forked from OSchip/llvm-project
368 lines
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ReStructuredText
368 lines
11 KiB
ReStructuredText
llvm-ar - LLVM archiver
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=======================
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SYNOPSIS
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--------
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**llvm-ar** [-]{dmpqrtx}[Rabfikou] [relpos] [count] <archive> [files...]
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DESCRIPTION
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-----------
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The **llvm-ar** command is similar to the common Unix utility, ``ar``. It
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archives several files together into a single file. The intent for this is
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to produce archive libraries by LLVM bitcode that can be linked into an
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LLVM program. However, the archive can contain any kind of file. By default,
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**llvm-ar** generates a symbol table that makes linking faster because
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only the symbol table needs to be consulted, not each individual file member
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of the archive.
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The **llvm-ar** command can be used to *read* SVR4, GNU and BSD style archive
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files. However, right now it can only write in the GNU format. If an
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SVR4 or BSD style archive is used with the ``r`` (replace) or ``q`` (quick
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update) operations, the archive will be reconstructed in GNU format.
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Here's where **llvm-ar** departs from previous ``ar`` implementations:
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*Symbol Table*
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Since **llvm-ar** supports bitcode files. The symbol table it creates
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is in GNU format and includes both native and bitcode files.
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*Long Paths*
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Currently **llvm-ar** can read GNU and BSD long file names, but only writes
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archives with the GNU format.
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OPTIONS
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-------
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The options to **llvm-ar** are compatible with other ``ar`` implementations.
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However, there are a few modifiers (*R*) that are not found in other ``ar``
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implementations. The options to **llvm-ar** specify a single basic operation to
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perform on the archive, a variety of modifiers for that operation, the name of
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the archive file, and an optional list of file names. These options are used to
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determine how **llvm-ar** should process the archive file.
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The Operations and Modifiers are explained in the sections below. The minimal
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set of options is at least one operator and the name of the archive. Typically
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archive files end with a ``.a`` suffix, but this is not required. Following
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the *archive-name* comes a list of *files* that indicate the specific members
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of the archive to operate on. If the *files* option is not specified, it
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generally means either "none" or "all" members, depending on the operation.
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Operations
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~~~~~~~~~~
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d
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Delete files from the archive. No modifiers are applicable to this operation.
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The *files* options specify which members should be removed from the
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archive. It is not an error if a specified file does not appear in the archive.
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If no *files* are specified, the archive is not modified.
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m[abi]
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Move files from one location in the archive to another. The *a*, *b*, and
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*i* modifiers apply to this operation. The *files* will all be moved
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to the location given by the modifiers. If no modifiers are used, the files
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will be moved to the end of the archive. If no *files* are specified, the
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archive is not modified.
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p
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Print files to the standard output. This operation simply prints the
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*files* indicated to the standard output. If no *files* are
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specified, the entire archive is printed. Printing bitcode files is
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ill-advised as they might confuse your terminal settings. The *p*
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operation never modifies the archive.
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q
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Quickly append files to the end of the archive. This operation quickly adds the
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*files* to the archive without checking for duplicates that should be
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removed first. If no *files* are specified, the archive is not modified.
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Because of the way that **llvm-ar** constructs the archive file, its dubious
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whether the *q* operation is any faster than the *r* operation.
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r[abu]
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Replace or insert file members. The *a*, *b*, and *u*
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modifiers apply to this operation. This operation will replace existing
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*files* or insert them at the end of the archive if they do not exist. If no
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*files* are specified, the archive is not modified.
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t[v]
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Print the table of contents. Without any modifiers, this operation just prints
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the names of the members to the standard output. With the *v* modifier,
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**llvm-ar** also prints out the file type (B=bitcode, S=symbol
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table, blank=regular file), the permission mode, the owner and group, the
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size, and the date. If any *files* are specified, the listing is only for
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those files. If no *files* are specified, the table of contents for the
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whole archive is printed.
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x[oP]
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Extract archive members back to files. The *o* modifier applies to this
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operation. This operation retrieves the indicated *files* from the archive
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and writes them back to the operating system's file system. If no
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*files* are specified, the entire archive is extract.
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Modifiers (operation specific)
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The modifiers below are specific to certain operations. See the Operations
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section (above) to determine which modifiers are applicable to which operations.
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[a]
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When inserting or moving member files, this option specifies the destination of
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the new files as being after the *relpos* member. If *relpos* is not found,
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the files are placed at the end of the archive.
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[b]
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When inserting or moving member files, this option specifies the destination of
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the new files as being before the *relpos* member. If *relpos* is not
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found, the files are placed at the end of the archive. This modifier is
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identical to the *i* modifier.
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[i]
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A synonym for the *b* option.
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[o]
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When extracting files, this option will cause **llvm-ar** to preserve the
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original modification times of the files it writes.
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[u]
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When replacing existing files in the archive, only replace those files that have
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a time stamp than the time stamp of the member in the archive.
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Modifiers (generic)
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~~~~~~~~~~~~~~~~~~~
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The modifiers below may be applied to any operation.
