fix ARM64 too, theoretically

1 files changed, 29 insertions, 2 deletions

diff --git a/lib/arm64/misc.h b/lib/arm64/misc.h
index 84bd638..c21bc0b 100644
--- a/lib/arm64/misc.h
+++ b/lib/arm64/misc.h
@@ -5,5 +5,32 @@
 #define TARGET_TRANSFORM_DIS_HEADER "arm64/transform-dis-arm64.inc.h"
 #define MIN_INSN_SIZE 4
 #define TD_MAX_REWRITTEN_SIZE (7 * 2 * 4) /* also conservative */
-struct arch_dis_ctx {};
-static inline void arch_dis_ctx_init(UNUSED struct arch_dis_ctx *ctx) {}
+
+struct arch_dis_ctx {
+    /* For transform_dis only - used to get temporary registers.  We assume
+     * that we can use any caller-saved or IP register which was not written,
+     * so r9-r18.
+     * This is a massive overestimate: we just OR in each instruction's bits
+     * 4:0 (Rd for data, Rt for loads, most common), 14:10 (Rt2 for load-pair
+     * instructions), and 20:16 (Rs for store-exclusive insturctions).  It
+     * would be easy to restrict the latter two to the few instructions that
+     * actually use them, but with 10 available registers, and a patch of at
+     * most 3 instructions (and none of the instructions that require a temp
+     * use Rt2/Rs or could read their Rd, so the third doesn't count), we won't
+     * run out even with the dumbest possible thing. */
+    uint32_t regs_possibly_written;
+};
+
+static inline void arch_dis_ctx_init(struct arch_dis_ctx *ctx) {
+    ctx->regs_possibly_written = 0;
+}
+
+static inline int arm64_get_unwritten_temp_reg(struct arch_dis_ctx *ctx) {
+    uint32_t avail = ~ctx->regs_possibly_written & ((1 << 19) - (1 << 9));
+    if (!avail)
+        __builtin_abort();
+    return 31 - __builtin_clz(avail);
+}
+
+#define CC_ARMCC         (CC_CONDITIONAL | 0x200)
+#define CC_XBXZ          (CC_CONDITIONAL | 0x400)