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Date: Wed, 22 Jun 2016 13:37:38 -0700
From: "Zhao, Weiming" <weimingz@...eaurora.org>
To: musl@...ts.openwall.com
Subject: Re: build musl for armv7m
How about using the following test?
!defined(__thumb__) || (__ARM_ARCH_7A__ || __ARM_ARCH_7R__ || __ARM_ARCH
> 7)
Because I think those instructions are ISA related, not just arm/thumb.
For example, using -mcpu=cortex-a8 -mthumb, the original code still
works. So if only testing __thumb__, the armv7-a thumb mode will fall
into the slow path too.
On 6/22/2016 12:19 PM, Rich Felker wrote:
> On Wed, Jun 22, 2016 at 12:08:13PM -0700, Zhao, Weiming wrote:
>> Thanks for reviewing.
>>
>> I add tests for ARMv7m for memcpy.
>>
>> For atomics.s, I think the below are equivalent:
>>
>> ldr ip,1f ==> assembler will computes the offset from current inst to the label
>>
>> - ldr ip,[pc,ip] ==> here the address to be loaded is current PC + ip
>> + add ip,pc,ip ==> here, the PC is the same as above
>> + ldr ip,[ip]
> In the original code, pc reads as the address of the instruction
> following the ".word" mnemonic (2 ARM insns ahead of the current
> instruction). In your version, I believe pc reads as the address of
> the .word (2 thumb insns ahead of the current insn) which would be
> wrong, but I may be wrong; one source I saw suggested that arithmetic
> on pc like this was not even defined in thumb mode on some models.
>
>> But I'm not familiar with the CP15 issue you mentioned.
>> So, anyway, I skip the change for atomics.s in this patch.
> OK. But just know that you can't expect it to work unless that's
> implemented.
>> diff --git a/src/string/arm/memcpy_le.S b/src/string/arm/memcpy_le.S
>> index 4db4844..1137f55 100644
>> --- a/src/string/arm/memcpy_le.S
>> +++ b/src/string/arm/memcpy_le.S
>> @@ -241,7 +241,12 @@ non_congruent:
>> beq 2f
>> ldr r5, [r1], #4
>> sub r2, r2, #4
>> +#if (__ARM_ARCH_7A || __ARM_ARCH_7R || __ARM_ARCH > 7)
>> orr r4, r3, r5, lsl lr
>> +#else
>> + lsl r4, r5, lr
>> + orr r4, r3, r4
>> +#endif
> These are not the right conditions. The selection should be made based
> on whether the code is being assembled as thumb, not on the ISA
> revision level. As written your patch uses the thumb code on all
> pre-v7 targets.
> Rich
--
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