linux-kernel - [PATCH] lib: uninline simple

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Date:   Fri, 11 Jun 2021 22:17:34 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     akpm@...ux-foundation.org
Cc:     linux-kernel@...r.kernel.org
Subject: [PATCH] lib: uninline simple_strtoull()

Gcc inlines simple_strtoull() too agressively.

Given that all 4 signatures match, everything very efficiently calls or
tailcalls into simple_strtoull():

	ffffffff81da0240 <simple_strtoll>:
	ffffffff81da0240:       80 3f 2d                cmp    BYTE PTR [rdi],0x2d
	ffffffff81da0243:       74 05                   je     ffffffff81da024a <simple_strtoll+0xa>
	ffffffff81da0245:       e9 76 ff ff ff          jmp    simple_strtoull
	ffffffff81da024a:       48 83 c7 01             add    rdi,0x1
	ffffffff81da024e:       e8 6d ff ff ff          call   simple_strtoull
	ffffffff81da0253:       48 f7 d8                neg    rax
	ffffffff81da0256:       c3                      ret

Space savings (on F34-ish .config)

	add/remove: 0/0 grow/shrink: 1/3 up/down: 52/-313 (-261)
	Function                                     old     new   delta
	vsscanf                                     2167    2219     +52
	simple_strtoul                                72       2     -70
	simple_strtoll                               143      23    -120
	simple_strtol                                143      20    -123

Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
---

 lib/vsprintf.c |    1 +
 1 file changed, 1 insertion(+)

--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -61,6 +61,7 @@
  *
  * This function has caveats. Please use kstrtoull instead.
  */
+noinline
 unsigned long long simple_strtoull(const char *cp, char **endp, unsigned int base)
 {
 	unsigned long long result;