Can spike-dasm disassemble specified extensions through the --isa option?

[ha0lyu]

When I run spike-dasm to disassemble instructions, it disassembled vector extension. When I specify the extensions, it ignored. It seems that this tool could disassemble any instruction.

I have read the code of spike-dasm.cc, it supports the DEFAULT_ISA, which is rv64imafdc_zicntr_zihpm. In the code, spike-dasm will parse isa option, but it fails to disassemble instructions of specified extensions. Is this normal?

version: latest(a2dcf1f), 1.1.1-dev

[aswaterman]

Yes, this is the intended behavior. We always try to disassemble an instruction even if it corresponds to an extension that isn't enabled.

For this program, the only purpose of the --isa argument is to disambiguate conflicting cases, where a given opcode corresponds to a different instruction depending on which extensions are enabled. For example:

$ echo "DASM(0xb842)"|spike-dasm --isa=rv64imac_zcmp_zcmt
cm.push {ra}, -16
$ echo "DASM(0xb842)"|spike-dasm --isa=rv64imafdc
c.fsdsp fa6, 48(sp)

[ha0lyu]

Hi @aswaterman,
Thanks for your reply. I got it.
I have another question about specified extensions disassemble.

For this program, the only purpose of the --isa argument is to disambiguate conflicting cases

Now, I want to change the source code to disassemble specified extensions by the --isa argument or another argument. I have checked the code: disasm.cc and isa_parser.h. The constructor function of class disassembler_t calls add_instructions function firstly. The add_instructions adds instructions according to *isa, then it adds instructions of each isa->extension_enable. Actually, this tool can not disassemble all instructions, it only supports rv32 and rv64 instructions. Here is my question: how can I change the code to support specified XLEN and extensions, such as rv32imcb, rv64gc, rv32gc, etc.

I need a tool to disassemble instructions. Since Spike is considered the golden model, I believe the best approach is to modify spike-dasm. As someone who is highly knowledgeable about Spike, could you please provide me with some guidance?

[aswaterman]

I’m not sure I follow exactly what you’re trying to do. Could you give some user stories (really just examples of input, command-line options, and desired output) that would illustrate your goal?

[ha0lyu]

For example, I run spike-dasm --isa=rv32i, spike-dasm will only disassemble rv32i instructions.

1. Such as bits= 0x3256 # c.fldsp ft4, 368(sp), this is a C extension instruction, spike-dasm will not disassemble it.
2. Such as bits = 0x0182b283 # ld t0, 24(t0), this is a RV64I instruction, spike-dasm will not disassemble it.

In another case, I run spike-dasm --isa=rv64g, it will disassemble RV32g instructions, but will not disassemble C extension instructions.
I am not sure am I understood, please let me know if you are confused. Thanks.

[aswaterman]

I think this should be straightforward. Let me try to prototype something.

[aswaterman]

See #1881

[ha0lyu]

I have tested it, it works. Nice job!
Thank you very much!

[aswaterman]

You're welcome!