Remove explicit width suffixes from Arm bignum assembly
Within the M-profile of the Arm architecture, some instructions
admit both a 16-bit and a 32-bit encoding. For those instructions,
some assemblers support the use of the .n (narrow) and .w (wide)
suffixes to force a choice of instruction encoding width.
Forcing the size of encodings may be useful to ensure alignment
of code, which can have a significant performance impact on some
microarchitectures.
It is for this reason that a previous commit introduced explicit
.w suffixes into what was believed to be M-profile only assembly
in library/bn_mul.h.
This change, however, introduced two issues:
- First, the assembly block in question is used also for Armv7-A
systems, on which the .n/.w distinction is not meaningful
(all instructions are 32-bit).
- Second, compiler support for .n/.w suffixes appears patchy,
leading to compilation failures even when building for M-profile
targets.
This commit removes the .w annotations in order to restore working
code, deferring controlled re-introduction for the sake of performance.
Fixes #6089.
Signed-off-by: Hanno Becker <hanno.becker@arm.com>
diff --git a/library/bn_mul.h b/library/bn_mul.h
index 962d7a9..20e0e53 100644
--- a/library/bn_mul.h
+++ b/library/bn_mul.h
@@ -717,10 +717,10 @@
#define MULADDC_X1_CORE \
".p2align 2 \n\t" \
- "ldr.w %[a], [%[in]], #4 \n\t" \
- "ldr.w %[b], [%[acc]] \n\t" \
+ "ldr %[a], [%[in]], #4 \n\t" \
+ "ldr %[b], [%[acc]] \n\t" \
"umaal %[b], %[carry], %[scalar], %[a] \n\t" \
- "str.w %[b], [%[acc]], #4 \n\t"
+ "str %[b], [%[acc]], #4 \n\t"
#define MULADDC_X1_STOP \
: [a] "=&r" (tmp_a), \
@@ -751,14 +751,14 @@
* 2 cycles, while subsequent loads/stores are single-cycle. */
#define MULADDC_X2_CORE \
".p2align 2 \n\t" \
- "ldr.w %[a0], [%[in]], #+8 \n\t" \
- "ldr.w %[b0], [%[acc]], #+8 \n\t" \
- "ldr.w %[a1], [%[in], #-4] \n\t" \
- "ldr.w %[b1], [%[acc], #-4] \n\t" \
+ "ldr %[a0], [%[in]], #+8 \n\t" \
+ "ldr %[b0], [%[acc]], #+8 \n\t" \
+ "ldr %[a1], [%[in], #-4] \n\t" \
+ "ldr %[b1], [%[acc], #-4] \n\t" \
"umaal %[b0], %[carry], %[scalar], %[a0] \n\t" \
"umaal %[b1], %[carry], %[scalar], %[a1] \n\t" \
- "str.w %[b0], [%[acc], #-8] \n\t" \
- "str.w %[b1], [%[acc], #-4] \n\t"
+ "str %[b0], [%[acc], #-8] \n\t" \
+ "str %[b1], [%[acc], #-4] \n\t"
#define MULADDC_X2_STOP \
: [a0] "=&r" (tmp_a0), \