[memprof] Use -memprof-runtime-default-options to set options during compile time (#118874)

Add the `__memprof_default_options_str` variable, initialized via the
`-memprof-runtime-default-options` LLVM flag, to hold the default options string
for memprof. This allows us to set these options during compile time in
the clang invocation.

Also update the docs to describe the various ways to set these options.

compiler-rt/include/sanitizer/memprof_interface.h

@@ -47,9 +47,9 @@ void SANITIZER_CDECL __memprof_print_accumulated_stats(void);
 
 /// User-provided default option settings.
 ///
-/// You can provide your own implementation of this function to return a string
-/// containing MemProf runtime options (for example,
-/// <c>verbosity=1:print_stats=1</c>).
+/// You can set these options via the -memprof-runtime-default-options LLVM flag
+/// or you can provide your own implementation of this function. See
+/// memprof_flags.h for more info.
 ///
 /// \returns Default options string.
 const char *SANITIZER_CDECL __memprof_default_options(void);

compiler-rt/lib/memprof/memprof_flags.cpp

@@ -89,5 +89,5 @@ void InitializeFlags() {
 } // namespace __memprof
 
 SANITIZER_INTERFACE_WEAK_DEF(const char *, __memprof_default_options, void) {
-  return "";
+  return __memprof_default_options_str;
 }

compiler-rt/lib/memprof/memprof_flags.h

@@ -17,13 +17,15 @@
 #include "sanitizer_common/sanitizer_flag_parser.h"
 #include "sanitizer_common/sanitizer_internal_defs.h"
 
-// MemProf flag values can be defined in four ways:
-// 1) initialized with default values at startup.
-// 2) overriden during compilation of MemProf runtime by providing
-//    compile definition MEMPROF_DEFAULT_OPTIONS.
-// 3) overriden from string returned by user-specified function
-//    __memprof_default_options().
-// 4) overriden from env variable MEMPROF_OPTIONS.
+// Default MemProf flags are defined in memprof_flags.inc and sancov_flags.inc.
+// These values can be overridded in a number of ways, each option overrides the
+// prior one:
+//  1) by setting MEMPROF_DEFAULT_OPTIONS during the compilation of the MemProf
+//     runtime
+//  2) by setting the LLVM flag -memprof-runtime-default-options during the
+//     compilation of your binary
+//  3) by overriding the user-specified function __memprof_default_options()
+//  4) by setting the environment variable MEMPROF_OPTIONS during runtime
 
 namespace __memprof {
 

compiler-rt/lib/memprof/memprof_interface_internal.h

@@ -40,6 +40,9 @@ void __memprof_record_access_range(void const volatile *addr, uptr size);
 
 SANITIZER_INTERFACE_ATTRIBUTE void __memprof_print_accumulated_stats();
 
+SANITIZER_INTERFACE_ATTRIBUTE SANITIZER_WEAK_ATTRIBUTE extern char
+    __memprof_default_options_str[1];
+
 SANITIZER_INTERFACE_ATTRIBUTE
 const char *__memprof_default_options();
 

compiler-rt/lib/memprof/memprof_rtl.cpp

@@ -27,6 +27,8 @@
 
 #include <time.h>
 
+SANITIZER_WEAK_ATTRIBUTE char __memprof_default_options_str[1];
+
 uptr __memprof_shadow_memory_dynamic_address; // Global interface symbol.
 
