[PATCH] D36080: [XRay][compiler-rt] Allow for building the XRay runtime without PREINIT initialization.

[Dean Michael Berris via Phabricator via llvm-commits]

dberris created this revision.
Herald added a subscriber: mgorny.

Define a build-time configuration option for the XRay runtime to
determine whether the archive will add an entry to the `.preinit_array`
section of the binary. We also allow for initializing the XRay data
structures with an explicit call to __xray_init(). This allows us to
give users the capability to initialize the XRay data structures on
demand.

This can allow us to start porting XRay to platforms where
`.preinit_array` isn't a supported section. It also allows us to limit
the effects of XRay in the initialization sequence for applications that
are sensitive to this kind of interference (i.e. large binaries) or
those that want to package XRay control in libraries.

Future changes should allow us to build two different library archives
for the XRay runtime, and allow clang users to determine which version
to link.


https://reviews.llvm.org/D36080

Files:
  CMakeLists.txt
  include/xray/xray_interface.h
  lib/xray/CMakeLists.txt
  lib/xray/xray_init.cc


Index: lib/xray/xray_init.cc
===================================================================
--- lib/xray/xray_init.cc
+++ lib/xray/xray_init.cc
@@ -47,7 +47,9 @@
 // __xray_init() will do the actual loading of the current process' memory map
 // and then proceed to look for the .xray_instr_map section/segment.
 void __xray_init() XRAY_NEVER_INSTRUMENT {
-  initializeFlags();
+  if (!__sanitizer::atomic_load(&XRayInitialized,
+                                __sanitizer::memory_order_acquire))
+    initializeFlags();
   if (__start_xray_instr_map == nullptr) {
     if (Verbosity())
       Report("XRay instrumentation map missing. Not initializing XRay.\n");
@@ -64,9 +66,13 @@
   __sanitizer::atomic_store(&XRayInitialized, true,
                             __sanitizer::memory_order_release);
 
+#ifndef XRAY_NO_PREINIT
   if (flags()->patch_premain)
     __xray_patch();
+#endif
 }
 
+#ifndef XRAY_NO_PREINIT
 __attribute__((section(".preinit_array"),
                used)) void (*__local_xray_preinit)(void) = __xray_init;
+#endif
Index: lib/xray/CMakeLists.txt
===================================================================
--- lib/xray/CMakeLists.txt
+++ lib/xray/CMakeLists.txt
@@ -62,6 +62,8 @@
 set(XRAY_COMMON_DEFINITIONS XRAY_HAS_EXCEPTIONS=1)
 append_list_if(
   COMPILER_RT_HAS_XRAY_COMPILER_FLAG XRAY_SUPPORTED=1 XRAY_COMMON_DEFINITIONS)
+append_list_if(
+  COMPILER_RT_BUILD_XRAY_NO_PREINIT XRAY_NO_PREINIT XRAY_COMMON_DEFINITIONS)
 
 add_compiler_rt_object_libraries(RTXray
   ARCHS ${XRAY_SUPPORTED_ARCH}
Index: include/xray/xray_interface.h
===================================================================
--- include/xray/xray_interface.h
+++ include/xray/xray_interface.h
@@ -106,6 +106,12 @@
 /// encounter errors (when there are no instrumented functions, etc.).
 extern size_t __xray_max_function_id();
 
+/// Initialize the required XRay data structures. This is useful in cases where
+/// users want to control precisely when the XRay instrumentation data
+/// structures are initialized, for example when the XRay library is built with
+/// the XRAY_NO_PREINIT preprocessor definition.
+extern void __xray_init();
+
 } // end extern "C"
 
 #endif // XRAY_XRAY_INTERFACE_H
Index: CMakeLists.txt
===================================================================
--- CMakeLists.txt
+++ CMakeLists.txt
@@ -36,6 +36,8 @@
 mark_as_advanced(COMPILER_RT_BUILD_SANITIZERS)
 option(COMPILER_RT_BUILD_XRAY "Build xray" ON)
 mark_as_advanced(COMPILER_RT_BUILD_XRAY)
+option(COMPILER_RT_BUILD_XRAY_NO_PREINIT "Build xray with no preinit patching" OFF)
+mark_as_advanced(COMPILER_RT_BUILD_XRAY_NO_PREINIT)
 
 set(COMPILER_RT_BAREMETAL_BUILD OFF CACHE BOOLEAN
   "Build for a bare-metal target.")


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