xref: /illumos-gate/usr/src/lib/libdwarf/common/dwarf_leb.c (revision 4d9fdb46)

/*
  Copyright (C) 2000,2004 Silicon Graphics, Inc.  All Rights Reserved.
  Portions Copyright 2011-2018 David Anderson. All Rights Reserved.

  This program is free software; you can redistribute it and/or modify it
  under the terms of version 2.1 of the GNU Lesser General Public License
  as published by the Free Software Foundation.

  This program is distributed in the hope that it would be useful, but
  WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

  Further, this software is distributed without any warranty that it is
  free of the rightful claim of any third person regarding infringement
  or the like.  Any license provided herein, whether implied or
  otherwise, applies only to this software file.  Patent licenses, if
  any, provided herein do not apply to combinations of this program with
  other software, or any other product whatsoever.

  You should have received a copy of the GNU Lesser General Public
  License along with this program; if not, write the Free Software
  Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston MA 02110-1301,
  USA.

*/


#include "config.h"
#include <stdio.h>
#include "dwarf_incl.h"
#include "dwarf_error.h"
#include "dwarf_util.h"

/*  Note that with 'make check')
    many of the test items
    only make sense if Dwarf_Unsigned (and Dwarf_Signed)
    are 64 bits.  The encode/decode logic should
    be fine whether those types are 64 or 32 bits.
    See runtests.sh */

/*  10 bytes of leb, 7 bits each part of the number, gives
    room for a 64bit number.
    While any number of leading zeroes would be legal, so
    no max is really truly required here, why would a
    compiler generate leading zeros?  That would
    be strange.
*/
#define BYTESLEBMAX 10
#define BITSPERBYTE 8


/* Decode ULEB with checking */
int
_dwarf_decode_u_leb128_chk(Dwarf_Small * leb128,
    Dwarf_Unsigned * leb128_length,
    Dwarf_Unsigned *outval,
    Dwarf_Byte_Ptr endptr)
{
    Dwarf_Unsigned byte     = 0;
    Dwarf_Unsigned word_number = 0;
    Dwarf_Unsigned number  = 0;
    unsigned shift      = 0;
    /*  The byte_length value will be a small non-negative integer. */
    unsigned byte_length   = 0;

    if (leb128 >=endptr) {
        return DW_DLV_ERROR;
    }
    /*  The following unrolls-the-loop for the first two bytes and
        unpacks into 32 bits to make this as fast as possible.
        word_number is assumed big enough that the shift has a defined
        result. */
    if ((*leb128 & 0x80) == 0) {
        if (leb128_length) {
            *leb128_length = 1;
        }
        *outval = *leb128;
        return DW_DLV_OK;
    } else {
        if ((leb128+1) >=endptr) {
            return DW_DLV_ERROR;
        }
        if ((*(leb128 + 1) & 0x80) == 0) {
            if (leb128_length) {
                *leb128_length = 2;
            }
            word_number = *leb128 & 0x7f;
            word_number |= (*(leb128 + 1) & 0x7f) << 7;
            *outval = word_number;
            return DW_DLV_OK;
        }
        /* Gets messy to hand-inline more byte checking. */
    }

    /*  The rest handles long numbers Because the 'number' may be larger
        than the default int/unsigned, we must cast the 'byte' before
        the shift for the shift to have a defined result. */
    number = 0;
    shift = 0;
    byte_length = 1;
    byte = *leb128;
    for (;;) {
        if (shift >= (sizeof(number)*BITSPERBYTE)) {
            return DW_DLV_ERROR;
        }
        number |= (byte & 0x7f) << shift;
        if ((byte & 0x80) == 0) {
            if (leb128_length) {
                *leb128_length = byte_length;
            }
            *outval = number;
            return DW_DLV_OK;
        }
        shift += 7;
        byte_length++;
        if (byte_length > BYTESLEBMAX) {
            /*  Erroneous input.  */
            if( leb128_length) {
                *leb128_length = BYTESLEBMAX;
            }
            break;
        }
        ++leb128;
        if ((leb128) >=endptr) {
            return DW_DLV_ERROR;
        }
        byte = *leb128;
    }
    return DW_DLV_ERROR;
}


#define BITSINBYTE 8

int
_dwarf_decode_s_leb128_chk(Dwarf_Small * leb128, Dwarf_Unsigned * leb128_length,
    Dwarf_Signed *outval,Dwarf_Byte_Ptr endptr)
{
    Dwarf_Unsigned byte   = 0;
    Dwarf_Signed number  = 0;
    Dwarf_Bool sign      = 0;
    Dwarf_Unsigned shift     = 0;
    /*  The byte_length value will be a small non-negative integer. */
    unsigned byte_length = 1;

    /*  byte_length being the number of bytes of data absorbed so far in
        turning the leb into a Dwarf_Signed. */
    if (!outval) {
        return DW_DLV_ERROR;
    }
    if (leb128 >= endptr) {
        return DW_DLV_ERROR;
    }
    byte   = *leb128;
    for (;;) {
        sign = byte & 0x40;
        if (shift >= (sizeof(number)*BITSPERBYTE)) {
            return DW_DLV_ERROR;
        }
        number |= ((Dwarf_Unsigned) ((byte & 0x7f))) << shift;
        shift += 7;

        if ((byte & 0x80) == 0) {
            break;
        }
        ++leb128;
        if (leb128 >= endptr) {
            return DW_DLV_ERROR;
        }
        byte = *leb128;
        byte_length++;
        if (byte_length > BYTESLEBMAX) {
            /*  Erroneous input. */
            if (leb128_length) {
                *leb128_length = BYTESLEBMAX;
            }
            return DW_DLV_ERROR;
        }
    }

    if (sign) {
        /* The following avoids undefined behavior. */
        unsigned shiftlim = sizeof(Dwarf_Signed) * BITSINBYTE -1;
        if (shift < shiftlim) {
            number |= -(Dwarf_Signed)(((Dwarf_Unsigned)1) << shift);
        } else if (shift == shiftlim) {
            number |= (((Dwarf_Unsigned)1) << shift);
        }
    }

    if (leb128_length) {
        *leb128_length = byte_length;
    }
    *outval = number;
    return DW_DLV_OK;
}