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BeefRT/gperftools/src/getpc.h

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+// Copyright (c) 2005, Google Inc.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// ---
+// Author: Craig Silverstein
+//
+// This is an internal header file used by profiler.cc.  It defines
+// the single (inline) function GetPC.  GetPC is used in a signal
+// handler to figure out the instruction that was being executed when
+// the signal-handler was triggered.
+//
+// To get this, we use the ucontext_t argument to the signal-handler
+// callback, which holds the full context of what was going on when
+// the signal triggered.  How to get from a ucontext_t to a Program
+// Counter is OS-dependent.
+
+#ifndef BASE_GETPC_H_
+#define BASE_GETPC_H_
+
+#include "config.h"
+
+// On many linux systems, we may need _GNU_SOURCE to get access to
+// the defined constants that define the register we want to see (eg
+// REG_EIP).  Note this #define must come first!
+#define _GNU_SOURCE 1
+// If #define _GNU_SOURCE causes problems, this might work instead.
+// It will cause problems for FreeBSD though!, because it turns off
+// the needed __BSD_VISIBLE.
+//#define _XOPEN_SOURCE 500
+
+#include <string.h>         // for memcmp
+#if defined(HAVE_SYS_UCONTEXT_H)
+#include <sys/ucontext.h>
+#elif defined(HAVE_UCONTEXT_H)
+#include <ucontext.h>       // for ucontext_t (and also mcontext_t)
+#elif defined(HAVE_CYGWIN_SIGNAL_H)
+#include <cygwin/signal.h>
+typedef ucontext ucontext_t;
+#endif
+
+
+// Take the example where function Foo() calls function Bar().  For
+// many architectures, Bar() is responsible for setting up and tearing
+// down its own stack frame.  In that case, it's possible for the
+// interrupt to happen when execution is in Bar(), but the stack frame
+// is not properly set up (either before it's done being set up, or
+// after it's been torn down but before Bar() returns).  In those
+// cases, the stack trace cannot see the caller function anymore.
+//
+// GetPC can try to identify this situation, on architectures where it
+// might occur, and unwind the current function call in that case to
+// avoid false edges in the profile graph (that is, edges that appear
+// to show a call skipping over a function).  To do this, we hard-code
+// in the asm instructions we might see when setting up or tearing
+// down a stack frame.
+//
+// This is difficult to get right: the instructions depend on the
+// processor, the compiler ABI, and even the optimization level.  This
+// is a best effort patch -- if we fail to detect such a situation, or
+// mess up the PC, nothing happens; the returned PC is not used for
+// any further processing.
+struct CallUnrollInfo {
+  // Offset from (e)ip register where this instruction sequence
+  // should be matched. Interpreted as bytes. Offset 0 is the next
+  // instruction to execute. Be extra careful with negative offsets in
+  // architectures of variable instruction length (like x86) - it is
+  // not that easy as taking an offset to step one instruction back!
+  int pc_offset;
+  // The actual instruction bytes. Feel free to make it larger if you
+  // need a longer sequence.
+  unsigned char ins[16];
+  // How many bytes to match from ins array?
+  int ins_size;
+  // The offset from the stack pointer (e)sp where to look for the
+  // call return address. Interpreted as bytes.
+  int return_sp_offset;
+};
+
+
+// The dereferences needed to get the PC from a struct ucontext were
+// determined at configure time, and stored in the macro
+// PC_FROM_UCONTEXT in config.h.  The only thing we need to do here,
+// then, is to do the magic call-unrolling for systems that support it.
+
+// -- Special case 1: linux x86, for which we have CallUnrollInfo
+#if defined(__linux) && defined(__i386) && defined(__GNUC__)
+static const CallUnrollInfo callunrollinfo[] = {
+  // Entry to a function:  push %ebp;  mov  %esp,%ebp
+  // Top-of-stack contains the caller IP.
+  { 0,
+    {0x55, 0x89, 0xe5}, 3,
+    0
+  },
+  // Entry to a function, second instruction:  push %ebp;  mov  %esp,%ebp
+  // Top-of-stack contains the old frame, caller IP is +4.
+  { -1,
+    {0x55, 0x89, 0xe5}, 3,
+    4
+  },
+  // Return from a function: RET.
+  // Top-of-stack contains the caller IP.
+  { 0,
+    {0xc3}, 1,
+    0
+  }
+};
+
+inline void* GetPC(const ucontext_t& signal_ucontext) {
+  // See comment above struct CallUnrollInfo.  Only try instruction
+  // flow matching if both eip and esp looks reasonable.
+  const int eip = signal_ucontext.uc_mcontext.gregs[REG_EIP];
+  const int esp = signal_ucontext.uc_mcontext.gregs[REG_ESP];
+  if ((eip & 0xffff0000) != 0 && (~eip & 0xffff0000) != 0 &&
+      (esp & 0xffff0000) != 0) {
+    char* eip_char = reinterpret_cast<char*>(eip);
+    for (int i = 0; i < sizeof(callunrollinfo)/sizeof(*callunrollinfo); ++i) {
+      if (!memcmp(eip_char + callunrollinfo[i].pc_offset,
+                  callunrollinfo[i].ins, callunrollinfo[i].ins_size)) {
+        // We have a match.
+        void **retaddr = (void**)(esp + callunrollinfo[i].return_sp_offset);
+        return *retaddr;
+      }
+    }
+  }
+  return (void*)eip;
+}
+
+// Special case #2: Windows, which has to do something totally different.
+#elif defined(_WIN32) || defined(__CYGWIN__) || defined(__CYGWIN32__) || defined(__MINGW32__)
+// If this is ever implemented, probably the way to do it is to have
+// profiler.cc use a high-precision timer via timeSetEvent:
+//    http://msdn2.microsoft.com/en-us/library/ms712713.aspx
+// We'd use it in mode TIME_CALLBACK_FUNCTION/TIME_PERIODIC.
+// The callback function would be something like prof_handler, but
+// alas the arguments are different: no ucontext_t!  I don't know
+// how we'd get the PC (using StackWalk64?)
+//    http://msdn2.microsoft.com/en-us/library/ms680650.aspx
+
+#include "base/logging.h"   // for RAW_LOG
+#ifndef HAVE_CYGWIN_SIGNAL_H
+typedef int ucontext_t;
+#endif
+
+inline void* GetPC(const struct ucontext_t& signal_ucontext) {
+  RAW_LOG(ERROR, "GetPC is not yet implemented on Windows\n");
+  return NULL;
+}
+
+// Normal cases.  If this doesn't compile, it's probably because
+// PC_FROM_UCONTEXT is the empty string.  You need to figure out
+// the right value for your system, and add it to the list in
+// configure.ac (or set it manually in your config.h).
+#else
+inline void* GetPC(const ucontext_t& signal_ucontext) {
+  return (void*)signal_ucontext.PC_FROM_UCONTEXT;   // defined in config.h
+}
+
+#endif
+
+#endif  // BASE_GETPC_H_