1.\"	$NetBSD: dwarf_new_expr.3,v 1.2 2014/03/09 16:58:04 christos Exp $
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3.\" Copyright (c) 2011 Kai Wang
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27.\" Id: dwarf_new_expr.3 2074 2011-10-27 03:34:33Z jkoshy
28.\"
29.Dd September 8, 2011
30.Os
31.Dt DWARF_NEW_EXPR 3
32.Sh NAME
33.Nm dwarf_new_expr
34.Nd create a location expression descriptor
35.Sh LIBRARY
36.Lb libdwarf
37.Sh SYNOPSIS
38.In libdwarf.h
39.Ft "Dwarf_P_Expr"
40.Fo dwarf_new_expr
41.Fa "Dwarf_P_Debug dbg"
42.Fa "Dwarf_Error *err"
43.Fc
44.Sh DESCRIPTION
45Function
46.Fn dwarf_new_expr
47allocates a DWARF location expression descriptor used to build up a
48location expression stream.
49.Pp
50The application can use the functions
51.Xr dwarf_add_expr_gen 3
52and
53.Xr dwarf_add_expr_addr_b 3
54to add location expression operators to the created descriptor.
55When done, the application can call the function
56.Xr dwarf_expr_into_block 3
57to retrieve the generated byte stream for the location expression,
58or call the function
59.Xr dwarf_add_AT_location_expr 3
60to create an attribute with the location expression stream as its
61value.
62.Pp
63Argument
64.Ar dbg
65should reference a DWARF producer instance allocated using
66.Xr dwarf_producer_init 3
67or
68.Xr dwarf_producer_init_b 3 .
69.Pp
70If argument
71.Ar err
72is not NULL, it will be used to store error information in case
73of an error.
74.Sh RETURN VALUES
75On success, function
76.Fn dwarf_new_expr
77returns the created location expression descriptor.
78In case of an error, function
79.Fn dwarf_new_expr
80returns
81.Dv DW_DLV_BADADDR
82and sets the argument
83.Ar err .
84.Sh ERRORS
85Function
86.Fn dwarf_new_expr
87can fail with:
88.Bl -tag -width ".Bq Er DW_DLE_ARGUMENT"
89.It Bq Er DW_DLE_ARGUMENT
90Argument
91.Ar dbg
92was NULL.
93.It Bq Er DW_DLE_MEMORY
94An out of memory condition was encountered during the execution of
95the function.
96.El
97.Sh EXAMPLES
98To create a location expression descriptor, add location expression
99operators to it and to retrieve the generated byte stream,
100use:
101.Bd -literal -offset indent
102Dwarf_P_Debug dbg;
103Dwarf_Error de;
104Dwarf_P_Expr pe;
105Dwarf_Addr buf;
106Dwarf_Unsigned len;
107
108/* ...Assume that `dbg' refers to a DWARF producer instance... */
109
110if ((pe = dwarf_new_expr(dbg, &de)) == DW_DLV_BADADDR) {
111	warnx("dwarf_new_expr failed: %s", dwarf_errmsg(-1));
112	return;
113}
114
115if (dwarf_add_expr_gen(pe, DW_OP_regx, 55, 0, &de) ==
116    DW_DLV_NOCOUNT) {
117	warnx("dwarf_add_expr_gen failed: %s", dwarf_errmsg(-1));
118	return;
119}
120
121if ((buf = dwarf_expr_into_block(pe, &len, &de)) ==
122    DW_DLV_BADADDR) {
123	warnx("dwarf_expr_into_block failed: %s",
124	    dwarf_errmsg(-1));
125	return;
126}
127.Ed
128.Sh SEE ALSO
129.Xr dwarf 3 ,
130.Xr dwarf_add_AT_location_expr 3 ,
131.Xr dwarf_add_expr_gen 3 ,
132.Xr dwarf_add_expr_addr 3 ,
133.Xr dwarf_add_expr_addr_b 3 ,
134.Xr dwarf_expr_current_offset 3 ,
135.Xr dwarf_expr_into_block 3 ,
136.Xr dwarf_producer_init 3 ,
137.Xr dwarf_producer_init_b 3
138