The following commit has been merged into the x86/percpu branch of tip:
Commit-ID: e39828d2c1c0781ccfcf742791daf88fdfa481ea
Gitweb: https://git.kernel.org/tip/e39828d2c1c0781ccfcf742791daf88fdfa481ea
Author: Uros Bizjak <ubizjak@xxxxxxxxx>
AuthorDate: Mon, 16 Oct 2023 22:07:30 +02:00
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Wed, 18 Oct 2023 14:09:16 +02:00
x86/percpu: Use the correct asm operand modifier in percpu_stable_op()
The "P" asm operand modifier is a x86 target-specific modifier.
When used for a constant, it drops all syntax-specific prefixes and
issues the bare constant. This modifier is not correct for address
handling, in this case a generic "a" operand modifier should be used.
The "a" asm operand modifier substitutes a memory reference, with the
actual operand treated as address. For x86_64, when a symbol is
provided, the "a" modifier emits "sym(%rip)" instead of "sym",
enabling shorter %rip-relative addressing.
Clang allows only "i" and "r" operand constraints with an "a" modifier,
so the patch normalizes the modifier/constraint pair to "a"/"i"
which is consistent between both compilers.
The patch reduces code size of a test build by 4072 bytes:
text data bss dec hex filename
25523268 4388300 808452 30720020 1d4c014 vmlinux-old.o
25519196 4388300 808452 30715948 1d4b02c vmlinux-new.o
[ mingo: Changelog clarity. ]
Signed-off-by: Uros Bizjak <ubizjak@xxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Uros Bizjak <ubizjak@xxxxxxxxx>
Cc: Sean Christopherson <seanjc@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20231016200755.287403-1-ubizjak@xxxxxxxxx
---
arch/x86/include/asm/percpu.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
index 5474690..ac3220a 100644
--- a/arch/x86/include/asm/percpu.h
+++ b/arch/x86/include/asm/percpu.h
@@ -194,9 +194,9 @@ do { \
#define percpu_stable_op(size, op, _var) \
({ \
__pcpu_type_##size pfo_val__; \
- asm(__pcpu_op2_##size(op, __force_percpu_arg(P[var]), "%[val]") \
+ asm(__pcpu_op2_##size(op, __force_percpu_arg(a[var]), "%[val]") \
: [val] __pcpu_reg_##size("=", pfo_val__) \
- : [var] "p" (&(_var))); \
+ : [var] "i" (&(_var))); \
(typeof(_var))(unsigned long) pfo_val__; \
})
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