[U-Boot] [PATCH v2 8/9] arm: use thumb interworking returns in libgcc

[Allen Martin]

On Wed, Aug 01, 2012 at 02:11:48PM -0700, V, Aneesh wrote:
> Hi Allen,
> 
> On Wed, Aug 1, 2012 at 1:32 PM, Allen Martin <amartin at nvidia.com<mailto:amartin at nvidia.com>> wrote:
> If CONFIG_SYS_THUMB_BUILD is enabled, use thumb interworking return
> instructions from libgcc routines, otherwise use ARM returns.
> 
> Signed-off-by: Allen Martin <amartin at nvidia.com<mailto:amartin at nvidia.com>>
> ---
>  arch/arm/include/asm/assembler.h |   10 ++++++++++
>  arch/arm/lib/_ashldi3.S          |    3 ++-
>  arch/arm/lib/_ashrdi3.S          |    3 ++-
>  arch/arm/lib/_divsi3.S           |   15 +++++++++++----
>  arch/arm/lib/_lshrdi3.S          |    3 ++-
>  arch/arm/lib/_modsi3.S           |    9 ++++++++-
>  arch/arm/lib/_udivsi3.S          |    8 +++++---
>  arch/arm/lib/_umodsi3.S          |   18 +++++++++++++++++-
>  arch/arm/lib/memcpy.S            |   10 ++++++++++
>  arch/arm/lib/memset.S            |    3 ++-
>  10 files changed, 69 insertions(+), 13 deletions(-)
> 
> diff --git a/arch/arm/include/asm/assembler.h b/arch/arm/include/asm/assembler.h
> index 5e4789b..25ece01 100644
> --- a/arch/arm/include/asm/assembler.h
> +++ b/arch/arm/include/asm/assembler.h
> @@ -13,6 +13,7 @@
>   *  Do not include any C declarations in this file - it is included by
>   *  assembler source.
>   */
> +#include <config.h>
> 
>  /*
>   * Endian independent macros for shifting bytes within registers.
> @@ -58,3 +59,12 @@
>   * Cache alligned
>   */
>  #define CALGN(code...) code
> +
> +/*
> + * return instruction
> + */
> +#ifdef CONFIG_SYS_THUMB_BUILD
> +#define RET    bx      lr
> +#else
> +#define RET    mov     pc, lr
> 
> Why not "bx lr" in all cases? In that case you can just replace all the instances of
> "mov pc, lr" directly by "bx lr" instead of this macro. That looks cleaner to me.

I didn't want to break any older ARM architectures that don't support the
bx instruction but use this code.


> BTW, as far as I remember when I did this originally my compiler was compiling
> all assembly functions in ARM and it was automatically converting "mov pc, lr" to
> "bx lr" ,where necessary. Maybe that was just my compiler and I don't remember
> the details now. Did you really face any issue with "mov pc, lr" making wrong jumps?

Yes, without this change if I disassemble the code I'm seeing it's
still a mov instruction and it hangs.

-Allen
-- 
nvpublic