[PATCH 2/2] ArmPkg/AsmMacroIoLib: force word alignment for functions

[PATCH 2/2] ArmPkg/AsmMacroIoLib: force word alignment for functions

[Ard Biesheuvel]

Without an explicit .align directive, the Clang assembler defaults to
no alignment, which may result in instructions appearing misaligned in
the final executable. So use word alignment in all cases.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
 ArmPkg/Include/AsmMacroIoLib.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/ArmPkg/Include/AsmMacroIoLib.h b/ArmPkg/Include/AsmMacroIoLib.h
index fb73ea9a4694..5e4de1f269c8 100644
--- a/ArmPkg/Include/AsmMacroIoLib.h
+++ b/ArmPkg/Include/AsmMacroIoLib.h
@@ -56,6 +56,7 @@
   .global   Name                  ; \
   .section  #Section, "ax"        ; \
   .type     Name, %function       ; \
+  .align    2                     ; \
   Name:
 
 #define ASM_FUNC(Name)            _ASM_FUNC(ASM_PFX(Name), .text. ## Name)
-- 
2.7.4

Re: [PATCH 2/2] ArmPkg/AsmMacroIoLib: force word alignment for functions

[Andrew Fish]

> On Sep 13, 2016, at 10:27 AM, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:
> 
> Without an explicit .align directive, the Clang assembler defaults to
> no alignment, which may result in instructions appearing misaligned in
> the final executable. So use word alignment in all cases.
> 
> Contributed-under: TianoCore Contribution Agreement 1.0
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> ---
> ArmPkg/Include/AsmMacroIoLib.h | 1 +
> 1 file changed, 1 insertion(+)
> 
> diff --git a/ArmPkg/Include/AsmMacroIoLib.h b/ArmPkg/Include/AsmMacroIoLib.h
> index fb73ea9a4694..5e4de1f269c8 100644
> --- a/ArmPkg/Include/AsmMacroIoLib.h
> +++ b/ArmPkg/Include/AsmMacroIoLib.h
> @@ -56,6 +56,7 @@
>   .global   Name                  ; \
>   .section  #Section, "ax"        ; \
>   .type     Name, %function       ; \
> +  .align    2                     ; \

Ard,

I've been burned in the past by as .align is bytes or power of 2 based on what the native assembler defaults to (over simplification). I'm not sure if that issues exists in the ARM world? 

Thanks,

Andrew Fish

>   Name:
> 
> #define ASM_FUNC(Name)            _ASM_FUNC(ASM_PFX(Name), .text. ## Name)
> -- 
> 2.7.4
> 
> _______________________________________________
> edk2-devel mailing list
> edk2-devel@lists.01.org
> https://lists.01.org/mailman/listinfo/edk2-devel

Re: [PATCH 2/2] ArmPkg/AsmMacroIoLib: force word alignment for functions

[Ard Biesheuvel]

On 13 September 2016 at 18:45, Andrew Fish <afish@apple.com> wrote:
>
>> On Sep 13, 2016, at 10:27 AM, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:
>>
>> Without an explicit .align directive, the Clang assembler defaults to
>> no alignment, which may result in instructions appearing misaligned in
>> the final executable. So use word alignment in all cases.
>>
>> Contributed-under: TianoCore Contribution Agreement 1.0
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
>> ---
>> ArmPkg/Include/AsmMacroIoLib.h | 1 +
>> 1 file changed, 1 insertion(+)
>>
>> diff --git a/ArmPkg/Include/AsmMacroIoLib.h b/ArmPkg/Include/AsmMacroIoLib.h
>> index fb73ea9a4694..5e4de1f269c8 100644
>> --- a/ArmPkg/Include/AsmMacroIoLib.h
>> +++ b/ArmPkg/Include/AsmMacroIoLib.h
>> @@ -56,6 +56,7 @@
>>   .global   Name                  ; \
>>   .section  #Section, "ax"        ; \
>>   .type     Name, %function       ; \
>> +  .align    2                     ; \
>
> Ard,
>
> I've been burned in the past by as .align is bytes or power of 2 based on what the native assembler defaults to (over simplification). I'm not sure if that issues exists in the ARM world?
>

The GNU assembler for ARM interprets this as power-of-2, and so does
Clang, according to my testing. Both support the .p2align directive as
well, which makes it 100% unambiguous, so I suppose I could use that
instead.

-- 
Ard.

Re: [PATCH 2/2] ArmPkg/AsmMacroIoLib: force word alignment for functions

[Andrew Fish]

> On Sep 13, 2016, at 10:49 AM, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:
> 
> On 13 September 2016 at 18:45, Andrew Fish <afish@apple.com> wrote:
>> 
>>> On Sep 13, 2016, at 10:27 AM, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:
>>> 
>>> Without an explicit .align directive, the Clang assembler defaults to
>>> no alignment, which may result in instructions appearing misaligned in
>>> the final executable. So use word alignment in all cases.
>>> 
>>> Contributed-under: TianoCore Contribution Agreement 1.0
>>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
>>> ---
>>> ArmPkg/Include/AsmMacroIoLib.h | 1 +
>>> 1 file changed, 1 insertion(+)
>>> 
>>> diff --git a/ArmPkg/Include/AsmMacroIoLib.h b/ArmPkg/Include/AsmMacroIoLib.h
>>> index fb73ea9a4694..5e4de1f269c8 100644
>>> --- a/ArmPkg/Include/AsmMacroIoLib.h
>>> +++ b/ArmPkg/Include/AsmMacroIoLib.h
>>> @@ -56,6 +56,7 @@
>>>  .global   Name                  ; \
>>>  .section  #Section, "ax"        ; \
>>>  .type     Name, %function       ; \
>>> +  .align    2                     ; \
>> 
>> Ard,
>> 
>> I've been burned in the past by as .align is bytes or power of 2 based on what the native assembler defaults to (over simplification). I'm not sure if that issues exists in the ARM world?
>> 
> 
> The GNU assembler for ARM interprets this as power-of-2, and so does
> Clang, according to my testing. Both support the .p2align directive as
> well, which makes it 100% unambiguous, so I suppose I could use that
> instead.
> 

I think all my pain has been the inconsistency on i386/IA32, but it left a mark. :). 

Thanks,

Andrew Fish

> -- 
> Ard.
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> edk2-devel mailing list
> edk2-devel@lists.01.org
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