[compiler-rt] [XRay] Basic initialization and flag definition for XRay runtime

Summary:
This patch implements the initialisation and patching routines for the XRay runtime, along with the necessary trampolines for function entry/exit handling. For now we only define the basic hooks for allowing an implementation to define a handler that gets run on function entry/exit. We expose a minimal API for controlling the behaviour of the runtime (patching, cleanup, and setting the handler to invoke when instrumenting).

Depends on D19904

Reviewers: echristo, kcc, rnk

Subscribers: rnk, mehdi_amini, llvm-commits

Differential Revision: https://reviews.llvm.org/D21612

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@276117 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 68 insertions, 0 deletions

diff --git a/lib/xray/xray_init.cc b/lib/xray/xray_init.cc
new file mode 100644
index 000000000..be5d76267
--- /dev/null
+++ b/lib/xray/xray_init.cc
@@ -0,0 +1,68 @@
+//===-- xray_init.cc --------------------------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file is a part of XRay, a dynamic runtime instrumentation system.
+//
+// XRay initialisation logic.
+//===----------------------------------------------------------------------===//
+
+#include <atomic>
+#include <fcntl.h>
+#include <strings.h>
+#include <unistd.h>
+
+#include "sanitizer_common/sanitizer_common.h"
+#include "xray_flags.h"
+#include "xray_interface_internal.h"
+#include "llvm/Support/ELF.h"
+
+extern "C" {
+extern void __xray_init();
+extern const XRaySledEntry __start_xray_instr_map[] __attribute__((weak));
+extern const XRaySledEntry __stop_xray_instr_map[] __attribute__((weak));
+}
+
+using namespace __xray;
+
+// We initialize some global variables that pertain to specific sections of XRay
+// data structures in the binary. We do this for the current process using
+// /proc/curproc/map and make sure that we're able to get it. We signal failure
+// via a global atomic boolean to indicate whether we've initialized properly.
+//
+std::atomic<bool> XRayInitialized{false};
+
+// This should always be updated before XRayInitialized is updated.
+std::atomic<__xray::XRaySledMap> XRayInstrMap{};
+
+// __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() {
+  InitializeFlags();
+  if (__start_xray_instr_map == nullptr) {
+    Report("XRay instrumentation map missing. Not initializing XRay.\n");
+    return;
+  }
+
+  // Now initialize the XRayInstrMap global struct with the address of the
+  // entries, reinterpreted as an array of XRaySledEntry objects. We use the
+  // virtual pointer we have from the section to provide us the correct
+  // information.
+  __xray::XRaySledMap SledMap{};
+  SledMap.Sleds = __start_xray_instr_map;
+  SledMap.Entries = __stop_xray_instr_map - __start_xray_instr_map;
+  XRayInstrMap.store(SledMap, std::memory_order_release);
+  XRayInitialized.store(true, std::memory_order_release);
+
+  // FIXME: Check the flag/environment before patching.
+  if (flags()->patch_premain)
+    __xray_patch();
+}
+
+__attribute__((section(".preinit_array"),
+               used)) void (*__local_xray_preinit)(void) = __xray_init;