src/stacktrace_libunwind-inl.h

// -*- Mode: C++; c-basic-offset: 2; indent-tabs-mode: nil -*-
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// ---
// Author: Arun Sharma
//
// Produce stack trace using libunwind

#ifndef BASE_STACKTRACE_LIBINWIND_INL_H_
#define BASE_STACKTRACE_LIBINWIND_INL_H_
// Note: this file is included into stacktrace.cc more than once.
// Anything that should only be defined once should be here:

// We only need local unwinder.
#define UNW_LOCAL_ONLY

extern "C" {
#include <assert.h>
#include <string.h>   // for memset()
#include <libunwind.h>
}
#include "gperftools/stacktrace.h"

#include "base/basictypes.h"
#include "base/logging.h"

// Sometimes, we can try to get a stack trace from within a stack
// trace, because libunwind can call mmap (maybe indirectly via an
// internal mmap based memory allocator), and that mmap gets trapped
// and causes a stack-trace request.  If were to try to honor that
// recursive request, we'd end up with infinite recursion or deadlock.
// Luckily, it's safe to ignore those subsequent traces.  In such
// cases, we return 0 to indicate the situation.
static __thread int recursive ATTR_INITIAL_EXEC;

#if defined(TCMALLOC_ENABLE_UNWIND_FROM_UCONTEXT) && (defined(__i386__) || defined(__x86_64__)) && defined(__GNU_LIBRARY__)
#define BASE_STACKTRACE_UNW_CONTEXT_IS_UCONTEXT 1
#endif

#endif  // BASE_STACKTRACE_LIBINWIND_INL_H_

// Note: this part of the file is included several times.
// Do not put globals below.

// The following 4 functions are generated from the code below:
//   GetStack{Trace,Frames}()
//   GetStack{Trace,Frames}WithContext()
//
// These functions take the following args:
//   void** result: the stack-trace, as an array
//   int* sizes: the size of each stack frame, as an array
//               (GetStackFrames* only)
//   int max_depth: the size of the result (and sizes) array(s)
//   int skip_count: how many stack pointers to skip before storing in result
//   void* ucp: a ucontext_t* (GetStack{Trace,Frames}WithContext only)
static int GET_STACK_TRACE_OR_FRAMES {
  void *ip;
  int n = 0;
  unw_cursor_t cursor;
  unw_context_t uc;
#if IS_STACK_FRAMES
  unw_word_t sp = 0, next_sp = 0;
#endif

  if (recursive) {
    return 0;
  }
  ++recursive;

#if (IS_WITH_CONTEXT && defined(BASE_STACKTRACE_UNW_CONTEXT_IS_UCONTEXT))
  if (ucp) {
    uc = *(static_cast<unw_context_t *>(const_cast<void *>(ucp)));
    /* this is a bit weird. profiler.cc calls us with signal's ucontext
     * yet passing us 2 as skip_count and essentially assuming we won't
     * use ucontext. */
    /* In order to fix that I'm going to assume that if ucp is
     * non-null we're asked to ignore skip_count in case we're
     * able to use ucp */
    skip_count = 0;
  } else {
    unw_getcontext(&uc);
    skip_count += 2;         // Do not include current and parent frame
  }
#else
  unw_getcontext(&uc);
  skip_count += 2;         // Do not include current and parent frame
#endif

  int ret = unw_init_local(&cursor, &uc);
  assert(ret >= 0);

  while (skip_count--) {
    if (unw_step(&cursor) <= 0) {
      goto out;
    }
#if IS_STACK_FRAMES
    if (unw_get_reg(&cursor, UNW_REG_SP, &next_sp)) {
      goto out;
    }
#endif
  }

  while (n < max_depth) {
    if (unw_get_reg(&cursor, UNW_REG_IP, (unw_word_t *) &ip) < 0) {
      break;
    }
#if IS_STACK_FRAMES
    sizes[n] = 0;
#endif
    result[n++] = ip;
    if (unw_step(&cursor) <= 0) {
      break;
    }
#if IS_STACK_FRAMES
    sp = next_sp;
    if (unw_get_reg(&cursor, UNW_REG_SP, &next_sp) , 0) {
      break;
    }
    sizes[n - 1] = next_sp - sp;
#endif
  }
out:
  --recursive;
  return n;
}