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

/*
  Copyright (C) 2014-2019 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.

*/

/*  The file and functions have  'xu' because
    the .debug_cu_index and .debug_tu_index
    sections have the same layout and this deals with both.

    This is DebugFission, part of DWARF5.

    It allows fast section access in a .dwp object file
    with debug-information to locate offsets
    within and between sections.

    See the DWARF5 Standard: section 7.3.5 and
    examples in Appendix F.3.

    A note about the index field from the index table.
    See DWARF5 7.5.3.5.
    The index table array index values are [1,S)
    These value ae used to call functions requestiong
    values from the offset table and size table.

    Inside the code in this file we subtract 1 and use
    0 origin as that is how we arranged the
    table access here.
    A zero in the index table is an unused signature
    table signature and unused index.

    By subtracting one and arranging things properly
    in the offset table and size table we can refer
    to the tables in an identical simple fashion
    These tables are thus U rows and N columns.
    Technically the Offset table physically
    row zero is a separate set of numbers translating
    the column number to a DW_SECT* value
    so callers can request specific bases(offsets)
    and sizes from the offset and size tables.
    But we change things a little internally so both
    tables look zero-origin.
*/
#include "config.h"
#include <stdio.h>
#ifdef HAVE_STDLIB_H
#include <stdlib.h>
#endif /* HAVE_STDLIB_H */
#include "dwarf_incl.h"
#include "dwarf_alloc.h"
#include "dwarf_error.h"
#include "dwarf_util.h"
#include "dwarf_xu_index.h"
#include "dwarfstring.h"

#define  HASHSIGNATURELEN 8
#define  LEN32BIT   4

#define TRUE 1
#define FALSE 0

/* The following actually assumes (as used here)
    that t is 8 bytes (integer) while s is
    also 8 bytes (Dwarf_Sig8 struct). */
#ifdef WORDS_BIGENDIAN
#define ASNAR(t,s,l)                   \
    do {                                    \
        unsigned tbyte = sizeof(t) - l;     \
        if (sizeof(t) < l) {                \
            _dwarf_error(dbg,error,DW_DLE_XU_HASH_INDEX_ERROR); \
            return DW_DLV_ERROR;             \
        }                                   \
        t = 0;                              \
        dbg->de_copy_word(((char *)&t)+tbyte ,&s[0],l);\
    } while (0)
#else /* LITTLE ENDIAN */
#define ASNAR(t,s,l)                 \
    do {                                \
        t = 0;                          \
        if (sizeof(t) < l) {            \
            _dwarf_error(dbg,error,DW_DLE_XU_HASH_INDEX_ERROR); \
            return DW_DLV_ERROR;         \
        }                               \
        dbg->de_copy_word(&t,&s[0],l);  \
    } while (0)
#endif /* end LITTLE- BIG-ENDIAN */

/* zerohashkey used as all-zero-bits for comparison. */
static const Dwarf_Sig8 zerohashkey;

#if 0
static void
dump_bytes(char * msg,Dwarf_Small * start, long len)
{
    Dwarf_Small *end = start + len;
    Dwarf_Small *cur = start;

    printf("%s ",msg);
    for (; cur < end; cur++) {
        printf("%02x ", *cur);
    }
    printf("\n");
}
#endif

/*  Precondition: headerline_offset + N*32 is within
    the section. */
static int
fill_in_offsets_headerline(Dwarf_Debug dbg,
    Dwarf_Xu_Index_Header xuhdr,
    Dwarf_Unsigned headerline_offset,
    Dwarf_Unsigned num_sects,
    Dwarf_Error *err)
{
    Dwarf_Small *section_start = xuhdr->gx_section_data;
    Dwarf_Small *section_end = xuhdr->gx_section_data+
        xuhdr->gx_section_length;
    Dwarf_Small *data = 0;
    unsigned i = 0;

    data = section_start +headerline_offset;
    for( ; i < num_sects ; ++i) {
        Dwarf_Unsigned v = 0;

        READ_UNALIGNED_CK(dbg,v, Dwarf_Unsigned,
            data,LEN32BIT,
            err,section_end);
        data += LEN32BIT;
        if (v > DW_SECT_RNGLISTS) {
            dwarfstring s;

            dwarfstring_constructor(&s);
            dwarfstring_append_printf_u(&s,
                "ERROR: DW_DLE_XU_NAME_COL_ERROR  The "
                "section number of %u ",v);
            dwarfstring_append(&s," is too high. "
                "There sections 1-8 are listed in "
                "DWARF5 table 7.1.");
            _dwarf_error_string(dbg, err, DW_DLE_XU_NAME_COL_ERROR,
                dwarfstring_string(&s));
            dwarfstring_destructor(&s);
            return DW_DLV_ERROR;
        }
        xuhdr->gx_section_id[i] = v;
    }
    return DW_DLV_OK;
}


/*  Read in a cu or tu section and
    return overview information.

