[tip: timers/vdso] asm-generic/bitsperlong.h: Add sanity checks for __BITS_PER_LONG

[tip-bot2 for Thomas Weißschuh]

The following commit has been merged into the timers/vdso branch of tip:

Commit-ID:     62357a5888ea6ef81f718eee20ad962a1101fb96
Gitweb:        https://git.kernel.org/tip/62357a5888ea6ef81f718eee20ad962a1101fb96
Author:        Thomas Weißschuh <thomas.weissschuh@xxxxxxxxxxxxx>
AuthorDate:    Mon, 02 Mar 2026 08:58:41 +01:00
Committer:     Thomas Gleixner <tglx@xxxxxxxxxx>
CommitterDate: Wed, 11 Mar 2026 10:15:43 +01:00

asm-generic/bitsperlong.h: Add sanity checks for __BITS_PER_LONG

The value of __BITS_PER_LONG from architecture-specific logic should
always match the generic one if that is available. It should also match
the actual C type 'long'.

Mismatches can happen for example when building the compat vDSO. Either
during the compilation, see commit 9a6d3ff10f7f ("arm64: uapi: Provide
correct __BITS_PER_LONG for the compat vDSO"), or when running sparse
when mismatched CHECKFLAGS are inherited from the kernel build.

Add some consistency checks which detect such issues early and clearly.

The kernel-internal BITS_PER_LONG is not checked as it is derived from
CONFIG_64BIT and therefore breaks for the compat vDSO. See the similar,
deactivated check above.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@xxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxx>
Acked-by: Arnd Bergmann <arnd@xxxxxxxx>
Link: https://patch.msgid.link/20260302-vdso-compat-checkflags-v2-5-78e55baa58ba@xxxxxxxxxxxxx
---
 include/asm-generic/bitsperlong.h |  9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/include/asm-generic/bitsperlong.h b/include/asm-generic/bitsperlong.h
index 1023e2a..90e8aee 100644
--- a/include/asm-generic/bitsperlong.h
+++ b/include/asm-generic/bitsperlong.h
@@ -19,6 +19,15 @@
 #error Inconsistent word size. Check asm/bitsperlong.h
 #endif
 
+#if __CHAR_BIT__ * __SIZEOF_LONG__ != __BITS_PER_LONG
+#error Inconsistent word size. Check asm/bitsperlong.h
+#endif
+
+#ifndef __ASSEMBLER__
+_Static_assert(sizeof(long) * 8 == __BITS_PER_LONG,
+	       "Inconsistent word size. Check asm/bitsperlong.h");
+#endif
+
 #ifndef BITS_PER_LONG_LONG
 #define BITS_PER_LONG_LONG 64
 #endif