tcg/riscv: Fix illegal shift instructions

Out-of-range shifts have undefined results, but must not trap.
Mask off immediate shift counts to solve this problem.

This bug can be reproduced by running the following guest instructions:

  xor %ecx,%ecx
  sar %cl,%eax
  cmovne %edi,%eax

After optimization, the tcg opcodes of the sar are

  movi_i32 tmp3,$0xffffffffffffffff  pref=all
  sar_i32 tmp3,eax,tmp3              dead: 2  pref=all
  mov_i32 cc_dst,eax                 sync: 0  dead: 1 pref=0xffc0300
  mov_i32 cc_src,tmp3                sync: 0  dead: 0 1  pref=all
  movi_i32 cc_op,$0x31               sync: 0  dead: 0  pref=all

The sar_i32 opcode is a shift by -1, which unmasked generates

  0x200808d618:  fffa5b9b          illegal

Signed-off-by: Zihao Yu <yuzihao@ict.ac.cn>
Message-Id: <20201216081206.9628-1-yuzihao@ict.ac.cn>
[rth: Reworded the patch description.]
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

diff --git a/tcg/riscv/tcg-target.c.inc b/tcg/riscv/tcg-target.c.inc
index d536f3ccc17cb336361aefefeb34b6d481d78993..4089e29cd953b11b769b535b0683ed37255e003c 100644 (file)
--- a/tcg/riscv/tcg-target.c.inc
+++ b/tcg/riscv/tcg-target.c.inc
@@ -1462,14 +1462,14 @@ static void tcg_out_op(TCGContext *s, TCGOpcode opc,
 
     case INDEX_op_shl_i32:
         if (c2) {
-            tcg_out_opc_imm(s, OPC_SLLIW, a0, a1, a2);
+            tcg_out_opc_imm(s, OPC_SLLIW, a0, a1, a2 & 0x1f);
         } else {
             tcg_out_opc_reg(s, OPC_SLLW, a0, a1, a2);
         }
         break;
     case INDEX_op_shl_i64:
         if (c2) {
-            tcg_out_opc_imm(s, OPC_SLLI, a0, a1, a2);
+            tcg_out_opc_imm(s, OPC_SLLI, a0, a1, a2 & 0x3f);
         } else {
             tcg_out_opc_reg(s, OPC_SLL, a0, a1, a2);
         }
@@ -1477,14 +1477,14 @@ static void tcg_out_op(TCGContext *s, TCGOpcode opc,
 
     case INDEX_op_shr_i32:
         if (c2) {
-            tcg_out_opc_imm(s, OPC_SRLIW, a0, a1, a2);
+            tcg_out_opc_imm(s, OPC_SRLIW, a0, a1, a2 & 0x1f);
         } else {
             tcg_out_opc_reg(s, OPC_SRLW, a0, a1, a2);
         }
         break;
     case INDEX_op_shr_i64:
         if (c2) {
-            tcg_out_opc_imm(s, OPC_SRLI, a0, a1, a2);
+            tcg_out_opc_imm(s, OPC_SRLI, a0, a1, a2 & 0x3f);
         } else {
             tcg_out_opc_reg(s, OPC_SRL, a0, a1, a2);
         }
@@ -1492,14 +1492,14 @@ static void tcg_out_op(TCGContext *s, TCGOpcode opc,
 
     case INDEX_op_sar_i32:
         if (c2) {
-            tcg_out_opc_imm(s, OPC_SRAIW, a0, a1, a2);
+            tcg_out_opc_imm(s, OPC_SRAIW, a0, a1, a2 & 0x1f);
         } else {
             tcg_out_opc_reg(s, OPC_SRAW, a0, a1, a2);
         }
         break;
     case INDEX_op_sar_i64:
         if (c2) {
-            tcg_out_opc_imm(s, OPC_SRAI, a0, a1, a2);
+            tcg_out_opc_imm(s, OPC_SRAI, a0, a1, a2 & 0x3f);
         } else {
             tcg_out_opc_reg(s, OPC_SRA, a0, a1, a2);
         }