Untitled Document: Archives

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### 2.8 Archives

Description
An archive (or library) is just another BFD. It has a symbol table, although there’s not much a user program will do with it.

The big difference between an archive BFD and an ordinary BFD is that the archive doesn’t have sections. Instead it has a chain of BFDs that are considered its contents. These BFDs can be manipulated like any other. The BFDs contained in an archive opened for reading will all be opened for reading. You may put either input or output BFDs into an archive opened for output; they will be handled correctly when the archive is closed.

Use `bfd_openr_next_archived_file` to step through the contents of an archive opened for input. You don’t have to read the entire archive if you don’t want to! Read it until you find what you want.

A BFD returned by `bfd_openr_next_archived_file` can be closed manually with `bfd_close`. If you do not close it, then a second iteration through the members of an archive may return the same BFD. If you close the archive BFD, then all the member BFDs will automatically be closed as well.

Archive contents of output BFDs are chained through the `archive_next` pointer in a BFD. The first one is findable through the `archive_head` slot of the archive. Set it with `bfd_set_archive_head` (q.v.). A given BFD may be in only one open output archive at a time.

As expected, the BFD archive code is more general than the archive code of any given environment. BFD archives may contain files of different formats (e.g., a.out and coff) and even different architectures. You may even place archives recursively into archives!

This can cause unexpected confusion, since some archive formats are more expressive than others. For instance, Intel COFF archives can preserve long filenames; SunOS a.out archives cannot. If you move a file from the first to the second format and back again, the filename may be truncated. Likewise, different a.out environments have different conventions as to how they truncate filenames, whether they preserve directory names in filenames, etc. When interoperating with native tools, be sure your files are homogeneous.

Beware: most of these formats do not react well to the presence of spaces in filenames. We do the best we can, but can’t always handle this case due to restrictions in the format of archives. Many Unix utilities are braindead in regards to spaces and such in filenames anyway, so this shouldn’t be much of a restriction.

Archives are supported in BFD in `archive.c`.

#### 2.8.1 Archive functions

#### 2.8.1.1 `bfd_get_next_mapent`

Synopsis

    symindex bfd_get_next_mapent
       (bfd *abfd, symindex previous, carsym **sym);

Description
Step through archive abfd’s symbol table (if it has one). Successively update sym with the next symbol’s information, returning that symbol’s (internal) index into the symbol table.

Supply `BFD_NO_MORE_SYMBOLS` as the previous entry to get the first one; returns `BFD_NO_MORE_SYMBOLS` when you’ve already got the last one.

A `carsym` is a canonical archive symbol. The only user-visible element is its name, a null-terminated string.

#### 2.8.1.2 `bfd_set_archive_head`

Synopsis

    bfd_boolean bfd_set_archive_head (bfd *output, bfd *new_head);

Description
Set the head of the chain of BFDs contained in the archive output to new_head.

#### 2.8.1.3 `bfd_openr_next_archived_file`

Synopsis

    bfd *bfd_openr_next_archived_file (bfd *archive, bfd *previous);

Description
Provided a BFD, archive, containing an archive and NULL, open an input BFD on the first contained element and returns that. Subsequent calls should pass the archive and the previous return value to return a created BFD to the next contained element. NULL is returned when there are no more.

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