    For libdwarf-internal lookups
    dwarf_init*() calls
    dwarf_get_xu_index_header() when
    the object file is opened and
    dwarf_xu_header_free() is called
    by dwarf_finish(), there is
    no need for users to do this.

    If one wants to call the various
    tu/cu functions oneself (possibly to print the
    .debug_cu_index or .debug_tu_index sections).
    then you will need to call dwarf_get_xu_index_header()
    and eventually dwarf_xu_header_free().

    The libdwarf-internal data is kept in Dwarf_Debug
    fields de_cu_hashindex_data/de_tu_hashindex_data.
*/
int
dwarf_get_xu_index_header(Dwarf_Debug dbg,
    /* Pass in section_type "tu" or "cu" */
    const char *     section_type,
    Dwarf_Xu_Index_Header * xuptr,
    Dwarf_Unsigned * version,
    Dwarf_Unsigned * number_of_columns, /* L section count.*/
    Dwarf_Unsigned * number_of_CUs,     /* U unit count    */
    Dwarf_Unsigned * number_of_slots,   /* S slot count    */
    /*  Standard says S > U DWARF5 sec 7.3.5.3 */
    const char    ** section_name,
    Dwarf_Error    * error)
{
    Dwarf_Xu_Index_Header indexptr = 0;
    int res = DW_DLV_ERROR;
    struct Dwarf_Section_s *sect = 0;
    Dwarf_Unsigned local_version = 0;
    Dwarf_Unsigned num_secs  = 0;
    Dwarf_Unsigned num_CUs  = 0;
    Dwarf_Unsigned num_slots  = 0;
    Dwarf_Small *data = 0;
    Dwarf_Unsigned tables_end_offset = 0;
    Dwarf_Unsigned hash_tab_offset = 0;
    Dwarf_Unsigned indexes_tab_offset = 0;
    Dwarf_Unsigned section_offsets_tab_offset = 0;
    Dwarf_Unsigned section_offsets_headerline_offset = 0;
    Dwarf_Unsigned section_sizes_tab_offset = 0;
    unsigned datalen32 = LEN32BIT;
    Dwarf_Small *section_end = 0;

    if (!strcmp(section_type,"cu") ) {
        sect = &dbg->de_debug_cu_index;
    } else if (!strcmp(section_type,"tu") ) {
        sect = &dbg->de_debug_tu_index;
    } else {
        _dwarf_error(dbg, error, DW_DLE_XU_TYPE_ARG_ERROR);
        return DW_DLV_ERROR;
    }
    if (!sect->dss_size) {
        return DW_DLV_NO_ENTRY;
    }
    if (!sect->dss_data) {
        res = _dwarf_load_section(dbg, sect,error);
        if (res != DW_DLV_OK) {
            return res;
        }
    }

    data = sect->dss_data;
    section_end = data + sect->dss_size;

    if (sect->dss_size < (4*datalen32) ) {
        dwarfstring m;

        dwarfstring_constructor(&m);
        dwarfstring_append_printf_s(&m,
            "DW_DLE_ERRONEOUS_XU_INDEX_SECTION: "
            "The size of the %s ",(char *)section_type);
        dwarfstring_append_printf_u(&m,
            " is just %u bytes, much to small to be "
            " a correct section",sect->dss_size);
        _dwarf_error_string(dbg, error,
            DW_DLE_ERRONEOUS_XU_INDEX_SECTION,
            dwarfstring_string(&m));
        dwarfstring_destructor(&m);
        return DW_DLV_ERROR;
    }
    READ_UNALIGNED_CK(dbg,local_version, Dwarf_Unsigned,
        data,datalen32,
        error,section_end);
    data += datalen32;

