[BOLT][WIP] Support restartable sequences in tcmalloc #157774
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maksfb
requested review from
aaupov,
rafaelauler,
ayermolo,
yota9,
paschalis-mpeis and
yozhu
as code owners
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@llvm/pr-subscribers-bolt Author: Maksim Panchenko (maksfb) ChangesFull diff: https://github.com/llvm/llvm-project/pull/157774.diff 5 Files Affected:
diff --git a/bolt/include/bolt/Rewrite/MetadataRewriters.h b/bolt/include/bolt/Rewrite/MetadataRewriters.h
index b71bd6cad2505..429c2d7712979 100644
--- a/bolt/include/bolt/Rewrite/MetadataRewriters.h
+++ b/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
diff --git a/bolt/lib/Rewrite/CMakeLists.txt b/bolt/lib/Rewrite/CMakeLists.txt
index 775036063dd5a..12914bfe64301 100644
--- a/bolt/lib/Rewrite/CMakeLists.txt
+++ b/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
diff --git a/bolt/lib/Rewrite/RSeqRewriter.cpp b/bolt/lib/Rewrite/RSeqRewriter.cpp
new file mode 100644
index 0000000000000..7cbe9ac17da52
--- /dev/null
+++ b/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->setSimple(false);
+ } 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);
+}
diff --git a/bolt/lib/Rewrite/RewriteInstance.cpp b/bolt/lib/Rewrite/RewriteInstance.cpp
index a6e4dbc9c192f..6e07d2ea8d975 100644
--- a/bolt/lib/Rewrite/RewriteInstance.cpp
+++ b/bolt/lib/Rewrite/RewriteInstance.cpp
@@ -3338,6 +3338,8 @@ void RewriteInstance::initializeMetadataManager() {
MetadataManager.registerRewriter(createPseudoProbeRewriter(*BC));
+ MetadataManager.registerRewriter(createRSeqRewriter(*BC));
+
MetadataManager.registerRewriter(createSDTRewriter(*BC));
}
diff --git a/bolt/test/X86/rseq.s b/bolt/test/X86/rseq.s
new file mode 100644
index 0000000000000..7ebc57e1128f4
--- /dev/null
+++ b/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
|
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Tried out the patch, it seems to successfully print out all the functions in info but the final binary still crashes. Test: back to just being TcmallocSlab_Internal_PopBatch/PushBatch and used this new version of bolt. Prints out: Moved the skip func from TcmallocSlab_Internal_PopBatch/PushBatch back to and it started working again. |
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Thanks for trying the patch out. I'm going to look more into it and specifically at the warnings. Meanwhile, I've updated the patch to ignore the |
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Thanks that seems to work! It also turns out almost all the functions on our skip list seem to have been there due to rseq related reasons. |
There was a problem hiding this comment.
Overall, the patch looks good, and it was verified that ignoring the function does the trick.
One thing it's not clear to me: is fixed code (non-pie) safe, given the heuristic won't detect which functions to ignore?
For the logs, would it be better to condense the BOLT-INFO messages into a warning summary like:
~ N functionsN functions were found in restartable sequences section and were ignored ..
possibly, including a hint to view full details at higher verbosity? Not a strong opinion.
I believe you will also suppress these messages?
BOLT-WARNING: no function found matching dynamic relocation in __rseq_cs
Hi Paschalis, what do you mean by static binaries? Note that we check both types of relocations. |
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Hey Maksim, sorry I meant fixed code, ie the non-pie case listed in the test. |
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For non-pie, we rely on linker's Let me take another look at the warnings. |
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