From: Ammar Faizi ammarfaizi2@gnuweeb.org
[ 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 --- 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 614c2c6b1959..68ca883abfdb 100644 --- a/arch/x86/lib/delay.c +++ b/arch/x86/lib/delay.c @@ -43,8 +43,8 @@ static void delay_loop(unsigned long loops) " jnz 2b \n" "3: dec %0 \n"
- : /* we don't need output */ - :"a" (loops) + : "+a" (loops) + : ); }