Targets - Untitled

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2.12 Targets

Description
Each port of BFD to a different machine requires the creation of a target back end. All the back end provides to the root part of BFD is a structure containing pointers to functions which perform certain low level operations on files. BFD translates the applications's requests through a pointer into calls to the back end routines.

When a file is opened with bfd_openr, its format and target are unknown. BFD uses various mechanisms to determine how to interpret the file. The operations performed are:

Create a BFD by calling the internal routine _bfd_new_bfd, then call bfd_find_target with the target string supplied to bfd_openr and the new BFD pointer.
If a null target string was provided to bfd_find_target, look up the environment variable GNUTARGET and use that as the target string.
If the target string is still NULL, or the target string is default, then use the first item in the target vector as the target type, and set target_defaulted in the BFD to cause bfd_check_format to loop through all the targets. See bfd_target. See Formats.
Otherwise, inspect the elements in the target vector one by one, until a match on target name is found. When found, use it.
Otherwise return the error bfd_error_invalid_target to bfd_openr.
bfd_openr attempts to open the file using bfd_open_file, and returns the BFD.

Once the BFD has been opened and the target selected, the file format may be determined. This is done by calling bfd_check_format on the BFD with a suggested format. If target_defaulted has been set, each possible target type is tried to see if it recognizes the specified format. bfd_check_format returns TRUE when the caller guesses right.