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

[Fangrui Song via llvm-commits]

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@@ -2139,17 +2139,44 @@ 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;
+constexpr uint32_t HEXAGON_MASK_END_PACKET = 3 << 14;
+constexpr uint32_t HEXAGON_END_OF_PACKET = 3 << 14;
+constexpr 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 =
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MaskRay wrote:

`InstWordContents` fix naming

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