[Qemu-devel] [PATCH v1 2/4] disas/riscv: Disassemble reserved compressed encodings as illegal

[Alistair Francis <alistair.francis@wdc.com>]

From: Michael Clark <mjc@sifive.com>

Due to the design of the disassembler, the immediate is not
known during decoding of the opcode; so to handle compressed
encodings with reserved immediate values (non-zero), we need
to add an additional check during decompression to match
reserved encodings with zero immediates and translate them
into the illegal instruction.

The following compressed opcodes have reserved encodings with
zero immediates: c.addi4spn, c.addi, c.lui, c.addi16sp, c.srli,
c.srai, c.andi and c.slli

Signed-off-by: Michael Clark <mjc@sifive.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
---
 disas/riscv.c | 51 ++++++++++++++++++++++++++++++++++-----------------
 1 file changed, 34 insertions(+), 17 deletions(-)

diff --git a/disas/riscv.c b/disas/riscv.c
index 59a9b0437a..3ab4586f0a 100644
--- a/disas/riscv.c
+++ b/disas/riscv.c
@@ -504,14 +504,19 @@ typedef struct {
     const rvc_constraint *constraints;
 } rv_comp_data;
 
+enum {
+    rvcd_imm_nz = 0x1
+};
+
 typedef struct {
     const char * const name;
     const rv_codec codec;
     const char * const format;
     const rv_comp_data *pseudo;
-    const int decomp_rv32;
-    const int decomp_rv64;
-    const int decomp_rv128;
+    const short decomp_rv32;
+    const short decomp_rv64;
+    const short decomp_rv128;
+    const short decomp_data;
 } rv_opcode_data;
 
