[lld] [lld] Add thunks for hexagon (PR #111217)

[Fangrui Song via llvm-commits]

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@@ -2054,18 +2054,46 @@ void ThunkCreator::mergeThunks(ArrayRef<OutputSection *> outputSections) {
       });
 }
 
-static int64_t getPCBias(Ctx &ctx, RelType type) {
-  if (ctx.arg.emachine != EM_ARM)
-    return 0;
-  switch (type) {
-  case R_ARM_THM_JUMP19:
-  case R_ARM_THM_JUMP24:
-  case R_ARM_THM_CALL:
-    return 4;
-  default:
-    return 8;
+static const uint32_t HEXAGON_MASK_END_PACKET = 3 << 14;
+static const uint32_t HEXAGON_END_OF_PACKET = 3 << 14;
+static const uint32_t HEXAGON_END_OF_DUPLEX = 0 << 14;
+
+// Return the distance between the packet start and the instruction in the
+// relocation.
+static int getHexagonPacketOffset(const InputSection &isec,
+                                  const Relocation &rel) {
+  const ArrayRef<uint8_t> SectContents = isec.content();
+
+  // Search back as many as 3 instructions.
+  for (unsigned i = 0;; i++) {
+    if (i == 3 || rel.offset < (i + 1) * 4)
+      return i * 4;
+    uint32_t instWord = 0;
+    const ArrayRef<uint8_t> InstWordContents =
+        SectContents.drop_front(rel.offset - (i + 1) * 4);
+    ::memcpy(&instWord, InstWordContents.data(), sizeof(instWord));
+    if (((instWord & HEXAGON_MASK_END_PACKET) == HEXAGON_END_OF_PACKET) ||
+        ((instWord & HEXAGON_MASK_END_PACKET) == HEXAGON_END_OF_DUPLEX))
+      return i * 4;
   }
 }
+static int64_t getPCBias(Ctx &ctx, const InputSection &isec,
+                         const Relocation &rel) {
+  if (ctx.arg.emachine == EM_ARM) {
+    switch (rel.type) {
+    case R_ARM_THM_JUMP19:
+    case R_ARM_THM_JUMP24:
+    case R_ARM_THM_CALL:
+      return 4;
+    default:
+      return 8;
+    }
+  }
+  if (ctx.arg.emachine == EM_HEXAGON) {
+    return -getHexagonPacketOffset(isec, rel);
----------------
MaskRay wrote:

https://llvm.org/docs/CodingStandards.html#don-t-use-braces-on-simple-single-statement-bodies-of-if-else-loop-statements

https://github.com/llvm/llvm-project/pull/111217