.\"	$NetBSD: dwarf_get_abbrev.3,v 1.3 2016/02/20 02:43:41 christos Exp $
.\"
.\" Copyright (c) 2011 Kai Wang
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" Id: dwarf_get_abbrev.3 2071 2011-10-27 03:20:00Z jkoshy 
.\"
.Dd March 27, 2011
.Os
.Dt DWARF_GET_ABBREV 3
.Sh NAME
.Nm dwarf_get_abbrev
.Nd retrieve abbreviation information
.Sh LIBRARY
.Lb libdwarf
.Sh SYNOPSIS
.In libdwarf.h
.Ft int
.Fo dwarf_get_abbrev
.Fa "Dwarf_Debug dbg"
.Fa "Dwarf_Unsigned offset"
.Fa "Dwarf_Abbrev *ret_abbrev"
.Fa "Dwarf_Unsigned *length"
.Fa "Dwarf_Unsigned *attr_count"
.Fa "Dwarf_Error *err"
.Fc
.Sh DESCRIPTION
Function
.Fn dwarf_get_abbrev
retrieves information about an abbreviation from the DWARF abbreviations
section,
.Dq ".debug_abbrev" .
Abbreviation information is returned using an opaque descriptor
of type
.Vt Dwarf_Abbrev .
The returned
.Vt Dwarf_Abbrev
descriptor may then be passed to the other abbreviation related APIs
in the DWARF(3) API to retrieve specific information about the
abbreviation.
.Pp
Argument
.Ar dbg
should reference a DWARF debug context allocated using
.Xr dwarf_init 3 .
.Pp
Argument
.Ar offset
should be an offset, relative to the
.Dq ".debug_abbrev"
section, to the start of an abbreviation entry.
.Pp
Argument
.Ar ret_abbrev
should point to a location that will hold a pointer to the
returned
.Vt Dwarf_Abbrev
descriptor.
.Pp
Argument
.Ar length
should point to a location that will hold the number of bytes used
by the abbrevation in the DWARF
.Dq ".debug_abbrev"
section.
.Pp
Argument
.Ar attr_count
should point to a location that will hold the number of
attributes in the abbrevation.
.Pp
If argument
.Ar err
is not NULL, it will be used to store error information in case of an
error.
.Ss Memory Management
The memory area used for the
.Vt Dwarf_Abbrev
descriptor returned in argument
.Ar ret_abbrev
is allocated by the
.Lb libdwarf .
Application code should use function
.Fn dwarf_dealloc
with the allocation type
.Dv DW_DLA_ABBREV
to free the memory area when the
.Vt Dwarf_Abbrev
descriptor is no longer needed.
.Ss Application Programming Notes
The last abbreviation entry in a standard DWARF abbreviation section
will have a special length value of 1.
.Sh RETURN VALUES
Function
.Fn dwarf_get_abbrev
returns
.Dv DW_DLV_OK
when it succeeds.
It returns
.Dv DW_DLV_NO_ENTRY
if there is no abbreviation information at offset
.Ar offset .
In case of an error, it returns
.Dv DW_DLV_ERROR
and sets the argument
.Ar err .
.Sh ERRORS
Function
.Fn dwarf_get_abbrev
can fail with:
.Bl -tag -width ".Bq Er DW_DLE_NO_ENTRY"
.It Bq Er DW_DLE_ARGUMENT
One of the arguments
.Ar dbg ,
.Ar ret_abbrev ,
.Ar length
or
.Ar attr_count
was NULL.
.It Bq Er DW_DLE_NO_ENTRY
There is no abbreviation information at offset
.Ar offset .
.El
.Sh EXAMPLE
To loop through all the abbreviation information associated with
a DWARF debug context, use:
.Bd -literal -offset indent
Dwarf_Debug dbg;
Dwarf_Abbrev ab;
Dwarf_Off aboff;
Dwarf_Unsigned length, attr_count;
Dwarf_Half tag;
Dwarf_Error de;
int ret;

while ((ret = dwarf_next_cu_header(dbg, NULL, NULL, &aboff,
    NULL, NULL, &de)) ==  DW_DLV_OK) {
	while ((ret = dwarf_get_abbrev(re->dbg, aboff, &ab, &length,
	    &attr_count, &de)) == DW_DLV_OK) {
		if (length == 1)	/* Last entry. */
			break;
		aboff += length;
		if (dwarf_get_abbrev_tag(ab, &tag, &de) != DW_DLV_OK) {
			warnx("dwarf_get_abbrev_tag failed: %s",
			    dwarf_errmsg(de));
			continue;
		}
	if (ret != DW_DLV_OK)
		warnx("dwarf_get_abbrev: %s", dwarf_errmsg(de));
}
if (ret == DW_DLV_ERROR)
	warnx("dwarf_next_cu_header: %s", dwarf_errmsg(de));
.Ed
.Sh SEE ALSO
.Xr dwarf 3 ,
.Xr dwarf_dealloc 3 ,
.Xr dwarf_get_abbrev_tag 3 ,
.Xr dwarf_get_abbrev_code 3 ,
.Xr dwarf_get_abbrev_children_flag 3 ,
.Xr dwarf_get_abbrev_entry 3