    /* reading N */
    READ_UNALIGNED_CK(dbg,num_secs, Dwarf_Unsigned,
        data,datalen32,
        error,section_end);
    data += datalen32;
    /* reading U */
    READ_UNALIGNED_CK(dbg,num_CUs, Dwarf_Unsigned,
        data,datalen32,
        error,section_end);
    data += datalen32;
    /* reading S */
    READ_UNALIGNED_CK(dbg,num_slots, Dwarf_Unsigned,
        data,datalen32,
        error,section_end);
    hash_tab_offset = datalen32*4;
    indexes_tab_offset = hash_tab_offset +
        (num_slots * HASHSIGNATURELEN);
    /*  Look for corrupt section data. */
    if (num_slots > sect->dss_size) {
        dwarfstring m;

        dwarfstring_constructor(&m);
        dwarfstring_append_printf_s(&m,
            "DW_DLE_ERRONEOUS_XU_INDEX_SECTION: "
            "The size of the %s ",(char *)section_type);
        dwarfstring_append_printf_u(&m,
            " is just %u bytes,",sect->dss_size);
        dwarfstring_append_printf_u(&m,
            "while the number of slots (S) is %u. "
            "which is clearly wrong",num_slots );
        _dwarf_error_string(dbg, error,
            DW_DLE_ERRONEOUS_XU_INDEX_SECTION,
            dwarfstring_string(&m));
        dwarfstring_destructor(&m);
        return DW_DLV_ERROR;
    }
    if ( (4*num_slots) > sect->dss_size) {
        dwarfstring m;

        dwarfstring_constructor(&m);
        dwarfstring_append_printf_s(&m,
            "DW_DLE_ERRONEOUS_XU_INDEX_SECTION: "
            "The size of the %s ",(char *)section_type);
        dwarfstring_append_printf_u(&m,
            " is just %u bytes,",sect->dss_size);
        dwarfstring_append_printf_u(&m,
            "while the number of slots bytes (S) is at least %u. "
            "which is clearly wrong",num_slots*4);
        _dwarf_error_string(dbg, error,
            DW_DLE_ERRONEOUS_XU_INDEX_SECTION,
            dwarfstring_string(&m));
        dwarfstring_destructor(&m);
        return DW_DLV_ERROR;
    }

    /*  This offset is to  1 row of N columns, each 32bit. */
    section_offsets_headerline_offset = indexes_tab_offset +
        (num_slots *datalen32);
    /*  Now we can make the real table part index normally.
        This offset is to  U row of N columns, each 32bit. */
    section_offsets_tab_offset = section_offsets_headerline_offset
        + (num_secs*datalen32);
    if ( num_secs > sect->dss_size) {
        dwarfstring m;

        dwarfstring_constructor(&m);
        dwarfstring_append_printf_s(&m,
            "DW_DLE_ERRONEOUS_XU_INDEX_SECTION: "
            "The size of the %s ",(char *)section_type);
        dwarfstring_append_printf_u(&m,
            " is just %u bytes,",sect->dss_size);
        dwarfstring_append_printf_u(&m,
            "while the number of sections/columns (S) is %u. "
            "which is clearly wrong",num_secs );
        _dwarf_error_string(dbg, error,
            DW_DLE_ERRONEOUS_XU_INDEX_SECTION,
            dwarfstring_string(&m));
        dwarfstring_destructor(&m);
        return DW_DLV_ERROR;
    }
    if ( (datalen32*num_secs) > sect->dss_size) {
        dwarfstring m;

        dwarfstring_constructor(&m);
        dwarfstring_append_printf_s(&m,
            "DW_DLE_ERRONEOUS_XU_INDEX_SECTION: "
            "The size of the %s ",(char *)section_type);
        dwarfstring_append_printf_u(&m,
            " is just %u bytes,",sect->dss_size);
        dwarfstring_append_printf_u(&m,
            "while the number of sections/columns bytes (S)"
            " is at least %u. "
            "which is clearly wrong",num_secs*4);
        _dwarf_error_string(dbg, error,
            DW_DLE_ERRONEOUS_XU_INDEX_SECTION,
            dwarfstring_string(&m));
        dwarfstring_destructor(&m);
        return DW_DLV_ERROR;
    }
    section_sizes_tab_offset = section_offsets_tab_offset +
        (num_CUs *num_secs* datalen32) ;
    tables_end_offset = section_sizes_tab_offset +
        (num_CUs * num_secs * datalen32);
    if ( tables_end_offset > sect->dss_size) {
        /* Something is badly wrong here. */
        dwarfstring m;