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[c]
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For all operations, **llvm-ar** will always create the archive if it doesn't
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exist. Normally, **llvm-ar** will print a warning message indicating that the
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archive is being created. Using this modifier turns off that warning.
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[s]
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This modifier requests that an archive index (or symbol table) be added to the
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archive. This is the default mode of operation. The symbol table will contain
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all the externally visible functions and global variables defined by all the
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bitcode files in the archive.
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[S]
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This modifier is the opposite of the *s* modifier. It instructs **llvm-ar** to
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not build the symbol table. If both *s* and *S* are used, the last modifier to
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occur in the options will prevail.
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[v]
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This modifier instructs **llvm-ar** to be verbose about what it is doing. Each
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editing operation taken against the archive will produce a line of output saying
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what is being done.
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STANDARDS
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---------
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The **llvm-ar** utility is intended to provide a superset of the IEEE Std 1003.2
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(POSIX.2) functionality for ``ar``. **llvm-ar** can read both SVR4 and BSD4.4 (or
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Mac OS X) archives. If the ``f`` modifier is given to the ``x`` or ``r`` operations
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then **llvm-ar** will write SVR4 compatible archives. Without this modifier,
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**llvm-ar** will write BSD4.4 compatible archives that have long names
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immediately after the header and indicated using the "#1/ddd" notation for the
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name in the header.
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FILE FORMAT
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-----------
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The file format for LLVM Archive files is similar to that of BSD 4.4 or Mac OSX
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archive files. In fact, except for the symbol table, the ``ar`` commands on those
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operating systems should be able to read LLVM archive files. The details of the
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file format follow.
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Each archive begins with the archive magic number which is the eight printable
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characters "!<arch>\n" where \n represents the newline character (0x0A).
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Following the magic number, the file is composed of even length members that
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begin with an archive header and end with a \n padding character if necessary
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(to make the length even). Each file member is composed of a header (defined
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below), an optional newline-terminated "long file name" and the contents of
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the file.
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The fields of the header are described in the items below. All fields of the
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header contain only ASCII characters, are left justified and are right padded
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with space characters.
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name - char[16]
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This field of the header provides the name of the archive member. If the name is
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longer than 15 characters or contains a slash (/) character, then this field
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contains ``#1/nnn`` where ``nnn`` provides the length of the name and the ``#1/``
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is literal. In this case, the actual name of the file is provided in the ``nnn``
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bytes immediately following the header. If the name is 15 characters or less, it
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is contained directly in this field and terminated with a slash (/) character.
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date - char[12]
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This field provides the date of modification of the file in the form of a
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decimal encoded number that provides the number of seconds since the epoch
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(since 00:00:00 Jan 1, 1970) per Posix specifications.
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uid - char[6]
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This field provides the user id of the file encoded as a decimal ASCII string.
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This field might not make much sense on non-Unix systems. On Unix, it is the
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same value as the st_uid field of the stat structure returned by the stat(2)
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operating system call.
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gid - char[6]
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This field provides the group id of the file encoded as a decimal ASCII string.
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This field might not make much sense on non-Unix systems. On Unix, it is the
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same value as the st_gid field of the stat structure returned by the stat(2)
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operating system call.
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mode - char[8]
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This field provides the access mode of the file encoded as an octal ASCII
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string. This field might not make much sense on non-Unix systems. On Unix, it
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is the same value as the st_mode field of the stat structure returned by the
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stat(2) operating system call.
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size - char[10]
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This field provides the size of the file, in bytes, encoded as a decimal ASCII
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string.
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fmag - char[2]
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This field is the archive file member magic number. Its content is always the
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two characters back tick (0x60) and newline (0x0A). This provides some measure
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utility in identifying archive files that have been corrupted.
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offset - vbr encoded 32-bit integer
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The offset item provides the offset into the archive file where the bitcode
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member is stored that is associated with the symbol. The offset value is 0
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based at the start of the first "normal" file member. To derive the actual
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file offset of the member, you must add the number of bytes occupied by the file
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signature (8 bytes) and the symbol tables. The value of this item is encoded
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using variable bit rate encoding to reduce the size of the symbol table.
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Variable bit rate encoding uses the high bit (0x80) of each byte to indicate
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if there are more bytes to follow. The remaining 7 bits in each byte carry bits
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from the value. The final byte does not have the high bit set.
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length - vbr encoded 32-bit integer
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The length item provides the length of the symbol that follows. Like this
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*offset* item, the length is variable bit rate encoded.
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symbol - character array
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The symbol item provides the text of the symbol that is associated with the
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*offset*. The symbol is not terminated by any character. Its length is provided
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by the *length* field. Note that is allowed (but unwise) to use non-printing
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characters (even 0x00) in the symbol. This allows for multiple encodings of
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symbol names.
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EXIT STATUS
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-----------
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If **llvm-ar** succeeds, it will exit with 0. A usage error, results
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in an exit code of 1. A hard (file system typically) error results in an
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exit code of 2. Miscellaneous or unknown errors result in an
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exit code of 3.
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SEE ALSO
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--------
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ar(1)
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