1.\" Copyright (c) 2011 Kai Wang
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25.\" $Id: dwarf_new_expr.3 3644 2018-10-15 19:55:01Z jkoshy $
26.\"
27.Dd September 8, 2011
28.Dt DWARF_NEW_EXPR 3
29.Os
30.Sh NAME
31.Nm dwarf_new_expr
32.Nd create a location expression descriptor
33.Sh LIBRARY
34.Lb libdwarf
35.Sh SYNOPSIS
36.In libdwarf.h
37.Ft "Dwarf_P_Expr"
38.Fo dwarf_new_expr
39.Fa "Dwarf_P_Debug dbg"
40.Fa "Dwarf_Error *err"
41.Fc
42.Sh DESCRIPTION
43Function
44.Fn dwarf_new_expr
45allocates a DWARF location expression descriptor used to build up a
46location expression stream.
47.Pp
48The application can use the functions
49.Xr dwarf_add_expr_gen 3
50and
51.Xr dwarf_add_expr_addr_b 3
52to add location expression operators to the created descriptor.
53When done, the application can call the function
54.Xr dwarf_expr_into_block 3
55to retrieve the generated byte stream for the location expression,
56or call the function
57.Xr dwarf_add_AT_location_expr 3
58to create an attribute with the location expression stream as its
59value.
60.Pp
61Argument
62.Ar dbg
63should reference a DWARF producer instance allocated using
64.Xr dwarf_producer_init 3
65or
66.Xr dwarf_producer_init_b 3 .
67.Pp
68If argument
69.Ar err
70is not NULL, it will be used to store error information in case
71of an error.
72.Sh RETURN VALUES
73On success, function
74.Fn dwarf_new_expr
75returns the created location expression descriptor.
76In case of an error, function
77.Fn dwarf_new_expr
78returns
79.Dv DW_DLV_BADADDR
80and sets the argument
81.Ar err .
82.Sh EXAMPLES
83To create a location expression descriptor, add location expression
84operators to it and to retrieve the generated byte stream,
85use:
86.Bd -literal -offset indent
87Dwarf_P_Debug dbg;
88Dwarf_Error de;
89Dwarf_P_Expr pe;
90Dwarf_Addr buf;
91Dwarf_Unsigned len;
92
93/* ...Assume that `dbg' refers to a DWARF producer instance... */
94
95if ((pe = dwarf_new_expr(dbg, &de)) == DW_DLV_BADADDR) {
96	warnx("dwarf_new_expr failed: %s", dwarf_errmsg(-1));
97	return;
98}
99
100if (dwarf_add_expr_gen(pe, DW_OP_regx, 55, 0, &de) ==
101    DW_DLV_NOCOUNT) {
102	warnx("dwarf_add_expr_gen failed: %s", dwarf_errmsg(-1));
103	return;
104}
105
106if ((buf = dwarf_expr_into_block(pe, &len, &de)) ==
107    DW_DLV_BADADDR) {
108	warnx("dwarf_expr_into_block failed: %s",
109	    dwarf_errmsg(-1));
110	return;
111}
112.Ed
113.Sh ERRORS
114Function
115.Fn dwarf_new_expr
116can fail with:
117.Bl -tag -width ".Bq Er DW_DLE_ARGUMENT"
118.It Bq Er DW_DLE_ARGUMENT
119Argument
120.Ar dbg
121was NULL.
122.It Bq Er DW_DLE_MEMORY
123An out of memory condition was encountered during the execution of
124the function.
125.El
126.Sh SEE ALSO
127.Xr dwarf 3 ,
128.Xr dwarf_add_AT_location_expr 3 ,
129.Xr dwarf_add_expr_addr 3 ,
130.Xr dwarf_add_expr_addr_b 3 ,
131.Xr dwarf_add_expr_gen 3 ,
132.Xr dwarf_expr_current_offset 3 ,
133.Xr dwarf_expr_into_block 3 ,
134.Xr dwarf_producer_init 3 ,
135.Xr dwarf_producer_init_b 3
136