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From: jacob navia <>
To: Jan Beulich <>
Cc: Palmer Dabbelt <>,, Paul Koning <>
Subject: Re: P.S. Follow up to my last post
Date: Mon, 28 Aug 2023 09:04:53 +0200	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

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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


> Le 28 août 2023 à 08:17, Jan Beulich <> 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

  reply	other threads:[~2023-08-28  7:05 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <>
2023-08-25 15:32 ` Palmer Dabbelt
2023-08-25 16:10   ` jacob navia
2023-08-25 17:03     ` Paul Koning
2023-08-25 19:44       ` jacob navia
2023-08-28  6:17         ` Jan Beulich
2023-08-28  7:04           ` jacob navia [this message]
2023-08-25 11:52 jacob navia
2023-08-25 12:00 ` Jan Beulich
2023-08-25 13:07   ` jacob navia
2023-08-25 13:30     ` Jan Beulich
2023-08-25 13:40       ` Paul Koning

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