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

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Message-ID: <7068F1FF-1266-447D-ACC8-2F1AD774F230@zytor.com>
Date: Wed, 27 Dec 2023 18:17:35 -0800
From: "H. Peter Anvin" <hpa@...or.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,
        linux-kernel@...r.kernel.org, Nick Desaulniers <nnn@...gle.com>
Subject: Re: [PATCH] x86/syscalls: shrink entry/syscall_32.i via IWYU

On December 27, 2023 4:26:14 PM PST, Al Viro <viro@...iv.linux.org.uk> wrote:
>On Wed, Dec 27, 2023 at 03:50:33PM -0800, H. Peter Anvin wrote:
>> > /*
>> >  * Only the low 32 bits of orig_ax are meaningful, so we return int.
>> >  * This importantly ignores the high bits on 64-bit, so comparisons
>> 
>> __visible is for LTO, no?
>
>If we need it in cases when array defined in entry/syscall_32.c and
>used in entry/common.c, I would respectfully suggest that whatever
>we need it for is misguided garbage.  I don't think that LTO does
>need it, though.  How is arch/x86/entry/{syscall_32,common}.c
>different from e.g. fs/{namespace,d_path}.c, where we have
>fs/namespace.c:100:__cacheline_aligned_in_smp DEFINE_SEQLOCK(mount_lock);
>and
>fs/d_path.c:166:        read_seqbegin_or_lock(&mount_lock, &m_seq);
>respectively?

You're correct of course; __visible for LTO is for functions called from assembly *at the point of definition*, not declaration and certainly not as a type.