[Qemu-devel] [PATCH v3 10/12] target-arm: A64: add support for conditional branches

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

From: Alexander Graf <agraf@suse.de>

This patch adds emulation for the conditional branch (b.cond) instruction.

Signed-off-by: Alexander Graf <agraf@suse.de>
[claudio: adapted to new decoder structure,
          reused arm infrastructure for checking the flags]
Signed-off-by: Claudio Fontana <claudio.fontana@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <rth@twiddle.net>
---
 target-arm/translate-a64.c |   29 +++++++++++++++++++++++++++--
 target-arm/translate.c     |   14 +++++++++-----
 target-arm/translate.h     |    2 ++
 3 files changed, 38 insertions(+), 7 deletions(-)

diff --git a/target-arm/translate-a64.c b/target-arm/translate-a64.c
index ce2f841..a6a1973 100644
--- a/target-arm/translate-a64.c
+++ b/target-arm/translate-a64.c
@@ -239,10 +239,35 @@ static void disas_test_b_imm(DisasContext *s, uint32_t insn)
     unsupported_encoding(s, insn);
 }
 
-/* Conditional branch (immediate) */
+/* C3.2.2 / C5.6.19 Conditional branch (immediate)
+ *  31           25  24  23                  5   4  3    0
+ * +---------------+----+---------------------+----+------+
+ * | 0 1 0 1 0 1 0 | o1 |         imm19       | o0 | cond |
+ * +---------------+----+---------------------+----+------+
+ */
 static void disas_cond_b_imm(DisasContext *s, uint32_t insn)
 {
-    unsupported_encoding(s, insn);
+    unsigned int cond;
+    uint64_t addr;
+
+    if ((insn & (1 << 4)) || (insn & (1 << 24))) {
+        unallocated_encoding(s);
+        return;
+    }
+    addr = s->pc + sextract32(insn, 5, 19) * 4 - 4;
+    cond = extract32(insn, 0, 4);
+
+    if (cond < 0x0e) {
+        /* genuinely conditional branches */
+        int label_match = gen_new_label();
+        arm_gen_test_cc(cond, label_match);
+        gen_goto_tb(s, 0, s->pc);
+        gen_set_label(label_match);
+        gen_goto_tb(s, 1, addr);
+    } else {
+        /* 0xe and 0xf are both "always" conditions */
+        gen_goto_tb(s, 0, addr);
+    }
 }
 
 /* C5.6.68 HINT */
diff --git a/target-arm/translate.c b/target-arm/translate.c
index 553bded..9e2d1eb 100644
--- a/target-arm/translate.c
+++ b/target-arm/translate.c
@@ -671,7 +671,11 @@ static void gen_thumb2_parallel_addsub(int op1, int op2, TCGv_i32 a, TCGv_i32 b)
 }
 #undef PAS_OP
 
-static void gen_test_cc(int cc, int label)
+/*
+ * generate a conditional branch based on ARM condition code cc.
+ * This is common between ARM and Aarch64 targets.
+ */
+void arm_gen_test_cc(int cc, int label)
 {
     TCGv_i32 tmp;
     int inv;
@@ -6903,7 +6907,7 @@ static void disas_arm_insn(CPUARMState * env, DisasContext *s)
         /* if not always execute, we generate a conditional jump to
            next instruction */
         s->condlabel = gen_new_label();
-        gen_test_cc(cond ^ 1, s->condlabel);
+        arm_gen_test_cc(cond ^ 1, s->condlabel);
         s->condjmp = 1;
     }
     if ((insn & 0x0f900000) == 0x03000000) {
@@ -8910,7 +8914,7 @@ static int disas_thumb2_insn(CPUARMState *env, DisasContext *s, uint16_t insn_hw
                 op = (insn >> 22) & 0xf;
                 /* Generate a conditional jump to next instruction.  */
                 s->condlabel = gen_new_label();
-                gen_test_cc(op ^ 1, s->condlabel);
+                arm_gen_test_cc(op ^ 1, s->condlabel);
                 s->condjmp = 1;
 
                 /* offset[11:1] = insn[10:0] */
@@ -9267,7 +9271,7 @@ static void disas_thumb_insn(CPUARMState *env, DisasContext *s)
         cond = s->condexec_cond;
         if (cond != 0x0e) {     /* Skip conditional when condition is AL. */
           s->condlabel = gen_new_label();
-          gen_test_cc(cond ^ 1, s->condlabel);
+          arm_gen_test_cc(cond ^ 1, s->condlabel);
           s->condjmp = 1;
         }
     }
@@ -9940,7 +9944,7 @@ static void disas_thumb_insn(CPUARMState *env, DisasContext *s)
         }
         /* generate a conditional jump to next instruction */
         s->condlabel = gen_new_label();
-        gen_test_cc(cond ^ 1, s->condlabel);
+        arm_gen_test_cc(cond ^ 1, s->condlabel);
         s->condjmp = 1;
 
         /* jump to the offset */
diff --git a/target-arm/translate.h b/target-arm/translate.h
index 23a45da..a6f6b3e 100644
--- a/target-arm/translate.h
+++ b/target-arm/translate.h
@@ -65,4 +65,6 @@ static inline void gen_a64_set_pc_im(uint64_t val)
 }
 #endif
 
+void arm_gen_test_cc(int cc, int label);
+
 #endif /* TARGET_ARM_TRANSLATE_H */
-- 
1.7.9.5