh, and lose the __visible/asmlinkage junk in there - none of that
> > stuff is used from asm these days.  See the patch below -
> > Untested But Should Work(tm):
>
> Unfortunately, there's this in kernel/trace/trace_syscalls.c:
>
> unsigned long __init __weak arch_syscall_addr(int nr)
> {
>         return (unsigned long)sys_call_table[nr];
> }
>
> How is that supposed to work for anything biarch?  Including
> amd64 with CONFIG_COMPAT enabled?

commit f431b634f24d ("tracing/syscalls: Allow archs to ignore tracing
compat syscalls")

added a comment block about ARCH_TRACE_IGNORE_COMPAT_SYSCALLS, which
is defined for x86 in arch/x86/include/asm/ftrace.h.

The implementation of arch_syscall_addr for mips is quite complex;
dependent on quite a few different configs.

-- 
Thanks,
~Nick Desaulniers