aboutsummaryrefslogtreecommitdiff
path: root/src/processor/stackwalker_x86.cc
blob: 2276374a1047c25a219dd26d02829af403aae855 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
// Copyright (c) 2006, 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.

// stackwalker_x86.cc: x86-specific stackwalker.
//
// See stackwalker_x86.h for documentation.
//
// Author: Mark Mentovai


#include "processor/postfix_evaluator-inl.h"

#include "processor/stackwalker_x86.h"
#include "google_breakpad/processor/call_stack.h"
#include "google_breakpad/processor/memory_region.h"
#include "google_breakpad/processor/stack_frame_cpu.h"
#include "processor/linked_ptr.h"
#include "processor/stack_frame_info.h"

namespace google_breakpad {


StackwalkerX86::StackwalkerX86(const SystemInfo *system_info,
                               const MDRawContextX86 *context,
                               MemoryRegion *memory,
                               const CodeModules *modules,
                               SymbolSupplier *supplier,
                               SourceLineResolverInterface *resolver)
    : Stackwalker(system_info, memory, modules, supplier, resolver),
      context_(context) {
  if (memory_->GetBase() + memory_->GetSize() - 1 > 0xffffffff) {
    // The x86 is a 32-bit CPU, the limits of the supplied stack are invalid.
    // Mark memory_ = NULL, which will cause stackwalking to fail.
    memory_ = NULL;
  }
}


StackFrame* StackwalkerX86::GetContextFrame() {
  if (!context_ || !memory_)
    return NULL;

  StackFrameX86 *frame = new StackFrameX86();

  // The instruction pointer is stored directly in a register, so pull it
  // straight out of the CPU context structure.
  frame->context = *context_;
  frame->context_validity = StackFrameX86::CONTEXT_VALID_ALL;
  frame->instruction = frame->context.eip;

  return frame;
}


StackFrame* StackwalkerX86::GetCallerFrame(
    const CallStack *stack,
    const vector< linked_ptr<StackFrameInfo> > &stack_frame_info) {
  if (!memory_ || !stack)
    return NULL;

  StackFrameX86 *last_frame = static_cast<StackFrameX86*>(
      stack->frames()->back());
  StackFrameInfo *last_frame_info = stack_frame_info.back().get();

  // This stackwalker sets each frame's %esp to its value immediately prior
  // to the CALL into the callee.  This means that %esp points to the last
  // callee argument pushed onto the stack, which may not be where %esp points
  // after the callee returns.  Specifically, the value is correct for the
  // cdecl calling convention, but not other conventions.  The cdecl
  // convention requires a caller to pop its callee's arguments from the
  // stack after the callee returns.  This is usually accomplished by adding
  // the known size of the arguments to %esp.  Other calling conventions,
  // including stdcall, thiscall, and fastcall, require the callee to pop any
  // parameters stored on the stack before returning.  This is usually
  // accomplished by using the RET n instruction, which pops n bytes off
  // the stack after popping the return address.
  //
  // Because each frame's %esp will point to a location on the stack after
  // callee arguments have been PUSHed, when locating things in a stack frame
  // relative to %esp, the size of the arguments to the callee need to be
  // taken into account.  This seems a little bit unclean, but it's better
  // than the alternative, which would need to take these same things into
  // account, but only for cdecl functions.  With this implementation, we get
  // to be agnostic about each function's calling convention.  Furthermore,
  // this is how Windows debugging tools work, so it means that the %esp
  // values produced by this stackwalker directly correspond to the %esp
  // values you'll see there.
  //
  // If the last frame has no callee (because it's the context frame), just
  // set the callee parameter size to 0: the stack pointer can't point to
  // callee arguments because there's no callee.  This is correct as long
  // as the context wasn't captured while arguments were being pushed for
  // a function call.  Note that there may be functions whose parameter sizes
  // are unknown, 0 is also used in that case.  When that happens, it should
  // be possible to walk to the next frame without reference to %esp.

  int frames_already_walked = stack_frame_info.size();
  u_int32_t last_frame_callee_parameter_size = 0;
  if (frames_already_walked >= 2) {
    StackFrameInfo *last_frame_callee_info =
        stack_frame_info[frames_already_walked - 2].get();
    if (last_frame_callee_info &&
        last_frame_callee_info->valid & StackFrameInfo::VALID_PARAMETER_SIZE) {
      last_frame_callee_parameter_size =
          last_frame_callee_info->parameter_size;
    }
  }

