From: Ammar Faizi ammarfaizi2@gnuweeb.org
stable inclusion from stable-v5.10.121 commit 58c7c015771479440ea90dd7e8abd18c600d40d7 category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I5L6CQ
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=...
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[ Upstream commit b86eb74098a92afd789da02699b4b0dd3f73b889 ]
The asm constraint does not reflect the fact that the asm statement can modify the value of the local variable loops. Which it does.
Specifying the wrong constraint may lead to undefined behavior, it may clobber random stuff (e.g. local variable, important temporary value in regs, etc.). This is especially dangerous when the compiler decides to inline the function and since it doesn't know that the value gets modified, it might decide to use it from a register directly without reloading it.
Change the constraint to "+a" to denote that the first argument is an input and an output argument.
[ bp: Fix typo, massage commit message. ]
Fixes: e01b70ef3eb3 ("x86: fix bug in arch/i386/lib/delay.c file, delay_loop function") Signed-off-by: Ammar Faizi ammarfaizi2@gnuweeb.org Signed-off-by: Borislav Petkov bp@suse.de Link: https://lore.kernel.org/r/20220329104705.65256-2-ammarfaizi2@gnuweeb.org Signed-off-by: Sasha Levin sashal@kernel.org Signed-off-by: Zheng Zengkai zhengzengkai@huawei.com Acked-by: Xie XiuQi xiexiuqi@huawei.com --- arch/x86/lib/delay.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/x86/lib/delay.c b/arch/x86/lib/delay.c index 65d15df6212d..0e65d00e2339 100644 --- a/arch/x86/lib/delay.c +++ b/arch/x86/lib/delay.c @@ -54,8 +54,8 @@ static void delay_loop(u64 __loops) " jnz 2b \n" "3: dec %0 \n"
- : /* we don't need output */ - :"a" (loops) + : "+a" (loops) + : ); }