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// -*- Mode: C++; c-basic-offset: 2; indent-tabs-mode: nil -*-

// 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_

// 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.

#ifdef __APPLE__

#include <limits.h>

#define _XOPEN_SOURCE 500

#endif

#include "vmprof_config.h"

#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;

#elif defined(HAVE_SIGNAL_H)

#include <signal.h>

#else

# error "don't know how to get the pc on this platform"

#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 Windows, which has to do something totally different.

#if 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

static intptr_t GetPC(ucontext_t *signal_ucontext) {

// RAW_LOG(ERROR, "GetPC is not yet implemented on Windows\n");

fprintf(stderr, "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

// vmrpof_config.h

#else

static intptr_t GetPC(ucontext_t *signal_ucontext) {

return signal_ucontext->PC_FROM_UCONTEXT; // defined in config.h

}

#endif

#endif // BASE_GETPC_H_

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