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/* Return backtrace of current program state.
Copyright (C) 2000-2020 Free Software Foundation, Inc.
Contributed by Martin Schwidefsky <schwidefsky@de.ibm.com>.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <libc-lock.h>
#include <dlfcn.h>
#include <execinfo.h>
#include <stddef.h>
#include <stdlib.h>
#include <unwind.h>
/* This is a global variable set at program start time. It marks the
highest used stack address. */
extern void *__libc_stack_end;
/* This is the stack layout we see for every non-leaf function.
size offset
%r15 -> +------------------+
4 | back chain | 0
4 | end of stack | 4
8 | glue | 8
8 | scratch | 16
40 | save area r6-r15 | 24
16 | save area f4,f6 | 64
16 | empty | 80
+------------------+
r14 in the save area holds the return address.
*/
struct layout
{
int back_chain;
int end_of_stack;
int glue[2];
int scratch[2];
int save_grps[10];
int save_fp[4];
int empty[2];
};
struct trace_arg
{
void **array;
int cnt, size;
};
#ifdef SHARED
static _Unwind_Reason_Code (*unwind_backtrace) (_Unwind_Trace_Fn, void *);
static _Unwind_Ptr (*unwind_getip) (struct _Unwind_Context *);
static void
init (void)
{
void *handle = __libc_dlopen ("libgcc_s.so.1");
if (handle == NULL)
return;
unwind_backtrace = __libc_dlsym (handle, "_Unwind_Backtrace");
unwind_getip = __libc_dlsym (handle, "_Unwind_GetIP");
if (unwind_getip == NULL)
unwind_backtrace = NULL;
}
static int
__backchain_backtrace (void **array, int size)
{
/* We assume that all the code is generated with frame pointers set. */
struct layout *stack;
int cnt = 0;
__asm__ ("LR %0,%%r15" : "=d" (stack) );
/* We skip the call to this function, it makes no sense to record it. */
stack = (struct layout *) stack->back_chain;
while (cnt < size)
{
if (stack == NULL || (void *) stack > __libc_stack_end)
/* This means the address is out of range. Note that for the
toplevel we see a frame pointer with value NULL which clearly is
out of range. */
break;
array[cnt++] = (void *) (stack->save_grps[8] & 0x7fffffff);
stack = (struct layout *) stack->back_chain;
}
return cnt;
}
#else
# define unwind_backtrace _Unwind_Backtrace
# define unwind_getip _Unwind_GetIP
#endif
static _Unwind_Reason_Code
backtrace_helper (struct _Unwind_Context *ctx, void *a)
{
struct trace_arg *arg = a;
/* We are first called with address in the __backtrace function.
Skip it. */
if (arg->cnt != -1)
arg->array[arg->cnt] = (void *) unwind_getip (ctx);
if (++arg->cnt == arg->size)
return _URC_END_OF_STACK;
return _URC_NO_REASON;
}
int
__backtrace (void **array, int size)
{
struct trace_arg arg = { .array = array, .size = size, .cnt = -1 };
if (size <= 0)
return 0;
#ifdef SHARED
__libc_once_define (static, once);
__libc_once (once, init);
if (unwind_backtrace == NULL)
return __backchain_backtrace (array, size);
#endif
unwind_backtrace (backtrace_helper, &arg);
return arg.cnt != -1 ? arg.cnt : 0;
}
weak_alias (__backtrace, backtrace)
libc_hidden_def (__backtrace)
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