/* Return backtrace of current program state.
   Copyright (C) 1998-2021 Free Software Foundation, Inc.
   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 Library General Public License as
   published by the Free Software Foundation; either version 2 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
   Library General Public License for more details.

   You should have received a copy of the GNU Library General Public
   License along with the GNU C Library; see the file COPYING.LIB.  If
   not, see <https://www.gnu.org/licenses/>.  */

#include <stddef.h>
#include <string.h>
#include <signal.h>
#include <stdint.h>

#include <execinfo.h>
#include <libc-vdso.h>

/* This is the stack layout we see with every stack frame.
   Note that every routine is required by the ABI to lay out the stack
   like this.

            +----------------+        +-----------------+
    %r1  -> | %r1 last frame--------> | %r1 last frame--->...  --> NULL
            |                |        |                 |
            | cr save        |        | cr save	  |
            |                |        |                 |
            | (unused)       |        | return address  |
            +----------------+        +-----------------+
*/
struct layout
{
  struct layout *next;
  long int condition_register;
  void *return_address;
};

/* Since the signal handler is just like any other function it needs to
   save/restore its LR and it will save it into callers stack frame.
   Since a signal handler doesn't have a caller, the kernel creates a
   dummy frame to make it look like it has a caller.  */
struct signal_frame_64 {
#define SIGNAL_FRAMESIZE 128
  char dummy[SIGNAL_FRAMESIZE];
  ucontext_t uc;
  /* We don't care about the rest, since the IP value is at 'uc' field.  */
};

/* Test if the address match to the inside the trampoline code.
   Up to and including kernel 5.8, returning from an interrupt or syscall to a
   signal handler starts execution directly at the handler's entry point, with
   LR set to address of the sigreturn trampoline (the vDSO symbol).
   Newer kernels will branch to signal handler from the trampoline instead, so
   checking the stacktrace against the vDSO entrypoint does not work in such
   case.
   The vDSO branches with a 'bctrl' instruction, so checking either the
   vDSO address itself and the next instruction should cover all kernel
   versions.  */
static inline bool
is_sigtramp_address (void *nip)
{
#ifdef HAVE_SIGTRAMP_RT64
  if (nip == GLRO (dl_vdso_sigtramp_rt64) ||
      nip == GLRO (dl_vdso_sigtramp_rt64) + 4)
    return true;
#endif
  return false;
}

int
__backtrace (void **array, int size)
{
  struct layout *current;
  int count;

  /* Force gcc to spill LR.  */
  asm volatile ("" : "=l"(current));

  /* Get the address on top-of-stack.  */
  asm volatile ("ld %0,0(1)" : "=r"(current));

  for (				count = 0;
       current != NULL && 	count < size;
       current = current->next, count++)
    {
      array[count] = current->return_address;

      /* Check if the symbol is the signal trampoline and get the interrupted
       * symbol address from the trampoline saved area.  */
      if (is_sigtramp_address (current->return_address))
        {
	  struct signal_frame_64 *sigframe = (struct signal_frame_64*) current;
	  if (count + 1 == size)
	    break;
          array[++count] = (void*) sigframe->uc.uc_mcontext.gp_regs[PT_NIP];
	  current = (void*) sigframe->uc.uc_mcontext.gp_regs[PT_R1];
	}
    }

  /* It's possible the second-last stack frame can't return
     (that is, it's __libc_start_main), in which case
     the CRT startup code will have set its LR to 'NULL'.  */
  if (count > 0 && array[count-1] == NULL)
    count--;

  return count;
}
weak_alias (__backtrace, backtrace)
libc_hidden_def (__backtrace)