From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave.Martin@arm.com (Dave Martin) Date: Wed, 30 Mar 2016 15:07:21 +0100 Subject: [PATCH 1/1] ARM : missing corrupted reg in __do_div_asm In-Reply-To: <56FB4784.1060105@rdamicro.com> References: <1459138743-10477-1-git-send-email-chengang.beijing@gmail.com> <3792990.eCI4tPEEyD@wuerfel> <20160329102605.GC3701@e103592.cambridge.arm.com> <20160329103418.GX19428@n2100.arm.linux.org.uk> <20160329105637.GD3701@e103592.cambridge.arm.com> <56FB4784.1060105@rdamicro.com> Message-ID: <20160330140718.GG3701@e103592.cambridge.arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Wed, Mar 30, 2016 at 03:27:01AM +0000, ??(Gangchen) wrote: > On 03/29/2016 06:56 PM, Dave Martin wrote: > > On Tue, Mar 29, 2016 at 11:34:18AM +0100, Russell King - ARM Linux wrote: > >> On Tue, Mar 29, 2016 at 11:26:05AM +0100, Dave Martin wrote: > >>> 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? > >> No, you can't. The clobber list is not allowed to specify registers > >> that may be used for input or output operands, and since __xl may be > >> r0, and __n _is_ r0, you can't specify r0 in the clobber list. > > Hmm, you're right -- in which case the change looks reasonable. > > > > I wonder whether the following would be cleaner than having these > > aliased arguments: > > > > asm( /* ... */ > > "bl __do_div64" > > : "+r" (__n), "=r" (__res) > > : "r" (__base) > > : "ip", "lr", "cc"); > > *n = __res; > > return __n >> 32; > > > > (providing that GCC doesn't make a mess of the "easy" shift). > I tried your proposal. It didn't make any difference: this is inline > function and gcc just ignores your trick. What doesn't work for you when using this method? Why does the fact that this is an inline function make a difference? Cheers ---Dave