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.\" Copyright (c) 2009 Joseph Koshy.  All rights reserved.
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.\" Id: dwarf_init.3 2122 2011-11-09 15:35:14Z jkoshy 
.\"
.Dd November 9, 2011
.Os
.Dt DWARF_INIT 3
.Sh NAME
.Nm dwarf_init ,
.Nm dwarf_elf_init
.Nd allocate a DWARF debug descriptor
.Sh LIBRARY
.Lb libdwarf
.Sh SYNOPSIS
.In libdwarf.h
.Ft int
.Fo dwarf_init
.Fa "int fd"
.Fa "int mode"
.Fa "Dwarf_Handler errhand"
.Fa "Dwarf_Ptr errarg"
.Fa "Dwarf_Debug *ret"
.Fa "Dwarf_Error *err"
.Fc
.Ft in
.Fo dwarf_elf_init
.Fa "Elf *elf"
.Fa "int mode"
.Fa "Dwarf_Handler errhand"
.Fa "Dwarf_Ptr errarg"
.Fa "Dwarf_Debug *ret"
.Fa "Dwarf_Error *err"
.Fc
.Sh DESCRIPTION
These functions allocate and return a
.Vt Dwarf_Debug
instance for the object denoted by argument
.Ar fd
or
.Ar elf .
This instance would be used for subsequent access to debugging information in the object by other functions in the DWARF(3) library.
.Pp
For function
.Fn dwarf_init ,
argument
.Ar fd
denotes an open file descriptor referencing a compilation object.
Function
.Fn dwarf_init
implicitly allocates an
.Vt Elf
descriptor for argument
.Ar fd .
.Pp
For function
.Fn dwarf_elf_init ,
argument
.Ar elf
denotes a descriptor returned by
.Xr elf_begin 3
or
.Xr elf_memory 3 .
.Pp
Argument
.Ar mode
specifies the access mode desired.
It should be at least as permissive as the mode with which
the file descriptor
.Ar fd
or the ELF descriptor
.Ar elf
was created with.
Legal values for argument
.Ar mode
are:
.Pp
.Bl -tag -width "DW_DLC_WRITE" -compact
.It DW_DLC_RDWR
Permit reading and writing of DWARF information.
.It DW_DLC_READ
Operate in read-only mode.
.It DW_DLC_WRITE
Permit writing of DWARF information.
.El
.Pp
Argument
.Ar errhand
denotes a function to be called in case of an error.
If this argument is
.Dv NULL
then a default error handling scheme is used.
See
.Xr dwarf 3
for a description of the error handling scheme used by the
DWARF(3) library.
.Pp
Argument
.Ar errarg
is passed to the error handler function denoted by argument
.Ar errhand
when it is invoked.
.Pp
Argument
.Ar ret
points to the memory location that will hold a
.Vt Dwarf_Debug
reference on a successful call these functions.
.Pp
Argument
.Ar err
references a memory location that would hold a
.Vt Dwarf_Error
descriptor in case of an error.
.Ss Memory Management
The
.Vt Dwarf_Debug
instance returned by these functions should be freed using
.Fn dwarf_finish .
.Sh RETURN VALUES
These functions return the following values:
.Bl -tag -width ".Bq Er DW_DLV_NO_ENTRY"
.It Bq Er DW_DLV_OK
This return value indicates a successful return.
.It Bq Er DW_DLV_ERROR
The operation failed.
.It Bq Er DW_DLV_NO_ENTRY
The object specified by arguments
.Ar "fd"
or
.Ar "elf"
did not contain debug information.
.El
.Sh IMPLEMENTATION NOTES
The current implementation does not support access modes
.Dv DW_DLC_RDWR
and
.Dv DW_DLC_WRITE .
.Sh EXAMPLES
To initialize a
.Vt Dwarf_Debug
instance from a open file descriptor referencing an ELF object, and
with the default error handler, use:
.Bd -literal -offset indent
Dwarf_Error err;
Dwarf_Debug dbg;

if (dwarf_init(fd, DW_DLC_READ, NULL, NULL, &dbg, &err) !=
    DW_DLV_OK)
	errx(EXIT_FAILURE, "dwarf_init: %s", dwarf_errmsg(err));
.Ed
.Sh SEE ALSO
.Xr dwarf 3 ,
.Xr dwarf_errmsg 3 ,
.Xr dwarf_finish 3 ,
.Xr dwarf_get_elf 3 ,
.Xr elf_begin 3 ,
.Xr elf_memory 3