[Qemu-devel] [PULL 08/29] target/arm: Introduce read_pc

[Peter Maydell <peter.maydell@linaro.org>]

From: Richard Henderson <richard.henderson@linaro.org>

We currently have 3 different ways of computing the architectural
value of "PC" as seen in the ARM ARM.

The value of s->pc has been incremented past the current insn,
but that is all.  Thus for a32, PC = s->pc + 4; for t32, PC = s->pc;
for t16, PC = s->pc + 2.  These differing computations make it
impossible at present to unify the various code paths.

With the newly introduced s->pc_curr, we can compute the correct
value for all cases, using the formula given in the ARM ARM.

This changes the behaviour for load_reg() and load_reg_var()
when called with reg==15 from a 32-bit Thumb instruction:
previously they would have returned the incorrect value
of pc_curr + 6, and now they will return the architecturally
correct value of PC, which is pc_curr + 4. This will not
affect well-behaved guest software, because all of the places
we call these functions from T32 code are instructions where
using r15 is UNPREDICTABLE. Using the architectural PC value
here is more consistent with the T16 and A32 behaviour.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20190807045335.1361-4-richard.henderson@linaro.org
[PMM: added commit message note about UNPREDICTABLE T32 cases]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 target/arm/translate.c | 59 ++++++++++++++++--------------------------
 1 file changed, 23 insertions(+), 36 deletions(-)

diff --git a/target/arm/translate.c b/target/arm/translate.c
index fed08c63f81..41523c0241f 100644
--- a/target/arm/translate.c
+++ b/target/arm/translate.c
@@ -196,17 +196,17 @@ static inline void store_cpu_offset(TCGv_i32 var, int offset)
 #define store_cpu_field(var, name) \
     store_cpu_offset(var, offsetof(CPUARMState, name))
 
+/* The architectural value of PC.  */
+static uint32_t read_pc(DisasContext *s)
+{
+    return s->pc_curr + (s->thumb ? 4 : 8);
+}
+
 /* Set a variable to the value of a CPU register.  */
 static void load_reg_var(DisasContext *s, TCGv_i32 var, int reg)
 {
     if (reg == 15) {
-        uint32_t addr;
-        /* normally, since we updated PC, we need only to add one insn */
-        if (s->thumb)
-            addr = (long)s->pc + 2;
-        else
-            addr = (long)s->pc + 4;
-        tcg_gen_movi_i32(var, addr);
+        tcg_gen_movi_i32(var, read_pc(s));
     } else {
         tcg_gen_mov_i32(var, cpu_R[reg]);
     }
@@ -7853,16 +7853,14 @@ static void disas_arm_insn(DisasContext *s, unsigned int insn)
             /* branch link and change to thumb (blx <offset>) */
             int32_t offset;
 
-            val = (uint32_t)s->pc;
             tmp = tcg_temp_new_i32();
-            tcg_gen_movi_i32(tmp, val);
+            tcg_gen_movi_i32(tmp, s->pc);
             store_reg(s, 14, tmp);
             /* Sign-extend the 24-bit offset */
             offset = (((int32_t)insn) << 8) >> 8;
+            val = read_pc(s);
             /* offset * 4 + bit24 * 2 + (thumb bit) */
             val += (offset << 2) | ((insn >> 23) & 2) | 1;
-            /* pipeline offset */
-            val += 4;
             /* protected by ARCH(5); above, near the start of uncond block */
             gen_bx_im(s, val);
             return;
@@ -9138,10 +9136,8 @@ static void disas_arm_insn(DisasContext *s, unsigned int insn)
                         } else {
                             /* store */
                             if (i == 15) {
-                                /* special case: r15 = PC + 8 */
-                                val = (long)s->pc + 4;
                                 tmp = tcg_temp_new_i32();
-                                tcg_gen_movi_i32(tmp, val);
+                                tcg_gen_movi_i32(tmp, read_pc(s));
                             } else if (user) {
                                 tmp = tcg_temp_new_i32();
                                 tmp2 = tcg_const_i32(i);
@@ -9207,15 +9203,13 @@ static void disas_arm_insn(DisasContext *s, unsigned int insn)
                 int32_t offset;
 