 // Allow the user to specify a profile output file via the binary.

compiler-rt/lib/memprof/weak_symbols.txt

@@ -1 +1 @@
-___memprof_default_options __memprof_profile_filename
+___memprof_default_options_str ___memprof_default_options __memprof_profile_filename

compiler-rt/test/memprof/TestCases/default_options.cpp

@@ -1,5 +1,8 @@
 // RUN: %clangxx_memprof -O2 %s -o %t && %run %t 2>&1 | FileCheck %s
 
+// Check that overriding __memprof_default_options() takes precedence over the LLVM flag
+// RUN: %clangxx_memprof -O2 %s -o %t-flag -mllvm -memprof-runtime-default-options="verbosity=0 help=0" && %run %t-flag 2>&1 | FileCheck %s
+
 const char *kMemProfDefaultOptions = "verbosity=1 help=1";
 
 extern "C" const char *__memprof_default_options() {

compiler-rt/test/memprof/TestCases/set_options.cpp

@@ -0,0 +1,16 @@
+// RUN: %clangxx_memprof %s -o %t-default
+// RUN: %run %t-default | FileCheck %s --check-prefix=DEFAULT
+
+// RUN: %clangxx_memprof %s -mllvm -memprof-runtime-default-options="print_text=true,log_path=stdout,atexit=false" -o %t
+// RUN: %run %t | FileCheck %s
+
+#include <sanitizer/memprof_interface.h>
+#include <stdio.h>
+
+int main() {
+  printf("Options: \"%s\"\n", __memprof_default_options());
+  return 0;
+}
+
+// DEFAULT: Options: ""
+// CHECK: Options: "print_text=true,log_path=stdout,atexit=false"

llvm/lib/Transforms/Instrumentation/MemProfiler.cpp

@@ -166,6 +166,11 @@ static cl::opt<bool>
                                      "context in this module's profiles"),
                             cl::Hidden, cl::init(false));
 
+static cl::opt<std::string>
+    MemprofRuntimeDefaultOptions("memprof-runtime-default-options",
+                                 cl::desc("The default memprof options"),
+                                 cl::Hidden, cl::init(""));
+
 extern cl::opt<bool> MemProfReportHintedSizes;
 
 // Instrumentation statistics
@@ -547,6 +552,20 @@ void createMemprofHistogramFlagVar(Module &M) {
   appendToCompilerUsed(M, MemprofHistogramFlag);
 }
 
+void createMemprofDefaultOptionsVar(Module &M) {
+  Constant *OptionsConst = ConstantDataArray::getString(
+      M.getContext(), MemprofRuntimeDefaultOptions, /*AddNull=*/true);
+  GlobalVariable *OptionsVar =
+      new GlobalVariable(M, OptionsConst->getType(), /*isConstant=*/true,
+                         GlobalValue::WeakAnyLinkage, OptionsConst,
+                         "__memprof_default_options_str");
+  Triple TT(M.getTargetTriple());
+  if (TT.supportsCOMDAT()) {
+    OptionsVar->setLinkage(GlobalValue::ExternalLinkage);
+    OptionsVar->setComdat(M.getOrInsertComdat(OptionsVar->getName()));
+  }
+}
+
 bool ModuleMemProfiler::instrumentModule(Module &M) {
 
   // Create a module constructor.
@@ -566,6 +585,8 @@ bool ModuleMemProfiler::instrumentModule(Module &M) {
 
   createMemprofHistogramFlagVar(M);
 
+  createMemprofDefaultOptionsVar(M);
+
   return true;
 }
 

llvm/test/Instrumentation/HeapProfiler/memprof-options.ll

@@ -0,0 +1,11 @@
+; RUN: opt < %s -mtriple=x86_64-unknown-linux -passes='function(memprof),memprof-module' -S | FileCheck %s --check-prefixes=CHECK,EMPTY
+; RUN: opt < %s -mtriple=x86_64-unknown-linux -passes='function(memprof),memprof-module' -S -memprof-runtime-default-options="verbose=1" | FileCheck %s --check-prefixes=CHECK,VERBOSE
+
+define i32 @main() {
+entry:
+  ret i32 0
+}
+
+; CHECK: $__memprof_default_options_str = comdat any
+; EMPTY: @__memprof_default_options_str = constant [1 x i8] zeroinitializer, comdat
+; VERBOSE: @__memprof_default_options_str = constant [10 x i8] c"verbose=1\00", comdat