fix my utter failure to handle branches/conditionals correctly (on ARM)

1 files changed, 49 insertions, 2 deletions

diff --git a/lib/arm/misc.h b/lib/arm/misc.h
index f8d593e..02b06fe 100644
--- a/lib/arm/misc.h
+++ b/lib/arm/misc.h
@@ -4,9 +4,56 @@
 #define TARGET_JUMP_PATCH_HDR "arm/jump-patch.h"
 #define TARGET_TRANSFORM_DIS_HEADER "arm/transform-dis-arm-multi.inc.h"
 #define MIN_INSN_SIZE 2
+/* each input instruction might turn into:
+ * - 2 bytes for Bcc, if in IT
+ * then ONE of:
+ * - 2/4 bytes for just the instruction
+ * - 2+8 bytes for branch (which in *valid* code rules out IT but whatever)
+ * - up to 7 4-byte insns for pcrel (if dest=pc, and while these can be subject
+ *   to IT, there can only reasonably be two per block, and if there are both
+ *   then that's an unconditional exit - but we don't enforce any of this
+ *   currently)
+ * - up to 7 4-byte insns for similar moves to PC that fall under 'data'
+ * the maximum number of possible inputs is 4, plus 4 extras if the last one
+ * was an IT (but in that case it can't be one of the above cases)
+ * while this looks huge, it's overly conservative and doesn't matter much,
+ * since only the actually used space will be taken up in the final output
+ */
+#define TD_MAX_REWRITTEN_SIZE (7*4*7 + 4) /* 196 */
+
 struct arch_dis_ctx {
-    unsigned thumb_it_length;
+    /* thumb? */
     bool pc_low_bit;
+    /* if thumb, IT cond for the next 5 instructions
+     * (5 because we still advance after IT) */
+    uint8_t it_conds[5];
+    /* for transform_dis - did we add space for a Bccrel? */
+    uint8_t bccrel_bits;
+    void *bccrel_p;
 };
-enum { IS_LDRD_STRD = 1 << 16 };
 
+static inline void arch_dis_ctx_init(struct arch_dis_ctx *ctx) {
+    ctx->pc_low_bit = false;
+    ctx->bccrel_p = NULL;
+    memset(ctx->it_conds, 0xe, 5);
+}
+
+static inline void advance_it_cond(struct arch_dis_ctx *ctx) {
+    ctx->it_conds[0] = ctx->it_conds[1];
+    ctx->it_conds[1] = ctx->it_conds[2];
+    ctx->it_conds[2] = ctx->it_conds[3];
+    ctx->it_conds[3] = ctx->it_conds[4];
+    ctx->it_conds[4] = 0xe;
+}
+
+#define DFLAG_IS_LDRD_STRD (1 << 16)
+
+/* Types of conditionals for 'branch' */
+/* a regular old branch-with-condition */
+#define CC_ARMCC         (CC_CONDITIONAL | 0x200)
+/* already in an IT block - in transform_dis this will be rewritten to a branch
+ * anyway, so it can be treated as unconditional; in jump_dis we have to know
+ * to keep going */
+#define CC_ALREADY_IN_IT (CC_CONDITIONAL | 0x400)
+/* CBZ/CBNZ is rewritten */
+#define CC_CBXZ          (CC_CONDITIONAL | 0x800)