glibc/sysdeps/generic/unwind-pe.h

/* Exception handling and frame unwind runtime interface routines.
   Copyright (C) 2001-2021 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 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/>.  */

/* @@@ Really this should be out of line, but this also causes link
   compatibility problems with the base ABI.  This is slightly better
   than duplicating code, however.  */

/* If using C++, references to abort have to be qualified with std::.  */
#ifdef __cplusplus
#define __gxx_abort std::abort
#else
#define __gxx_abort abort
#endif

/* Pointer encodings, from dwarf2.h.  */
#define DW_EH_PE_absptr         0x00
#define DW_EH_PE_omit           0xff

#define DW_EH_PE_uleb128        0x01
#define DW_EH_PE_udata2         0x02
#define DW_EH_PE_udata4         0x03
#define DW_EH_PE_udata8         0x04
#define DW_EH_PE_sleb128        0x09
#define DW_EH_PE_sdata2         0x0A
#define DW_EH_PE_sdata4         0x0B
#define DW_EH_PE_sdata8         0x0C
#define DW_EH_PE_signed         0x08

#define DW_EH_PE_pcrel          0x10
#define DW_EH_PE_textrel        0x20
#define DW_EH_PE_datarel        0x30
#define DW_EH_PE_funcrel        0x40
#define DW_EH_PE_aligned        0x50

#define DW_EH_PE_indirect	0x80


#if defined(_LIBC)

/* Prototypes.  */
extern unsigned int size_of_encoded_value (unsigned char encoding)
  attribute_hidden;

extern const unsigned char *read_encoded_value_with_base
  (unsigned char encoding, _Unwind_Ptr base,
   const unsigned char *p, _Unwind_Ptr *val)
  attribute_hidden;

extern const unsigned char * read_encoded_value
  (struct _Unwind_Context *context, unsigned char encoding,
   const unsigned char *p, _Unwind_Ptr *val)
  attribute_hidden;

extern const unsigned char * read_uleb128 (const unsigned char *p,
					   _Unwind_Word *val)
  attribute_hidden;
extern const unsigned char * read_sleb128 (const unsigned char *p,
					   _Unwind_Sword *val)
  attribute_hidden;

#endif
#if defined(_LIBC) && defined(_LIBC_DEFINITIONS)

#ifdef _LIBC
#define STATIC
#else
#define STATIC static
#endif

/* Given an encoding, return the number of bytes the format occupies.
   This is only defined for fixed-size encodings, and so does not
   include leb128.  */

STATIC unsigned int
size_of_encoded_value (unsigned char encoding)
{
  if (encoding == DW_EH_PE_omit)
    return 0;

  switch (encoding & 0x07)
    {
    case DW_EH_PE_absptr:
      return sizeof (void *);
    case DW_EH_PE_udata2:
      return 2;
    case DW_EH_PE_udata4:
      return 4;
    case DW_EH_PE_udata8:
      return 8;
    }
  __gxx_abort ();
}

#ifndef NO_BASE_OF_ENCODED_VALUE

/* Given an encoding and an _Unwind_Context, return the base to which
   the encoding is relative.  This base may then be passed to
   read_encoded_value_with_base for use when the _Unwind_Context is
   not available.  */

STATIC _Unwind_Ptr
base_of_encoded_value (unsigned char encoding, struct _Unwind_Context *context)
{
  if (encoding == DW_EH_PE_omit)
    return 0;

  switch (encoding & 0x70)
    {
    case DW_EH_PE_absptr:
    case DW_EH_PE_pcrel:
    case DW_EH_PE_aligned:
      return 0;

    case DW_EH_PE_textrel:
      return _Unwind_GetTextRelBase (context);
    case DW_EH_PE_datarel:
      return _Unwind_GetDataRelBase (context);
    case DW_EH_PE_funcrel:
      return _Unwind_GetRegionStart (context);
    }
  __gxx_abort ();
}

#endif

/* Read an unsigned leb128 value from P, store the value in VAL, return
   P incremented past the value.  We assume that a word is large enough to
   hold any value so encoded; if it is smaller than a pointer on some target,
   pointers should not be leb128 encoded on that target.  */

