1elf_update(3ELF) ELF Library Functions elf_update(3ELF)
2
6 elf_update - update an ELF descriptor
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9 cc [ flag ... ] file ... -lelf [ library ... ]
10 #include <libelf.h>
11 off_t elf_update(Elf *elf, Elf_Cmd cmd);
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16 The elf_update() function causes the library to examine the information
17 associated with an ELF descriptor, elf, and to recalculate the struc‐
18 tural data needed to generate the file's image.
19 The cmd argument can have the following values:
22 ELF_C_NULL This value tells elf_update() to recalculate various
24 values, updating only the ELF descriptor's memory struc‐
25 tures. Any modified structures are flagged with the
26 ELF_F_DIRTY bit. A program thus can update the struc‐
27 tural information and then reexamine them without chang‐
28 ing the file associated with the ELF descriptor. Because
29 this does not change the file, the ELF descriptor may
30 allow reading, writing, or both reading and writing (see
31 elf_begin(3ELF)).
32 ELF_C_WRITE If cmd has this value, elf_update() duplicates its
35 ELF_C_NULL actions and also writes any ``dirty'' infor‐
36 mation associated with the ELF descriptor to the file.
37 That is, when a program has used elf_getdata(3ELF) or
38 the elf_flagdata(3ELF) facilities to supply new (or
39 update existing) information for an ELF descriptor,
40 those data will be examined, coordinated, translated if
41 necessary (see elf32_xlatetof(3ELF)), and written to the
42 file. When portions of the file are written, any
43 ELF_F_DIRTY bits are reset, indicating those items no
44 longer need to be written to the file (see elf_flag‐
45 data(3ELF)). The sections' data are written in the order
46 of their section header entries, and the section header
47 table is written to the end of the file. When the ELF
48 descriptor was created with elf_begin(), it must have
49 allowed writing the file. That is, the elf_begin() com‐
50 mand must have been either ELF_C_RDWR or ELF_C_WRITE.
51 If elf_update() succeeds, it returns the total size of the file image
55 (not the memory image), in bytes. Otherwise an error occurred, and the
56 function returns −1.
57 When updating the internal structures, elf_update() sets some members
60 itself. Members listed below are the application's responsibility and
61 retain the values given by the program.
62 The following table shows ELF Header members:
65 Member Notes
70 e_ident[EI_DATA] Library controls other e_ident values
72 e_type
73 e_machine
74 e_version
75 e_entry
76 e_phoff Only when ELF_F_LAYOUT asserted
77 e_shoff Only when ELF_F_LAYOUT asserted
78 e_flags
79 e_shstrndx
80 The following table shows the Program Header members:
84 Member Notes
89 p_type The application controls all
91 p_offset program header entries
92 p_vaddr
93 p_paddr
94 p_filesz
95 p_memsz
96 p_flags
97 p_align
98 The following table shows the Section Header members:
102 Member Notes
107 sh_name
109 sh_type
110 sh_flags
111 sh_addr
112 sh_offset Only when ELF_F_LAYOUT asserted
113 sh_size Only when ELF_F_LAYOUT asserted
114 sh_link
115 sh_info
116 sh_addralign Only when ELF_F_LAYOUT asserted
117 sh_entsize
118 The following table shows the Data Descriptor members:
122 Member Notes
127 d_buf
129 d_type
130 d_size
131 d_off Only when ELF_F_LAYOUT asserted
132 d_align
134 d_version
135 Note that the program is responsible for two particularly important
139 members (among others) in the ELF header. The e_version member controls
140 the version of data structures written to the file. If the version is
141 EV_NONE, the library uses its own internal version. The
142 e_ident[EI_DATA] entry controls the data encoding used in the file. As
143 a special case, the value may be ELFDATANONE to request the native data
144 encoding for the host machine. An error occurs in this case if the
145 native encoding doesn't match a file encoding known by the library.
146 Further note that the program is responsible for the sh_entsize section
149 header member. Although the library sets it for sections with known
150 types, it cannot reliably know the correct value for all sections. Con‐
151 sequently, the library relies on the program to provide the values for
152 unknown section types. If the entry size is unknown or not applicable,
153 the value should be set to 0.
154 When deciding how to build the output file, elf_update() obeys the
157 alignments of individual data buffers to create output sections. A sec‐
158 tion's most strictly aligned data buffer controls the section's align‐
159 ment. The library also inserts padding between buffers, as necessary,
160 to ensure the proper alignment of each buffer.
161
163 See attributes(5) for descriptions of the following attributes:
164 ┌─────────────────────────────┬─────────────────────────────┐
169 │ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
170 ├─────────────────────────────┼─────────────────────────────┤
171 │Interface Stability │Stable │
172 ├─────────────────────────────┼─────────────────────────────┤
173 │MT-Level │MT-Safe │
174 └─────────────────────────────┴─────────────────────────────┘
175
177 elf(3ELF), elf32_fsize(3ELF), elf32_getehdr(3ELF), elf32_getshdr(3ELF),
178 elf32_xlatetof(3ELF), elf_begin(3ELF), elf_flagdata(3ELF), elf_get‐
179 data(3ELF), libelf(3LIB), attributes(5)
180
182 As mentioned above, the ELF_C_WRITE command translates data as neces‐
183 sary, before writing them to the file. This translation is not always
184 transparent to the application program. If a program has obtained
185 pointers to data associated with a file (for example, see elf32_gete‐
186 hdr(3ELF) and elf_getdata(3ELF)), the program should reestablish the
187 pointers after calling elf_update().
188SunOS 5.11 11 Jul 2001 elf_update(3ELF)