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Re: [PATCH] arm: Update strcpy.c to use UAL syntax.
- From: "Richard Earnshaw (lists)" <Richard dot Earnshaw at arm dot com>
- To: Ian Tessier <itessier at google dot com>, newlib at sourceware dot org
- Date: Fri, 21 Jul 2017 11:21:33 +0100
- Subject: Re: [PATCH] arm: Update strcpy.c to use UAL syntax.
- Authentication-results: sourceware.org; auth=none
- References: <20170719210243.8975-1-itessier@google.com>
On 19/07/17 22:02, Ian Tessier via newlib wrote:
> With this change the arm platform can now be fully compiled with Clang.
>
> Tested by comparing the output with GCC 4.8.2, and Clang 4.0, using a
> variety of arches, big/little endianness, and arm/thumb mode to verify
> the generated assembly output matches between GCC vs Clang with UAL, and
> also GCC with UAL vs GCC with non-UAL, for all preprocessor code blocks.
>
> The only difference found is an extra nop at the end of the function
> when compiled with GCC using armv7-a/thumb/little-endian/-O2 compared to
> Clang. The nop is not emitted when compiled in big-endian mode.
> ---
> newlib/libc/machine/arm/strcpy.c | 13 +++++++------
> 1 file changed, 7 insertions(+), 6 deletions(-)
>
> diff --git a/newlib/libc/machine/arm/strcpy.c b/newlib/libc/machine/arm/strcpy.c
> index f1205b9c1..154451110 100644
> --- a/newlib/libc/machine/arm/strcpy.c
> +++ b/newlib/libc/machine/arm/strcpy.c
> @@ -42,6 +42,7 @@ char* __attribute__((naked))
> strcpy (char* dst, const char* src)
> {
> asm (
> + ".syntax unified\n\t"
> #if !(defined(__OPTIMIZE_SIZE__) || defined (PREFER_SIZE_OVER_SPEED) || \
> (defined (__thumb__) && !defined (__thumb2__)))
> #ifdef _ISA_ARM_7
> @@ -127,15 +128,15 @@ strcpy (char* dst, const char* src)
> #ifdef __ARMEB__
> "tst r2, #0xff00\n\t"
> "iteet ne\n\t"
> - "strneh r2, [ip], #2\n\t"
> + "strhne r2, [ip], #2\n\t"
> "lsreq r2, r2, #8\n\t"
> - "streqb r2, [ip]\n\t"
> + "strbeq r2, [ip]\n\t"
> "tstne r2, #0xff\n\t"
> #else
> "tst r2, #0xff\n\t"
> "itet ne\n\t"
> - "strneh r2, [ip], #2\n\t"
> - "streqb r2, [ip]\n\t"
> + "strhne r2, [ip], #2\n\t"
> + "strbeq r2, [ip]\n\t"
> "tstne r2, #0xff00\n\t"
> #endif
> "bne 5b\n\t"
> @@ -162,9 +163,9 @@ strcpy (char* dst, const char* src)
> "mov r3, r0\n\t"
> "1:\n\t"
> "ldrb r2, [r1]\n\t"
> - "add r1, r1, #1\n\t"
> + "adds r1, #1\n\t"
> "strb r2, [r3]\n\t"
> - "add r3, r3, #1\n\t"
> + "adds r3, #1\n\t"
> "cmp r2, #0\n\t"
> "bne 1b\n\t"
> "bx lr\n\t"
>
This doesn't compile on ARMv4t - you've missed the "mov r3, r0"
instruction in the final hunk.
Fixed thusly (pushed).
-------------
ARMv4t does not support mov between two low registers. Now we use
unified syntax mov instructions need converting to movs.
---
newlib/libc/machine/arm/strcpy.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/newlib/libc/machine/arm/strcpy.c b/newlib/libc/machine/arm/strcpy.c
index 1544511..111528e 100644
--- a/newlib/libc/machine/arm/strcpy.c
+++ b/newlib/libc/machine/arm/strcpy.c
@@ -160,7 +160,7 @@ strcpy (char* dst, const char* src)
"bne 1b\n\t"
"bx lr\n\t"
#else
- "mov r3, r0\n\t"
+ "movs r3, r0\n\t"
"1:\n\t"
"ldrb r2, [r1]\n\t"
"adds r1, #1\n\t"