STATIC const unsigned char *
read_uleb128 (const unsigned char *p, _Unwind_Word *val)
{
  unsigned int shift = 0;
  unsigned char byte;
  _Unwind_Word result;

  result = 0;
  do
    {
      byte = *p++;
      result |= (byte & 0x7f) << shift;
      shift += 7;
    }
  while (byte & 0x80);

  *val = result;
  return p;
}

/* Similar, but read a signed leb128 value.  */

STATIC const unsigned char *
read_sleb128 (const unsigned char *p, _Unwind_Sword *val)
{
  unsigned int shift = 0;
  unsigned char byte;
  _Unwind_Word result;

  result = 0;
  do
    {
      byte = *p++;
      result |= (byte & 0x7f) << shift;
      shift += 7;
    }
  while (byte & 0x80);

  /* Sign-extend a negative value.  */
  if (shift < 8 * sizeof (result) && (byte & 0x40) != 0)
    result |= -(1L << shift);

  *val = (_Unwind_Sword) result;
  return p;
}

/* Load an encoded value from memory at P.  The value is returned in VAL;
   The function returns P incremented past the value.  BASE is as given
   by base_of_encoded_value for this encoding in the appropriate context.  */

STATIC const unsigned char *
read_encoded_value_with_base (unsigned char encoding, _Unwind_Ptr base,
			      const unsigned char *p, _Unwind_Ptr *val)
{
  union unaligned
    {
      void *ptr;
      unsigned u2 __attribute__ ((mode (HI)));
      unsigned u4 __attribute__ ((mode (SI)));
      unsigned u8 __attribute__ ((mode (DI)));
      signed s2 __attribute__ ((mode (HI)));
      signed s4 __attribute__ ((mode (SI)));
      signed s8 __attribute__ ((mode (DI)));
    } __attribute__((__packed__));

  union unaligned *u = (union unaligned *) p;
  _Unwind_Internal_Ptr result;

  if (encoding == DW_EH_PE_aligned)
    {
      _Unwind_Internal_Ptr a = (_Unwind_Internal_Ptr) p;
      a = (a + sizeof (void *) - 1) & - sizeof (void *);
      result = *(_Unwind_Internal_Ptr *) a;
      p = (const unsigned char *) (a + sizeof (void *));
    }
  else
    {
      switch (encoding & 0x0f)
	{
	case DW_EH_PE_absptr:
	  result = (_Unwind_Internal_Ptr) u->ptr;
	  p += sizeof (void *);
	  break;

	case DW_EH_PE_uleb128:
	  {
	    _Unwind_Word tmp;
	    p = read_uleb128 (p, &tmp);
	    result = (_Unwind_Internal_Ptr) tmp;
	  }
	  break;

	case DW_EH_PE_sleb128:
	  {
	    _Unwind_Sword tmp;
	    p = read_sleb128 (p, &tmp);
	    result = (_Unwind_Internal_Ptr) tmp;
	  }
	  break;

	case DW_EH_PE_udata2:
	  result = u->u2;
	  p += 2;
	  break;
	case DW_EH_PE_udata4:
	  result = u->u4;
	  p += 4;
	  break;
	case DW_EH_PE_udata8:
	  result = u->u8;
	  p += 8;
	  break;

	case DW_EH_PE_sdata2:
	  result = u->s2;
	  p += 2;
	  break;
	case DW_EH_PE_sdata4:
	  result = u->s4;
	  p += 4;
	  break;
	case DW_EH_PE_sdata8:
	  result = u->s8;
	  p += 8;
	  break;

	default:
	  __gxx_abort ();
	}

      if (result != 0)
	{
	  result += ((encoding & 0x70) == DW_EH_PE_pcrel
		     ? (_Unwind_Internal_Ptr) u : base);
	  if (encoding & DW_EH_PE_indirect)
	    result = *(_Unwind_Internal_Ptr *) result;
	}
    }

  *val = result;
  return p;
}

#ifndef NO_BASE_OF_ENCODED_VALUE

/* Like read_encoded_value_with_base, but get the base from the context
   rather than providing it directly.  */

STATIC const unsigned char *
read_encoded_value (struct _Unwind_Context *context, unsigned char encoding,
		    const unsigned char *p, _Unwind_Ptr *val)
{
  return read_encoded_value_with_base (encoding,
		base_of_encoded_value (encoding, context),
		p, val);
}

#endif
#endif /* _LIBC */