[llvm] [BOLT] Support runtime library hook via DT_INIT_ARRAY (PR #167467)

[Maksim Panchenko via llvm-commits]

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@@ -1411,6 +1441,60 @@ void RewriteInstance::discoverBOLTReserved() {
   NextAvailableAddress = BC->BOLTReserved.start();
 }
 
+Error RewriteInstance::discoverRtInitAddress() {
+  if (BC->HasInterpHeader && opts::RuntimeLibInitHook == opts::RLIH_ENTRY_POINT)
+    return Error::success();
+
+  // Use DT_INIT if it's available.
+  if (BC->InitAddress && opts::RuntimeLibInitHook <= opts::RLIH_INIT) {
+    BC->StartFunctionAddress = BC->InitAddress;
+    return Error::success();
+  }
+
+  if (!BC->InitArrayAddress || !BC->InitArraySize) {
+    return createStringError(std::errc::not_supported,
+                             "Instrumentation of shared library needs either "
+                             "DT_INIT or DT_INIT_ARRAY");
+  }
+
+  if (*BC->InitArraySize < BC->AsmInfo->getCodePointerSize()) {
+    return createStringError(std::errc::not_supported,
+                             "Need at least 1 DT_INIT_ARRAY slot");
+  }
+
+  ErrorOr<BinarySection &> InitArraySection =
+      BC->getSectionForAddress(*BC->InitArrayAddress);
+  if (auto EC = InitArraySection.getError())
+    return errorCodeToError(EC);
+
+  if (const Relocation *Reloc = InitArraySection->getDynamicRelocationAt(0)) {
+    if (Reloc->isRelative()) {
+      BC->StartFunctionAddress = Reloc->Addend;
+    } else {
+      MCSymbol *Sym = Reloc->Symbol;
+      if (!Sym)
+        return createStringError(
+            std::errc::not_supported,
+            "Failed to locate symbol for 0 entry of .init_array");
+      const BinaryFunction *BF = BC->getFunctionForSymbol(Sym);
+      if (!BF)
+        return createStringError(
+            std::errc::not_supported,
+            "Failed to locate binary function for 0 entry of .init_array");
+      BC->StartFunctionAddress = BF->getAddress() + Reloc->Addend;
+    }
+    return Error::success();
+  }
+
+  if (const Relocation *Reloc = InitArraySection->getRelocationAt(0)) {
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maksfb wrote:

Likewise.

https://github.com/llvm/llvm-project/pull/167467