Re: P.S. Follow up to my last post

[jacob navia <jacob@jacob.remcomp.fr>]

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OK

Just do nothing. It is the best solution.

The assembler doesn’t assemble instructions recognized by the machine it is running on?

The user should use the undocumented march=xxx option. And if he doesn’t read the inexistent documentation, that’s his/her fault.

Thank you very much for your attention

Jacob


> Le 28 août 2023 à 08:17, Jan Beulich <jbeulich@suse.com> a écrit :
> 
> On 25.08.2023 21:44, jacob navia wrote:
>> I am just invoking the assembler with its default settings:
>> 
>> ~/star64 $ as -o test.o test.s
>> 
>> The assembler is testing the default architecture here:
>> Function: riscv_ip
>> 
>> 	for (; insn && insn->name && strcmp(insn->name,str) == 0; insn++) {
>> #if 0
>> 		if ((insn->xlen_requirement != 0) && (xlen != insn->xlen_requirement))
>> 			continue;
>> 
>> 		if (!riscv_multi_subset_supports(&riscv_rps_as,insn->insn_class)) {
>> 			error.missing_ext = riscv_multi_subset_supports_ext(&riscv_rps_as,
>> 							    insn->insn_class);
>> 			continue;
>> 		}
>> #endif
>> 
>> The #if 0/#endif were added by me. I think those tests do not belong here. The assembler should assemble and not test if the instruction is legal. If the instruction is illegal the program will crash at run-time, something not that unusual if you are programming in assembler!
> 
> Having a program crash at runtime when this can be avoided at build time is
> deemed undesirable by many people, including me. I did point out before that
> there are two approaches for assemblers - default-enabling everything and
> default-disabling everything except the base architecture insns. To a large
> part this is a decision to be taken by the people writing an assembler. But
> there are technical constraints as well: As soon as you have two conflicting
> extensions (which RISC-V was always allowing for, and which it now actively
> has), the former model won't work very well anymore.
> 
> Of course you're free to propose a patch allowing the alternative model (via
> command line option and/or directive). Obviously whether that'll be approved
> is unknown up front.
> 
>> And if you are assembling compiler output, it is up to the compiler to furnish the correct instructions.
> 
> Yes. Plus, with an assembler following the former model, the necessary
> directives. (As an aside, compilers aren't bug-free, and hence the assembler
> still applying some sanity checks makes some sense.)
> 
>> Tiny-asm doesn’t test any instruction compliance and that is why it works out of the box!
> 
> As said, which model to use is up to the writers of any particular assembler.
> 
> Jan