1// Copyright (c) 2007, Google Inc.
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3//
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29
30// ---
31// Author: Craig Silverstein
32//
33// Produce stack trace.  I'm guessing (hoping!) the code is much like
34// for x86.  For apple machines, at least, it seems to be; see
35//    http://developer.apple.com/documentation/mac/runtimehtml/RTArch-59.html
36//    http://www.linux-foundation.org/spec/ELF/ppc64/PPC-elf64abi-1.9.html#STACK
37// Linux has similar code: http://patchwork.ozlabs.org/linuxppc/patch?id=8882
38
39#ifndef BASE_STACKTRACE_POWERPC_INL_H_
40#define BASE_STACKTRACE_POWERPC_INL_H_
41// Note: this file is included into stacktrace.cc more than once.
42// Anything that should only be defined once should be here:
43
44#include <stdint.h>   // for uintptr_t
45#include <stdlib.h>   // for NULL
46#include <gperftools/stacktrace.h>
47
48// Given a pointer to a stack frame, locate and return the calling
49// stackframe, or return NULL if no stackframe can be found. Perform sanity
50// checks (the strictness of which is controlled by the boolean parameter
51// "STRICT_UNWINDING") to reduce the chance that a bad pointer is returned.
52template<bool STRICT_UNWINDING>
53static void **NextStackFrame(void **old_sp) {
54  void **new_sp = (void **) *old_sp;
55
56  // Check that the transition from frame pointer old_sp to frame
57  // pointer new_sp isn't clearly bogus
58  if (STRICT_UNWINDING) {
59    // With the stack growing downwards, older stack frame must be
60    // at a greater address that the current one.
61    if (new_sp <= old_sp) return NULL;
62    // Assume stack frames larger than 100,000 bytes are bogus.
63    if ((uintptr_t)new_sp - (uintptr_t)old_sp > 100000) return NULL;
64  } else {
65    // In the non-strict mode, allow discontiguous stack frames.
66    // (alternate-signal-stacks for example).
67    if (new_sp == old_sp) return NULL;
68    // And allow frames upto about 1MB.
69    if ((new_sp > old_sp)
70        && ((uintptr_t)new_sp - (uintptr_t)old_sp > 1000000)) return NULL;
71  }
72  if ((uintptr_t)new_sp & (sizeof(void *) - 1)) return NULL;
73  return new_sp;
74}
75
76// This ensures that GetStackTrace stes up the Link Register properly.
77void StacktracePowerPCDummyFunction() __attribute__((noinline));
78void StacktracePowerPCDummyFunction() { __asm__ volatile(""); }
79#endif  // BASE_STACKTRACE_POWERPC_INL_H_
80
81// Note: this part of the file is included several times.
82// Do not put globals below.
83
84// The following 4 functions are generated from the code below:
85//   GetStack{Trace,Frames}()
86//   GetStack{Trace,Frames}WithContext()
87//
88// These functions take the following args:
89//   void** result: the stack-trace, as an array
90//   int* sizes: the size of each stack frame, as an array
91//               (GetStackFrames* only)
92//   int max_depth: the size of the result (and sizes) array(s)
93//   int skip_count: how many stack pointers to skip before storing in result
94//   void* ucp: a ucontext_t* (GetStack{Trace,Frames}WithContext only)
95int GET_STACK_TRACE_OR_FRAMES {
96  void **sp;
97  // Apple OS X uses an old version of gnu as -- both Darwin 7.9.0 (Panther)
98  // and Darwin 8.8.1 (Tiger) use as 1.38.  This means we have to use a
99  // different asm syntax.  I don't know quite the best way to discriminate
100  // systems using the old as from the new one; I've gone with __APPLE__.
101  // TODO(csilvers): use autoconf instead, to look for 'as --version' == 1 or 2
102#ifdef __APPLE__
103  __asm__ volatile ("mr %0,r1" : "=r" (sp));
104#else
105  __asm__ volatile ("mr %0,1" : "=r" (sp));
106#endif
107
108  // On PowerPC, the "Link Register" or "Link Record" (LR), is a stack
109  // entry that holds the return address of the subroutine call (what
110  // instruction we run after our function finishes).  This is the
111  // same as the stack-pointer of our parent routine, which is what we
112  // want here.  While the compiler will always(?) set up LR for
113  // subroutine calls, it may not for leaf functions (such as this one).
114  // This routine forces the compiler (at least gcc) to push it anyway.
115  StacktracePowerPCDummyFunction();
116
117#if IS_STACK_FRAMES
118  // Note we do *not* increment skip_count here for the SYSV ABI.  If
119  // we did, the list of stack frames wouldn't properly match up with
120  // the list of return addresses.  Note this means the top pc entry
121  // is probably bogus for linux/ppc (and other SYSV-ABI systems).
122#else
123  // The LR save area is used by the callee, so the top entry is bogus.
124  skip_count++;
125#endif
126
127  int n = 0;
128  while (sp && n < max_depth) {
129    // The GetStackFrames routine is called when we are in some
130    // informational context (the failure signal handler for example).
131    // Use the non-strict unwinding rules to produce a stack trace
132    // that is as complete as possible (even if it contains a few
133    // bogus entries in some rare cases).
134    void **next_sp = NextStackFrame<!IS_STACK_FRAMES>(sp);
135
136    if (skip_count > 0) {
137      skip_count--;
138    } else {
139      // PowerPC has 3 main ABIs, which say where in the stack the
140      // Link Register is.  For DARWIN and AIX (used by apple and
141      // linux ppc64), it's in sp[2].  For SYSV (used by linux ppc),
142      // it's in sp[1].
143#if defined(_CALL_AIX) || defined(_CALL_DARWIN)
144      result[n] = *(sp+2);
145#elif defined(_CALL_SYSV)
146      result[n] = *(sp+1);
147#elif defined(__APPLE__) || (defined(__linux) && defined(__PPC64__))
148      // This check is in case the compiler doesn't define _CALL_AIX/etc.
149      result[n] = *(sp+2);
150#elif defined(__linux)
151      // This check is in case the compiler doesn't define _CALL_SYSV.
152      result[n] = *(sp+1);
153#else
154#error Need to specify the PPC ABI for your archiecture.
155#endif
156
157#if IS_STACK_FRAMES
158      if (next_sp > sp) {
159        sizes[n] = (uintptr_t)next_sp - (uintptr_t)sp;
160      } else {
161        // A frame-size of 0 is used to indicate unknown frame size.
162        sizes[n] = 0;
163      }
164#endif
165      n++;
166    }
167    sp = next_sp;
168  }
169  return n;
170}
171