From: Keith Packard <keithp@keithp.com>
To: newlib@sourceware.org
Subject: [PATCH] arm/strlen-thumb2-Os.S: Correct assembly syntax for ldrb instruction
Date: Tue, 12 May 2020 10:58:30 -0700 [thread overview]
Message-ID: <20200512175830.1186422-1-keithp@keithp.com> (raw)
We want to use a post-indexed addressing mode (which means use the
original register contents as the address, then increment that
register) which is only valid in Encoding T3 of the LDRB instruction.
According to the ARMv7-M Architecture Reference Manual, the assembly
syntax for Encoding T3 does not include the '.W' width specifier as
that is used to specify Encoding T2, presumably to provide a wider
immediate field for possible relocations.
GAS allows the .W specifier for this addressing mode and generates
identical output with and without it. clang does not allow the .W
specifier for this addressing mode, so removing it offers wider
portability and closer adherance to the ARM assembly syntax
specification.
Signed-off-by: Keith Packard <keithp@keithp.com>
---
newlib/libc/machine/arm/strlen-thumb2-Os.S | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/newlib/libc/machine/arm/strlen-thumb2-Os.S b/newlib/libc/machine/arm/strlen-thumb2-Os.S
index 961f41a0a..aed8adf33 100644
--- a/newlib/libc/machine/arm/strlen-thumb2-Os.S
+++ b/newlib/libc/machine/arm/strlen-thumb2-Os.S
@@ -45,7 +45,7 @@
def_fn strlen p2align=1
mov r3, r0
-1: ldrb.w r2, [r3], #1
+1: ldrb r2, [r3], #1
cmp r2, #0
bne 1b
subs r0, r3, r0
--
2.26.2
next reply other threads:[~2020-05-12 17:58 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-12 17:58 Keith Packard [this message]
2020-05-15 13:25 ` Richard Earnshaw
2020-05-15 14:38 ` Emmanuel Blot
2020-05-15 15:19 ` Keith Packard
2020-05-15 15:44 ` Richard Earnshaw
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