  // Set up the dictionary for the PostfixEvaluator.  %ebp and %esp are used
  // in each program string, and their previous values are known, so set them
  // here.  .cbCalleeParams is an Breakpad extension that allows us to use
  // the PostfixEvaluator engine when certain types of debugging information
  // are present without having to write the constants into the program string
  // as literals.
  PostfixEvaluator<u_int32_t>::DictionaryType dictionary;
  dictionary["$ebp"] = last_frame->context.ebp;
  dictionary["$esp"] = last_frame->context.esp;
  dictionary[".cbCalleeParams"] = last_frame_callee_parameter_size;

  if (last_frame_info && last_frame_info->valid == StackFrameInfo::VALID_ALL) {
    // FPO debugging data is available.  Initialize constants.
    dictionary[".cbSavedRegs"] = last_frame_info->saved_register_size;
    dictionary[".cbLocals"] = last_frame_info->local_size;
    dictionary[".raSearchStart"] = last_frame->context.esp +
                                   last_frame_callee_parameter_size +
                                   last_frame_info->local_size +
                                   last_frame_info->saved_register_size;
  }
  if (last_frame_info &&
      last_frame_info->valid & StackFrameInfo::VALID_PARAMETER_SIZE) {
    // This is treated separately because it can either come from FPO data or
    // from other debugging data.
    dictionary[".cbParams"] = last_frame_info->parameter_size;
  }

  // Decide what type of program string to use.  The program string is in
  // postfix notation and will be passed to PostfixEvaluator::Evaluate.
  // Given the dictionary and the program string, it is possible to compute
  // the return address and the values of other registers in the calling
  // function.
  string program_string;
  if (last_frame_info && last_frame_info->valid == StackFrameInfo::VALID_ALL) {
    // FPO data available.
    if (!last_frame_info->program_string.empty()) {
      // The FPO data has its own program string, which will tell us how to
      // get to the caller frame, and may even fill in the values of
      // nonvolatile registers and provide pointers to local variables and
      // parameters.
      program_string = last_frame_info->program_string;
    } else if (last_frame_info->allocates_base_pointer) {
      // The function corresponding to the last frame doesn't use the frame
      // pointer for conventional purposes, but it does allocate a new
      // frame pointer and use it for its own purposes.  Its callee's
      // information is still accessed relative to %esp, and the previous
      // value of %ebp can be recovered from a location in its stack frame,
      // within the saved-register area.
      //
      // Functions that fall into this category use the %ebp register for
      // a purpose other than the frame pointer.  They restore the caller's
      // %ebp before returning.  These functions create their stack frame
      // after a CALL by decrementing the stack pointer in an amount
      // sufficient to store local variables, and then PUSHing saved
      // registers onto the stack.  Arguments to a callee function, if any,
      // are PUSHed after that.  Walking up to the caller, therefore,
      // can be done solely with calculations relative to the stack pointer
      // (%esp).  The return address is recovered from the memory location
      // above the known sizes of the callee's parameters, saved registers,
      // and locals.  The caller's stack pointer (the value of %esp when
      // the caller executed CALL) is the location immediately above the
      // saved return address.  The saved value of %ebp to be restored for
      // the caller is at a known location in the saved-register area of
      // the stack frame.
      //
      // %eip_new = *(%esp_old + callee_params + saved_regs + locals)
      // %ebp_new = *(%esp_old + callee_params + saved_regs - 8)
      // %esp_new = %esp_old + callee_params + saved_regs + locals + 4
      program_string = "$eip .raSearchStart ^ = "
                       "$ebp $esp .cbCalleeParams + .cbSavedRegs + 8 - ^ = "
                       "$esp .raSearchStart 4 + =";
    } else {
      // The function corresponding to the last frame doesn't use %ebp at
      // all.  The callee frame is located relative to %esp.  %ebp is reset
      // to itself only to cause it to appear to have been set in
      // dictionary_validity.
      //
      // The called procedure's instruction pointer and stack pointer are
      // recovered in the same way as the case above, except that no
      // frame pointer (%ebp) is used at all, so it is not saved anywhere
      // in the callee's stack frame and does not need to be recovered.
      // Because %ebp wasn't used in the callee, whatever value it has
      // is the value that it had in the caller, so it can be carried
      // straight through without bringing its validity into question.
      //
      // %eip_new = *(%esp_old + callee_params + saved_regs + locals)
      // %esp_new = %esp_old + callee_params + saved_regs + locals + 4
      // %ebp_new = %ebp_old
      program_string = "$eip .raSearchStart ^ = "
                       "$esp .raSearchStart 4 + = "
                       "$ebp $ebp =";
    }
  } else {
    // No FPO information is available for the last frame.  Assume that the
    // standard %ebp-using x86 calling convention is in use.
    //
    // The typical x86 calling convention, when frame pointers are present,
    // is for the calling procedure to use CALL, which pushes the return
    // address onto the stack and sets the instruction pointer (%eip) to
    // the entry point of the called routine.  The called routine then
    // PUSHes the calling routine's frame pointer (%ebp) onto the stack
    // before copying the stack pointer (%esp) to the frame pointer (%ebp).
    // Therefore, the calling procedure's frame pointer is always available
    // by dereferencing the called procedure's frame pointer, and the return
    // address is always available at the memory location immediately above
    // the address pointed to by the called procedure's frame pointer.  The
    // calling procedure's stack pointer (%esp) is 8 higher than the value
    // of the called procedure's frame pointer at the time the calling
    // procedure made the CALL: 4 bytes for the return address pushed by the
    // CALL itself, and 4 bytes for the callee's PUSH of the caller's frame
    // pointer.
    //
    // %eip_new = *(%ebp_old + 4)
    // %esp_new = %ebp_old + 8
    // %ebp_new = *(%ebp_old)
    program_string = "$eip $ebp 4 + ^ = "
                     "$esp $ebp 8 + = "
                     "$ebp $ebp ^ =";
  }

