[XRay] Add -fxray-default-options to pass build-time defined XRay options

mshockwave · mshockwave · commit 95ee4bd09aa4 · 2024-11-19T13:09:21.000-08:00
This is useful in cases where setting the `XRAY_OPTIONS` environment
variable might be difficult. Plus, it's a convenient way to populate
XRay options when you always want the instrumentation to be enabled.

The implementation follows what memory profiler and PGO did for their
profile file name and profile version, respectively: insert a weak
linkage global variable carrying the option string, which is then
intercepted by compiler-rt during xray's option parsing phase.
diff --git a/clang/include/clang/Basic/CodeGenOptions.h b/clang/include/clang/Basic/CodeGenOptions.h
@@ -399,6 +399,10 @@ class CodeGenOptions : public CodeGenOptionsBase {
   /// Set of XRay instrumentation kinds to emit.
   XRayInstrSet XRayInstrumentationBundle;
 
+  /// Default XRay options. Will be overrided by the XRAY_OPTIONS
+  /// environment variable during run-time.
+  std::string XRayDefaultOptions;
+
   std::vector<std::string> DefaultFunctionAttrs;
 
   /// List of dynamic shared object files to be loaded as pass plugins.
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
@@ -2882,6 +2882,12 @@ defm xray_instrument : BoolFOption<"xray-instrument",
           "Generate XRay instrumentation sleds on function entry and exit">,
   NegFlag<SetFalse>>;
 
+def fxray_default_options_EQ :
+  Joined<["-"], "fxray-default-options=">,
+  Group<f_Group>, Visibility<[ClangOption, CC1Option]>,
+  HelpText<"Default XRay options. Can be overwritten by XRAY_OPTIONS environment variable during run-time.">,
+  MarshallingInfoString<CodeGenOpts<"XRayDefaultOptions">>;
+
 def fxray_instruction_threshold_EQ :
   Joined<["-"], "fxray-instruction-threshold=">,
   Group<f_Group>, Visibility<[ClangOption, CC1Option]>,
diff --git a/clang/lib/CodeGen/BackendUtil.cpp b/clang/lib/CodeGen/BackendUtil.cpp
@@ -77,6 +77,7 @@
 #include "llvm/Transforms/Instrumentation/SanitizerBinaryMetadata.h"
 #include "llvm/Transforms/Instrumentation/SanitizerCoverage.h"
 #include "llvm/Transforms/Instrumentation/ThreadSanitizer.h"
+#include "llvm/Transforms/Instrumentation/XRayPreparation.h"
 #include "llvm/Transforms/ObjCARC.h"
 #include "llvm/Transforms/Scalar/EarlyCSE.h"
 #include "llvm/Transforms/Scalar/GVN.h"
@@ -1062,6 +1063,13 @@ void EmitAssemblyHelper::RunOptimizationPipeline(
       });
     }
 
+    if (CodeGenOpts.XRayInstrumentFunctions &&
+        !CodeGenOpts.XRayDefaultOptions.empty()) {
+      PB.registerOptimizerLastEPCallback(
+          [](ModulePassManager &MPM, OptimizationLevel Level,
+             ThinOrFullLTOPhase) { MPM.addPass(XRayPreparationPass()); });
+    }
+
     if (CodeGenOpts.FatLTO) {
       MPM.addPass(PB.buildFatLTODefaultPipeline(
           Level, PrepareForThinLTO,
diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -448,6 +448,14 @@ CodeGenModule::CodeGenModule(ASTContext &C,
   if (Context.getTargetInfo().getTriple().getArch() == llvm::Triple::x86)
     getModule().addModuleFlag(llvm::Module::Error, "NumRegisterParameters",
                               CodeGenOpts.NumRegisterParameters);
+
+  // Insert XRay default options if it hasn't been done.
+  if (CodeGenOpts.XRayInstrumentFunctions &&
+      !CodeGenOpts.XRayDefaultOptions.empty() &&
+      !getModule().getModuleFlag("xray-default-opts"))
+    getModule().addModuleFlag(
+        llvm::Module::Error, "xray-default-opts",
+        llvm::MDString::get(LLVMContext, CodeGenOpts.XRayDefaultOptions));
 }
 
