[Qemu-devel] [PULL 14/48] i386: hvf: Fix register refs if REX is present

[Paolo Bonzini <pbonzini@redhat.com>]

From: Roman Bolshakov <r.bolshakov@yadro.com>

According to Intel(R)64 and IA-32 Architectures Software Developer's
Manual, the following one-byte registers should be fetched when REX
prefix is present (sorted by reg encoding index):
AL, CL, DL, BL, SPL, BPL, SIL, DIL, R8L - R15L

The first 8 are fetched if REX.R is zero, the last 8 if non-zero.

The following registers should be fetched for instructions without REX
prefix (also sorted by reg encoding index):
AL, CL, DL, BL, AH, CH, DH, BH

Current emulation code doesn't handle accesses to SPL, BPL, SIL, DIL
when REX is present, thefore an instruction 40883e "mov %dil,(%rsi)" is
decoded as "mov %bh,(%rsi)".

That caused an infinite loop in vp_reset:
https://lists.gnu.org/archive/html/qemu-devel/2018-10/msg03293.html

Signed-off-by: Roman Bolshakov <r.bolshakov@yadro.com>
Message-Id: <20181018134401.44471-1-r.bolshakov@yadro.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 target/i386/hvf/x86_decode.c | 67 +++++++++++++++++++++++++-------------------
 target/i386/hvf/x86_decode.h |  6 ++--
 2 files changed, 42 insertions(+), 31 deletions(-)

diff --git a/target/i386/hvf/x86_decode.c b/target/i386/hvf/x86_decode.c
index 2d7540f..2e33b69 100644
--- a/target/i386/hvf/x86_decode.c
+++ b/target/i386/hvf/x86_decode.c
@@ -113,7 +113,8 @@ static void decode_modrm_reg(CPUX86State *env, struct x86_decode *decode,
 {
     op->type = X86_VAR_REG;
     op->reg = decode->modrm.reg;
-    op->ptr = get_reg_ref(env, op->reg, decode->rex.r, decode->operand_size);
+    op->ptr = get_reg_ref(env, op->reg, decode->rex.rex, decode->rex.r,
+                          decode->operand_size);
 }
 
 static void decode_rax(CPUX86State *env, struct x86_decode *decode,
@@ -121,7 +122,8 @@ static void decode_rax(CPUX86State *env, struct x86_decode *decode,
 {
     op->type = X86_VAR_REG;
     op->reg = R_EAX;
-    op->ptr = get_reg_ref(env, op->reg, 0, decode->operand_size);
+    op->ptr = get_reg_ref(env, op->reg, decode->rex.rex, 0,
+                          decode->operand_size);
 }
 
 static inline void decode_immediate(CPUX86State *env, struct x86_decode *decode,
@@ -263,16 +265,16 @@ static void decode_incgroup(CPUX86State *env, struct x86_decode *decode)
 {
     decode->op[0].type = X86_VAR_REG;
     decode->op[0].reg = decode->opcode[0] - 0x40;
-    decode->op[0].ptr = get_reg_ref(env, decode->op[0].reg, decode->rex.b,
-                                    decode->operand_size);
+    decode->op[0].ptr = get_reg_ref(env, decode->op[0].reg, decode->rex.rex,
+                                    decode->rex.b, decode->operand_size);
 }
 
 static void decode_decgroup(CPUX86State *env, struct x86_decode *decode)
 {
     decode->op[0].type = X86_VAR_REG;
     decode->op[0].reg = decode->opcode[0] - 0x48;
-    decode->op[0].ptr = get_reg_ref(env, decode->op[0].reg, decode->rex.b,
-                                    decode->operand_size);
+    decode->op[0].ptr = get_reg_ref(env, decode->op[0].reg, decode->rex.rex,
+                                    decode->rex.b, decode->operand_size);
 }
 
 static void decode_incgroup2(CPUX86State *env, struct x86_decode *decode)
@@ -288,16 +290,16 @@ static void decode_pushgroup(CPUX86State *env, struct x86_decode *decode)
 {
     decode->op[0].type = X86_VAR_REG;
     decode->op[0].reg = decode->opcode[0] - 0x50;
-    decode->op[0].ptr = get_reg_ref(env, decode->op[0].reg, decode->rex.b,
-                                    decode->operand_size);
+    decode->op[0].ptr = get_reg_ref(env, decode->op[0].reg, decode->rex.rex,
+                                    decode->rex.b, decode->operand_size);
 }
 
