linux-kernel - Re: [PATCH v3 2/9] x86/entry/vdso: refactor the vdso build

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Message-ID: <CAMzpN2iwrzKzhif7WXsoQi=4OdBENZMV14Hm2a5ePukywNgh1w@mail.gmail.com>
Date: Thu, 13 Nov 2025 13:38:05 -0500
From: Brian Gerst <brgerst@...il.com>
To: "H. Peter Anvin" <hpa@...or.com>
Cc: "Jason A. Donenfeld" <Jason@...c4.com>, "Peter Zijlstra (Intel)" <peterz@...radead.org>, "Theodore Ts'o" <tytso@....edu>, 
	Thomas Weißschuh <thomas.weissschuh@...utronix.de>, 
	Xin Li <xin@...or.com>, Andrew Cooper <andrew.cooper3@...rix.com>, 
	Andy Lutomirski <luto@...nel.org>, Ard Biesheuvel <ardb@...nel.org>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, Ingo Molnar <mingo@...hat.com>, 
	James Morse <james.morse@....com>, Jarkko Sakkinen <jarkko@...nel.org>, 
	Josh Poimboeuf <jpoimboe@...nel.org>, Kees Cook <kees@...nel.org>, Nam Cao <namcao@...utronix.de>, 
	Oleg Nesterov <oleg@...hat.com>, Perry Yuan <perry.yuan@....com>, 
	Thomas Gleixner <tglx@...utronix.de>, Thomas Huth <thuth@...hat.com>, Uros Bizjak <ubizjak@...il.com>, 
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, linux-sgx@...r.kernel.org, 
	x86@...nel.org
Subject: Re: [PATCH v3 2/9] x86/entry/vdso: refactor the vdso build

On Wed, Nov 12, 2025 at 3:23 PM H. Peter Anvin <hpa@...or.com> wrote:
>
> - Separate out the vdso sources into common, vdso32, and vdso64
>   directories.
> - Move the vdso2c tool to arch/x86/tools.
> - Build the 32- and 64-bit vdsos in their respective subdirectories;
>   this greatly simplifies the build flags handling.
> - Unify the mangling of Makefile flags between the 32- and 64-bit
>   vdso code as much as possible; all common rules are put in
>   arch/x86/entry/vdso/common/Makefile.include. The remaining
>   is very simple for 32 bits; the 64-bit one is only slightly more
>   complicated because it contains the x32 generation rule.
> - Define __DISABLE_EXPORTS when building the vdso. This need seems to
>   have been masked by different ordering compile flags before.
> - Change CONFIG_X86_64 to BUILD_VDSO32_64 in vdso32/system_call.S,
>   to make it compatible with including fake_32bit_build.h.
> - The -fcf-protection= option was "leaking" from the kernel build,
>   for reasons that was not clear to me. Futhermore, several
>   distributions ship with it set to a default value other than
>   "-fcf-protection=none". Make it match the configuration options
>   for *user space*.
>
> Note that this patch may seem large, but the vast majority of it is
> simply code movement.

Some of these changes (like moving vdso2c) can be split out into
smaller patches.