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 26  .Dd January 26, 2011
 27  .Os
 28  .Dt ELF_GETDATA 3
 29  .Sh NAME
 30  .Nm elf_getdata ,
 31  .Nm elf_newdata ,
 32  .Nm elf_rawdata
 33  .Nd iterate through or allocate section data
 34  .Sh LIBRARY
 35  .Lb libelf
 36  .Sh SYNOPSIS
 37  .In libelf.h
 38  .Ft "Elf_Data *"
 39  .Fn elf_getdata "Elf_Scn *scn" "Elf_Data *data"
 40  .Ft "Elf_Data *"
 41  .Fn elf_newdata "Elf_Scn *scn"
 42  .Ft "Elf_Data *"
 43  .Fn elf_rawdata "Elf_Scn *scn" "Elf_Data *data"
 44  .Sh DESCRIPTION
 45  These functions are used to access and manipulate data descriptors
 46  associated with section descriptors.
 47  Data descriptors used by the ELF library are described in
 48  .Xr elf 3 .
 49  .Pp
 50  Function
 51  .Fn elf_getdata
 52  will return the next data descriptor associated with section descriptor
 53  .Ar scn .
 54  The returned data descriptor will be setup to contain translated data.
 55  Argument
 56  .Ar data
 57  may be NULL, in which case the function returns the first data descriptor
 58  associated with section
 59  .Ar scn .
 60  If argument
 61  .Ar data
 62  is not NULL, it must be a pointer to a data descriptor associated with
 63  section descriptor
 64  .Ar scn ,
 65  and function
 66  .Fn elf_getdata
 67  will return a pointer to the next data descriptor for the section,
 68  or NULL when the end of the section's descriptor list is reached.
 69  .Pp
 70  Function
 71  .Fn elf_newdata
 72  will allocate a new data descriptor and append it to the list of data
 73  descriptors associated with section descriptor
 74  .Ar scn .
 75  The new data descriptor will be initialized as follows:
 76  .Bl -tag -width "d_version" -compact -offset indent
 77  .It Va d_align
 78  Set to 1.
 79  .It Va d_buf
 80  Initialized to NULL.
 81  .It Va d_off
 82  Set to (off_t) -1.
 83  This field is under application control if the
 84  .Dv ELF_F_LAYOUT
 85  flag was set on the ELF descriptor.
 86  .It Va d_size
 87  Set to zero.
 88  .It Va d_type
 89  Initialized to
 90  .Dv ELF_T_BYTE .
 91  .It Va d_version
 92  Set to the current working version of the library, as set by
 93  .Xr elf_version 3 .
 94  .El
 95  The application must set these values as appropriate before
 96  calling
 97  .Xr elf_update 3 .
 98  Section
 99  .Ar scn
100  must be associated with an ELF file opened for writing.
101  If the application has not requested full control of layout by
102  setting the
103  .Dv ELF_F_LAYOUT
104  flag on descriptor
105  .Ar elf ,
106  then the data referenced by the returned descriptor will be positioned
107  after the existing content of the section, honoring the file alignment
108  specified in member
109  .Va d_align .
110  On successful completion of a call to
111  .Fn elf_newdata ,
112  the ELF library will mark the section
113  .Ar scn
114  as
115  .Dq dirty .
116  .Pp
117  Function
118  .Fn elf_rawdata
119  is used to step through the data descriptors associated with
120  section
121  .Ar scn .
122  In contrast to function
123  .Fn elf_getdata ,
124  this function returns untranslated data.
125  If argument
126  .Ar data
127  is NULL, the first data descriptor associated with section
128  .Ar scn
129  is returned.
130  If argument
131  .Ar data
132  is not NULL, is must be a data descriptor associated with
133  section
134  .Ar scn ,
135  and function
136  .Fn elf_rawdata
137  will return the next data descriptor in the list, or NULL
138  if no further descriptors are present.
139  Function
140  .Fn elf_rawdata
141  always returns
142  .Vt Elf_Data
143  structures of type
144  .Dv ELF_T_BYTE .
145  .Ss Special handling of zero-sized and SHT_NOBITS sections
146  For sections of type
147  .Dv SHT_NOBITS,
148  and for zero-sized sections,
149  the functions
150  .Fn elf_getdata
151  and
152  .Fn elf_rawdata
153  return a pointer to a valid
154  .Vt Elf_Data
155  structure that has its
156  .Va d_buf
157  member set to NULL and its
158  .Va d_size
159  member set to the size of the section.
160  .Pp
161  If an application wishes to create a section of type
162  .Dv SHT_NOBITS ,
163  it should add a data buffer to the section using function
164  .Fn elf_newdata .
165  It should then set the
166  .Va d_buf
167  and
168  .Va d_size
169  members of the returned
170  .Vt Elf_Data
171  structure to NULL and the desired size of the section respectively.
172  .Sh RETURN VALUES
173  These functions return a valid pointer to a data descriptor if successful, or
174  NULL if an error occurs.
175  .Sh ERRORS
176  These functions may fail with the following errors:
177  .Bl -tag -width "[ELF_E_RESOURCE]" 
178  .It Bq Er ELF_E_ARGUMENT
179  Either of the arguments
180  .Ar scn
181  or
182  .Ar data
183  was NULL.
184  .It Bq Er ELF_E_ARGUMENT
185  The data descriptor referenced by argument
186  .Ar data
187  is not associated with section descriptor
188  .Ar scn .
189  .It Bq Er ELF_E_ARGUMENT
190  The section denoted by argument
191  .Ar scn
192  had no data associated with it.
193  .It Bq Er ELF_E_DATA
194  Retrieval of data from the underlying object failed.
195  .It Bq Er ELF_E_RESOURCE
196  An out of memory condition was detected.
197  .It Bq Er ELF_E_SECTION
198  Section
199  .Ar scn
200  had type
201  .Dv SHT_NULL .
202  .It Bq Er ELF_E_SECTION
203  The type of the section
204  .Ar scn
205  was not recognized by the library.
206  .It Bq Er ELF_E_SECTION
207  The size of the section
208  .Ar scn
209  is not a multiple of the file size for its section type.
210  .It Bq Er ELF_E_SECTION
211  The file offset for section
212  .Ar scn
213  is incorrect.
214  .It Bq Er ELF_E_UNIMPL
215  The section type associated with section
216  .Ar scn
217  is currently unsupported by the library.
218  .El
219  .Sh SEE ALSO
220  .Xr elf 3 ,
221  .Xr elf_flagdata 3 ,
222  .Xr elf_flagscn 3 ,
223  .Xr elf_getscn 3 ,
224  .Xr elf_getshdr 3 ,
225  .Xr elf_newscn 3 ,
226  .Xr elf_rawfile 3 ,
227  .Xr elf_update 3 ,
228  .Xr elf_version 3 ,
229  .Xr gelf 3