Print RISCV compressed instructions with "c." prefix

[OBarronCS]

Work environment

Questions	Answers
Capstone module affected	RISCV
Version/git commit	6.0.0 alpha 7

With the release of CapstoneV6 Alpha 7, the default display of RISCV compressed instructions changed. Previously, they were prefixed with a c., such as c.li, or c.j. By default, this no longer occurs.

The "+noalias" options brings back the original behavior, but it as has the downside of applying to all instructions, not just compressed instructions. It would be nice to have a version of the "+noalias" option that only applies to compressed instructions.

Current behavior

[ubuntu:~]$ cstool -d riscv64 "9142"
 0  91 42        li	t0, 4
	ID: 519 (c_lhu)
	Is alias: 0 ((null)) with REAL operand set
	op_count: 2
		operands[0].type: REG = t0
		operands[0].access: WRITE
		operands[1].type: IMM = 0x4
		operands[1].access: READ

	Groups: HasStdExtCOrZca 

As an aside, the "Is alias" is zero, but doing "riscv64+noalias" prints c.li, like below. If it's not an alias, should noalias apply?

Requested behavior

Add a "+nocompressedalias", or something like that, flag so that when programmatically disassembling, the c. prefix is shown for compressed instructions, as was the default prior to Capstone6 Alpha 7, but other aliases are kept intact.

cstool -d riscv64+nocompressedalias "9142"
 0  91 42        c.li	t0, 4
	ID: 519 (c_lhu)
	op_count: 2
		operands[0].type: REG = t0
		operands[0].access: WRITE
		operands[1].type: IMM = 0x4
		operands[1].access: READ

	Groups: HasStdExtCOrZca 

The check for CS_OPT_SYNTAX_NO_ALIAS_TEXT currently occurs here:

capstone/arch/RISCV/RISCVInstPrinter.c

Lines 376 to 410 in b56a28e

	MCInst_setIsAlias(MI, false);
	// print the exact instruction text and done
	if (MI->csh->syntax & CS_OPT_SYNTAX_NO_ALIAS_TEXT) {
	printInstruction(MI, MI->address, O);
	} else {
	/* the instruction might be an alias, including in the case of a compressed instruction */
	MCInst Uncompressed;
	MCInst_Init(&Uncompressed, MI->csh->arch);
	MCInst *McInstr = MI;
	if (uncompressInst(&Uncompressed, MI)) {
	McInstr = &Uncompressed;
	Uncompressed.address = MI->address;
	Uncompressed.MRI = MI->MRI;
	Uncompressed.csh = MI->csh;
	Uncompressed.flat_insn = MI->flat_insn;
	}
	if (printAliasInstr(McInstr, MI->address, O)) {
	MCInst_setIsAlias(MI, true);
	if (!map_use_alias_details(MI) && detail_is_set(MI)) {
	// disable actual printing
	SStream_Close(O);
	memset(MI->flat_insn->detail->riscv.operands, 0,
	sizeof(MI->flat_insn->detail->riscv
	.operands));
	MI->flat_insn->detail->riscv.op_count = 0;
	// re-disassemble again in order to obtain the full details
	// including the whole operands array
	printInstruction(MI, MI->address, O);
	// re-open the stream to restore the usual state
	SStream_Open(O);
	}
	} else
	printInstruction(McInstr, MI->address, O);

[Rot127]

@moste00 Should be rather straight forward to implement I think?

[moste00]

@moste00 Should be rather straight forward to implement I think?

Probably yes, the compressed instructions have their own detection condition that fires separately from the rest of the aliases.

I will try my hand at this.