[PATCH v2 08/12] target-arm: A64: add support for B and BL insns

[Peter Maydell <peter.maydell@xxxxxxxxxx>]

From: Alexander Graf <agraf@xxxxxxx>

Implement the B and BL instructions (PC relative branches and calls).

For convenience in managing TCG temporaries which might be generated
if a source register is the zero-register XZR, we provide a simple
mechanism for creating a new temp which is automatically freed at the
end of decode of the instruction.

Signed-off-by: Alexander Graf <agraf@xxxxxxx>
[claudio: renamed functions, adapted to new decoder layout]
Signed-off-by: Claudio Fontana <claudio.fontana@xxxxxxxxxx>
Signed-off-by: Peter Maydell <peter.maydell@xxxxxxxxxx>
---
 target-arm/translate-a64.c |   45 ++++++++++++++++++++++++++++++++++++++++++--
 target-arm/translate.h     |    3 +++
 2 files changed, 46 insertions(+), 2 deletions(-)

diff --git a/target-arm/translate-a64.c b/target-arm/translate-a64.c
index 1e2b371..b413966 100644
--- a/target-arm/translate-a64.c
+++ b/target-arm/translate-a64.c
@@ -160,16 +160,53 @@ static void unallocated_encoding(DisasContext *s)
         unallocated_encoding(s);                                         \
     } while (0);
 
+static void free_tmp_a64(DisasContext *s)
+{
+    int i;
+    for (i = 0; i < s->tmp_a64_count; i++) {
+        tcg_temp_free_i64(s->tmp_a64[i]);
+    }
+    s->tmp_a64_count = 0;
+}
+
+static TCGv_i64 new_tmp_a64_zero(DisasContext *s)
+{
+    assert(s->tmp_a64_count < TMP_A64_MAX);
+    return s->tmp_a64[s->tmp_a64_count++] = tcg_const_i64(0);
+}
+
+static TCGv_i64 cpu_reg(DisasContext *s, int reg)
+{
+    if (reg == 31) {
+        return new_tmp_a64_zero(s);
+    } else {
+        return cpu_X[reg];
+    }
+}
+
 /*
  * the instruction disassembly implemented here matches
  * the instruction encoding classifications in chapter 3 (C3)
  * of the ARM Architecture Reference Manual (DDI0487A_a)
  */
 
-/* Unconditional branch (immediate) */
+/* C3.2.7 Unconditional branch (immediate)
+ *   31  30       26 25                                  0
+ * +----+-----------+-------------------------------------+
+ * | op | 0 0 1 0 1 |                 imm26               |
+ * +----+-----------+-------------------------------------+
+ */
 static void disas_uncond_b_imm(DisasContext *s, uint32_t insn)
 {
-    unsupported_encoding(s, insn);
+    uint64_t addr = s->pc + sextract32(insn, 0, 26) * 4 - 4;
+
+    if (insn & (1 << 31)) {
+        /* C5.6.26 BL Branch with link */
+        tcg_gen_movi_i64(cpu_reg(s, 30), s->pc);
+    }
+
+    /* C5.6.20 B Branch / C5.6.26 BL Branch with link */
+    gen_goto_tb(s, 0, addr);
 }
 
 /* Compare & branch (immediate) */
@@ -651,6 +688,9 @@ static void disas_a64_insn(CPUARMState *env, DisasContext *s)
         assert(FALSE); /* all 15 cases should be handled above */
         break;
     }
+
+    /* if we allocated any temporaries, free them here */
+    free_tmp_a64(s);
 }
 
 void gen_intermediate_code_internal_a64(ARMCPU *cpu,
@@ -680,6 +720,7 @@ void gen_intermediate_code_internal_a64(ARMCPU *cpu,
     dc->condjmp = 0;
 
     dc->aarch64 = 1;
+    dc->tmp_a64_count = 0;
     dc->thumb = 0;
     dc->bswap_code = 0;
     dc->condexec_mask = 0;
diff --git a/target-arm/translate.h b/target-arm/translate.h
index 8789181..23a45da 100644
--- a/target-arm/translate.h
+++ b/target-arm/translate.h
@@ -24,6 +24,9 @@ typedef struct DisasContext {
     int vec_len;
     int vec_stride;
     int aarch64;
+#define TMP_A64_MAX 16
+    int tmp_a64_count;
+    TCGv_i64 tmp_a64[TMP_A64_MAX];
 } DisasContext;
 
 extern TCGv_ptr cpu_env;
-- 
1.7.9.5

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