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Date: Thu, 25 Jun 2020 17:50:42 -0400
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: [PATCH v2] Add big-endian support to ARM assembler memcpy
On Tue, Jan 21, 2020 at 10:52:15AM -0800, Andre McCurdy wrote:
> Allow the existing ARM assembler memcpy implementation to be used for
> both big and little endian targets.
> ---
>
> Exactly the same changes as before but rebased to account for
> whitespace changes in the preceding patch to add Thumb2 support.
>
> COPYRIGHT | 2 +-
> src/string/arm/{memcpy_le.S => memcpy.S} | 101 ++++++++++++++++++++++-
> src/string/arm/memcpy.c | 3 -
> 3 files changed, 98 insertions(+), 8 deletions(-)
> rename src/string/arm/{memcpy_le.S => memcpy.S} (82%)
> delete mode 100644 src/string/arm/memcpy.c
>
> diff --git a/COPYRIGHT b/COPYRIGHT
> index e6472371..d3edc2a2 100644
> --- a/COPYRIGHT
> +++ b/COPYRIGHT
> @@ -127,7 +127,7 @@ Copyright © 2017-2018 Arm Limited
> and labelled as such in comments in the individual source files. All
> have been licensed under extremely permissive terms.
>
> -The ARM memcpy code (src/string/arm/memcpy_el.S) is Copyright © 2008
> +The ARM memcpy code (src/string/arm/memcpy.S) is Copyright © 2008
> The Android Open Source Project and is licensed under a two-clause BSD
> license. It was taken from Bionic libc, used on Android.
>
> diff --git a/src/string/arm/memcpy_le.S b/src/string/arm/memcpy.S
> similarity index 82%
> rename from src/string/arm/memcpy_le.S
> rename to src/string/arm/memcpy.S
> index 7b35d305..869e3448 100644
> --- a/src/string/arm/memcpy_le.S
> +++ b/src/string/arm/memcpy.S
> @@ -1,5 +1,3 @@
> -#if !__ARMEB__
> -
> /*
> * Copyright (C) 2008 The Android Open Source Project
> * All rights reserved.
> @@ -42,7 +40,7 @@
> * code safely callable from thumb mode, adjusting the return
> * instructions to be compatible with pre-thumb ARM cpus, removal of
> * prefetch code that is not compatible with older cpus and support for
> - * building as thumb 2.
> + * building as thumb 2 and big-endian.
> */
>
> .syntax unified
> @@ -227,24 +225,45 @@ non_congruent:
> * becomes aligned to 32 bits (r5 = nb of words to copy for alignment)
> */
> movs r5, r5, lsl #31
> +
> +#if __ARMEB__
> + movmi r3, r3, ror #24
> + strbmi r3, [r0], #1
> + movcs r3, r3, ror #24
> + strbcs r3, [r0], #1
> + movcs r3, r3, ror #24
> + strbcs r3, [r0], #1
> +#else
> strbmi r3, [r0], #1
> movmi r3, r3, lsr #8
> strbcs r3, [r0], #1
> movcs r3, r3, lsr #8
> strbcs r3, [r0], #1
> movcs r3, r3, lsr #8
> +#endif
>
> cmp r2, #4
> blo partial_word_tail
>
> +#if __ARMEB__
> + mov r3, r3, lsr r12
> + mov r3, r3, lsl r12
> +#endif
> +
> /* Align destination to 32 bytes (cache line boundary) */
> 1: tst r0, #0x1c
> beq 2f
> ldr r5, [r1], #4
> sub r2, r2, #4
> +#if __ARMEB__
> + mov r4, r5, lsr lr
> + orr r4, r4, r3
> + mov r3, r5, lsl r12
> +#else
> mov r4, r5, lsl lr
> orr r4, r4, r3
> mov r3, r5, lsr r12
> +#endif
Am I missing something or are both cases identical here? That would
either indicate this is gratuitous or there's a bug here and they were
intended not to be the same.
> [...]
> @@ -350,9 +429,15 @@ less_than_thirtytwo:
>
> 1: ldr r5, [r1], #4
> sub r2, r2, #4
> +#if __ARMEB__
> + mov r4, r5, lsr lr
> + orr r4, r4, r3
> + mov r3, r5, lsl r12
> +#else
> mov r4, r5, lsl lr
> orr r4, r4, r3
> mov r3, r5, lsr r12
> +#endif
And again here.
Rich
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