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$FreeBSD: releng/10.2/lib/libelf/elf_getdata.3 246978 2013-02-19 03:23:13Z markj $
.Dd February 18, 2013 .Dt ELF_GETDATA 3 .Os .Sh NAME .Nm elf_getdata , .Nm elf_newdata , .Nm elf_rawdata .Nd iterate through or allocate section data .Sh LIBRARY .Lb libelf .Sh SYNOPSIS n libelf.h .Ft "Elf_Data *" .Fn elf_getdata "Elf_Scn *scn" "Elf_Data *data" .Ft "Elf_Data *" .Fn elf_newdata "Elf_Scn *scn" .Ft "Elf_Data *" .Fn elf_rawdata "Elf_Scn *scn" "Elf_Data *data" .Sh DESCRIPTION These functions are used to access and manipulate data descriptors associated with section descriptors. Data descriptors used by the ELF library are described in .Xr elf 3 .
p Function .Fn elf_getdata will return the next data descriptor associated with section descriptor .Ar scn . The returned data descriptor will be setup to contain translated data. Argument .Ar data may be NULL, in which case the function returns the first data descriptor associated with section .Ar scn . If argument .Ar data is not NULL, it must be a pointer to a data descriptor associated with section descriptor .Ar scn , and function .Fn elf_getdata will return a pointer to the next data descriptor for the section, or NULL when the end of the section's descriptor list is reached.
p Function .Fn elf_newdata will allocate a new data descriptor and append it to the list of data descriptors associated with section descriptor .Ar scn . The new data descriptor will be initialized as follows: l -tag -width "d_version" -compact -offset indent t Va d_align Set to 1. t Va d_buf Initialized to NULL. t Va d_off Set to (off_t) -1. This field is under application control if the .Dv ELF_F_LAYOUT flag was set on the ELF descriptor. t Va d_size Set to zero. t Va d_type Initialized to .Dv ELF_T_BYTE . t Va d_version Set to the current working version of the library, as set by .Xr elf_version 3 . .El The application must set these values as appropriate before calling .Xr elf_update 3 . Section .Ar scn must be associated with an ELF file opened for writing. If the application has not requested full control of layout by setting the .Dv ELF_F_LAYOUT flag on descriptor .Ar elf , then the data referenced by the returned descriptor will be positioned after the existing content of the section, honoring the file alignment specified in member .Va d_align . On successful completion of a call to .Fn elf_newdata , the ELF library will mark the section .Ar scn as .Dq dirty .
p Function .Fn elf_rawdata is used to step through the data descriptors associated with section .Ar scn . In contrast to function .Fn elf_getdata , this function returns untranslated data. If argument .Ar data is NULL, the first data descriptor associated with section .Ar scn is returned. If argument .Ar data is not NULL, is must be a data descriptor associated with section .Ar scn , and function .Fn elf_rawdata will return the next data descriptor in the list, or NULL if no further descriptors are present. Function .Fn elf_rawdata always returns .Vt Elf_Data structures of type .Dv ELF_T_BYTE . .Ss Special handling of zero-sized and SHT_NOBITS sections For sections of type .Dv SHT_NOBITS , and for zero-sized sections, the functions .Fn elf_getdata and .Fn elf_rawdata return a pointer to a valid .Vt Elf_Data structure that has its .Va d_buf member set to NULL and its .Va d_size member set to the size of the section.
p If an application wishes to create a section of type .Dv SHT_NOBITS , it should add a data buffer to the section using function .Fn elf_newdata . It should then set the .Va d_buf and .Va d_size members of the returned .Vt Elf_Data structure to NULL and the desired size of the section respectively. .Sh RETURN VALUES These functions return a valid pointer to a data descriptor if successful, or NULL if an error occurs. .Sh ERRORS These functions may fail with the following errors: l -tag -width "[ELF_E_RESOURCE]" t Bq Er ELF_E_ARGUMENT Arguments .Ar scn was NULL. t Bq Er ELF_E_ARGUMENT Data descriptor .Ar data was not associated with section descriptor .Ar scn . t Bq Er ELF_E_RESOURCE An out of memory condition was detected. t Bq Er ELF_E_SECTION Section .Ar scn had type .Dv SHT_NULL . t Bq Er ELF_E_SECTION The type of the section .Ar scn was not recognized by the library. t Bq Er ELF_E_SECTION The size of the section .Ar scn is not a multiple of the file size for its section type. t Bq Er ELF_E_SECTION The file offset for section .Ar scn is incorrect. .El .Sh SEE ALSO .Xr elf 3 , .Xr elf_flagdata 3 , .Xr elf_flagscn 3 , .Xr elf_getscn 3 , .Xr elf_getshdr 3 , .Xr elf_newscn 3 , .Xr elf_rawfile 3 , .Xr elf_update 3 , .Xr elf_version 3 , .Xr gelf 3