On Mon, Jul 31, 2023 at 11:33:20AM -0700, Richard Bagley wrote:
> The recent commit 36df75a0a9 corrected one aspect of LUI disassembly
> by recovering the immediate argument from the result of LUI with a
> shift right by 12. However, the shift right will left-fill with the
> sign. By applying a mask we recover an unsigned representation of the
> 20-bit field (which includes a sign bit).
>
> Example:
> 0xfffff000 >> 12 = 0xffffffff
> 0xfffff000 >> 12 & 0xfffff = 0x000fffff
>
> Fixes: 36df75a0a9 ("riscv/disas: Fix disas output of upper immediates")
> Signed-off-by: Richard Bagley <rbag...@ventanamicro.com>
> ---
> disas/riscv.c | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/disas/riscv.c b/disas/riscv.c
> index 4023e3fc65..690eb4a1ac 100644
> --- a/disas/riscv.c
> +++ b/disas/riscv.c
> @@ -4723,9 +4723,12 @@ static void format_inst(char *buf, size_t buflen,
> size_t tab, rv_decode *dec)
> break;
> case 'U':
> fmt++;
> - snprintf(tmp, sizeof(tmp), "%d", dec->imm >> 12);
> - append(buf, tmp, buflen);
> - if (*fmt == 'o') {
> + if (*fmt == 'i') {
> + snprintf(tmp, sizeof(tmp), "%d", dec->imm >> 12 & 0xfffff);
Why are we correcting LUI's output, but still outputting sign-extended
values for AUIPC?
We can't assemble 'auipc a1, 0xffffffff' or 'auipc a1, -1' without getting
Error: lui expression not in range 0..1048575
(and additionally for 0xffffffff)
Error: value of 00000ffffffff000 too large for field of 4 bytes at
0000000000000000
either.
(I see that the assembler's error messages state 'lui', but I was trying
'auipc'.)
I'm using as from gnu binutils 2.40.0.20230214.
(And, FWIW, I agree with Richard Henderson that these instructions should
accept negative values.)
Thanks,
drew
> + append(buf, tmp, buflen);
> + } else if (*fmt == 'o') {
> + snprintf(tmp, sizeof(tmp), "%d", dec->imm >> 12);
> + append(buf, tmp, buflen);
> while (strlen(buf) < tab * 2) {
> append(buf, " ", buflen);
> }
> --
> 2.34.1
>
>
