1// Copyright (c) 2005, Google Inc. 2// All rights reserved. 3// 4// Redistribution and use in source and binary forms, with or without 5// modification, are permitted provided that the following conditions are 6// met: 7// 8// * Redistributions of source code must retain the above copyright 9// notice, this list of conditions and the following disclaimer. 10// * Redistributions in binary form must reproduce the above 11// copyright notice, this list of conditions and the following disclaimer 12// in the documentation and/or other materials provided with the 13// distribution. 14// * Neither the name of Google Inc. nor the names of its 15// contributors may be used to endorse or promote products derived from 16// this software without specific prior written permission. 17// 18// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 19// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 20// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 21// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 22// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 23// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 24// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 25// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 26// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 27// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 28// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 29 30// --- 31// Author: Craig Silverstein 32// 33// This is an internal header file used by profiler.cc. It defines 34// the single (inline) function GetPC. GetPC is used in a signal 35// handler to figure out the instruction that was being executed when 36// the signal-handler was triggered. 37// 38// To get this, we use the ucontext_t argument to the signal-handler 39// callback, which holds the full context of what was going on when 40// the signal triggered. How to get from a ucontext_t to a Program 41// Counter is OS-dependent. 42 43#ifndef BASE_GETPC_H_ 44#define BASE_GETPC_H_ 45 46#include "config.h" 47 48// On many linux systems, we may need _GNU_SOURCE to get access to 49// the defined constants that define the register we want to see (eg 50// REG_EIP). Note this #define must come first! 51#define _GNU_SOURCE 1 52// If #define _GNU_SOURCE causes problems, this might work instead. 53// It will cause problems for FreeBSD though!, because it turns off 54// the needed __BSD_VISIBLE. 55//#define _XOPEN_SOURCE 500 56 57#include <string.h> // for memcmp 58#if defined(HAVE_SYS_UCONTEXT_H) 59#include <sys/ucontext.h> 60#elif defined(HAVE_UCONTEXT_H) 61#include <ucontext.h> // for ucontext_t (and also mcontext_t) 62#elif defined(HAVE_CYGWIN_SIGNAL_H) 63#include <cygwin/signal.h> 64typedef ucontext ucontext_t; 65#endif 66 67 68// Take the example where function Foo() calls function Bar(). For 69// many architectures, Bar() is responsible for setting up and tearing 70// down its own stack frame. In that case, it's possible for the 71// interrupt to happen when execution is in Bar(), but the stack frame 72// is not properly set up (either before it's done being set up, or 73// after it's been torn down but before Bar() returns). In those 74// cases, the stack trace cannot see the caller function anymore. 75// 76// GetPC can try to identify this situation, on architectures where it 77// might occur, and unwind the current function call in that case to 78// avoid false edges in the profile graph (that is, edges that appear 79// to show a call skipping over a function). To do this, we hard-code 80// in the asm instructions we might see when setting up or tearing 81// down a stack frame. 82// 83// This is difficult to get right: the instructions depend on the 84// processor, the compiler ABI, and even the optimization level. This 85// is a best effort patch -- if we fail to detect such a situation, or 86// mess up the PC, nothing happens; the returned PC is not used for 87// any further processing. 88struct CallUnrollInfo { 89 // Offset from (e)ip register where this instruction sequence 90 // should be matched. Interpreted as bytes. Offset 0 is the next 91 // instruction to execute. Be extra careful with negative offsets in 92 // architectures of variable instruction length (like x86) - it is 93 // not that easy as taking an offset to step one instruction back! 94 int pc_offset; 95 // The actual instruction bytes. Feel free to make it larger if you 96 // need a longer sequence. 97 char ins[16]; 98 // How many bytes to match from ins array? 99 int ins_size; 100 // The offset from the stack pointer (e)sp where to look for the 101 // call return address. Interpreted as bytes. 102 int return_sp_offset; 103}; 104 105 106// The dereferences needed to get the PC from a struct ucontext were 107// determined at configure time, and stored in the macro 108// PC_FROM_UCONTEXT in config.h. The only thing we need to do here, 109// then, is to do the magic call-unrolling for systems that support it. 110 111// -- Special case 1: linux x86, for which we have CallUnrollInfo 112#if defined(__linux) && defined(__i386) && defined(__GNUC__) 113static const CallUnrollInfo callunrollinfo[] = { 114 // Entry to a function: push %ebp; mov %esp,%ebp 115 // Top-of-stack contains the caller IP. 116 { 0, 117 {0x55, 0x89, 0xe5}, 3, 118 0 119 }, 120 // Entry to a function, second instruction: push %ebp; mov %esp,%ebp 121 // Top-of-stack contains the old frame, caller IP is +4. 122 { -1, 123 {0x55, 0x89, 0xe5}, 3, 124 4 125 }, 126 // Return from a function: RET. 127 // Top-of-stack contains the caller IP. 128 { 0, 129 {0xc3}, 1, 130 0 131 } 132}; 133 134inline void* GetPC(const ucontext_t& signal_ucontext) { 135 // See comment above struct CallUnrollInfo. Only try instruction 136 // flow matching if both eip and esp looks reasonable. 137 const int eip = signal_ucontext.uc_mcontext.gregs[REG_EIP]; 138 const int esp = signal_ucontext.uc_mcontext.gregs[REG_ESP]; 139 if ((eip & 0xffff0000) != 0 && (~eip & 0xffff0000) != 0 && 140 (esp & 0xffff0000) != 0) { 141 char* eip_char = reinterpret_cast<char*>(eip); 142 for (int i = 0; i < sizeof(callunrollinfo)/sizeof(*callunrollinfo); ++i) { 143 if (!memcmp(eip_char + callunrollinfo[i].pc_offset, 144 callunrollinfo[i].ins, callunrollinfo[i].ins_size)) { 145 // We have a match. 146 void **retaddr = (void**)(esp + callunrollinfo[i].return_sp_offset); 147 return *retaddr; 148 } 149 } 150 } 151 return (void*)eip; 152} 153 154// Special case #2: Windows, which has to do something totally different. 155#elif defined(_WIN32) || defined(__CYGWIN__) || defined(__CYGWIN32__) || defined(__MINGW32__) 156// If this is ever implemented, probably the way to do it is to have 157// profiler.cc use a high-precision timer via timeSetEvent: 158// http://msdn2.microsoft.com/en-us/library/ms712713.aspx 159// We'd use it in mode TIME_CALLBACK_FUNCTION/TIME_PERIODIC. 160// The callback function would be something like prof_handler, but 161// alas the arguments are different: no ucontext_t! I don't know 162// how we'd get the PC (using StackWalk64?) 163// http://msdn2.microsoft.com/en-us/library/ms680650.aspx 164 165#include "base/logging.h" // for RAW_LOG 166#ifndef HAVE_CYGWIN_SIGNAL_H 167typedef int ucontext_t; 168#endif 169 170inline void* GetPC(const struct ucontext_t& signal_ucontext) { 171 RAW_LOG(ERROR, "GetPC is not yet implemented on Windows\n"); 172 return NULL; 173} 174 175// Normal cases. If this doesn't compile, it's probably because 176// PC_FROM_UCONTEXT is the empty string. You need to figure out 177// the right value for your system, and add it to the list in 178// configure.ac (or set it manually in your config.h). 179#else 180inline void* GetPC(const ucontext_t& signal_ucontext) { 181 return (void*)signal_ucontext.PC_FROM_UCONTEXT; // defined in config.h 182} 183 184#endif 185 186#endif // BASE_GETPC_H_ 187