[SanitizeCoverage] Add support for NoSanitizeCoverage function attribute

We really ought to support no_sanitize("coverage") in line with other
sanitizers. This came up again in discussions on the Linux-kernel
mailing lists, because we currently do workarounds using objtool to
remove coverage instrumentation. Since that support is only on x86, to
continue support coverage instrumentation on other architectures, we
must support selectively disabling coverage instrumentation via function
attributes.

Unfortunately, for SanitizeCoverage, it has not been implemented as a
sanitizer via fsanitize= and associated options in Sanitizers.def, but
rolls its own option fsanitize-coverage. This meant that we never got
"automatic" no_sanitize attribute support.

Implement no_sanitize attribute support by special-casing the string
"coverage" in the NoSanitizeAttr implementation. To keep the feature as
unintrusive to existing IR generation as possible, define a new negative
function attribute NoSanitizeCoverage to propagate the information
through to the instrumentation pass.

Fixes: https://bugs.llvm.org/show_bug.cgi?id=49035

Reviewed By: vitalybuka, morehouse

Differential Revision: https://reviews.llvm.org/D102772

1 files changed, 10 insertions, 1 deletions

diff --git a/clang/lib/CodeGen/CodeGenFunction.cpp b/clang/lib/CodeGen/CodeGenFunction.cpp
index d4f0464..518305e 100644
--- a/clang/lib/CodeGen/CodeGenFunction.cpp
+++ b/clang/lib/CodeGen/CodeGenFunction.cpp
@@ -734,8 +734,10 @@ void CodeGenFunction::StartFunction(GlobalDecl GD, QualType RetTy,
   } while (0);
 
   if (D) {
-    // Apply the no_sanitize* attributes to SanOpts.
+    bool NoSanitizeCoverage = false;
+
     for (auto Attr : D->specific_attrs<NoSanitizeAttr>()) {
+      // Apply the no_sanitize* attributes to SanOpts.
       SanitizerMask mask = Attr->getMask();
       SanOpts.Mask &= ~mask;
       if (mask & SanitizerKind::Address)
@@ -746,7 +748,14 @@ void CodeGenFunction::StartFunction(GlobalDecl GD, QualType RetTy,
         SanOpts.set(SanitizerKind::KernelHWAddress, false);
       if (mask & SanitizerKind::KernelHWAddress)
         SanOpts.set(SanitizerKind::HWAddress, false);
+
+      // SanitizeCoverage is not handled by SanOpts.
+      if (Attr->hasCoverage())
+        NoSanitizeCoverage = true;
     }
+
+    if (NoSanitizeCoverage && CGM.getCodeGenOpts().hasSanitizeCoverage())
+      Fn->addFnAttr(llvm::Attribute::NoSanitizeCoverage);
   }
 
   // Apply sanitizer attributes to the function.