[BOLT][WIP] Support restartable sequences in tcmalloc

bolt/include/bolt/Rewrite/MetadataRewriters.h

@@ -19,12 +19,14 @@ class BinaryContext;
 
 // The list of rewriter build functions.
 
-std::unique_ptr<MetadataRewriter> createLinuxKernelRewriter(BinaryContext &);
-
 std::unique_ptr<MetadataRewriter> createBuildIDRewriter(BinaryContext &);
 
+std::unique_ptr<MetadataRewriter> createLinuxKernelRewriter(BinaryContext &);
+
 std::unique_ptr<MetadataRewriter> createPseudoProbeRewriter(BinaryContext &);
 
+std::unique_ptr<MetadataRewriter> createRSeqRewriter(BinaryContext &);
+
 std::unique_ptr<MetadataRewriter> createSDTRewriter(BinaryContext &);
 
 } // namespace bolt

bolt/lib/Rewrite/CMakeLists.txt

@@ -24,6 +24,7 @@ add_llvm_library(LLVMBOLTRewrite
   BuildIDRewriter.cpp
   PseudoProbeRewriter.cpp
   RewriteInstance.cpp
+  RSeqRewriter.cpp
   SDTRewriter.cpp
 
   NO_EXPORT

bolt/lib/Rewrite/RSeqRewriter.cpp

@@ -0,0 +1,71 @@
+//===- bolt/Rewrite/RSeqRewriter.cpp --------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// Basic support for restartable sequences used by tcmalloc. Prevent critical
+// section overrides by ignoring optimizations in containing functions.
+//
+// References:
+//   * https://google.github.io/tcmalloc/rseq.html
+//   * tcmalloc/internal/percpu_rseq_x86_64.S
+//
+//===----------------------------------------------------------------------===//
+
+#include "bolt/Core/BinaryFunction.h"
+#include "bolt/Rewrite/MetadataRewriter.h"
+#include "bolt/Rewrite/MetadataRewriters.h"
+#include "llvm/Support/Errc.h"
+
+using namespace llvm;
+using namespace bolt;
+
+namespace {
+
+class RSeqRewriter final : public MetadataRewriter {
+public:
+  RSeqRewriter(StringRef Name, BinaryContext &BC)
+      : MetadataRewriter(Name, BC) {}
+
+  Error postCFGInitializer() override {
+    for (const BinarySection &Section : BC.allocatableSections()) {
+      if (Section.getName() != "__rseq_cs")
+        continue;
+
+      auto handleRelocation = [&](const Relocation &Rel) {
+        BinaryFunction *BF = nullptr;
+        if (Rel.Symbol)
+          BF = BC.getFunctionForSymbol(Rel.Symbol);
+        else if (Relocation::isRelative(Rel.Type))
+          BF = BC.getBinaryFunctionContainingAddress(Rel.Addend);
+
+        if (BF) {
+          BC.outs() << "BOLT-INFO: restartable sequence detected in " << *BF
+                    << ". Function will not be optimized\n";
+          BF->setIgnored();
+        } else {
+          BC.errs() << "BOLT-WARNING: no function found matching dynamic "
+                       "relocation in __rseq_cs\n";
+        }
+      };
+
+      for (const Relocation &Rel : Section.dynamicRelocations())
+        handleRelocation(Rel);
+
+      for (const Relocation &Rel : Section.relocations())
+        handleRelocation(Rel);
+    }
+
+    return Error::success();
+  }
+};
+
+} // namespace
+
+std::unique_ptr<MetadataRewriter>
+llvm::bolt::createRSeqRewriter(BinaryContext &BC) {
+  return std::make_unique<RSeqRewriter>("rseq-cs-rewriter", BC);
+}

bolt/lib/Rewrite/RewriteInstance.cpp

@@ -3338,6 +3338,8 @@ void RewriteInstance::initializeMetadataManager() {
 
   MetadataManager.registerRewriter(createPseudoProbeRewriter(*BC));
 
+  MetadataManager.registerRewriter(createRSeqRewriter(*BC));
+
   MetadataManager.registerRewriter(createSDTRewriter(*BC));
 }
 

bolt/test/X86/rseq.s

@@ -0,0 +1,32 @@
+## Check that llvm-bolt avoids optimization of functions referenced from
+## __rseq_cs section, i.e. containing critical sections used by restartable
+## sequences in tcmalloc.
+
+# RUN: %clang %cflags %s -o %t -nostdlib -no-pie -Wl,-q
+# RUN: llvm-bolt %t -o %t.bolt --print-cfg 2>&1 \
+# RUN:   | FileCheck %s --check-prefix=CHECK-NO-PIE
+# RUN: %clang %cflags %s -o %t.pie -nostdlib -pie -Wl,-q
+# RUN: llvm-bolt %t.pie -o %t.pie.bolt 2>&1 \
+# RUN:   | FileCheck %s --check-prefix=CHECK-PIE
+
+# CHECK-NO-PIE: Binary Function "_start"
+# CHECK-NO-PIE: IsSimple
+# CHECK-NO-PIE-SAME: 0
+
+# CHECK-PIE: restartable sequence detected in _start
+
+.global _start
+  .type _start, %function
+_start:
+        pushq %rbp
+        mov %rsp, %rbp
+.L1:
+        pop %rbp
+        retq
+.size _start, .-_start
+
+.reloc 0, R_X86_64_NONE
+
+.section __rseq_cs, "aw"
+.balign 32
+  .quad  .L1