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Date: Wed, 22 Jun 2016 15:19:40 -0400
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: build musl for armv7m
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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