1 files changed, 32 insertions, 0 deletions
diff --git a/lib/x86/jump-patch.h b/lib/x86/jump-patch.h
new file mode 100644
index 0000000..efd4825
--- /dev/null
+++ b/lib/x86/jump-patch.h
@@ -0,0 +1,32 @@
+#pragma once
+#define MAX_JUMP_PATCH_SIZE 5
+
+static inline int jump_patch_size(uintptr_t pc, uintptr_t dpc,
+                                  UNUSED struct arch_dis_ctx arch,
+                                  bool force) {
+    uintptr_t diff = pc - (dpc + 5);
+    /* fits in 32? */
+    if (diff == (uintptr_t) (int32_t) diff)
+        return 5;
+    else
+        return force ? (2+4+8) : -1;
+}
+
+static inline void make_jump_patch(void **codep, UNUSED uintptr_t pc,
+                                   uintptr_t dpc,
+                                   UNUSED struct arch_dis_ctx arch) {
+    uintptr_t diff = pc - (dpc + 5);
+    uint8_t *code = *codep;
+    if (diff == (uintptr_t) (int32_t) diff) {
+        *(uint8_t *) code = 0xe9;
+        *(uint32_t *) (code + 1) = diff;
+        *codep = code + 5;
+    } else {
+        /* jmpq *(%rip) */
+        *code++ = 0xff;
+        *code++ = 0x25;
+        *(uint32_t *) code = 0; code += 4;
+        *(uint64_t *) code = dpc; code += 8;
+        *codep = code;
+    }
+}