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

[Vasily Leonenko via llvm-commits]

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@@ -1448,26 +1536,101 @@ Error RewriteInstance::discoverRtFiniAddress() {
                            "No relocation for first DT_FINI_ARRAY slot");
 }
 
-void RewriteInstance::updateRtFiniReloc() {
+Error RewriteInstance::updateRtInitReloc() {
+  if (BC->HasInterpHeader && opts::RuntimeLibInitHook == opts::RLIH_ENTRY_POINT)
+    return Error::success();
+
+  // Updating DT_INIT is handled by patchELFDynamic.
+  if (BC->InitAddress && opts::RuntimeLibInitHook <= opts::RLIH_INIT)
+    return Error::success();
+
+  const RuntimeLibrary *RT = BC->getRuntimeLibrary();
+  if (!RT || !RT->getRuntimeStartAddress())
+    return Error::success();
+
+  if (!BC->InitArrayAddress)
+    return Error::success();
+
+  if (!BC->InitArrayAddress || !BC->InitArraySize)
+    return createStringError(std::errc::not_supported,
+                             "inconsistent .init_array state");
+
+  ErrorOr<BinarySection &> InitArraySection =
+      BC->getSectionForAddress(*BC->InitArrayAddress);
+  if (!InitArraySection)
+    return createStringError(std::errc::not_supported, ".init_array removed");
+
+  if (std::optional<Relocation> Reloc =
+          InitArraySection->takeDynamicRelocationAt(0)) {
+    if (Reloc->isRelative()) {
+      if (Reloc->Addend != BC->StartFunctionAddress)
+        return createStringError(std::errc::not_supported,
+                                 "inconsistent .init_array dynamic relocation");
+      Reloc->Addend = RT->getRuntimeStartAddress();
+      InitArraySection->addDynamicRelocation(*Reloc);
+    } 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");
+      if (BF->getAddress() + Reloc->Addend != BC->StartFunctionAddress)
+        return createStringError(std::errc::not_supported,
+                                 "inconsistent .init_array dynamic relocation");
+      InitArraySection->addDynamicRelocation(Relocation{
+          /*Offset*/ 0, /*Symbol*/ nullptr, /*Type*/ Relocation::getAbs64(),
+          /*Addend*/ RT->getRuntimeStartAddress(), /*Value*/ 0});
+    }
+  }
+  // Update the static relocation by adding a pending relocation which will get
+  // patched when flushPendingRelocations is called in rewriteFile. Note that
+  // flushPendingRelocations will calculate the value to patch as
+  // "Symbol + Addend". Since we don't have a symbol, just set the addend to the
+  // desired value.
+  InitArraySection->addPendingRelocation(Relocation{
+      /*Offset*/ 0, /*Symbol*/ nullptr, /*Type*/ Relocation::getAbs64(),
+      /*Addend*/ RT->getRuntimeStartAddress(), /*Value*/ 0});
+  outs() << "BOLT-INFO: Runtime library initialization was hooked via 1st "
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vleonen wrote:

Done for this and other similar comments

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