mirrors/linux
1
0
Fork 0
mirror of https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git synced 2026-04-13 20:14:37 -04:00
Code Issues Packages Projects Releases Wiki Activity

s390/uaccess: Optimize raw_copy_from_user() / raw_copy_to_user() for constant sizes

Browse Source 
Avoid that the compiler generates an mvcos loop for constant sizes
smaller than 4096 bytes. The mvcos instruction copies between zero and
4096 bytes (effective length) with one operation. Therefore it is not
necessary to implement a loop for sizes smaller or equal to 4096
bytes.

This reduces the kernel text size by ~50kb (defconfig, gcc 14.2.0):
add/remove: 4/5 grow/shrink: 6/471 up/down: 2294/-51700 (-49406)

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
2025-02-11 20:19:29 +01:00
committed by Vasily Gorbik
parent 10a79b6fdd
commit 88e87cb7b8
1 changed files with 4 additions and 0 deletions
Download Patch File Download Diff File Expand all files Collapse all files

4
arch/s390/include/asm/uaccess.h
View File

@@ -49,6 +49,8 @@ raw_copy_from_user(void *to, const void __user *from, unsigned long size)
: CC_OUT(cc, cc), [size] "+d" (size), [to] "=Q" (*(char *)to)
: [spec] "I" (0x81), [from] "Q" (*(const char __user *)from)
: CC_CLOBBER_LIST("memory", "0"));
if (__builtin_constant_p(osize) && osize <= 4096)
return osize - size;
if (likely(CC_TRANSFORM(cc) == 0))
return osize - size;
size -= 4096;
@@ -75,6 +77,8 @@ raw_copy_to_user(void __user *to, const void *from, unsigned long size)
: CC_OUT(cc, cc), [size] "+d" (size), [to] "=Q" (*(char __user *)to)
: [spec] "I" (0x81), [from] "Q" (*(const char *)from)
: CC_CLOBBER_LIST("memory", "0"));
if (__builtin_constant_p(osize) && osize <= 4096)
return osize - size;
if (likely(CC_TRANSFORM(cc) == 0))
return osize - size;
size -= 4096;