                 /* branch (and link) */
-                val = (int32_t)s->pc;
                 if (insn & (1 << 24)) {
                     tmp = tcg_temp_new_i32();
-                    tcg_gen_movi_i32(tmp, val);
+                    tcg_gen_movi_i32(tmp, s->pc);
                     store_reg(s, 14, tmp);
                 }
                 offset = sextract32(insn << 2, 0, 26);
-                val += offset + 4;
-                gen_jmp(s, val);
+                gen_jmp(s, read_pc(s) + offset);
             }
             break;
         case 0xc:
@@ -9573,12 +9567,7 @@ static void disas_thumb2_insn(DisasContext *s, uint32_t insn)
                 tcg_temp_free_i32(addr);
             } else if ((insn & (7 << 5)) == 0) {
                 /* Table Branch.  */
-                if (rn == 15) {
-                    addr = tcg_temp_new_i32();
-                    tcg_gen_movi_i32(addr, s->pc);
-                } else {
-                    addr = load_reg(s, rn);
-                }
+                addr = load_reg(s, rn);
                 tmp = load_reg(s, rm);
                 tcg_gen_add_i32(addr, addr, tmp);
                 if (insn & (1 << 4)) {
@@ -9594,7 +9583,7 @@ static void disas_thumb2_insn(DisasContext *s, uint32_t insn)
                 }
                 tcg_temp_free_i32(addr);
                 tcg_gen_shli_i32(tmp, tmp, 1);
-                tcg_gen_addi_i32(tmp, tmp, s->pc);
+                tcg_gen_addi_i32(tmp, tmp, read_pc(s));
                 store_reg(s, 15, tmp);
             } else {
                 bool is_lasr = false;
@@ -10327,7 +10316,7 @@ static void disas_thumb2_insn(DisasContext *s, uint32_t insn)
                     tcg_gen_movi_i32(cpu_R[14], s->pc | 1);
                 }
 
-                offset += s->pc;
+                offset += read_pc(s);
                 if (insn & (1 << 12)) {
                     /* b/bl */
                     gen_jmp(s, offset);
@@ -10568,7 +10557,7 @@ static void disas_thumb2_insn(DisasContext *s, uint32_t insn)
                 offset |= (insn & (1 << 11)) << 8;
 
                 /* jump to the offset */
-                gen_jmp(s, s->pc + offset);
+                gen_jmp(s, read_pc(s) + offset);
             }
         } else {
             /*
@@ -11062,7 +11051,7 @@ static void disas_thumb_insn(DisasContext *s, uint32_t insn)
         if (insn & (1 << 11)) {
             rd = (insn >> 8) & 7;
             /* load pc-relative.  Bit 1 of PC is ignored.  */
-            val = s->pc + 2 + ((insn & 0xff) * 4);
+            val = read_pc(s) + ((insn & 0xff) * 4);
             val &= ~(uint32_t)2;
             addr = tcg_temp_new_i32();
             tcg_gen_movi_i32(addr, val);
@@ -11449,7 +11438,7 @@ static void disas_thumb_insn(DisasContext *s, uint32_t insn)
         } else {
             /* PC. bit 1 is ignored.  */
             tmp = tcg_temp_new_i32();
-            tcg_gen_movi_i32(tmp, (s->pc + 2) & ~(uint32_t)2);
+            tcg_gen_movi_i32(tmp, read_pc(s) & ~(uint32_t)2);
         }
         val = (insn & 0xff) * 4;
         tcg_gen_addi_i32(tmp, tmp, val);
@@ -11569,9 +11558,7 @@ static void disas_thumb_insn(DisasContext *s, uint32_t insn)
                 tcg_gen_brcondi_i32(TCG_COND_NE, tmp, 0, s->condlabel);
             tcg_temp_free_i32(tmp);
             offset = ((insn & 0xf8) >> 2) | (insn & 0x200) >> 3;
-            val = (uint32_t)s->pc + 2;
-            val += offset;
-            gen_jmp(s, val);
+            gen_jmp(s, read_pc(s) + offset);
             break;
 
         case 15: /* IT, nop-hint.  */
@@ -11735,7 +11722,7 @@ static void disas_thumb_insn(DisasContext *s, uint32_t insn)
         arm_skip_unless(s, cond);
 
         /* jump to the offset */
-        val = (uint32_t)s->pc + 2;
+        val = read_pc(s);
         offset = ((int32_t)insn << 24) >> 24;
         val += offset << 1;
         gen_jmp(s, val);
@@ -11761,9 +11748,9 @@ static void disas_thumb_insn(DisasContext *s, uint32_t insn)
             break;
         }
         /* unconditional branch */
-        val = (uint32_t)s->pc;
+        val = read_pc(s);
         offset = ((int32_t)insn << 21) >> 21;
-        val += (offset << 1) + 2;
+        val += offset << 1;
         gen_jmp(s, val);
         break;
 
@@ -11787,7 +11774,7 @@ static void disas_thumb_insn(DisasContext *s, uint32_t insn)
             /* 0b1111_0xxx_xxxx_xxxx : BL/BLX prefix */
             uint32_t uoffset = ((int32_t)insn << 21) >> 9;
 
-            tcg_gen_movi_i32(cpu_R[14], s->pc + 2 + uoffset);
+            tcg_gen_movi_i32(cpu_R[14], read_pc(s) + uoffset);
         }
         break;
     }
-- 
2.20.1