Re: [PATCH] EmbeddedPkg/GdbDebugAgent ARM: use modern dialect for ldm/stm instructions

[Leif Lindholm <leif.lindholm@linaro.org>]

On Wed, Dec 12, 2018 at 10:12:11AM +0100, Ard Biesheuvel wrote:
> Clang does not like the legacy 32-bit assembler syntax used in the
> gdbstub exception handling routines, so update them to something
> more fashionable.
> 
> So switch the order of the conditional suffix

Yes, this is essentially a bugfix. The syntax change predates ARM's
involvement in EDK2.

> and the increment/decrement
> specifier, and use decrement-after (da) and increment-before (ib) as
> appropriate for an empty descending stack.

But I very much prefer the FA/FD/EA/ED syntax. It gives symmetry,
which helps me a lot when dealing with 7-character mnemonics.
These aliases are also defined in the ARM ARM and won't be going away.

/
    Leif

> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> ---
>  EmbeddedPkg/Library/GdbDebugAgent/Arm/ExceptionSupport.ARMv6.S | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/EmbeddedPkg/Library/GdbDebugAgent/Arm/ExceptionSupport.ARMv6.S b/EmbeddedPkg/Library/GdbDebugAgent/Arm/ExceptionSupport.ARMv6.S
> index df1543a6d242..924578c7af2f 100644
> --- a/EmbeddedPkg/Library/GdbDebugAgent/Arm/ExceptionSupport.ARMv6.S
> +++ b/EmbeddedPkg/Library/GdbDebugAgent/Arm/ExceptionSupport.ARMv6.S
> @@ -57,6 +57,7 @@ GCC_ASM_EXPORT(AsmCommonExceptionEntry)
>  GCC_ASM_EXPORT(GdbExceptionHandler)
>  
>  .text
> +.syntax unified
>  .align 3
>  
>  
> @@ -198,9 +199,9 @@ ASM_PFX(AsmCommonExceptionEntry):
>    and       R3, R1, #0x1f           @ Check CPSR to see if User or System Mode
>    cmp       R3, #0x1f               @ if ((CPSR == 0x10) || (CPSR == 0x1df))
>    cmpne     R3, #0x10               @
> -  stmeqed   R2, {lr}^               @   save unbanked lr
> +  stmdaeq   R2, {lr}^               @   save unbanked lr
>                                      @ else
> -  stmneed   R2, {lr}                @   save SVC lr
> +  stmdane   R2, {lr}                @   save SVC lr
>  
>  
>    ldr       R5, [SP, #0x58]         @ PC is the LR pushed by srsfd
> @@ -245,9 +246,9 @@ GdbExceptionHandler (
>    and       R1, R1, #0x1f           @ Check to see if User or System Mode
>    cmp       R1, #0x1f               @ if ((CPSR == 0x10) || (CPSR == 0x1f))
>    cmpne     R1, #0x10               @
> -  ldmeqed   R2, {lr}^               @   restore unbanked lr
> +  ldmibeq   R2, {lr}^               @   restore unbanked lr
>                                      @ else
> -  ldmneed   R3, {lr}                @   restore SVC lr, via ldmfd SP!, {LR}
> +  ldmibne   R3, {lr}                @   restore SVC lr, via ldmfd SP!, {LR}
>  
>    ldmfd     SP!,{R0-R12}            @ Restore general purpose registers
>                                      @ Exception handler can not change SP
> -- 
> 2.19.2
>