// Copyright (c) 2007, Google Inc.
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//
// Author: Craig Silverstein
//
// Produce stack trace. I'm guessing (hoping!) the code is much like
// for x86. For apple machines, at least, it seems to be; see
// http://developer.apple.com/documentation/mac/runtimehtml/RTArch-59.html
// http://www.linux-foundation.org/spec/ELF/ppc64/PPC-elf64abi-1.9.html#STACK
// Linux has similar code: http://patchwork.ozlabs.org/linuxppc/patch?id=8882
#include <stdio.h>
#include <stdint.h> // for uintptr_t
#include "stacktrace.h"
_START_GOOGLE_NAMESPACE_
// Given a pointer to a stack frame, locate and return the calling
// stackframe, or return NULL if no stackframe can be found. Perform sanity
// checks (the strictness of which is controlled by the boolean parameter
// "STRICT_UNWINDING") to reduce the chance that a bad pointer is returned.
template<bool STRICT_UNWINDING>
static void **NextStackFrame(void **old_sp) {
void **new_sp = (void **) *old_sp;
// Check that the transition from frame pointer old_sp to frame
// pointer new_sp isn't clearly bogus
if (STRICT_UNWINDING) {
// With the stack growing downwards, older stack frame must be
// at a greater address that the current one.
if (new_sp <= old_sp) return NULL;
// Assume stack frames larger than 100,000 bytes are bogus.
if ((uintptr_t)new_sp - (uintptr_t)old_sp > 100000) return NULL;
} else {
// In the non-strict mode, allow discontiguous stack frames.
// (alternate-signal-stacks for example).
if (new_sp == old_sp) return NULL;
// And allow frames upto about 1MB.
if ((new_sp > old_sp)
&& ((uintptr_t)new_sp - (uintptr_t)old_sp > 1000000)) return NULL;
}
if ((uintptr_t)new_sp & (sizeof(void *) - 1)) return NULL;
return new_sp;
}
// This ensures that GetStackTrace stes up the Link Register properly.
void StacktracePowerPCDummyFunction() __attribute__((noinline));
void StacktracePowerPCDummyFunction() { __asm__ volatile(""); }
// If you change this function, also change GetStackFrames below.
int GetStackTrace(void** result, int max_depth, int skip_count) {
void **sp;
// Apple OS X uses an old version of gnu as -- both Darwin 7.9.0 (Panther)
// and Darwin 8.8.1 (Tiger) use as 1.38. This means we have to use a
// different asm syntax. I don't know quite the best way to discriminate
// systems using the old as from the new one; I've gone with __APPLE__.
#ifdef __APPLE__
__asm__ volatile ("mr %0,r1" : "=r" (sp));
#else
__asm__ volatile ("mr %0,1" : "=r" (sp));
#endif
// On PowerPC, the "Link Register" or "Link Record" (LR), is a stack
// entry that holds the return address of the subroutine call (what
// instruction we run after our function finishes). This is the
// same as the stack-pointer of our parent routine, which is what we
// want here. While the compiler will always(?) set up LR for
// subroutine calls, it may not for leaf functions (such as this one).
// This routine forces the compiler (at least gcc) to push it anyway.
StacktracePowerPCDummyFunction();
// The LR save area is used by the callee, so the top entry is bogus.
skip_count++;
int n = 0;
while (sp && n < max_depth) {
if (skip_count > 0) {
skip_count--;
} else {
// PowerPC has 3 main ABIs, which say where in the stack the
// Link Register is. For DARWIN and AIX (used by apple and
// linux ppc64), it's in sp[2]. For SYSV (used by linux ppc),
// it's in sp[1].
#if defined(_CALL_AIX) || defined(_CALL_DARWIN)
result[n++] = *(sp+2);
#elif defined(_CALL_SYSV)
result[n++] = *(sp+1);
#elif defined(__APPLE__) || ((defined(__linux) || defined(__linux__)) && defined(__PPC64__))
// This check is in case the compiler doesn't define _CALL_AIX/etc.
result[n++] = *(sp+2);
#elif defined(__linux)
// This check is in case the compiler doesn't define _CALL_SYSV.
result[n++] = *(sp+1);
#else
#error Need to specify the PPC ABI for your archiecture.
#endif
}
// Use strict unwinding rules.
sp = NextStackFrame<true>(sp);
}
return n;
}
_END_GOOGLE_NAMESPACE_