 CodeGenModule::~CodeGenModule() {}
diff --git a/clang/lib/Driver/XRayArgs.cpp b/clang/lib/Driver/XRayArgs.cpp
@@ -200,6 +200,9 @@ void XRayArgs::addArgs(const ToolChain &TC, const ArgList &Args,
     Args.addOptInFlag(CmdArgs, options::OPT_fxray_shared,
                       options::OPT_fno_xray_shared);
 
+  if (const Arg *A = Args.getLastArg(options::OPT_fxray_default_options_EQ))
+    A->render(Args, CmdArgs);
+
   if (const Arg *A =
           Args.getLastArg(options::OPT_fxray_instruction_threshold_EQ)) {
     int Value;
diff --git a/clang/test/CodeGen/xray-default-options.c b/clang/test/CodeGen/xray-default-options.c
@@ -0,0 +1,7 @@
+// RUN: %clang_cc1 -fxray-instrument -fxray-default-options='patch_premain=true,xray_mode=xray-basic' \
+// RUN:     -std=c11 -triple x86_64-unknown-unknown -emit-llvm -o - %s | FileCheck %s
+
+void justAFunction() {
+}
+
+// CHECK: !{{[0-9]+}} = !{i32 1, !"xray-default-opts", !"patch_premain=true,xray_mode=xray-basic"}
diff --git a/compiler-rt/lib/xray/CMakeLists.txt b/compiler-rt/lib/xray/CMakeLists.txt
@@ -7,6 +7,7 @@ set(XRAY_SOURCES
   xray_flags.cpp
   xray_interface.cpp
   xray_log_interface.cpp
+  xray_options_var.cpp
   xray_utils.cpp
   )
 
diff --git a/compiler-rt/lib/xray/xray_flags.cpp b/compiler-rt/lib/xray/xray_flags.cpp
@@ -67,6 +67,10 @@ void initializeFlags() XRAY_NEVER_INSTRUMENT {
   const char *XRayCompileFlags = useCompilerDefinedFlags();
   XRayParser.ParseString(XRayCompileFlags);
 
+  // Override from compile-time options.
+  if (XRAY_OPTIONS_VAR[0] != 0)
+    XRayParser.ParseString(XRAY_OPTIONS_VAR);
+
   // Override from environment variables.
   XRayParser.ParseStringFromEnv("XRAY_OPTIONS");
 
diff --git a/compiler-rt/lib/xray/xray_flags.h b/compiler-rt/lib/xray/xray_flags.h
@@ -17,6 +17,12 @@
 #include "sanitizer_common/sanitizer_flag_parser.h"
 #include "sanitizer_common/sanitizer_internal_defs.h"
 
+#define XRAY_OPTIONS_VAR __llvm_xray_options
+
+extern "C" {
+extern char XRAY_OPTIONS_VAR[1];
+}
+
 namespace __xray {
 
 struct Flags {
diff --git a/compiler-rt/lib/xray/xray_options_var.cpp b/compiler-rt/lib/xray/xray_options_var.cpp
@@ -0,0 +1,24 @@
+/*===----- xray_options_var.cpp - XRay option variable setup  -------------===*\
+|*
+|* 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
+|*
+\*===----------------------------------------------------------------------===*/
+
+#include "xray_flags.h"
+
+// FIXME: Generalize these. See lib/profile/InstrProfilingPort.h and
+// include/profile/InstrProfData.inc
+#define COMPILER_RT_VISIBILITY __attribute__((visibility("hidden")))
+#define COMPILER_RT_WEAK __attribute__((weak))
+
+extern "C" {
+/* char __llvm_xray_options[1]
+ *
+ * The runtime should only provide its own definition of this symbol when the
+ * user has not specified one. Set this up by moving the runtime's copy of this
+ * symbol to an object file within the archive.
+ */
+COMPILER_RT_WEAK COMPILER_RT_VISIBILITY char XRAY_OPTIONS_VAR[1] = {0};
+}
diff --git a/compiler-rt/test/xray/TestCases/Posix/default-options.cpp b/compiler-rt/test/xray/TestCases/Posix/default-options.cpp
@@ -0,0 +1,12 @@
+// RUN: %clang_xray -g -fxray-default-options='patch_premain=true:verbosity=1:xray_mode=xray-basic' -o %t %s
+// RUN: rm -f xray-log.default-options.*
+// RUN: %run %t 2>&1 | FileCheck %s
+// RUN: rm -f xray-log.default-options.*
+//
+// REQUIRES: target={{(aarch64|loongarch64|x86_64)-.*}}
+// REQUIRES: built-in-llvm-tree
+__attribute__((xray_always_instrument)) void always() {}
+
+int main() { always(); }
+
+// CHECK: =={{[0-9].*}}==XRay: Log file in '{{.*}}'
diff --git a/llvm/docs/XRay.rst b/llvm/docs/XRay.rst
@@ -157,7 +157,8 @@ Also by default the filename of the XRay trace is ``xray-log.XXXXXX`` where the
 ``XXXXXX`` part is randomly generated.
 
