target/i386: Fix VSIB decode

With normal SIB, index == 4 indicates no index.
With VSIB, there is no exception for VR4/VR12.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2474
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Link: https://lore.kernel.org/r/20240805003130.1421051-3-richard.henderson@linaro.org
Cc: qemu-stable@nongnu.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

2 files changed, 12 insertions, 11 deletions

diff --git a/target/i386/tcg/decode-new.c.inc b/target/i386/tcg/decode-new.c.inc
index d2da1d396d..b22210f45d 100644
--- a/target/i386/tcg/decode-new.c.inc
+++ b/target/i386/tcg/decode-new.c.inc
@@ -1811,7 +1811,8 @@ static int decode_modrm(DisasContext *s, CPUX86State *env, X86DecodedInsn *decod
     } else {
         op->has_ea = true;
         op->n = -1;
-        decode->mem = gen_lea_modrm_0(env, s, get_modrm(s, env));
+        decode->mem = gen_lea_modrm_0(env, s, modrm,
+                                      decode->e.vex_class == 12);
     }
     return modrm;
 }
diff --git a/target/i386/tcg/translate.c b/target/i386/tcg/translate.c
index 95bad55bf4..b72864bf01 100644
--- a/target/i386/tcg/translate.c
+++ b/target/i386/tcg/translate.c
@@ -1523,7 +1523,7 @@ typedef struct AddressParts {
 } AddressParts;
 
 static AddressParts gen_lea_modrm_0(CPUX86State *env, DisasContext *s,
-                                    int modrm)
+                                    int modrm, bool is_vsib)
 {
     int def_seg, base, index, scale, mod, rm;
     target_long disp;
@@ -1552,7 +1552,7 @@ static AddressParts gen_lea_modrm_0(CPUX86State *env, DisasContext *s,
             int code = x86_ldub_code(env, s);
             scale = (code >> 6) & 3;
             index = ((code >> 3) & 7) | REX_X(s);
-            if (index == 4) {
+            if (index == 4 && !is_vsib) {
                 index = -1;  /* no index */
             }
             base = (code & 7) | REX_B(s);
@@ -1682,21 +1682,21 @@ static TCGv gen_lea_modrm_1(DisasContext *s, AddressParts a, bool is_vsib)
 
 static void gen_lea_modrm(CPUX86State *env, DisasContext *s, int modrm)
 {
-    AddressParts a = gen_lea_modrm_0(env, s, modrm);
+    AddressParts a = gen_lea_modrm_0(env, s, modrm, false);
     TCGv ea = gen_lea_modrm_1(s, a, false);
     gen_lea_v_seg(s, ea, a.def_seg, s->override);
 }
 
 static void gen_nop_modrm(CPUX86State *env, DisasContext *s, int modrm)
 {
-    (void)gen_lea_modrm_0(env, s, modrm);
+    (void)gen_lea_modrm_0(env, s, modrm, false);
 }
 
 /* Used for BNDCL, BNDCU, BNDCN.  */
 static void gen_bndck(CPUX86State *env, DisasContext *s, int modrm,
                       TCGCond cond, TCGv_i64 bndv)
 {
-    AddressParts a = gen_lea_modrm_0(env, s, modrm);
+    AddressParts a = gen_lea_modrm_0(env, s, modrm, false);
     TCGv ea = gen_lea_modrm_1(s, a, false);
 
     tcg_gen_extu_tl_i64(s->tmp1_i64, ea);
@@ -2417,7 +2417,7 @@ static bool disas_insn_x87(DisasContext *s, CPUState *cpu, int b)
     op = ((b & 7) << 3) | ((modrm >> 3) & 7);
     if (mod != 3) {
         /* memory op */
-        AddressParts a = gen_lea_modrm_0(env, s, modrm);
+        AddressParts a = gen_lea_modrm_0(env, s, modrm, false);
         TCGv ea = gen_lea_modrm_1(s, a, false);
         TCGv last_addr = tcg_temp_new();
         bool update_fdp = true;
@@ -3078,7 +3078,7 @@ static void disas_insn_old(DisasContext *s, CPUState *cpu, int b)
         rm = (modrm & 7) | REX_B(s);
         gen_op_mov_v_reg(s, MO_32, s->T1, reg);
         if (mod != 3) {
-            AddressParts a = gen_lea_modrm_0(env, s, modrm);
+            AddressParts a = gen_lea_modrm_0(env, s, modrm, false);
             /* specific case: we need to add a displacement */
             gen_exts(ot, s->T1);
             tcg_gen_sari_tl(s->tmp0, s->T1, 3 + ot);
@@ -3635,7 +3635,7 @@ static void disas_insn_old(DisasContext *s, CPUState *cpu, int b)
                 }
             } else if (mod != 3) {
                 /* bndldx */
-                AddressParts a = gen_lea_modrm_0(env, s, modrm);
+                AddressParts a = gen_lea_modrm_0(env, s, modrm, false);
                 if (reg >= 4
                     || (prefixes & PREFIX_LOCK)
                     || s->aflag == MO_16
@@ -3679,7 +3679,7 @@ static void disas_insn_old(DisasContext *s, CPUState *cpu, int b)
                     || s->aflag == MO_16) {
                     goto illegal_op;
                 }
-                AddressParts a = gen_lea_modrm_0(env, s, modrm);
+                AddressParts a = gen_lea_modrm_0(env, s, modrm, false);
                 if (a.base >= 0) {
                     tcg_gen_extu_tl_i64(cpu_bndl[reg], cpu_regs[a.base]);
                     if (!CODE64(s)) {
@@ -3740,7 +3740,7 @@ static void disas_insn_old(DisasContext *s, CPUState *cpu, int b)
                 }
             } else if (mod != 3) {
                 /* bndstx */
-                AddressParts a = gen_lea_modrm_0(env, s, modrm);
+                AddressParts a = gen_lea_modrm_0(env, s, modrm, false);
                 if (reg >= 4
                     || (prefixes & PREFIX_LOCK)
                     || s->aflag == MO_16