 static void decode_popgroup(CPUX86State *env, struct x86_decode *decode)
 {
     decode->op[0].type = X86_VAR_REG;
     decode->op[0].reg = decode->opcode[0] - 0x58;
-    decode->op[0].ptr = get_reg_ref(env, decode->op[0].reg, decode->rex.b,
-                                    decode->operand_size);
+    decode->op[0].ptr = get_reg_ref(env, decode->op[0].reg, decode->rex.rex,
+                                    decode->rex.b, decode->operand_size);
 }
 
 static void decode_jxx(CPUX86State *env, struct x86_decode *decode)
@@ -378,16 +380,16 @@ static void decode_xchgroup(CPUX86State *env, struct x86_decode *decode)
 {
     decode->op[0].type = X86_VAR_REG;
     decode->op[0].reg = decode->opcode[0] - 0x90;
-    decode->op[0].ptr = get_reg_ref(env, decode->op[0].reg, decode->rex.b,
-                                    decode->operand_size);
+    decode->op[0].ptr = get_reg_ref(env, decode->op[0].reg, decode->rex.rex,
+                                    decode->rex.b, decode->operand_size);
 }
 
 static void decode_movgroup(CPUX86State *env, struct x86_decode *decode)
 {
     decode->op[0].type = X86_VAR_REG;
     decode->op[0].reg = decode->opcode[0] - 0xb8;
-    decode->op[0].ptr = get_reg_ref(env, decode->op[0].reg, decode->rex.b,
-                                    decode->operand_size);
+    decode->op[0].ptr = get_reg_ref(env, decode->op[0].reg, decode->rex.rex,
+                                    decode->rex.b, decode->operand_size);
     decode_immediate(env, decode, &decode->op[1], decode->operand_size);
 }
 
@@ -402,8 +404,8 @@ static void decode_movgroup8(CPUX86State *env, struct x86_decode *decode)
 {
     decode->op[0].type = X86_VAR_REG;
     decode->op[0].reg = decode->opcode[0] - 0xb0;
-    decode->op[0].ptr = get_reg_ref(env, decode->op[0].reg, decode->rex.b,
-                                    decode->operand_size);
+    decode->op[0].ptr = get_reg_ref(env, decode->op[0].reg, decode->rex.rex,
+                                    decode->rex.b, decode->operand_size);
     decode_immediate(env, decode, &decode->op[1], decode->operand_size);
 }
 
@@ -412,7 +414,8 @@ static void decode_rcx(CPUX86State *env, struct x86_decode *decode,
 {
     op->type = X86_VAR_REG;
     op->reg = R_ECX;
-    op->ptr = get_reg_ref(env, op->reg, decode->rex.b, decode->operand_size);
+    op->ptr = get_reg_ref(env, op->reg, decode->rex.rex, decode->rex.b,
+                          decode->operand_size);
 }
 
 struct decode_tbl {
@@ -639,8 +642,8 @@ static void decode_bswap(CPUX86State *env, struct x86_decode *decode)
 {
     decode->op[0].type = X86_VAR_REG;
     decode->op[0].reg = decode->opcode[1] - 0xc8;
-    decode->op[0].ptr = get_reg_ref(env, decode->op[0].reg, decode->rex.b,
-                                    decode->operand_size);
+    decode->op[0].ptr = get_reg_ref(env, decode->op[0].reg, decode->rex.rex,
+                                    decode->rex.b, decode->operand_size);
 }
 
 static void decode_d9_4(CPUX86State *env, struct x86_decode *decode)
@@ -1686,7 +1689,8 @@ calc_addr:
     }
 }
 
-target_ulong get_reg_ref(CPUX86State *env, int reg, int is_extended, int size)
+target_ulong get_reg_ref(CPUX86State *env, int reg, int rex, int is_extended,
+                         int size)
 {
     target_ulong ptr = 0;
     int which = 0;
@@ -1698,7 +1702,7 @@ target_ulong get_reg_ref(CPUX86State *env, int reg, int is_extended, int size)
 
     switch (size) {
     case 1:
-        if (is_extended || reg < 4) {
+        if (is_extended || reg < 4 || rex) {
             which = 1;
             ptr = (target_ulong)&RL(env, reg);
         } else {
@@ -1714,10 +1718,11 @@ target_ulong get_reg_ref(CPUX86State *env, int reg, int is_extended, int size)
     return ptr;
 }
 