 These options can be controlled through the ``XRAY_OPTIONS`` environment
-variable, where we list down the options and their defaults below.
+variable during program run-time, where we list down the options and their
+defaults below.
 
 +-------------------+-----------------+---------------+------------------------+
 | Option            | Type            | Default       | Description            |
@@ -177,6 +178,18 @@ variable, where we list down the options and their defaults below.
 |                   |                 |               | level.                 |
 +-------------------+-----------------+---------------+------------------------+
 
+In addition to environment variable, you can also use ``-fxray-default-options``
+to specify default XRay options during program build time.
+
+For example, programs built with the following flags automatically use
+'patch_premain=true,xray_mode=basic' by default even without setting ``XRAY_OPTIONS``.
+
+::
+
+  clang -fxray-instrument -fxray-default-options='patch_premain=true,xray_mode=basic' ...
+
+Note that you still can override options designated by ``-fxray-default-options``
+using ``XRAY_OPTIONS`` during run-time.
 
 If you choose to not use the default logging implementation that comes with the
 XRay runtime and/or control when/how the XRay instrumentation runs, you may use
diff --git a/llvm/include/llvm/Transforms/Instrumentation/XRayPreparation.h b/llvm/include/llvm/Transforms/Instrumentation/XRayPreparation.h
@@ -0,0 +1,24 @@
+//===- XRayPreparation.h - Preparation for XRay instrumentation -*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// This Pass does some IR-level preparations (e.g. inserting global variable
+// that carries default options, if there is any) for XRay instrumentation.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_TRANSFORMS_INSTRUMENTATION_XRAYPREPARATION_H
+#define LLVM_TRANSFORMS_INSTRUMENTATION_XRAYPREPARATION_H
+
+#include "llvm/IR/PassManager.h"
+
+namespace llvm {
+struct XRayPreparationPass : public PassInfoMixin<XRayPreparationPass> {
+  PreservedAnalyses run(Module &, ModuleAnalysisManager &);
+};
+} // namespace llvm
+#endif
diff --git a/llvm/lib/Passes/PassBuilder.cpp b/llvm/lib/Passes/PassBuilder.cpp
@@ -221,6 +221,7 @@
 #include "llvm/Transforms/Instrumentation/SanitizerBinaryMetadata.h"
 #include "llvm/Transforms/Instrumentation/SanitizerCoverage.h"
 #include "llvm/Transforms/Instrumentation/ThreadSanitizer.h"
+#include "llvm/Transforms/Instrumentation/XRayPreparation.h"
 #include "llvm/Transforms/ObjCARC.h"
 #include "llvm/Transforms/Scalar/ADCE.h"
 #include "llvm/Transforms/Scalar/AlignmentFromAssumptions.h"
diff --git a/llvm/lib/Passes/PassRegistry.def b/llvm/lib/Passes/PassRegistry.def
@@ -157,6 +157,7 @@ MODULE_PASS("tsan-module", ModuleThreadSanitizerPass())
 MODULE_PASS("verify", VerifierPass())
 MODULE_PASS("view-callgraph", CallGraphViewerPass())
 MODULE_PASS("wholeprogramdevirt", WholeProgramDevirtPass())
+MODULE_PASS("xray-preparation", XRayPreparationPass())
 #undef MODULE_PASS
 
