[clang] Emitting a warning if optimizations are enabled with sanitizers #95934
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@llvm/pr-subscribers-clang-driver @llvm/pr-subscribers-clang Author: None (Ritanya-B-Bharadwaj) ChangesSanitizers achieve better accuracy with lower optimization levels, and it is generally recommended to use To ensure transparency, we should issue a warning when optimization levels other than Full diff: https://github.com/llvm/llvm-project/pull/95934.diff 3 Files Affected:
diff --git a/clang/include/clang/Basic/DiagnosticDriverKinds.td b/clang/include/clang/Basic/DiagnosticDriverKinds.td
index 1ca2cb85565a1..bd254bcaf5d97 100644
--- a/clang/include/clang/Basic/DiagnosticDriverKinds.td
+++ b/clang/include/clang/Basic/DiagnosticDriverKinds.td
@@ -477,6 +477,8 @@ def warn_drv_disabling_vptr_no_rtti_default : Warning<
def warn_drv_object_size_disabled_O0 : Warning<
"the object size sanitizer has no effect at -O0, but is explicitly enabled: %0">,
InGroup<InvalidCommandLineArgument>, DefaultWarnNoWerror;
+def warn_sanitizer_with_optimization : Warning<
+ "enabling optimizations with sanitizers may potentially reduce effectiveness">;
def warn_ignoring_verify_debuginfo_preserve_export : Warning<
"ignoring -fverify-debuginfo-preserve-export=%0 because "
"-fverify-debuginfo-preserve wasn't enabled">,
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 331cf6e713d89..2d72b3eb62308 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -6208,6 +6208,12 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
PScpu::addProfileRTArgs(TC, Args, CmdArgs);
PScpu::addSanitizerArgs(TC, Args, CmdArgs);
}
+
+ // Emit a warning if optimizations are enabled with sanitizers
+ if (Args.hasArg(options::OPT_fsanitize_EQ) &&
+ (Args.hasArg(options::OPT_Ofast) || Args.hasArg(options::OPT_O))) {
+ D.Diag(diag::warn_sanitizer_with_optimization);
+ }
// Pass options for controlling the default header search paths.
if (Args.hasArg(options::OPT_nostdinc)) {
diff --git a/clang/test/Driver/fsanitize.c b/clang/test/Driver/fsanitize.c
index 08e9c78f9d1d2..5657bb9a6da26 100644
--- a/clang/test/Driver/fsanitize.c
+++ b/clang/test/Driver/fsanitize.c
@@ -1038,3 +1038,10 @@
// RUN: not %clang --target=aarch64-none-elf -fsanitize=dataflow %s -### 2>&1 | FileCheck %s -check-prefix=UNSUPPORTED-BAREMETAL
// RUN: not %clang --target=arm-arm-none-eabi -fsanitize=shadow-call-stack %s -### 2>&1 | FileCheck %s -check-prefix=UNSUPPORTED-BAREMETAL
// UNSUPPORTED-BAREMETAL: unsupported option '-fsanitize={{.*}}' for target
+
+// RUN: %clang -O0 -O1 -fsanitize=address %s -### 2>&1 | FileCheck %s -check-prefix=CHECK-SAN-OPT-WARN
+// RUN: %clang -Ofast -fsanitize=address %s -### 2>&1 | FileCheck %s -check-prefix=CHECK-SAN-OPT-WARN
+// RUN: %clang -O3 -fsanitize=address %s -### 2>&1 | FileCheck %s -check-prefix=CHECK-SAN-OPT-WARN
+// RUN: %clang -O2 -fsanitize=thread %s -### 2>&1 | FileCheck %s -check-prefix=CHECK-SAN-OPT-WARN
+// RUN: %clang -O1 -fsanitize=thread %s -### 2>&1 | FileCheck %s -check-prefix=CHECK-SAN-OPT-WARN
+// CHECK-SAN-OPT-WARN: warning: enabling optimizations with sanitizers may potentially reduce effectiveness
|
| "the object size sanitizer has no effect at -O0, but is explicitly enabled: %0">, | ||
| InGroup<InvalidCommandLineArgument>, DefaultWarnNoWerror; | ||
| def warn_sanitizer_with_optimization : Warning< | ||
| "enabling optimizations with sanitizers may potentially reduce effectiveness">; |
There was a problem hiding this comment.
| "enabling optimizations with sanitizers may potentially reduce effectiveness">; | |
| "enabling optimizations may reduce the effectiveness of sanitizers">; |
| // RUN: %clang -O3 -fsanitize=address %s -### 2>&1 | FileCheck %s -check-prefix=CHECK-SAN-OPT-WARN | ||
| // RUN: %clang -O2 -fsanitize=thread %s -### 2>&1 | FileCheck %s -check-prefix=CHECK-SAN-OPT-WARN | ||
| // RUN: %clang -O1 -fsanitize=thread %s -### 2>&1 | FileCheck %s -check-prefix=CHECK-SAN-OPT-WARN | ||
| // CHECK-SAN-OPT-WARN: warning: enabling optimizations with sanitizers may potentially reduce effectiveness |
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| // CHECK-SAN-OPT-WARN: warning: enabling optimizations with sanitizers may potentially reduce effectiveness | |
| // CHECK-SAN-OPT-WARN: warning: enabling optimizations may reduce the effectiveness of sanitizers |
|
ping |
AaronBallman
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AaronBallman
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I'm not certain we should issue a diagnostic when optimizations are enabled with sanitizers. For example, there is explicit documentation that users should use -O1 with address sanitizer and similarly, users should use -O2 with the thread sanitizer.
So perhaps this is a matter that's better handled with documentation so we can explain the tradeoffs to users?
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I agree that we should not add a driver diagnostic. |
5 participants
Sanitizers achieve better accuracy with lower optimization levels, and it is generally recommended to use
-O0(the default optimization level) when using sanitizers for the most accurate results. However, many users might not be aware of this recommendation.To ensure transparency, we should issue a warning when optimization levels other than
-O0are enabled alongside sanitizers. This warning will inform users that higher optimization levels can reduce the effectiveness of sanitizers, thereby making them aware of the potential impact on the accuracy of sanitizer.