        dwarfstring_constructor(&m);
        dwarfstring_append_printf_u(&m,"ERROR: "
            "DW_DLE_ERRONEOUS_XU_INDEX_SECTION as the end offset "
            "0x%lx is greater than ",tables_end_offset);
        dwarfstring_append_printf_u(&m,"the section size "
            "0x%lx.",sect->dss_size);
        _dwarf_error_string(dbg, error,
            DW_DLE_ERRONEOUS_XU_INDEX_SECTION,
            dwarfstring_string(&m));
        dwarfstring_destructor(&m);
        return DW_DLV_ERROR;
    }
    indexptr = (Dwarf_Xu_Index_Header)
        _dwarf_get_alloc(dbg,DW_DLA_XU_INDEX,1);
    if (indexptr == NULL) {
        _dwarf_error(dbg, error, DW_DLE_ALLOC_FAIL);
        return (DW_DLV_ERROR);
    }
    /*  Only "cu" or "tu" allowed, that is checked above.
        But for safety we just copy the allowed bytes*/
    indexptr->gx_type[0] = section_type[0];
    indexptr->gx_type[1] = section_type[1];
    indexptr->gx_type[2] = 0;
    indexptr->gx_dbg = dbg;
    indexptr->gx_section_length = sect->dss_size;
    indexptr->gx_section_data   = sect->dss_data;
    indexptr->gx_section_name   = sect->dss_name;
    indexptr->gx_version        = local_version;
    indexptr->gx_column_count_sections = num_secs;
    indexptr->gx_units_in_index = num_CUs;
    indexptr->gx_slots_in_hash  = num_slots;
    indexptr->gx_hash_table_offset  =  hash_tab_offset;
    indexptr->gx_index_table_offset = indexes_tab_offset;
    indexptr->gx_section_offsets_headerline_offset=
        section_offsets_headerline_offset;
    indexptr->gx_section_offsets_offset= section_offsets_tab_offset;
    indexptr->gx_section_sizes_offset  = section_sizes_tab_offset;
    res = fill_in_offsets_headerline(dbg,indexptr,
        section_offsets_headerline_offset,
        num_secs,error);
    if (res != DW_DLV_OK) {
        return res;
    }
    *xuptr             =     indexptr;
    *version           = indexptr->gx_version;
    *number_of_columns = indexptr->gx_column_count_sections;
    *number_of_CUs     = indexptr->gx_units_in_index;
    *number_of_slots   = indexptr->gx_slots_in_hash;
    *section_name      = indexptr->gx_section_name;
    return DW_DLV_OK;
}



int dwarf_get_xu_index_section_type(Dwarf_Xu_Index_Header xuhdr,
    /*  the function returns a pointer to
        the immutable string "tu" or "cu" via
        this arg. Do not free.  */
    const char ** typename,
    /*  the function returns a pointer to
        the immutable section name. Do not free.
        .debug_cu_index or .debug_tu_index */
    const char ** sectionname,
    UNUSEDARG Dwarf_Error * err)
{
    *typename    = &xuhdr->gx_type[0];
    *sectionname = xuhdr->gx_section_name;
    return DW_DLV_OK;
}

/*  Index values 0 to S-1 are valid. */
int dwarf_get_xu_hash_entry(Dwarf_Xu_Index_Header xuhdr,
    Dwarf_Unsigned    index,
    /* returns the hash value. 64 bits. */
    Dwarf_Sig8     *  hash_value,

    /* returns the index into rows of offset/size tables. */
    Dwarf_Unsigned *  index_to_sections,
    Dwarf_Error *     err)
{
    Dwarf_Debug dbg = xuhdr->gx_dbg;
    Dwarf_Small *hashtab = xuhdr->gx_section_data +
        xuhdr->gx_hash_table_offset;
    Dwarf_Small *indextab = xuhdr->gx_section_data +
        xuhdr->gx_index_table_offset;
    Dwarf_Small *indexentry = 0;
    Dwarf_Small *hashentry = 0;
    Dwarf_Sig8 hashval;
    Dwarf_Unsigned indexval = 0;
    Dwarf_Small *section_end = xuhdr->gx_section_data +
        xuhdr->gx_section_length;

    hashval  = zerohashkey;
    if (xuhdr->gx_slots_in_hash > 0) {
        if (index >= xuhdr->gx_slots_in_hash) {
            dwarfstring m;

            dwarfstring_constructor(&m);
            dwarfstring_append_printf_u(&m,
                "DW_DLE_XU_HASH_ROW_ERROR the index passed in, "
                " %u, is greater than the number of slots "
                " in the hash table.",index);
            _dwarf_error_string(dbg, err,  DW_DLE_XU_HASH_ROW_ERROR,
                dwarfstring_string(&m));
            dwarfstring_destructor(&m);
            return DW_DLV_ERROR;
        }
        hashentry = hashtab + (index * HASHSIGNATURELEN);
        memcpy(&hashval,hashentry,sizeof(hashval));
    } else {
        _dwarf_error_string(dbg, err,  DW_DLE_XU_HASH_ROW_ERROR,
            "DW_DLE_XU_HASH_ROW_ERROR the number of slots is zero"
            " which seems wrong.");
        return DW_DLV_ERROR;
    }

    indexentry = indextab + (index * LEN32BIT);
    memcpy(hash_value,&hashval,sizeof(hashval));
    READ_UNALIGNED_CK(dbg,indexval,Dwarf_Unsigned, indexentry,
        LEN32BIT,
        err,section_end);
    indexentry += LEN32BIT;
    if (indexval > xuhdr->gx_units_in_index) {
        _dwarf_error(dbg, err,  DW_DLE_XU_HASH_INDEX_ERROR);
        return DW_DLV_ERROR;
    }

