On Mon, Jan 31, 2022 at 9:32 PM Philipp Tomsich
<philipp.toms...@vrull.eu> wrote:
>
> To split up the decoder into multiple functions (both to support
> vendor-specific opcodes in separate files and to simplify maintenance
> of orthogonal extensions), this changes decode_op to iterate over a
> table of decoders predicated on guard functions.
>
> This commit only adds the new structure and the table, allowing for
> the easy addition of additional decoders in the future.
>
> Signed-off-by: Philipp Tomsich <philipp.toms...@vrull.eu>
> Reviewed-by: Richard Henderson <richard.hender...@linaro.org>
Reviewed-by: Alistair Francis <alistair.fran...@wdc.com>
Alistair
>
> ---
>
> (no changes since v4)
>
> Changes in v4:
> - add braces to comply with coding standard (as suggested by Richard)
> - merge the two if-statements to reduce clutter after (now that the
> braces have been added)
>
> Changes in v3:
> - expose only the DisasContext* to predicate functions
> - mark the table of decoder functions as static
> - drop the inline from always_true_p, until the need arises (i.e.,
> someone finds a use for it and calls it directly)
> - rewrite to drop the 'handled' temporary in iterating over the
> decoder table, removing the assignment in the condition of the if
>
> Changes in v2:
> - (new patch) iterate over a table of guarded decoder functions
>
> target/riscv/translate.c | 32 +++++++++++++++++++++++++++-----
> 1 file changed, 27 insertions(+), 5 deletions(-)
>
> diff --git a/target/riscv/translate.c b/target/riscv/translate.c
> index f19d5cd0c0..30b1b68341 100644
> --- a/target/riscv/translate.c
> +++ b/target/riscv/translate.c
> @@ -111,6 +111,11 @@ static inline bool has_ext(DisasContext *ctx, uint32_t
> ext)
> return ctx->misa_ext & ext;
> }
>
> +static bool always_true_p(DisasContext *ctx __attribute__((__unused__)))
> +{
> + return true;
> +}
> +
> #ifdef TARGET_RISCV32
> #define get_xl(ctx) MXL_RV32
> #elif defined(CONFIG_USER_ONLY)
> @@ -855,15 +860,26 @@ static uint32_t opcode_at(DisasContextBase *dcbase,
> target_ulong pc)
>
> static void decode_opc(CPURISCVState *env, DisasContext *ctx, uint16_t
> opcode)
> {
> - /* check for compressed insn */
> + /*
> + * A table with predicate (i.e., guard) functions and decoder functions
> + * that are tested in-order until a decoder matches onto the opcode.
> + */
> + static const struct {
> + bool (*guard_func)(DisasContext *);
> + bool (*decode_func)(DisasContext *, uint32_t);
> + } decoders[] = {
> + { always_true_p, decode_insn32 },
> + };
> +
> + /* Check for compressed insn */
> if (extract16(opcode, 0, 2) != 3) {
> if (!has_ext(ctx, RVC)) {
> gen_exception_illegal(ctx);
> } else {
> ctx->opcode = opcode;
> ctx->pc_succ_insn = ctx->base.pc_next + 2;
> - if (!decode_insn16(ctx, opcode)) {
> - gen_exception_illegal(ctx);
> + if (decode_insn16(ctx, opcode)) {
> + return;
> }
> }
> } else {
> @@ -873,10 +889,16 @@ static void decode_opc(CPURISCVState *env, DisasContext
> *ctx, uint16_t opcode)
> ctx->base.pc_next + 2));
> ctx->opcode = opcode32;
> ctx->pc_succ_insn = ctx->base.pc_next + 4;
> - if (!decode_insn32(ctx, opcode32)) {
> - gen_exception_illegal(ctx);
> +
> + for (size_t i = 0; i < ARRAY_SIZE(decoders); ++i) {
> + if (decoders[i].guard_func(ctx) &&
> + decoders[i].decode_func(ctx, opcode32)) {
> + return;
> + }
> }
> }
> +
> + gen_exception_illegal(ctx);
> }
>
> static void riscv_tr_init_disas_context(DisasContextBase *dcbase, CPUState
> *cs)
> --
> 2.33.1
>
>
