.\" Copyright (c) 2011 Kai Wang
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.\" $Id: dwarf_new_expr.3 3644 2018-10-15 19:55:01Z jkoshy $
.\"
.Dd September 8, 2011
.Dt DWARF_NEW_EXPR 3
.Os
.Sh NAME
.Nm dwarf_new_expr
.Nd create a location expression descriptor
.Sh LIBRARY
.Lb libdwarf
.Sh SYNOPSIS
.In libdwarf.h
.Ft "Dwarf_P_Expr"
.Fo dwarf_new_expr
.Fa "Dwarf_P_Debug dbg"
.Fa "Dwarf_Error *err"
.Fc
.Sh DESCRIPTION
Function
.Fn dwarf_new_expr
allocates a DWARF location expression descriptor used to build up a
location expression stream.
.Pp
The application can use the functions
.Xr dwarf_add_expr_gen 3
and
.Xr dwarf_add_expr_addr_b 3
to add location expression operators to the created descriptor.
When done, the application can call the function
.Xr dwarf_expr_into_block 3
to retrieve the generated byte stream for the location expression,
or call the function
.Xr dwarf_add_AT_location_expr 3
to create an attribute with the location expression stream as its
value.
.Pp
Argument
.Ar dbg
should reference a DWARF producer instance allocated using
.Xr dwarf_producer_init 3
or
.Xr dwarf_producer_init_b 3 .
.Pp
If argument
.Ar err
is not NULL, it will be used to store error information in case
of an error.
.Sh RETURN VALUES
On success, function
.Fn dwarf_new_expr
returns the created location expression descriptor.
In case of an error, function
.Fn dwarf_new_expr
returns
.Dv DW_DLV_BADADDR
and sets the argument
.Ar err .
.Sh EXAMPLES
To create a location expression descriptor, add location expression
operators to it and to retrieve the generated byte stream,
use:
.Bd -literal -offset indent
Dwarf_P_Debug dbg;
Dwarf_Error de;
Dwarf_P_Expr pe;
Dwarf_Addr buf;
Dwarf_Unsigned len;

/* ...Assume that `dbg' refers to a DWARF producer instance... */

if ((pe = dwarf_new_expr(dbg, &de)) == DW_DLV_BADADDR) {
	warnx("dwarf_new_expr failed: %s", dwarf_errmsg(-1));
	return;
}

if (dwarf_add_expr_gen(pe, DW_OP_regx, 55, 0, &de) ==
    DW_DLV_NOCOUNT) {
	warnx("dwarf_add_expr_gen failed: %s", dwarf_errmsg(-1));
	return;
}

if ((buf = dwarf_expr_into_block(pe, &len, &de)) ==
    DW_DLV_BADADDR) {
	warnx("dwarf_expr_into_block failed: %s",
	    dwarf_errmsg(-1));
	return;
}
.Ed
.Sh ERRORS
Function
.Fn dwarf_new_expr
can fail with:
.Bl -tag -width ".Bq Er DW_DLE_ARGUMENT"
.It Bq Er DW_DLE_ARGUMENT
Argument
.Ar dbg
was NULL.
.It Bq Er DW_DLE_MEMORY
An out of memory condition was encountered during the execution of
the function.
.El
.Sh SEE ALSO
.Xr dwarf 3 ,
.Xr dwarf_add_AT_location_expr 3 ,
.Xr dwarf_add_expr_addr 3 ,
.Xr dwarf_add_expr_addr_b 3 ,
.Xr dwarf_add_expr_gen 3 ,
.Xr dwarf_expr_current_offset 3 ,
.Xr dwarf_expr_into_block 3 ,
.Xr dwarf_producer_init 3 ,
.Xr dwarf_producer_init_b 3