-target_ulong get_reg_val(CPUX86State *env, int reg, int is_extended, int size)
+target_ulong get_reg_val(CPUX86State *env, int reg, int rex, int is_extended,
+                         int size)
 {
     target_ulong val = 0;
-    memcpy(&val, (void *)get_reg_ref(env, reg, is_extended, size), size);
+    memcpy(&val, (void *)get_reg_ref(env, reg, rex, is_extended, size), size);
     return val;
 }
 
@@ -1739,7 +1744,8 @@ static target_ulong get_sib_val(CPUX86State *env, struct x86_decode *decode,
         if (base_reg == R_ESP || base_reg == R_EBP) {
             *sel = R_SS;
         }
-        base = get_reg_val(env, decode->sib.base, decode->rex.b, addr_size);
+        base = get_reg_val(env, decode->sib.base, decode->rex.rex,
+                           decode->rex.b, addr_size);
     }
 
     if (decode->rex.x) {
@@ -1747,7 +1753,8 @@ static target_ulong get_sib_val(CPUX86State *env, struct x86_decode *decode,
     }
 
     if (index_reg != R_ESP) {
-        scaled_index = get_reg_val(env, index_reg, decode->rex.x, addr_size) <<
+        scaled_index = get_reg_val(env, index_reg, decode->rex.rex,
+                                   decode->rex.x, addr_size) <<
                                    decode->sib.scale;
     }
     return base + scaled_index;
@@ -1776,7 +1783,8 @@ void calc_modrm_operand32(CPUX86State *env, struct x86_decode *decode,
         if (decode->modrm.rm == R_EBP || decode->modrm.rm == R_ESP) {
             seg = R_SS;
         }
-        ptr += get_reg_val(env, decode->modrm.rm, decode->rex.b, addr_size);
+        ptr += get_reg_val(env, decode->modrm.rm, decode->rex.rex,
+                           decode->rex.b, addr_size);
     }
 
     if (X86_DECODE_CMD_LEA == decode->cmd) {
@@ -1805,7 +1813,8 @@ void calc_modrm_operand64(CPUX86State *env, struct x86_decode *decode,
     } else if (0 == mod && 5 == rm) {
         ptr = RIP(env) + decode->len + (int32_t) offset;
     } else {
-        ptr = get_reg_val(env, src, decode->rex.b, 8) + (int64_t) offset;
+        ptr = get_reg_val(env, src, decode->rex.rex, decode->rex.b, 8) +
+              (int64_t) offset;
     }
 
     if (X86_DECODE_CMD_LEA == decode->cmd) {
@@ -1822,8 +1831,8 @@ void calc_modrm_operand(CPUX86State *env, struct x86_decode *decode,
     if (3 == decode->modrm.mod) {
         op->reg = decode->modrm.reg;
         op->type = X86_VAR_REG;
-        op->ptr = get_reg_ref(env, decode->modrm.rm, decode->rex.b,
-                              decode->operand_size);
+        op->ptr = get_reg_ref(env, decode->modrm.rm, decode->rex.rex,
+                              decode->rex.b, decode->operand_size);
         return;
     }
 
diff --git a/target/i386/hvf/x86_decode.h b/target/i386/hvf/x86_decode.h
index 5ab6f31..ef4bcab 100644
--- a/target/i386/hvf/x86_decode.h
+++ b/target/i386/hvf/x86_decode.h
@@ -303,8 +303,10 @@ uint64_t sign(uint64_t val, int size);
 
 uint32_t decode_instruction(CPUX86State *env, struct x86_decode *decode);
 
-target_ulong get_reg_ref(CPUX86State *env, int reg, int is_extended, int size);
-target_ulong get_reg_val(CPUX86State *env, int reg, int is_extended, int size);
+target_ulong get_reg_ref(CPUX86State *env, int reg, int rex, int is_extended,
+                         int size);
+target_ulong get_reg_val(CPUX86State *env, int reg, int rex, int is_extended,
+                         int size);
 void calc_modrm_operand(CPUX86State *env, struct x86_decode *decode,
                         struct x86_decode_op *op);
 target_ulong decode_linear_addr(CPUX86State *env, struct x86_decode *decode,
-- 
1.8.3.1