[XRay] [clang] Allow logging the first argument of a function call.

Summary:
Functions with the "xray_log_args" attribute will tell LLVM to emit a special
XRay sled for compiler-rt to copy any call arguments to your logging handler.

Reviewers: dberris

Reviewed By: dberris

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D29704

llvm-svn: 296999

2 files changed, 20 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CodeGenFunction.cpp b/clang/lib/CodeGen/CodeGenFunction.cpp
index 1ebfd798c55..bad963b6fa3 100644
--- a/clang/lib/CodeGen/CodeGenFunction.cpp
+++ b/clang/lib/CodeGen/CodeGenFunction.cpp
@@ -779,6 +779,10 @@ void CodeGenFunction::StartFunction(GlobalDecl GD,
         Fn->addFnAttr("function-instrument", "xray-always");
       if (XRayAttr->neverXRayInstrument())
         Fn->addFnAttr("function-instrument", "xray-never");
+      if (const auto *LogArgs = D->getAttr<XRayLogArgsAttr>()) {
+        Fn->addFnAttr("xray-log-args",
+                      llvm::utostr(LogArgs->getArgumentCount()));
+      }
     } else {
       Fn->addFnAttr(
           "xray-instruction-threshold",
diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
index 9b15a06de9f..3979383966c 100644
--- a/clang/lib/Sema/SemaDeclAttr.cpp
+++ b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -4424,6 +4424,19 @@ static void handleTypeTagForDatatypeAttr(Sema &S, Decl *D,
                                     Attr.getAttributeSpellingListIndex()));
 }
 
+static void handleXRayLogArgsAttr(Sema &S, Decl *D,
+                                  const AttributeList &Attr) {
+  uint64_t ArgCount;
+  if (!checkFunctionOrMethodParameterIndex(S, D, Attr, 1, Attr.getArgAsExpr(0),
+                                           ArgCount))
+    return;
+
+  // ArgCount isn't a parameter index [0;n), it's a count [1;n] - hence + 1.
+  D->addAttr(::new (S.Context)
+             XRayLogArgsAttr(Attr.getRange(), S.Context, ++ArgCount,
+             Attr.getAttributeSpellingListIndex()));
+}
+
 //===----------------------------------------------------------------------===//
 // Checker-specific attribute handlers.
 //===----------------------------------------------------------------------===//
@@ -6285,6 +6298,9 @@ static void ProcessDeclAttribute(Sema &S, Scope *scope, Decl *D,
   case AttributeList::AT_XRayInstrument:
     handleSimpleAttribute<XRayInstrumentAttr>(S, D, Attr);
     break;
+  case AttributeList::AT_XRayLogArgs:
+    handleXRayLogArgsAttr(S, D, Attr);
+    break;
   }
 }