[wasm] Avoid manual relocation of target address

In PatchTrampolineAndStubCalls, use a second iterator over the original
relocation info, to avoid having to reconstruct the original target of
the branch by manually applying the delta between the old and new code.

This way, we do not need to make assumptions regarding how code targets are
encoded.


Change-Id: I551ad8a3a654ead63ea88c8ce1d8c9e1927436b0
Reviewed-on: https://chromium-review.googlesource.com/995442Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Georgia Kouveli <georgia.kouveli@arm.com>
Cr-Commit-Position: refs/heads/master@{#52365}

src/wasm/wasm-code-manager.cc

@@ -71,14 +71,15 @@ void PatchTrampolineAndStubCalls(
   // targets to call the new trampolines and stubs.
   intptr_t delta =
       new_code->instructions().start() - original_code->instructions().start();
+  int mask = RelocInfo::kApplyMask | RelocInfo::kCodeTargetMask;
+  RelocIterator orig_it(original_code->instructions(),
+                        original_code->reloc_info(),
+                        original_code->constant_pool(), mask);
   for (RelocIterator it(new_code->instructions(), new_code->reloc_info(),
-                        new_code->constant_pool(),
-                        RelocInfo::kCodeTargetMask | RelocInfo::kApplyMask);
-       !it.done(); it.next()) {
-    bool relocate =
-        RelocInfo::ModeMask(it.rinfo()->rmode()) & RelocInfo::kApplyMask;
+                        new_code->constant_pool(), mask);
+       !it.done(); it.next(), orig_it.next()) {
     if (RelocInfo::IsCodeTarget(it.rinfo()->rmode())) {
-      Address target = it.rinfo()->target_address() - (relocate ? delta : 0);
+      Address target = orig_it.rinfo()->target_address();
 #if V8_TARGET_ARCH_X64 || V8_TARGET_ARCH_S390X
       auto found = reverse_lookup.find(target);
       DCHECK(found != reverse_lookup.end());