Re: [PATCH] arm: Update strcpy.c to use UAL syntax.

["Ian Tessier via newlib" <newlib at sourceware dot org>]

Oops, I did indeed leave out armv(4|5)t. Thanks for fixing it.

Interestingly, with the non-UAL version of strcpy.c the mov
instruction gets emitted as "adds r3, r0, #0", while in UAL (both
gcc/clang) it's emitted as "movs r3, r0".

On Fri, Jul 21, 2017 at 2:11 PM, Ian Tessier <itessier@google.com> wrote:
> Oops, I did indeed leave out armv(4|5)t. Thanks for fixing it.
>
> Interestingly, with the non-UAL version of strcpy.c the mov instruction gets
> emitted as "adds r3, r0, #0", while in UAL (both gcc/clang) it's emitted as
> "movs r3, r0".
>
> On Fri, Jul 21, 2017 at 3:21 AM, Richard Earnshaw (lists)
> <Richard.Earnshaw@arm.com> wrote:
>>
>> 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(-)
>>
>>
>