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24.\" $Id: elf_getscn.3 3639 2018-10-14 14:07:02Z jkoshy $
25.\"
26.Dd September 24, 2018
27.Dt ELF_GETSCN 3
28.Os
29.Sh NAME
30.Nm elf_getscn ,
31.Nm elf_ndxscn ,
32.Nm elf_newscn ,
33.Nm elf_nextscn
34.Nd get/allocate section information for an ELF object
35.Sh LIBRARY
36.Lb libelf
37.Sh SYNOPSIS
38.In libelf.h
39.Ft "Elf_Scn *"
40.Fn elf_getscn "Elf *elf" "size_t index"
41.Ft size_t
42.Fn elf_ndxscn "Elf_Scn *scn"
43.Ft "Elf_Scn *"
44.Fn elf_newscn "Elf *elf"
45.Ft "Elf_Scn *"
46.Fn elf_nextscn "Elf *elf" "Elf_Scn *scn"
47.Sh DESCRIPTION
48These functions are used to iterate through the sections associated
49with an ELF descriptor.
50.Pp
51Function
52.Fn elf_getscn
53will return a section descriptor for the section at index
54.Ar index
55in the object denoted by ELF descriptor
56.Ar elf .
57An error will be signalled if the specified section does not
58exist.
59.Pp
60Function
61.Fn elf_ndxscn
62returns the section table index associated with section descriptor
63.Ar scn .
64.Pp
65Function
66.Fn elf_newscn
67creates a new section and appends it to the list of sections
68associated with descriptor
69.Ar elf .
70The library will automatically increment the
71.Va e_shnum
72field of the ELF header associated with descriptor
73.Ar elf ,
74and will set the
75.Dv ELF_F_DIRTY
76flag on the returned section descriptor.
77For ELF descriptors opened for writing, the ELF library will
78automatically create an empty section at index zero
79.Dv ( SHN_UNDEF )
80on the first call to
81.Fn elf_newscn .
82.Pp
83Function
84.Fn elf_nextscn
85takes a section descriptor
86.Ar scn
87and returns a pointer to the section descriptor at the next higher
88index.
89As a consequence,
90.Fn elf_nextscn
91will never return a pointer to the empty section at index zero
92.Dv ( SHN_UNDEF ) .
93Argument
94.Ar scn
95is allowed to be NULL, in which case this function will return a
96pointer to the section descriptor at index 1.
97If no further sections are present, function
98.Fn elf_nextscn
99will return a NULL pointer.
100.Sh RETURN VALUES
101Functions
102.Fn elf_getscn ,
103.Fn elf_newscn
104and
105.Fn elf_nextscn
106return a valid pointer to a section descriptor if successful, or
107NULL if an error occurs.
108.Pp
109Function
110.Fn elf_ndxscn
111returns a valid section table index if successful, or
112.Dv SHN_UNDEF
113if an error occurs.
114.Sh ERRORS
115These functions may fail with the following errors:
116.Bl -tag -width "[ELF_E_RESOURCE]"
117.It Bq Er ELF_E_ARGUMENT
118Arguments
119.Ar elf
120or
121.Ar scn
122were NULL.
123.It Bq Er ELF_E_ARGUMENT
124Argument
125.Ar index
126exceeded the current number of sections in the ELF object.
127.It Bq Er ELF_E_ARGUMENT
128Argument
129.Ar elf
130was not a descriptor for an ELF file.
131.It Bq Er ELF_E_ARGUMENT
132Section descriptor
133.Ar scn
134was not associated with ELF descriptor
135.Ar elf .
136.It Bq Er ELF_E_CLASS
137Descriptor
138.Ar elf
139was of an unknown ELF class.
140.It Bq Er ELF_E_SECTION
141Argument
142.Ar elf
143specified extended section numbering in the ELF header with the section header at
144index
145.Dv SHN_UNDEF
146not being of type
147.Dv SHT_NULL .
148.El
149.Sh SEE ALSO
150.Xr elf 3 ,
151.Xr elf_flagdata 3 ,
152.Xr elf_flagscn 3 ,
153.Xr elf_getdata 3 ,
154.Xr elf_getshdr 3 ,
155.Xr gelf 3
156