[clang] [llvm] [SanitizerCoverage] Add an option to gate the invocation of the tracing callbacks (PR #108328)
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Wed Sep 11 21:14:31 PDT 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-clang
Author: None (thetruestblue)
<details>
<summary>Changes</summary>
Implement -sanitizer-coverage-gated-trace-callbacks to gate the invocation of the tracing callbacks based on the value of a global variable, which is stored in a specific section.
When this option is enabled, the instrumentation will not call into the runtime-provided callbacks for tracing, thus only incurring in a trivial branch without going through a function call. It is up to the runtime to toggle the value of the global variable in order to enable tracing.
This option is only supported for trace-pc-guard.
Note: will add additional support for trace-cmp in a follow up PR.
Patch by Filippo Bigarella
rdar://101626834
---
Full diff: https://github.com/llvm/llvm-project/pull/108328.diff
3 Files Affected:
- (added) clang/test/CodeGen/sanitize-coverage-gated-callbacks.c (+42)
- (modified) llvm/include/llvm/Transforms/Instrumentation.h (+1)
- (modified) llvm/lib/Transforms/Instrumentation/SanitizerCoverage.cpp (+60-3)
``````````diff
diff --git a/clang/test/CodeGen/sanitize-coverage-gated-callbacks.c b/clang/test/CodeGen/sanitize-coverage-gated-callbacks.c
new file mode 100644
index 00000000000000..9a00d91d5ad086
--- /dev/null
+++ b/clang/test/CodeGen/sanitize-coverage-gated-callbacks.c
@@ -0,0 +1,42 @@
+// RUN: %clang %s -target arm64-apple-darwin -emit-llvm -S -fsanitize-coverage=trace-pc-guard -mllvm -sanitizer-coverage-gated-trace-callbacks=1 -o - | FileCheck %s --check-prefixes=CHECK,GATED
+// RUN: %clang %s -target arm64-apple-darwin -emit-llvm -S -fsanitize-coverage=trace-pc-guard -mllvm -sanitizer-coverage-gated-trace-callbacks=0 -o - | FileCheck %s --check-prefixes=CHECK,PLAIN
+// RUN: not %clang %s -target arm64-apple-darwin -emit-llvm -S -fsanitize-coverage=trace-pc -mllvm -sanitizer-coverage-gated-trace-callbacks=1 -o /dev/null 2>&1 | FileCheck %s --check-prefixes=INCOMPATIBLE
+// RUN: not %clang %s -target arm64-apple-darwin -emit-llvm -S -fsanitize-coverage=inline-8bit-counters -mllvm -sanitizer-coverage-gated-trace-callbacks=1 -o /dev/null 2>&1 | FileCheck %s --check-prefixes=INCOMPATIBLE
+// RUN: not %clang %s -target arm64-apple-darwin -emit-llvm -S -fsanitize-coverage=inline-bool-flag -mllvm -sanitizer-coverage-gated-trace-callbacks=1 -o /dev/null 2>&1 | FileCheck %s --check-prefixes=INCOMPATIBLE
+
+// Verify that we do not emit the __sancov_gate section for "plain" trace-pc-guard
+// GATED: section "__DATA,__sancov_gate"
+// PLAIN-NOT: section "__DATA,__sancov_gate"
+
+// Produce an error for all incompatible sanitizer coverage modes.
+// INCOMPATIBLE: error: 'sanitizer-coverage-gated-trace-callbacks' is only supported with trace-pc-guard
+
+int x[10];
+
+// CHECK: define{{.*}} void @foo
+void foo(int n, int m) {
+ // COM: Verify that we're emitting the call to __sanitizer_cov_trace_pc_guard upon
+ // COM: checking the value of __sancov_should_track.
+ // GATED: [[VAL:%.*]] = load i64, {{.*}}@__sancov_should_track
+ // GATED-NOT: [[VAL:%.*]] = load i64, i64* @__sancov_should_track
+ // GATED-NEXT: [[CMP:%.*]] = icmp ne i64 [[VAL]], 0
+ // GATED-NEXT: br i1 [[CMP]], label %[[L_TRUE:.*]], label %[[L_FALSE:.*]], !prof [[WEIGHTS:!.+]]
+ // GATED: [[L_TRUE]]:
+ // GATED-NEXT: call void @__sanitizer_cov_trace_pc_guard
+ // GATED: br i1 [[CMP]], label %[[L_TRUE_2:.*]], label %[[L_FALSE_2:.*]]
+ // GATED: [[L_TRUE_2]]:
+ // GATED-NEXT: call void @__sanitizer_cov_trace_pc_guard
+ // GATED: [[WEIGHTS]] = !{!"branch_weights", i32 1, i32 100000}
+
+ // COM: With the non-gated instrumentation, we should not emit the
+ // COM: __sancov_should_track global.
