Tiny asm (continued)

Tiny asm (continued)

[jacob navia]

Hi
The assembler checks at each instruction if the instruction is within the selected subset of risc-v extensions or not. I do not quite understand why this check is done here.

I suppose that gcc, before emitting any instruction does this check too, somewhere. Because if an instruction is emitted to the assembler and the assembler rejects it, there is no way to pass that information back to the compiler, and emitting an obscure error message about some instruction not being legal will not help the user at all that probably doesn’t know any assembler language.

I would like to drop this test in tiny-asm, but I am not 100% sure that it is really redundant. The checks are expensive to do, and they are done at EACH instruction...

In the other hand, if the assembler doesn’t catch a faulty instruction, the user will know that at runtime (maybe) with an illegal instruction exception or similar… That would make bugs very difficult to find.

Question then: can the assembler assume that gcc emits correct instructions?

Thanks in advance for your attention.

Jacob

Re: Tiny asm (continued)

[Andrew Pinski]

On Sun, Jul 9, 2023 at 11:24 PM jacob navia <jacob@jacob.remcomp.fr> wrote:
>
> Hi
> The assembler checks at each instruction if the instruction is within the selected subset of risc-v extensions or not. I do not quite understand why this check is done here.
>
> I suppose that gcc, before emitting any instruction does this check too, somewhere. Because if an instruction is emitted to the assembler and the assembler rejects it, there is no way to pass that information back to the compiler, and emitting an obscure error message about some instruction not being legal will not help the user at all that probably doesn’t know any assembler language.
>
> I would like to drop this test in tiny-asm, but I am not 100% sure that it is really redundant. The checks are expensive to do, and they are done at EACH instruction...
>
> In the other hand, if the assembler doesn’t catch a faulty instruction, the user will know that at runtime (maybe) with an illegal instruction exception or similar… That would make bugs very difficult to find.
>
> Question then: can the assembler assume that gcc emits correct instructions?

Two things, inline-asm and hand written assembly code.

>
> Thanks in advance for your attention.
>
> Jacob