Building a kernel with CONFIG_CC_OPTIMISE_FOR_SIZE leads to
the following functions being copied several times in vmlinux:
31 times __ilog2_u32()
34 times fls()
Disassembly follows:
c00f476c <fls>:
c00f476c: 7c 63 00 34 cntlzw r3,r3
c00f4770: 20 63 00 20 subfic r3,r3,32
c00f4774: 4e 80 00 20 blr
c00f4778 <__ilog2_u32>:
c00f4778: 94 21 ff f0 stwu r1,-16(r1)
c00f477c: 7c 08 02 a6 mflr r0
c00f4780: 90 01 00 14 stw r0,20(r1)
c00f4784: 4b ff ff e9 bl c00f476c <fls>
c00f4788: 80 01 00 14 lwz r0,20(r1)
c00f478c: 38 63 ff ff addi r3,r3,-1
c00f4790: 7c 08 03 a6 mtlr r0
c00f4794: 38 21 00 10 addi r1,r1,16
c00f4798: 4e 80 00 20 blr
When forcing inlining of fls(), we get
c0008b80 <__ilog2_u32>:
c0008b80: 7c 63 00 34 cntlzw r3,r3
c0008b84: 20 63 00 1f subfic r3,r3,31
c0008b88: 4e 80 00 20 blr
vmlinux size gets reduced by 1 kbyte with that change.
Signed-off-by: Christophe Leroy <[email protected]>
---
arch/powerpc/include/asm/bitops.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/powerpc/include/asm/bitops.h b/arch/powerpc/include/asm/bitops.h
index f18b1eac6b54..7df7fee774e5 100644
--- a/arch/powerpc/include/asm/bitops.h
+++ b/arch/powerpc/include/asm/bitops.h
@@ -288,7 +288,7 @@ static __always_inline void arch___clear_bit_unlock(int nr, volatile unsigned lo
* fls: find last (most-significant) bit set.
* Note fls(0) = 0, fls(1) = 1, fls(0x80000000) = 32.
*/
-static inline int fls(unsigned int x)
+static __always_inline int fls(unsigned int x)
{
int lz;
@@ -306,7 +306,7 @@ static inline int fls(unsigned int x)
* 32-bit fls calls.
*/
#ifdef CONFIG_PPC64
-static inline int fls64(__u64 x)
+static __always_inline int fls64(__u64 x)
{
int lz;
--
2.34.1
On Fri, 11 Feb 2022 09:51:32 +0100, Christophe Leroy wrote:
> Building a kernel with CONFIG_CC_OPTIMISE_FOR_SIZE leads to
> the following functions being copied several times in vmlinux:
>
> 31 times __ilog2_u32()
> 34 times fls()
>
> Disassembly follows:
>
> [...]
Applied to powerpc/next.
[1/1] powerpc/bitops: Force inlining of fls()
https://git.kernel.org/powerpc/c/0b0057cc4193c7cd9c0829a440e4901b29ce4ff8
cheers