diff mbox series

[183/227] mm: uninline copy_overflow()

Message ID 20220322214750.0C9DCC340EC@smtp.kernel.org (mailing list archive)
State New
Headers show
Series [001/227] linux/kthread.h: remove unused macros | expand

Commit Message

Andrew Morton March 22, 2022, 9:47 p.m. UTC 
From: Christophe Leroy <christophe.leroy@csgroup.eu>
Subject: mm: uninline copy_overflow()

While building a small config with CONFIG_CC_OPTIMISE_FOR_SIZE, I ended up
with more than 50 times the following function in vmlinux because GCC
doesn't honor the 'inline' keyword:

	c00243bc <copy_overflow>:
	c00243bc:	94 21 ff f0 	stwu    r1,-16(r1)
	c00243c0:	7c 85 23 78 	mr      r5,r4
	c00243c4:	7c 64 1b 78 	mr      r4,r3
	c00243c8:	3c 60 c0 62 	lis     r3,-16286
	c00243cc:	7c 08 02 a6 	mflr    r0
	c00243d0:	38 63 5e e5 	addi    r3,r3,24293
	c00243d4:	90 01 00 14 	stw     r0,20(r1)
	c00243d8:	4b ff 82 45 	bl      c001c61c <__warn_printk>
	c00243dc:	0f e0 00 00 	twui    r0,0
	c00243e0:	80 01 00 14 	lwz     r0,20(r1)
	c00243e4:	38 21 00 10 	addi    r1,r1,16
	c00243e8:	7c 08 03 a6 	mtlr    r0
	c00243ec:	4e 80 00 20 	blr

With -Winline, GCC tells:

	/include/linux/thread_info.h:212:20: warning: inlining failed in call to 'copy_overflow': call is unlikely and code size would grow [-Winline]

copy_overflow() is a non conditional warning called by
check_copy_size() on an error path.

check_copy_size() have to remain inlined in order to benefit
from constant folding, but copy_overflow() is not worth inlining.

Uninline the warning when CONFIG_BUG is selected.

When CONFIG_BUG is not selected, WARN() does nothing so skip it.

This reduces the size of vmlinux by almost 4kbytes.

Link: https://lkml.kernel.org/r/e1723b9cfa924bcefcd41f69d0025b38e4c9364e.1644819985.git.christophe.leroy@csgroup.eu
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: David Laight <David.Laight@ACULAB.COM>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/thread_info.h |    5 ++++-
 mm/maccess.c                |    6 ++++++
 2 files changed, 10 insertions(+), 1 deletion(-)
diff mbox series

Patch

--- a/include/linux/thread_info.h~mm-uninline-copy_overflow
+++ a/include/linux/thread_info.h
@@ -209,9 +209,12 @@  __bad_copy_from(void);
 extern void __compiletime_error("copy destination size is too small")
 __bad_copy_to(void);
 
+void __copy_overflow(int size, unsigned long count);
+
 static inline void copy_overflow(int size, unsigned long count)
 {
-	WARN(1, "Buffer overflow detected (%d < %lu)!\n", size, count);
+	if (IS_ENABLED(CONFIG_BUG))
+		__copy_overflow(size, count);
 }
 
 static __always_inline __must_check bool
--- a/mm/maccess.c~mm-uninline-copy_overflow
+++ a/mm/maccess.c
@@ -335,3 +335,9 @@  long strnlen_user_nofault(const void __u
 
 	return ret;
 }
+
+void __copy_overflow(int size, unsigned long count)
+{
+	WARN(1, "Buffer overflow detected (%d < %lu)!\n", size, count);
+}
+EXPORT_SYMBOL(__copy_overflow);