linux-kernel - [PATCH 1/4] sparc64: vdso: Use 32-bit CHECKFLAGS for compat vDSO

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Message-Id: <20260116-vdso-compat-checkflags-v1-1-4a83b4fbb0d3@linutronix.de>
Date: Fri, 16 Jan 2026 08:40:24 +0100
From: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
To: "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, "H. Peter Anvin" <hpa@...or.com>, 
 Arnd Bergmann <arnd@...db.de>, 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>
Cc: sparclinux@...r.kernel.org, linux-kernel@...r.kernel.org, 
 linux-arch@...r.kernel.org, linux-s390@...r.kernel.org, 
 Thomas Weißschuh <thomas.weissschuh@...utronix.de>, 
 kernel test robot <lkp@...el.com>
Subject: [PATCH 1/4] sparc64: vdso: Use 32-bit CHECKFLAGS for compat vDSO

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: From: kernel test robot <lkp@...el.com>
Closes: https://lore.kernel.org/lkml/202511030021.9v1mIgts-lkp@intel.com/
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@...utronix.de>

---
The actual false-positive is only reported when SPARC is converted over
to the generic vDSO library. However the issue is already present.
To avoid dependencies between different patch queues, I have this patch
in this one.
---
 arch/sparc/vdso/Makefile | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/sparc/vdso/Makefile b/arch/sparc/vdso/Makefile
index 13f1d7be00f1..945d917b0058 100644
--- a/arch/sparc/vdso/Makefile
+++ b/arch/sparc/vdso/Makefile
@@ -90,6 +90,9 @@ KBUILD_CFLAGS_32 += -DDISABLE_BRANCH_PROFILING
 KBUILD_CFLAGS_32 += -mv8plus
 $(obj)/vdso32.so.dbg: KBUILD_CFLAGS = $(KBUILD_CFLAGS_32)

+CHECKFLAGS_32 := $(CHECKFLAGS) -U__sparc_v9__ -U__arch64__ -m32
+$(obj)/vdso32.so.dbg: CHECKFLAGS = $(CHECKFLAGS_32)
+
 $(obj)/vdso32.so.dbg: FORCE \
 			$(obj)/vdso32/vdso32.lds \
 			$(obj)/vdso32/vclock_gettime.o \

-- 
2.52.0