    *index_to_sections = indexval;
    return DW_DLV_OK;
}


static const char * dwp_secnames[] = {
"No name for zero",
"DW_SECT_INFO"        /* 1 */ /*".debug_info.dwo"*/,
"DW_SECT_TYPES"       /* 2 */ /*".debug_types.dwo"*/,
"DW_SECT_ABBREV"      /* 3 */ /*".debug_abbrev.dwo"*/,
"DW_SECT_LINE"        /* 4 */ /*".debug_line.dwo"*/,
"DW_SECT_LOC"         /* 5 */ /*".debug_loc.dwo"*/,
"DW_SECT_STR_OFFSETS" /* 6 */ /*".debug_str_offsets.dwo"*/,
"DW_SECT_MACRO"       /* 7 */ /*".debug_macro.dwo"*/,
"DW_SECT_RNGLISTS"       /* 8 */ /*".debug_rnglists.dwo"*/,
"No name > 8",
};

/*  Row 0 of the Table of Section Offsets,
    columns 0 to L-1,  are the section id's,
    and names, such as DW_SECT_INFO (ie, 1)  */
int
dwarf_get_xu_section_names(Dwarf_Xu_Index_Header xuhdr,
    Dwarf_Unsigned  column_index,
    Dwarf_Unsigned* number,
    const char **   name,
    Dwarf_Error *   err)
{
    Dwarf_Unsigned sec_num = 0;
    Dwarf_Debug dbg = xuhdr->gx_dbg;

    if( column_index >= xuhdr->gx_column_count_sections) {
        dwarfstring s;

        dwarfstring_constructor(&s);
        dwarfstring_append_printf_u(&s,
            "ERROR: DW_DLE_XU_NAME_COL_ERROR as the "
            "column index of %u ",column_index);
        dwarfstring_append_printf_u(&s," is too high. "
            "There are %u sections.",
            xuhdr->gx_column_count_sections);
        _dwarf_error_string(dbg, err, DW_DLE_XU_NAME_COL_ERROR,
            dwarfstring_string(&s));
        dwarfstring_destructor(&s);
        return DW_DLV_ERROR;
    }
    sec_num = xuhdr->gx_section_id[column_index];
    if (sec_num < 1) {
        return DW_DLV_NO_ENTRY;
    }
    *number = sec_num;
    *name =  dwp_secnames[sec_num];
    return DW_DLV_OK;
}


/*  Rows 0 to U-1
    col 0 to L-1
    are section offset and length values from
    the Table of Section Offsets and Table of Section Sizes.
    The formally the table of section offsets is a header
    line of the section offsets we subtract 1 from
    the incoming irow_index as our tables are
    now zero origin. */
int
dwarf_get_xu_section_offset(Dwarf_Xu_Index_Header xuhdr,
    Dwarf_Unsigned  irow_index,
    Dwarf_Unsigned  column_index,
    Dwarf_Unsigned* sec_offset,
    Dwarf_Unsigned* sec_size,
    Dwarf_Error *   err)
{
    /* We use zero origin in the arrays, Users see
        one origin from the hash table. */
    Dwarf_Debug dbg = xuhdr->gx_dbg;
    /* get to base of tables first. */
    Dwarf_Small *offsetrow =  xuhdr->gx_section_offsets_offset +
        xuhdr->gx_section_data;
    Dwarf_Small *sizerow =  xuhdr->gx_section_sizes_offset +
        xuhdr->gx_section_data;
    Dwarf_Small *offsetentry = 0;
    Dwarf_Small *sizeentry =  0;
    Dwarf_Unsigned offset = 0;
    Dwarf_Unsigned size = 0;
    Dwarf_Unsigned column_count = xuhdr->gx_column_count_sections;
    Dwarf_Small *section_end = xuhdr->gx_section_data +
        xuhdr->gx_section_length;
    Dwarf_Unsigned row_index = irow_index-1;

    if(!irow_index) {
        dwarfstring s;