+ // PLAIN-NOT: __sancov_should_track
+ // But we should still be emitting the calls to the callback.
+ // PLAIN: call void @__sanitizer_cov_trace_pc_guard
+ if (n) {
+ x[n] = 42;
+ if (m) {
+ x[m] = 41;
+ }
+ }
+}
diff --git a/llvm/include/llvm/Transforms/Instrumentation.h b/llvm/include/llvm/Transforms/Instrumentation.h
index 1a4824a806dc6e..4f67d079d14696 100644
--- a/llvm/include/llvm/Transforms/Instrumentation.h
+++ b/llvm/include/llvm/Transforms/Instrumentation.h
@@ -161,6 +161,7 @@ struct SanitizerCoverageOptions {
bool TraceLoads = false;
bool TraceStores = false;
bool CollectControlFlow = false;
+ bool GatedCallbacks = false;
SanitizerCoverageOptions() = default;
};
diff --git a/llvm/lib/Transforms/Instrumentation/SanitizerCoverage.cpp b/llvm/lib/Transforms/Instrumentation/SanitizerCoverage.cpp
index 6a89cee9aaf6cc..2bea101b18c81b 100644
--- a/llvm/lib/Transforms/Instrumentation/SanitizerCoverage.cpp
+++ b/llvm/lib/Transforms/Instrumentation/SanitizerCoverage.cpp
@@ -16,6 +16,7 @@
#include "llvm/Analysis/GlobalsModRef.h"
#include "llvm/Analysis/PostDominators.h"
#include "llvm/IR/Constant.h"
+#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/EHPersonalities.h"
@@ -28,6 +29,8 @@
#include "llvm/IR/MDBuilder.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Type.h"
+#include "llvm/IR/ValueSymbolTable.h"
+#include "llvm/InitializePasses.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/SpecialCaseList.h"
#include "llvm/Support/VirtualFileSystem.h"
@@ -82,8 +85,10 @@ const char SanCovCountersSectionName[] = "sancov_cntrs";
const char SanCovBoolFlagSectionName[] = "sancov_bools";
const char SanCovPCsSectionName[] = "sancov_pcs";
const char SanCovCFsSectionName[] = "sancov_cfs";
+const char SanCovCallbackGateSectionName[] = "sancov_gate";
const char SanCovLowestStackName[] = "__sancov_lowest_stack";
+const char SanCovCallbackGateName[] = "__sancov_should_track";
static cl::opt<int> ClCoverageLevel(
"sanitizer-coverage-level",
@@ -152,6 +157,12 @@ static cl::opt<bool>
ClCollectCF("sanitizer-coverage-control-flow",
cl::desc("collect control flow for each function"), cl::Hidden);
+static cl::opt<bool> ClGatedCallbacks(
+ "sanitizer-coverage-gated-trace-callbacks",
+ cl::desc("Gate the invocation of the tracing callbacks on a global "
+ "variable. Currently only supported for trace-pc-guard."),
+ cl::Hidden, cl::init(false));
+
namespace {
SanitizerCoverageOptions getOptions(int LegacyCoverageLevel) {
@@ -194,6 +205,7 @@ SanitizerCoverageOptions OverrideFromCL(SanitizerCoverageOptions Options) {
Options.StackDepth |= ClStackDepth;
Options.TraceLoads |= ClLoadTracing;
Options.TraceStores |= ClStoreTracing;
+ Options.GatedCallbacks |= ClGatedCallbacks;
if (!Options.TracePCGuard && !Options.TracePC &&
!Options.Inline8bitCounters && !Options.StackDepth &&
!Options.InlineBoolFlag && !Options.TraceLoads && !Options.TraceStores)
@@ -239,8 +251,9 @@ class ModuleSanitizerCoverage {
const char *Section);
GlobalVariable *CreatePCArray(Function &F, ArrayRef<BasicBlock *> AllBlocks);
void CreateFunctionLocalArrays(Function &F, ArrayRef<BasicBlock *> AllBlocks);
+ Value *CreateFunctionLocalGateCmp(IRBuilder<> &IRB);
void InjectCoverageAtBlock(Function &F, BasicBlock &BB, size_t Idx,
- bool IsLeafFunc = true);
+ Value *&FunctionGateCmp, bool IsLeafFunc = true);
Function *CreateInitCallsForSections(Module &M, const char *CtorName,
const char *InitFunctionName, Type *Ty,
const char *Section);
@@ -265,6 +278,7 @@ class ModuleSanitizerCoverage {
FunctionCallee SanCovTraceGepFunction;
