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: Thu, 31 Mar 2016 11:20:24 +0000 [thread overview]
Message-ID: <56FD07F5.9060300@rdamicro.com> (raw)
In-Reply-To: <20160331103020.GH3701@e103592.cambridge.arm.com>
On 03/31/2016 06:30 PM, Dave Martin wrote:
> On Thu, Mar 31, 2016 at 07:56:05AM +0000, ??(Gangchen) wrote:
>> On 03/30/2016 10:07 PM, Dave Martin wrote:
>>> On Wed, Mar 30, 2016 at 03:27:01AM +0000, ??(Gangchen) wrote:
>>>> On 03/29/2016 06:56 PM, Dave Martin wrote:
> [...]
>
>>>>> 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?
>> With the help of other colleagues, I understand your proposal now.
>> I create a patch and I can verify that it works!
> Ah, OK. I was wondering whether I made a mistake somewhere.
>
>> Should I submit it, as it seems better than this one I sent?
> It's up to you -- I think my approach is a bit cleaner, but your
> approach worked too and is not vulnerable to compilers that generate
> silly code for (uint64_t) >> 32.
(uint64_t) >> 32 is pretty much the standard way to get upper half of an
uint64 variable, compiler should not
generate silly code for this.
> Note that I only tested my code for little endian -- it should do the
> right thing for BE, but I recommend that you try it and examine the
> generated code, to make sure.
I don't have a BE system to test, but I did check assembly code
generated for BE system and didn't find
anything wrong.
I will update the new patch soon.
The following is my test code and assembly dump for BE system of the
function.
typedef unsigned long long ull;
ull mydiv64y(ull tt, unsigned base, unsigned *p)
{
ull t = tt;
*p = do_div(t, base);
*p = do_div(tt, base+1);
return tt;
}
/mnt/2nd_disk/rdaMicro/aosp_4.4/test_modules/div_test/.tmp_test_div.o:
file format elf32-bigarm
Disassembly of section .text:
00000000 <mydiv64y>:
0: e92d 47f0 stmdb sp!, {r4, r5, r6, r7, r8, r9, sl, lr}
4: 4607 mov r7, r0
6: 2600 movs r6, #0
8: 4698 mov r8, r3
a: ea57 0306 orrs.w r3, r7, r6
e: 4681 mov r9, r0
10: 460d mov r5, r1
12: 4692 mov sl, r2
14: d111 bne.n 3a <mydiv64y+0x3a>
16: f102 0401 add.w r4, r2, #1
1a: 4608 mov r0, r1
1c: 4621 mov r1, r4
1e: f7ff fffe bl 0 <__aeabi_uidivmod>
22: 4628 mov r0, r5
24: 460f mov r7, r1
26: 4621 mov r1, r4
28: f7ff fffe bl 0 <__aeabi_uidiv>
2c: 4632 mov r2, r6
2e: 4601 mov r1, r0
30: f8c8 7000 str.w r7, [r8]
34: 4610 mov r0, r2
36: e8bd 87f0 ldmia.w sp!, {r4, r5, r6, r7, r8, r9, sl, pc}
3a: 4614 mov r4, r2
3c: f7ff fffe bl 0 <__do_div64>
40: f10a 0401 add.w r4, sl, #1
44: f8c8 0000 str.w r0, [r8]
48: 4629 mov r1, r5
4a: 4648 mov r0, r9
4c: f7ff fffe bl 0 <__do_div64>
50: 4619 mov r1, r3
52: 4607 mov r7, r0
54: e7ec b.n 30 <mydiv64y+0x30>
56: bf00 nop
>
> Cheers
> ---Date
next prev parent reply other threads:[~2016-03-31 11:20 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)
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) [this message]
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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