        dwarfstring_constructor(&s);
        dwarfstring_append(&s,
            "ERROR: DW_DLE_ERRONEOUS_XU_INDEX_SECTION "
            "The row index passed to dwarf_get_xu_section_offset() "
            "is zero, which is not a valid row in "
            " the offset-table or the size table as we think"
            " of them as 1-origin.");
        _dwarf_error_string(dbg, err, DW_DLE_XU_NAME_COL_ERROR,
            dwarfstring_string(&s));
        dwarfstring_destructor(&s);
        return DW_DLV_ERROR;
    }
    if( row_index >= xuhdr->gx_units_in_index) {
        dwarfstring s;

        dwarfstring_constructor(&s);
        dwarfstring_append_printf_u(&s,
            "ERROR: DW_DLE_XU_NAME_COL_ERROR as the "
            "row index of %u ",row_index);
        dwarfstring_append_printf_u(&s," is too high. "
            "Valid units must be < %u ",xuhdr->gx_units_in_index);
        _dwarf_error_string(dbg, err, DW_DLE_XU_NAME_COL_ERROR,
            dwarfstring_string(&s));
        dwarfstring_destructor(&s);
        return DW_DLV_ERROR;
    }

    if( column_index >=  xuhdr->gx_column_count_sections) {
        dwarfstring s;

        dwarfstring_constructor(&s);
        dwarfstring_append_printf_u(&s,
            "ERROR: DW_DLE_XU_NAME_COL_ERROR as the "
            "column index of %u ",column_index);
        dwarfstring_append_printf_u(&s," is too high. "
            "Valid column indexes  must be < %u ",
            xuhdr->gx_column_count_sections);
        _dwarf_error_string(dbg, err, DW_DLE_XU_NAME_COL_ERROR,
            dwarfstring_string(&s));
        dwarfstring_destructor(&s);
        return DW_DLV_ERROR;
    }
    /*  As noted above we have hidden the extra initial
        row from the offsets table so it is just
        0 to U-1. */
    offsetrow = offsetrow + (row_index*column_count * LEN32BIT);
    offsetentry = offsetrow + (column_index *  LEN32BIT);

    sizerow = sizerow + (row_index*column_count * LEN32BIT);
    sizeentry = sizerow + (column_index *  LEN32BIT);

    {
        READ_UNALIGNED_CK(dbg,offset,Dwarf_Unsigned,
            offsetentry,
            LEN32BIT,err,section_end);
        offsetentry += LEN32BIT;

        READ_UNALIGNED_CK(dbg,size,Dwarf_Unsigned,
            sizeentry,
            LEN32BIT,err,section_end);
        sizeentry += LEN32BIT;
    }
    *sec_offset = offset;
    *sec_size =  size;
    return DW_DLV_OK;
}


static int
_dwarf_search_fission_for_key(UNUSEDARG Dwarf_Debug dbg,
    Dwarf_Xu_Index_Header xuhdr,
    Dwarf_Sig8 *key_in,
    Dwarf_Unsigned * percu_index_out,
    Dwarf_Error *error)
{
    Dwarf_Unsigned key = 0;
    Dwarf_Unsigned primary_hash = 0;
    Dwarf_Unsigned hashprime = 0;
    Dwarf_Unsigned slots =  xuhdr->gx_slots_in_hash;
    Dwarf_Unsigned mask = slots -1;
    Dwarf_Sig8 hashentry_key;
    Dwarf_Unsigned percu_index = 0;

    hashentry_key = zerohashkey;
    /*  Look for corrupt section data. */
    if (slots > xuhdr->gx_section_length) {
        dwarfstring s;

        dwarfstring_constructor(&s);
        dwarfstring_append_printf_u(&s,
            "ERROR: DW_DLE_XU_NAME_COL_ERROR as the "
            "slots count of %u ",slots);
        dwarfstring_append_printf_u(&s," is too high. "
            "given the section length of %u\n",
            xuhdr->gx_section_length);
        _dwarf_error_string(dbg, error, DW_DLE_XU_NAME_COL_ERROR,
            dwarfstring_string(&s));
        dwarfstring_destructor(&s);
        return DW_DLV_ERROR;
    }
    if ( (4*slots) > xuhdr->gx_section_length) {
        dwarfstring s;