FunctionCallee SanCovTraceSwitchFunction;
GlobalVariable *SanCovLowestStack;
+ GlobalVariable *SanCovCallbackGate;
Type *PtrTy, *IntptrTy, *Int64Ty, *Int32Ty, *Int16Ty, *Int8Ty, *Int1Ty;
Module *CurModule;
std::string CurModuleUniqueId;
@@ -478,6 +492,23 @@ bool ModuleSanitizerCoverage::instrumentModule() {
if (Options.StackDepth && !SanCovLowestStack->isDeclaration())
SanCovLowestStack->setInitializer(Constant::getAllOnesValue(IntptrTy));
+ if (Options.GatedCallbacks) {
+ if (!Options.TracePCGuard) {
+ C->emitError(StringRef("'") + ClGatedCallbacks.ArgStr +
+ "' is only supported with trace-pc-guard");
+ return true;
+ }
+
+ SanCovCallbackGate = cast<GlobalVariable>(
+ M.getOrInsertGlobal(SanCovCallbackGateName, Int64Ty));
+ SanCovCallbackGate->setSection(
+ getSectionName(SanCovCallbackGateSectionName));
+ SanCovCallbackGate->setInitializer(Constant::getNullValue(Int64Ty));
+ SanCovCallbackGate->setLinkage(GlobalVariable::LinkOnceAnyLinkage);
+ SanCovCallbackGate->setVisibility(GlobalVariable::HiddenVisibility);
+ appendToCompilerUsed(M, SanCovCallbackGate);
+ }
+
SanCovTracePC = M.getOrInsertFunction(SanCovTracePCName, VoidTy);
SanCovTracePCGuard =
M.getOrInsertFunction(SanCovTracePCGuardName, VoidTy, PtrTy);
@@ -774,13 +805,22 @@ void ModuleSanitizerCoverage::CreateFunctionLocalArrays(
FunctionPCsArray = CreatePCArray(F, AllBlocks);
}
+Value *ModuleSanitizerCoverage::CreateFunctionLocalGateCmp(IRBuilder<> &IRB) {
+ auto Load = IRB.CreateLoad(Int64Ty, SanCovCallbackGate);
+ Load->setNoSanitizeMetadata();
+ auto Cmp = IRB.CreateIsNotNull(Load);
+ Cmp->setName("sancov gate cmp");
+ return Cmp;
+}
+
bool ModuleSanitizerCoverage::InjectCoverage(Function &F,
ArrayRef<BasicBlock *> AllBlocks,
bool IsLeafFunc) {
if (AllBlocks.empty()) return false;
CreateFunctionLocalArrays(F, AllBlocks);
+ Value *FunctionGateCmp = nullptr;
for (size_t i = 0, N = AllBlocks.size(); i < N; i++)
- InjectCoverageAtBlock(F, *AllBlocks[i], i, IsLeafFunc);
+ InjectCoverageAtBlock(F, *AllBlocks[i], i, FunctionGateCmp, IsLeafFunc);
return true;
}
@@ -943,6 +983,7 @@ void ModuleSanitizerCoverage::InjectTraceForCmp(
void ModuleSanitizerCoverage::InjectCoverageAtBlock(Function &F, BasicBlock &BB,
size_t Idx,
+ Value *&FunctionGateCmp,
bool IsLeafFunc) {
BasicBlock::iterator IP = BB.getFirstInsertionPt();
bool IsEntryBB = &BB == &F.getEntryBlock();
@@ -968,7 +1009,23 @@ void ModuleSanitizerCoverage::InjectCoverageAtBlock(Function &F, BasicBlock &BB,
IRB.CreateAdd(IRB.CreatePointerCast(FunctionGuardArray, IntptrTy),
ConstantInt::get(IntptrTy, Idx * 4)),
PtrTy);
- IRB.CreateCall(SanCovTracePCGuard, GuardPtr)->setCannotMerge();
+ if (Options.GatedCallbacks) {
+ if (!FunctionGateCmp) {
+ // Create this in the entry block
+ assert(IsEntryBB);
+ FunctionGateCmp = CreateFunctionLocalGateCmp(IRB);
+ }
+ // Set the branch weights in order to minimize the price paid when the
+ // gate is turned off, allowing the default enablement of this
+ // instrumentation with as little of a performance cost as possible
+ auto Weights = MDBuilder(*C).createBranchWeights(1, 100000);
+ auto ThenTerm =
+ SplitBlockAndInsertIfThen(FunctionGateCmp, &*IP, false, Weights);
+ IRBuilder<> ThenIRB(ThenTerm);
+ ThenIRB.CreateCall(SanCovTracePCGuard, GuardPtr)->setCannotMerge();
+ } else {
+ IRB.CreateCall(SanCovTracePCGuard, GuardPtr)->setCannotMerge();
+ }
}
if (Options.Inline8bitCounters) {
auto CounterPtr = IRB.CreateGEP(
``````````
</details>
https://github.com/llvm/llvm-project/pull/108328
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