  // Now crank it out, making sure that the program string set the three
  // required variables.
  PostfixEvaluator<u_int32_t> evaluator =
      PostfixEvaluator<u_int32_t>(&dictionary, memory_);
  PostfixEvaluator<u_int32_t>::DictionaryValidityType dictionary_validity;
  if (!evaluator.Evaluate(program_string, &dictionary_validity) ||
      dictionary_validity.find("$eip") == dictionary_validity.end() ||
      dictionary_validity.find("$esp") == dictionary_validity.end() ||
      dictionary_validity.find("$ebp") == dictionary_validity.end()) {
    return NULL;
  }

  // Treat an instruction address of 0 as end-of-stack.  Treat incorrect stack
  // direction as end-of-stack to enforce progress and avoid infinite loops.
  if (dictionary["$eip"] == 0 ||
      dictionary["$esp"] <= last_frame->context.esp) {
    return NULL;
  }

  // Create a new stack frame (ownership will be transferred to the caller)
  // and fill it in.
  StackFrameX86 *frame = new StackFrameX86();

  frame->context = last_frame->context;
  frame->context.eip = dictionary["$eip"];
  frame->context.esp = dictionary["$esp"];
  frame->context.ebp = dictionary["$ebp"];
  frame->context_validity = StackFrameX86::CONTEXT_VALID_EIP |
                                StackFrameX86::CONTEXT_VALID_ESP |
                                StackFrameX86::CONTEXT_VALID_EBP;

  // These are nonvolatile (callee-save) registers, and the program string
  // may have filled them in.
  if (dictionary_validity.find("$ebx") != dictionary_validity.end()) {
    frame->context.ebx = dictionary["$ebx"];
    frame->context_validity |= StackFrameX86::CONTEXT_VALID_EBX;
  }
  if (dictionary_validity.find("$esi") != dictionary_validity.end()) {
    frame->context.esi = dictionary["$esi"];
    frame->context_validity |= StackFrameX86::CONTEXT_VALID_ESI;
  }
  if (dictionary_validity.find("$edi") != dictionary_validity.end()) {
    frame->context.edi = dictionary["$edi"];
    frame->context_validity |= StackFrameX86::CONTEXT_VALID_EDI;
  }

  // frame->context.eip is the return address, which is one instruction
  // past the CALL that caused us to arrive at the callee.  Set
  // frame->instruction to one less than that.  This won't reference the
  // beginning of the CALL instruction, but it's guaranteed to be within the
  // CALL, which is sufficient to get the source line information to match up
  // with the line that contains a function call.  Callers that require the
  // exact return address value may access the context.eip field of
  // StackFrameX86.
  frame->instruction = frame->context.eip - 1;

  return frame;
}


}  // namespace google_breakpad