linux-kernel - Re: [PATCH 2/4] x86/vdso: Use 32-bit CHECKFLAGS for compat vDSO

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Message-ID: <0177FB0A-44F0-4D28-8DAD-2BAACC598373@zytor.com>
Date: Sat, 17 Jan 2026 14:02:47 -0800
From: "H. Peter Anvin" <hpa@...or.com>
To: Thomas Weißschuh <thomas.weissschuh@...utronix.de>,
        Arnd Bergmann <arnd@...db.de>
CC: "David S . Miller" <davem@...emloft.net>,
        Andreas Larsson <andreas@...sler.com>,
        Andy Lutomirski <luto@...nel.org>, Thomas Gleixner <tglx@...nel.org>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>, sparclinux@...r.kernel.org,
        linux-kernel@...r.kernel.org, Linux-Arch <linux-arch@...r.kernel.org>,
        linux-s390@...r.kernel.org, Sun Jian <sun.jian.kdev@...il.com>
Subject: Re: [PATCH 2/4] x86/vdso: Use 32-bit CHECKFLAGS for compat vDSO

On January 16, 2026 12:09:34 AM PST, "Thomas Weißschuh" <thomas.weissschuh@...utronix.de> wrote:
>On Fri, Jan 16, 2026 at 08:49:12AM +0100, Arnd Bergmann wrote:
>> On Fri, Jan 16, 2026, at 08:40, Thomas Weißschuh wrote:
>> > When building the compat vDSO the CHECKFLAGS from the 64-bit kernel
>> > are used. These are combined with the 32-bit CFLAGS. This confuses
>> > sparse, producing false-positive warnings or potentially missing
>> > real issues.
>> >
>> > Manually override the CHECKFLAGS for the compat vDSO with the correct
>> > 32-bit configuration.
>> >
>> > Reported-by: Sun Jian <sun.jian.kdev@...il.com>
>> > Closes: 
>> > https://lore.kernel.org/lkml/20260114084529.1676356-1-sun.jian.kdev@gmail.com/
>> > Signed-off-by: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
>> 
>> Acked-by: Arnd Bergmann <arnd@...db.de>
>> 
>> > +CHECKFLAGS_32 := $(CHECKFLAGS) -U__x86_64__ -D__i386__ -m32
>> > +
>> >  $(obj)/vdso32.so.dbg: KBUILD_CFLAGS = $(KBUILD_CFLAGS_32)
>> > +$(obj)/vdso32.so.dbg: CHECKFLAGS = $(CHECKFLAGS_32)
>> 
>> Have you checked if something like this is needed for x32 as well?
>
>It didn't show up in my testing. I think this is explained by the x32 vDSO
>being built as 64-bit and only converted to x32 afterwards.
>
>Thomas

This is going to crash hard with the changes in tip:x86/entry.

But yes, the x32 vdso is currently really just a wrapped version on the 64-bit code, and as long as there are no pointers to pointers used in the vdso ABI there isn't really a reason to change that.