From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave.Martin@arm.com (Dave Martin) Date: Tue, 29 Mar 2016 11:26:05 +0100 Subject: [PATCH 1/1] ARM : missing corrupted reg in __do_div_asm In-Reply-To: <3792990.eCI4tPEEyD@wuerfel> References: <1459138743-10477-1-git-send-email-chengang.beijing@gmail.com> <3792990.eCI4tPEEyD@wuerfel> Message-ID: <20160329102605.GC3701@e103592.cambridge.arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Tue, Mar 29, 2016 at 12:19:49PM +0200, Arnd Bergmann wrote: > On Monday 28 March 2016 12:19:03 Chen Gang wrote: > > __xl(R0 in little endian system, or R1 in big endian system) is corrupted > > after calling __do_div64 and compiler is not informed about this in > > macro __do_div_asm. If n is used again afterwards, __xl won't be > > reloaded and n will contain incorrect value. > > > > Signed-off-by: Chen Gang > > Signed-off-by: Chen Gang > > --- > > How did you find this? Did you run into this problem on a live system > or see it through inspection? > > > arch/arm/include/asm/div64.h | 6 ++++-- > > 1 file changed, 4 insertions(+), 2 deletions(-) > > > > diff --git a/arch/arm/include/asm/div64.h b/arch/arm/include/asm/div64.h > > index e1f0776..1a6e91a 100644 > > --- a/arch/arm/include/asm/div64.h > > +++ b/arch/arm/include/asm/div64.h > > @@ -35,12 +35,14 @@ static inline uint32_t __div64_32(uint64_t *n, uint32_t base) > > register unsigned long long __n asm("r0") = *n; > > register unsigned long long __res asm("r2"); > > register unsigned int __rem asm(__xh); > > + register unsigned int __clobber asm(__xl); > > asm( __asmeq("%0", __xh) > > __asmeq("%1", "r2") > > + __asmeq("%3", "r0") > > + __asmeq("%4", "r4") > > __asmeq("%2", "r0") > > - __asmeq("%3", "r4") > > "bl __do_div64" > > - : "=r" (__rem), "=r" (__res) > > + : "=r" (__rem), "=r" (__res), "=r" (__clobber) > > : "r" (__n), "r" (__base) > > : "ip", "lr", "cc"); > > *n = __res; > > Doesn't the clobber normally go in the third line along with > "ip" and "lr"? Since __xl is not used for any real argument to the asm, I think we can just add __xl to the clobber list directly, without needing to introduce an extra register variable ... no? Cheers ---Dave