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// Copyright 2007 and onwards Google Inc.
// 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 <stdint.h> // for uintptr_t
#include <stdlib.h> // for NULL
#include <google/stacktrace.h>
// 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 to reduce the chance that a bad pointer is returned.
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 (new_sp <= old_sp) return NULL;
if ((uintptr_t)new_sp & (sizeof(void *) - 1)) return NULL;
if ((uintptr_t)new_sp - (uintptr_t)old_sp > 100000) return NULL;
return new_sp;
}
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__.
// TODO(csilvers): use autoconf instead, to look for 'as --version' == 1 or 2
#ifdef __APPLE__
__asm__ volatile ("mr %0,r1" : "=r" (sp));
#else
__asm__ volatile ("mr %0,1" : "=r" (sp));
#endif
int n = 0;
while (sp && n < max_depth) {
if (skip_count > 0) {
skip_count--;
} else {
// sp[2] holds the "Link Record", according to RTArch-59.html.
// On PPC, the Link Record is 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. We believe that
// the compiler will always set up the LR for subroutine calls.
//
// It may be possible to get the stack-pointer of the parent
// routine directly. In my experiments, this code works:
// result[n++] = NextStackFrame(sp)[-18]
// But I'm not sure what this is doing, exactly, or how reliable it is.
result[n++] = *(sp+2); // sp[2] holds the Link Record (return address)
}
sp = NextStackFrame(sp);
}
return n;
}
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