On 13/1/22 21:20, Philipp Tomsich 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>
---
Changes in v2:
- (new patch) iterate over a table of guarded decoder functions
target/riscv/translate.c | 38 ++++++++++++++++++++++++++++++++------
1 file changed, 32 insertions(+), 6 deletions(-)
diff --git a/target/riscv/translate.c b/target/riscv/translate.c
index 615048ec87..2cbf9cbb6f 100644
--- a/target/riscv/translate.c
+++ b/target/riscv/translate.c
@@ -116,6 +116,12 @@ static inline bool has_ext(DisasContext *ctx, uint32_t ext)
return ctx->misa_ext & ext;
}
+static inline bool always_true_p(CPURISCVState *env __attribute__((__unused__)),
+ DisasContext *ctx
__attribute__((__unused__)))
+{
+ return true;
+}
+
#ifdef TARGET_RISCV32
#define get_xl(ctx) MXL_RV32
#elif defined(CONFIG_USER_ONLY)
@@ -844,16 +850,28 @@ 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 */
+ /* If not handled, we'll raise an illegal instruction exception */
+ bool handled = false;
+
+ /*
+ * A table with predicate (i.e., guard) functions and decoder functions
+ * that are tested in-order until a decoder matches onto the opcode.
+ */
+ const struct {
+ bool (*guard_func)(CPURISCVState *, 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);
- }
+ handled = decode_insn16(ctx, opcode);
}
} else {
uint32_t opcode32 = opcode;
@@ -862,10 +880,18 @@ 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(env, ctx))
+ continue;
+
+ if ((handled = decoders[i].decode_func(ctx, opcode32)))
+ break;
Again, while we might check whether "Vendor Extensions" are enabled or
not at runtime, they are specific to a (vendor) core model, so we know
their availability at instantiation time.
I don't understand the need to iterate. You can check for vendor
extensions in riscv_tr_init_disas_context() and set a vendor_decoder()
handler in DisasContext, which ends calling the generic decode_opc()
one.
}
}
+
+ if (!handled)
+ gen_exception_illegal(ctx);
}
static void riscv_tr_init_disas_context(DisasContextBase *dcbase, CPUState *cs)
