From mboxrd@z Thu Jan 1 00:00:00 1970 From: linux@arm.linux.org.uk (Russell King - ARM Linux) Date: Tue, 29 Mar 2016 11:34:18 +0100 Subject: [PATCH 1/1] ARM : missing corrupted reg in __do_div_asm In-Reply-To: <20160329102605.GC3701@e103592.cambridge.arm.com> References: <1459138743-10477-1-git-send-email-chengang.beijing@gmail.com> <3792990.eCI4tPEEyD@wuerfel> <20160329102605.GC3701@e103592.cambridge.arm.com> Message-ID: <20160329103418.GX19428@n2100.arm.linux.org.uk> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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. -- RMK's Patch system: http://www.arm.linux.org.uk/developer/patches/ FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net.