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s390/lowcore: Use inline qualifier for get_lowcore() inline assembly

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Use asm_inline to let the compiler know that the get_lowcore() inline
assembly has the smallest possible size. The ALTERNATIVE construct is used
to generate a single instruction, however the macro expands to multiple
lines. GCC uses the number of lines of an inline assembly to count the
number of instructions within an inline assembly, which then has an effect
on inlining decisions.

In order to avoid incorrect assumptions use asm_inline. The result is that
more functions are inlined, which results in a small growth of the kernel
image:

add/remove: 59/480 grow/shrink: 854/647 up/down: 168780/-162394 (6386)

Reviewed-by: Juergen Christ <jchrist@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
This commit is contained in:
Heiko Carstens
2025-03-10 10:33:38 +01:00
committed by Vasily Gorbik
parent 20de8f8d31
commit 430693c836
1 changed files with 6 additions and 3 deletions
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9
arch/s390/include/asm/lowcore.h
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@@ -223,9 +223,12 @@ static __always_inline struct lowcore *get_lowcore(void)
if (__is_defined(__DECOMPRESSOR))
return NULL;
asm(ALTERNATIVE("llilh %[lc],0", "llilh %[lc],%[alt]", ALT_FEATURE(MFEATURE_LOWCORE))
: [lc] "=d" (lc)
: [alt] "i" (LOWCORE_ALT_ADDRESS >> 16));
asm_inline(
ALTERNATIVE(" llilh %[lc],0",
" llilh %[lc],%[alt]",
ALT_FEATURE(MFEATURE_LOWCORE))
: [lc] "=d" (lc)
: [alt] "i" (LOWCORE_ALT_ADDRESS >> 16));
return lc;
}