From: gangchen@rdamicro•com (陈刚(Gangchen))
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH 1/1] ARM : missing corrupted reg in __do_div_asm
Date: Wed, 30 Mar 2016 03:27:01 +0000 [thread overview]
Message-ID: <56FB4784.1060105@rdamicro.com> (raw)
In-Reply-To: <20160329105637.GD3701@e103592.cambridge.arm.com>
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 <gangchen@rdamicro•com>
>>>>> Signed-off-by: Chen Gang <chengang.beijing@gmail•com>
>>>>> ---
>>>> 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.
>
> Cheers
> ---Dave
next prev parent reply other threads:[~2016-03-30 3:27 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-28 4:19 [PATCH 1/1] ARM : missing corrupted reg in __do_div_asm Chen Gang
2016-03-29 10:19 ` Arnd Bergmann
2016-03-29 10:26 ` Dave Martin
2016-03-29 10:34 ` Russell King - ARM Linux
2016-03-29 10:56 ` Dave Martin
2016-03-30 3:27 ` 陈刚(Gangchen) [this message]
2016-03-30 14:07 ` Dave Martin
2016-03-31 7:56 ` 陈刚(Gangchen)
2016-03-31 10:30 ` Dave Martin
2016-03-31 11:20 ` 陈刚(Gangchen)
2016-03-31 11:41 ` Dave Martin
2016-04-01 4:22 ` [PATCH V3 1/1] ARM : missing corrupted reg in __div64_32 chengang
2016-04-01 8:56 ` Dave Martin
2016-04-01 10:28 ` [PATCH V4 " chengang
2016-04-01 11:03 ` Dave Martin
2016-04-01 11:25 ` [PATCH V5 " chengang
2016-04-01 11:34 ` Dave P Martin
2016-04-01 11:35 ` [PATCH V4 " 陈刚(Gangchen)
2016-03-31 11:41 ` [PATCH v2 " Chen Gang
2016-03-29 10:58 ` [PATCH 1/1] ARM : missing corrupted reg in __do_div_asm 陈刚(Gangchen)
[not found] </home/gachen/Re: [PATCH 1_1] ARM:r0 is also corrupted after calling __do_div64..eml>
2015-06-02 6:13 ` Chen Gang
2015-06-08 5:30 ` Chen Gang
2015-06-09 13:09 ` Russell King - ARM Linux
2015-06-28 11:29 ` Chen Gang
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