libgcc/config/pa/linux-unwind.h

/* DWARF2 EH unwinding support for PA Linux.
   Copyright (C) 2004-2021 Free Software Foundation, Inc.

This file is part of GCC.

GCC is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3, or (at your option)
any later version.

GCC 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 General Public License for more details.

Under Section 7 of GPL version 3, you are granted additional
permissions described in the GCC Runtime Library Exception, version
3.1, as published by the Free Software Foundation.

You should have received a copy of the GNU General Public License and
a copy of the GCC Runtime Library Exception along with this program;
see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
<http://www.gnu.org/licenses/>.  */


/* Do code reading to identify a signal frame, and set the frame
   state data appropriately.  See unwind-dw2.c for the structs.  */

/* Don't use this if inhibit_libc is set.
   The build for this target will fail trying to include missing headers. */
#ifndef inhibit_libc
#include <signal.h>
#include <sys/ucontext.h>

/* Return TRUE if read access to *P is allowed.  */

static inline long
pa32_read_access_ok (void *p)
{
  long ret;

  __asm__ ("proberi (%1),3,%0" : "=r" (ret) : "r" (p) :);
  return ret;
}

/* Unfortunately, because of various bugs and changes to the kernel,
   we have several cases to deal with.

   In 2.4, the signal trampoline is 4 words, and (CONTEXT)->ra should
   point directly at the beginning of the trampoline and struct rt_sigframe.

   In <= 2.6.5-rc2-pa3, the signal trampoline is 9 words, and 
   (CONTEXT)->ra points at the 4th word in the trampoline structure.  This 
   is wrong, it should point at the 5th word.  This is fixed in 2.6.5-rc2-pa4.

   To detect these cases, we first take (CONTEXT)->ra, align it to 64-bytes
   to get the beginning of the signal frame, and then check offsets 0, 4
   and 5 to see if we found the beginning of the trampoline.  This will
   tell us how to locate the sigcontext structure.

   Note that with a 2.4 64-bit kernel, the signal context is not properly
   passed back to userspace so the unwind will not work correctly.

   There is also a bug in various glibc versions.  The (CONTEXT)->ra
   for the outermost frame is not marked as undefined, so we need to
   check whether read access is allowed for all the accesses used in
   searching for the signal trampoline.  */

#define MD_FALLBACK_FRAME_STATE_FOR pa32_fallback_frame_state

static _Unwind_Reason_Code
pa32_fallback_frame_state (struct _Unwind_Context *context,
			   _Unwind_FrameState *fs)
{
  unsigned long sp = (unsigned long)context->ra & ~63;
  unsigned int *pc = (unsigned int *)sp;
  unsigned long off;
  _Unwind_Ptr new_cfa;
  int i;
  struct sigcontext *sc;
  struct rt_sigframe {
    siginfo_t info;
    ucontext_t uc;
  } *frame;

  /* rt_sigreturn trampoline:
     3419000x ldi 0, %r25 or ldi 1, %r25   (x = 0 or 2)
     3414015a ldi __NR_rt_sigreturn, %r20
     e4008200 be,l 0x100(%sr2, %r0), %sr0, %r31
     08000240 nop  */

  if (pa32_read_access_ok (pc)
      && (pc[0] == 0x34190000 || pc[0] == 0x34190002))
    off = 4*4;
  else if (pa32_read_access_ok (&pc[4])
	   && (pc[4] == 0x34190000 || pc[4] == 0x34190002))
    {
      pc += 4;
      off = 10 * 4;
    }
  else if (pa32_read_access_ok (&pc[5])
	   && (pc[5] == 0x34190000 || pc[5] == 0x34190002))
    {
      pc += 5;
      off = 10 * 4;
    }
  else
    {
      /* We may have to unwind through an alternate signal stack.
	 We assume that the alignment of the alternate signal stack
	 is BIGGEST_ALIGNMENT (i.e., that it has been allocated using
	 malloc).  As a result, we can't distinguish trampolines
	 used prior to 2.6.5-rc2-pa4.  However after 2.6.5-rc2-pa4,
	 the return address of a signal trampoline will be on an odd
	 word boundary and we can then determine the frame offset.  */
      sp = (unsigned long)context->ra;
      pc = (unsigned int *)sp;
      if ((sp & 4)
	  && pa32_read_access_ok (pc)
	  && (pc[0] == 0x34190000 || pc[0] == 0x34190002))
	off = 5 * 4;
      else
	return _URC_END_OF_STACK;
    }

  if (!pa32_read_access_ok (&pc[3])
      || pc[1] != 0x3414015a
      || pc[2] != 0xe4008200
      || pc[3] != 0x08000240)
    return _URC_END_OF_STACK;

  frame = (struct rt_sigframe *)(sp + off);
  sc = (struct sigcontext *)&frame->uc.uc_mcontext;

  new_cfa = sc->sc_gr[30];
  fs->regs.cfa_how = CFA_REG_OFFSET;
  fs->regs.cfa_reg = 30;
  fs->regs.cfa_offset = new_cfa - (long) context->cfa;
  for (i = 1; i <= 31; i++)
    {
      fs->regs.reg[i].how = REG_SAVED_OFFSET;
      fs->regs.reg[i].loc.offset = (long)&sc->sc_gr[i] - new_cfa;
    }
  for (i = 4; i <= 31; i++)
    {
      /* FP regs have left and right halves */
      fs->regs.reg[2*i+24].how = REG_SAVED_OFFSET;
      fs->regs.reg[2*i+24].loc.offset
	= (long)&sc->sc_fr[i] - new_cfa;
      fs->regs.reg[2*i+24+1].how = REG_SAVED_OFFSET;
      fs->regs.reg[2*i+24+1].loc.offset
	= (long)&sc->sc_fr[i] + 4 - new_cfa;
    }
  fs->regs.reg[88].how = REG_SAVED_OFFSET;
  fs->regs.reg[88].loc.offset = (long) &sc->sc_sar - new_cfa;
  fs->regs.reg[__LIBGCC_DWARF_ALT_FRAME_RETURN_COLUMN__].how
    = REG_SAVED_OFFSET;
  fs->regs.reg[__LIBGCC_DWARF_ALT_FRAME_RETURN_COLUMN__].loc.offset
    = (long) &sc->sc_iaoq[0] - new_cfa;
  fs->retaddr_column = __LIBGCC_DWARF_ALT_FRAME_RETURN_COLUMN__;
  fs->signal_frame = 1;
  return _URC_NO_REASON;
}
#endif /* inhibit_libc */