linux-kernel - [PATCH v2 07/13] math64: Always inline u128 version of mul_u64_u64

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Date:   Fri, 19 May 2023 12:21:05 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     bigeasy@...utronix.de
Cc:     mark.rutland@....com, maz@...nel.org, catalin.marinas@....com,
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Subject: [PATCH v2 07/13] math64: Always inline u128 version of mul_u64_u64_shr()

In order to prevent the following complaint from happening, always
inline the u128 variant of mul_u64_u64_shr() -- which is what x86_64
will use.

  vmlinux.o: warning: objtool: read_hv_sched_clock_tsc+0x5a: call to mul_u64_u64_shr.constprop.0() leaves .noinstr.text section

It should compile into something like:

  asm("mul	%[mul];"
      "shrd	%rdx, %rax, %cl"
      : "+&a" (a)
      : "c" shift, [mul] "r" (mul)
      : "d");

Which is silly not to inline, but it happens.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 include/linux/math64.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/include/linux/math64.h
+++ b/include/linux/math64.h
@@ -168,7 +168,7 @@ static __always_inline u64 mul_u64_u32_s
 #endif /* mul_u64_u32_shr */
 
 #ifndef mul_u64_u64_shr
-static inline u64 mul_u64_u64_shr(u64 a, u64 mul, unsigned int shift)
+static __always_inline u64 mul_u64_u64_shr(u64 a, u64 mul, unsigned int shift)
 {
 	return (u64)(((unsigned __int128)a * mul) >> shift);
 }