 #ifndef MODULE_PASS_WITH_PARAMS
diff --git a/llvm/lib/Transforms/Instrumentation/CMakeLists.txt b/llvm/lib/Transforms/Instrumentation/CMakeLists.txt
@@ -26,6 +26,7 @@ add_llvm_component_library(LLVMInstrumentation
   ThreadSanitizer.cpp
   HWAddressSanitizer.cpp
   RealtimeSanitizer.cpp
+  XRayPreparation.cpp
 
   ADDITIONAL_HEADER_DIRS
   ${LLVM_MAIN_INCLUDE_DIR}/llvm/Transforms
diff --git a/llvm/lib/Transforms/Instrumentation/XRayPreparation.cpp b/llvm/lib/Transforms/Instrumentation/XRayPreparation.cpp
@@ -0,0 +1,49 @@
+//===- XRayPreparation.cpp - Preparation for XRay instrumentation -------- ===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// This Pass does some IR-level preparations (e.g. inserting global variable
+// that carries default options, if there is any) for XRay instrumentation.
+//
+//===---------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Instrumentation/XRayPreparation.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/Module.h"
+#include "llvm/TargetParser/Triple.h"
+
+using namespace llvm;
+
+static void createXRayDefaultOptionsVar(Module &M, StringRef DefaultOptions) {
+  Constant *DefaultOptionsConst =
+      ConstantDataArray::getString(M.getContext(), DefaultOptions, true);
+  // This global variable will be passed into XRay's compiler-rt and used as
+  // the initial set of XRay options.
+  GlobalVariable *DefaultOptsVar = new GlobalVariable(
+      M, DefaultOptionsConst->getType(), true, GlobalValue::WeakAnyLinkage,
+      DefaultOptionsConst, "__llvm_xray_options");
+  DefaultOptsVar->setVisibility(GlobalValue::HiddenVisibility);
+  Triple TT(M.getTargetTriple());
+  if (TT.supportsCOMDAT()) {
+    DefaultOptsVar->setLinkage(GlobalValue::ExternalLinkage);
+    DefaultOptsVar->setComdat(M.getOrInsertComdat("__llvm_xray_options"));
+  }
+}
+
+PreservedAnalyses XRayPreparationPass::run(Module &M,
+                                           ModuleAnalysisManager &MAM) {
+  // XRay default options.
+  if (const auto *DefaultOpts =
+          dyn_cast_or_null<MDString>(M.getModuleFlag("xray-default-opts"))) {
+    createXRayDefaultOptionsVar(M, DefaultOpts->getString());
+    PreservedAnalyses PA;
+    PA.preserveSet<CFGAnalyses>();
+    return PA;
+  }
+
+  return PreservedAnalyses::all();
+}
diff --git a/llvm/test/CodeGen/X86/xray-default-options.ll b/llvm/test/CodeGen/X86/xray-default-options.ll
@@ -0,0 +1,10 @@
+; RUN: opt -S -p xray-preparation < %s | FileCheck %s
+
+target triple = "x86_64-unknown-linux-gnu"
+
+; CHECK: $__llvm_xray_options = comdat any
+; CHECK: @__llvm_xray_options = hidden constant [40 x i8] c"patch_premain=true,xray_mode=xray-basic\00", comdat
+
+!llvm.module.flags = !{!0}
+
+!0 = !{i32 1, !"xray-default-opts", !"patch_premain=true,xray_mode=xray-basic"}

Original file line number	Diff line number	Diff line change
`@@ -7,6 +7,7 @@ set(XRAY_SOURCES`
`7`	`7`	`xray_flags.cpp`
`8`	`8`	`xray_interface.cpp`
`9`	`9`	`xray_log_interface.cpp`
	`10`	`+ xray_options_var.cpp`
`10`	`11`	`xray_utils.cpp`
`11`	`12`	`)`
`12`	`13`