 /* register names */
@@ -1011,7 +1016,7 @@ const rv_opcode_data opcode_data[] = {
     { "fcvt.q.lu", rv_codec_r_m, rv_fmt_rm_frd_rs1, NULL, 0, 0, 0 },
     { "fmv.x.q", rv_codec_r, rv_fmt_rd_frs1, NULL, 0, 0, 0 },
     { "fmv.q.x", rv_codec_r, rv_fmt_frd_rs1, NULL, 0, 0, 0 },
-    { "c.addi4spn", rv_codec_ciw_4spn, rv_fmt_rd_rs1_imm, NULL, rv_op_addi, rv_op_addi, rv_op_addi },
+    { "c.addi4spn", rv_codec_ciw_4spn, rv_fmt_rd_rs1_imm, NULL, rv_op_addi, rv_op_addi, rv_op_addi, rvcd_imm_nz },
     { "c.fld", rv_codec_cl_ld, rv_fmt_frd_offset_rs1, NULL, rv_op_fld, rv_op_fld, 0 },
     { "c.lw", rv_codec_cl_lw, rv_fmt_rd_offset_rs1, NULL, rv_op_lw, rv_op_lw, rv_op_lw },
     { "c.flw", rv_codec_cl_lw, rv_fmt_frd_offset_rs1, NULL, rv_op_flw, 0, 0 },
@@ -1019,14 +1024,14 @@ const rv_opcode_data opcode_data[] = {
     { "c.sw", rv_codec_cs_sw, rv_fmt_rs2_offset_rs1, NULL, rv_op_sw, rv_op_sw, rv_op_sw },
     { "c.fsw", rv_codec_cs_sw, rv_fmt_frs2_offset_rs1, NULL, rv_op_fsw, 0, 0 },
     { "c.nop", rv_codec_ci_none, rv_fmt_none, NULL, rv_op_addi, rv_op_addi, rv_op_addi },
-    { "c.addi", rv_codec_ci, rv_fmt_rd_rs1_imm, NULL, rv_op_addi, rv_op_addi, rv_op_addi },
+    { "c.addi", rv_codec_ci, rv_fmt_rd_rs1_imm, NULL, rv_op_addi, rv_op_addi, rv_op_addi, rvcd_imm_nz },
     { "c.jal", rv_codec_cj_jal, rv_fmt_rd_offset, NULL, rv_op_jal, 0, 0 },
     { "c.li", rv_codec_ci_li, rv_fmt_rd_rs1_imm, NULL, rv_op_addi, rv_op_addi, rv_op_addi },
-    { "c.addi16sp", rv_codec_ci_16sp, rv_fmt_rd_rs1_imm, NULL, rv_op_addi, rv_op_addi, rv_op_addi },
-    { "c.lui", rv_codec_ci_lui, rv_fmt_rd_imm, NULL, rv_op_lui, rv_op_lui, rv_op_lui },
-    { "c.srli", rv_codec_cb_sh6, rv_fmt_rd_rs1_imm, NULL, rv_op_srli, rv_op_srli, rv_op_srli },
-    { "c.srai", rv_codec_cb_sh6, rv_fmt_rd_rs1_imm, NULL, rv_op_srai, rv_op_srai, rv_op_srai },
-    { "c.andi", rv_codec_cb_imm, rv_fmt_rd_rs1_imm, NULL, rv_op_andi, rv_op_andi, rv_op_andi },
+    { "c.addi16sp", rv_codec_ci_16sp, rv_fmt_rd_rs1_imm, NULL, rv_op_addi, rv_op_addi, rv_op_addi, rvcd_imm_nz },
+    { "c.lui", rv_codec_ci_lui, rv_fmt_rd_imm, NULL, rv_op_lui, rv_op_lui, rv_op_lui, rvcd_imm_nz },
+    { "c.srli", rv_codec_cb_sh6, rv_fmt_rd_rs1_imm, NULL, rv_op_srli, rv_op_srli, rv_op_srli, rvcd_imm_nz },
+    { "c.srai", rv_codec_cb_sh6, rv_fmt_rd_rs1_imm, NULL, rv_op_srai, rv_op_srai, rv_op_srai, rvcd_imm_nz },
+    { "c.andi", rv_codec_cb_imm, rv_fmt_rd_rs1_imm, NULL, rv_op_andi, rv_op_andi, rv_op_andi, rvcd_imm_nz },
     { "c.sub", rv_codec_cs, rv_fmt_rd_rs1_rs2, NULL, rv_op_sub, rv_op_sub, rv_op_sub },
     { "c.xor", rv_codec_cs, rv_fmt_rd_rs1_rs2, NULL, rv_op_xor, rv_op_xor, rv_op_xor },
     { "c.or", rv_codec_cs, rv_fmt_rd_rs1_rs2, NULL, rv_op_or, rv_op_or, rv_op_or },
@@ -1036,7 +1041,7 @@ const rv_opcode_data opcode_data[] = {
     { "c.j", rv_codec_cj, rv_fmt_rd_offset, NULL, rv_op_jal, rv_op_jal, rv_op_jal },
     { "c.beqz", rv_codec_cb, rv_fmt_rs1_rs2_offset, NULL, rv_op_beq, rv_op_beq, rv_op_beq },
     { "c.bnez", rv_codec_cb, rv_fmt_rs1_rs2_offset, NULL, rv_op_bne, rv_op_bne, rv_op_bne },
-    { "c.slli", rv_codec_ci_sh6, rv_fmt_rd_rs1_imm, NULL, rv_op_slli, rv_op_slli, rv_op_slli },
+    { "c.slli", rv_codec_ci_sh6, rv_fmt_rd_rs1_imm, NULL, rv_op_slli, rv_op_slli, rv_op_slli, rvcd_imm_nz },
     { "c.fldsp", rv_codec_ci_ldsp, rv_fmt_frd_offset_rs1, NULL, rv_op_fld, rv_op_fld, rv_op_fld },
     { "c.lwsp", rv_codec_ci_lwsp, rv_fmt_rd_offset_rs1, NULL, rv_op_lw, rv_op_lw, rv_op_lw },
     { "c.flwsp", rv_codec_ci_lwsp, rv_fmt_frd_offset_rs1, NULL, rv_op_flw, 0, 0 },
@@ -2795,8 +2800,12 @@ static void decode_inst_decompress_rv32(rv_decode *dec)
 {
     int decomp_op = opcode_data[dec->op].decomp_rv32;
     if (decomp_op != rv_op_illegal) {
-        dec->op = decomp_op;
-        dec->codec = opcode_data[decomp_op].codec;
+        if ((opcode_data[dec->op].decomp_data & rvcd_imm_nz) && dec->imm == 0) {
+            dec->op = rv_op_illegal;
+        } else {
+            dec->op = decomp_op;
+            dec->codec = opcode_data[decomp_op].codec;
+        }
     }
 }
 
@@ -2804,8 +2813,12 @@ static void decode_inst_decompress_rv64(rv_decode *dec)
 {
     int decomp_op = opcode_data[dec->op].decomp_rv64;
     if (decomp_op != rv_op_illegal) {
-        dec->op = decomp_op;
-        dec->codec = opcode_data[decomp_op].codec;
+        if ((opcode_data[dec->op].decomp_data & rvcd_imm_nz) && dec->imm == 0) {
+            dec->op = rv_op_illegal;
+        } else {
+            dec->op = decomp_op;
+            dec->codec = opcode_data[decomp_op].codec;
+        }
     }
 }
 
@@ -2813,8 +2826,12 @@ static void decode_inst_decompress_rv128(rv_decode *dec)
 {
     int decomp_op = opcode_data[dec->op].decomp_rv128;
     if (decomp_op != rv_op_illegal) {
-        dec->op = decomp_op;
-        dec->codec = opcode_data[decomp_op].codec;
+        if ((opcode_data[dec->op].decomp_data & rvcd_imm_nz) && dec->imm == 0) {
+            dec->op = rv_op_illegal;
+        } else {
+            dec->op = decomp_op;
+            dec->codec = opcode_data[decomp_op].codec;
+        }
     }
 }
 
-- 
2.21.0