[cfe-dev] Clang assembler missed features

[Roberto E. Vargas Caballero via cfe-dev]

Hello,


> Although I can't speak for the whole community, my predictions:
> - .func and .endfunc are unlikely as this is documented only to do
> something when the stabs debugging is enabled and clang is unlikely to
> support stabs. See https://sourceforge.net/p/libjpeg-turbo/bugs/72/

Ok, it seems that we actually don't need them. One problem less.

> - Subtraction of relative labels is unlikely in a .if statement. MC
> can produce absolute values for relative labels in some cases but it
> requires a layout. Instruction relaxation, such as turning a 16-bit
> Thumb branch into a 32-bit Thumb 2 branch if the distance requires it,
> means that the distance between 2 labels isn't known until the layout
> finalises. For .if the expression evaluation needs to occur before
> relaxation as the result of the .if could affect relaxation. In theory
> it could be possible to alter the assembler to calculate part of the
> layout inline and handle some expressions, but I don't think that the
> disruption to the implementation would be worth it.

I understand the problem. We use these .if to verify some conditions
related to the size of some parts of the code:

        .macro check_vector_size since
         .if (. - \since) > (32*4))
               error "Vector exceeds 32 instructions"
        .endif

I suppose GNU As does some strange thing with .if to avoid the problem
(some delayed evaluation?).

Other thing that I didn't commented in the previous mail is related to
preprocesed assembler files, where consecutive strings are not dealt as
one string, as it is mandatory in C/C++ and GNU as does. This is not a
big problem for us, because we can change the code where we use that.

Anyway, thank you for your answer.


Best regards,
Roberto
IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you.