Re: [PATCH] disas/riscv: Further correction to LUI disassembly

[Richard Henderson <richard.henderson@linaro.org>]

On 8/7/23 15:01, Richard Bagley wrote:
> I do apologize, but I do not understand your remark at all. Could I trouble you to spell 
> this out.
> 
> In:
> +                snprintf(tmp, sizeof(tmp), "%d", dec->imm >> 12 & 0xfffff);
> 0xfffff is a mask which recovers the 20 bit field used to represent the immediate in the 
> instruction encoding.
> 
> You seem to be responding to the syntax, which is unrelated to my change.
> But I did notice it is the case that both GCC and LLVM disassemblers do not accept signed 
> integer arguments to LUI:
> lui r1, -1
> but instead require
> lui r1, 0xfffff

Your language is confusing.  Disassembler or assembler?  A disassembler would not "accept" 
but "output" arguments for LUI.

If the assembler rejects "lui r1, -1", that would be a bug, because the field *is* signed.

For the disassembler, the field *is* signed, therefore outputting a signed value is 
correct.  Outputting an unsigned hex value hides the fact that bit 31 is the sign.

To my mind this is exactly the same as emitting a signed value for the immediate in ADDI.


r~