        dwarfstring_constructor(&s);
        dwarfstring_append_printf_u(&s,
            "ERROR: DW_DLE_XU_NAME_COL_ERROR as the "
            "slots count *4 of %u ",slots*4);
        dwarfstring_append_printf_u(&s," is too high. "
            "given the section length of %u\n",
            xuhdr->gx_section_length);
        _dwarf_error_string(dbg, error, DW_DLE_XU_NAME_COL_ERROR,
            dwarfstring_string(&s));
        dwarfstring_destructor(&s);
        return DW_DLV_ERROR;
    }
    if (sizeof (key) != sizeof(key_in)) {
        /* The hash won't work right in this case */
        _dwarf_error(dbg, error, DW_DLE_XU_HASH_ROW_ERROR);
    }
    ASNAR(key,key_in,sizeof(*key_in));
    primary_hash = key & mask;
    hashprime =  (((key >>32) &mask) |1);
    while (1) {
        int res = 0;

        res = dwarf_get_xu_hash_entry(xuhdr,
            primary_hash,&hashentry_key,
            &percu_index,error);
        if (res != DW_DLV_OK) {
            return res;
        }
        if (percu_index == 0 &&
            !memcmp(&hashentry_key,&zerohashkey,sizeof(Dwarf_Sig8))) {
            return DW_DLV_NO_ENTRY;
        }
        if (!memcmp(key_in,&hashentry_key,sizeof(Dwarf_Sig8))) {
            /* FOUND */
            *percu_index_out = percu_index;
            return  DW_DLV_OK;
        }
        primary_hash = (primary_hash + hashprime) % slots;
    }
    /* ASSERT: Cannot get here. */
    return DW_DLV_NO_ENTRY;
}

/* Slow. Consider tsearch. */
/* For type units and for CUs. */
/* We're finding an index entry refers
   to a global offset in some CU
   and hence is unique in the target. */
static int
_dwarf_search_fission_for_offset(Dwarf_Debug dbg,
    Dwarf_Xu_Index_Header xuhdr,
    Dwarf_Unsigned offset,
    Dwarf_Unsigned dfp_sect_num, /* DW_SECT_INFO or TYPES */
    Dwarf_Unsigned * percu_index_out,
    Dwarf_Sig8 * key_out,
    Dwarf_Error *error)
{
    Dwarf_Unsigned i = 0;
    Dwarf_Unsigned m = 0;
    int secnum_index = -1;  /* N index */
    int res = 0;

    for ( i = 0; i< xuhdr->gx_column_count_sections; i++) {
        /*  We could put the secnums array into xuhdr
            if looping here is too slow. */
        const char *name = 0;
        Dwarf_Unsigned num = 0;
        res = dwarf_get_xu_section_names(xuhdr,i,&num,&name,error);
        if (res != DW_DLV_OK) {
            return res;
        }
        if (num == dfp_sect_num) {
            secnum_index = i;
            break;
        }
    }
    if (secnum_index == -1) {
        _dwarf_error(dbg,error,DW_DLE_FISSION_SECNUM_ERR);
        return DW_DLV_ERROR;
    }
    for ( m = 0; m < xuhdr->gx_slots_in_hash; ++m) {
        Dwarf_Sig8 hash;
        Dwarf_Unsigned indexn = 0;
        Dwarf_Unsigned sec_offset = 0;
        Dwarf_Unsigned sec_size = 0;

        res = dwarf_get_xu_hash_entry(xuhdr,m,&hash,&indexn,error);
        if (res != DW_DLV_OK) {
            return res;
        }
        if (indexn == 0 &&
            !memcmp(&hash,&zerohashkey,sizeof(Dwarf_Sig8))) {
            /* Empty slot. */
            continue;
        }

        res = dwarf_get_xu_section_offset(xuhdr,
            indexn,secnum_index,&sec_offset,&sec_size,error);
        if (res != DW_DLV_OK) {
            return res;
        }
        if (sec_offset != offset) {
            continue;
        }
        *percu_index_out = indexn;
        *key_out = hash;
        return DW_DLV_OK;
    }
    return DW_DLV_NO_ENTRY;
}

static int
_dwarf_get_xuhdr(Dwarf_Debug dbg,
   const char *sigtype,
   Dwarf_Xu_Index_Header *xuout,
   Dwarf_Error *error)
{
   if (!strcmp(sigtype,"tu")) {
        if (!dbg->de_tu_hashindex_data) {
            return DW_DLV_NO_ENTRY;
        }
        *xuout = dbg->de_tu_hashindex_data;
    } else if (!strcmp(sigtype,"cu")) {
        if (!dbg->de_cu_hashindex_data) {
            return DW_DLV_NO_ENTRY;
        }
        *xuout = dbg->de_cu_hashindex_data;
    } else {
        _dwarf_error(dbg,error,DW_DLE_SIG_TYPE_WRONG_STRING);
        return DW_DLV_ERROR;
    }
    return DW_DLV_OK;

