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

[Fangrui Song via llvm-commits]

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@@ -1365,6 +1380,39 @@ bool PPC64LongBranchThunk::isCompatibleWith(const InputSection &isec,
   return rel.type == R_PPC64_REL24 || rel.type == R_PPC64_REL14;
 }
 
+// Hexagon Target Thunks
+static uint64_t getHexagonThunkDestVA(Ctx &ctx, const Symbol &s, int64_t a) {
+  uint64_t v = s.isInPlt(ctx) ? s.getPltVA(ctx) : s.getVA(ctx, a);
+  return SignExtend64<32>(v); // FIXME: sign extend to 64-bit?
+}
+
+void HexagonThunk::writeTo(uint8_t *buf) {
+  uint64_t s = getHexagonThunkDestVA(ctx, destination, addend);
+  uint64_t p = getThunkTargetSym()->getVA(ctx);
+
+  if (ctx.arg.isPic) {
+    write32(ctx, buf + 0, 0x00004000); // {  immext(#0)
+    ctx.target->relocateNoSym(buf, R_HEX_B32_PCREL_X, s - p);
+    write32(ctx, buf + 4, 0x6a49c00e); //    r14 = add(pc,##0) }
+    ctx.target->relocateNoSym(buf + 4, R_HEX_6_PCREL_X, s - p);
+
+    write32(ctx, buf + 8, 0x528ec000); // {  jumpr r14 }
+  } else {
+    write32(ctx, buf + 0, 0x00004000); //  { immext
+    ctx.target->relocateNoSym(buf, R_HEX_B32_PCREL_X, s - p);
+    write32(ctx, buf + 4, 0x5800c000); //    jump <> }
+    ctx.target->relocateNoSym(buf + 4, R_HEX_B22_PCREL_X, s - p);
+  }
+}
+void HexagonThunk::addSymbols(ThunkSection &isec) {
+  Symbol *enclosing = isec.getEnclosingSymbol(RelOffset);
+  StringRef src = enclosing ? enclosing->getName() : isec.name;
+
+  addSymbol(saver().save("__trampoline_for_" + destination.getName() +
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MaskRay wrote:

Perhaps `__hexagon_thunk_` that is shorter? The symbol name should not be depended by tools, i.e. it's the tool's responsibility to adapt linker changes.

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