}

static int
transform_xu_to_dfp(Dwarf_Xu_Index_Header xuhdr,
    Dwarf_Unsigned percu_index,
    Dwarf_Sig8 *key,
    const char *sig_type,
    Dwarf_Debug_Fission_Per_CU *  percu_out,
    Dwarf_Error *error)
{
    unsigned i = 0;
    unsigned l = 0;
    unsigned n = 1;
    unsigned max_cols = xuhdr->gx_column_count_sections;  /* L */
    unsigned secnums[DW_FISSION_SECT_COUNT];
    int res;
    for ( i = 0; i< max_cols; i++) {
        /*  We could put the secnums array into xuhdr
            if recreating it is too slow. */
        const char *name = 0;
        Dwarf_Unsigned num = 0;
        res = dwarf_get_xu_section_names(xuhdr,i,&num,&name,error);
        if (res != DW_DLV_OK) {
            return res;
        }
        secnums[i] = num;
    }
    n = percu_index;
    for(l = 0; l < max_cols; ++l) {  /* L */
        Dwarf_Unsigned sec_off = 0;
        Dwarf_Unsigned sec_size = 0;
        unsigned l_as_sect = secnums[l];
        res = dwarf_get_xu_section_offset(xuhdr,n,l,
            &sec_off,&sec_size,error);
        if (res != DW_DLV_OK) {
            return res;
        }
        percu_out->pcu_offset[l_as_sect] = sec_off;
        percu_out->pcu_size[l_as_sect] = sec_size;
    }
    percu_out->pcu_type = sig_type;
    percu_out->pcu_index = percu_index;
    percu_out->pcu_hash = *key;
    return DW_DLV_OK;
}

/*  This should only be called for a CU, never a TU.
    For a TU the type hash is known while reading
    the TU Header.  Not so for a CU. */
int
_dwarf_get_debugfission_for_offset(Dwarf_Debug dbg,
    Dwarf_Off    offset_wanted,
    const char * key_type, /*  "cu" or "tu" */
    struct Dwarf_Debug_Fission_Per_CU_s *  percu_out,
    Dwarf_Error *error)
{
    Dwarf_Xu_Index_Header xuhdr = 0;
    int sres = 0;
    Dwarf_Unsigned percu_index = 0;
    Dwarf_Unsigned sect_index_base = 0;
    Dwarf_Sig8 key;

    sect_index_base = DW_SECT_INFO;
    key = zerohashkey;
    sres = _dwarf_get_xuhdr(dbg,key_type, &xuhdr,error);
    if (sres != DW_DLV_OK) {
        return sres;
    }
    sres = _dwarf_search_fission_for_offset(dbg,
        xuhdr,offset_wanted, sect_index_base, &percu_index,
        &key,
        error);
    if (sres != DW_DLV_OK) {
        return sres;
    }
    sres = transform_xu_to_dfp(xuhdr,percu_index,&key,
        key_type,percu_out, error);
    return sres;

}
int
dwarf_get_debugfission_for_key(Dwarf_Debug dbg,
    Dwarf_Sig8 *  key  /* pointer to hash signature */,
    const char * key_type  /*  "cu" or "tu" */,
    Dwarf_Debug_Fission_Per_CU *  percu_out,
    Dwarf_Error *  error )
{
    int sres = 0;
    Dwarf_Unsigned percu_index = 0;
    Dwarf_Xu_Index_Header xuhdr = 0;

    sres = _dwarf_load_debug_info(dbg,error);
    if (sres == DW_DLV_ERROR) {
        return sres;
    }
    sres = _dwarf_load_debug_types(dbg,error);
    if (sres == DW_DLV_ERROR) {
        return sres;
    }
    /*  Returns already existing xuhdr */
    sres = _dwarf_get_xuhdr(dbg,key_type, &xuhdr,error);
    if (sres != DW_DLV_OK) {
        return sres;
    }
    /*  Search in that xu data. */
    sres = _dwarf_search_fission_for_key(dbg,
        xuhdr,key,&percu_index,error);
    if (sres != DW_DLV_OK) {
        return sres;
    }
    sres = transform_xu_to_dfp(xuhdr,percu_index,key,
        key_type,percu_out,error);
    return sres;
}

void
dwarf_xu_header_free(Dwarf_Xu_Index_Header indexptr)
{
    if(indexptr) {
        Dwarf_Debug dbg = indexptr->gx_dbg;
        dwarf_dealloc(dbg,indexptr,DW_DLA_XU_INDEX);
    }
}