cord(1)cord(1)NAMEcord - Rearrange procedures in an executable file to facilitate better
cache mapping
SYNOPSIScord [-vV] [-o outfile] [-f] [-c cachesize] [-p maxphases] obj-file
reorder-file
OPTIONS
The cord command accepts the following options: Prints verbose informa‐
tion. This includes listing those procedures that are considered part
of other procedures and that cannot be rearranged (that is, assembler
procedures that may contain relative branches to other procedures
instead of relocatable branches). The listing also lists those proce‐
dures in the flipped area (if any) and a mapping of old location to
new. Displays the version of the cord command. Specifies the output
file. If not specified, a.out is used. Flips the first cachepage size
procedures. When cord was written, the assumption was that procedures
would be reordered by procedure density (cycles/byte). This option
ensures that the densest part of each page following the first cachep‐
age would conflict with the least-dense part of the first cachepage.
Specifies the cache size (in bytes) of the machine on which you want to
execute. This only affects the -f option. If not specified, 65536 is
used. Specifies the maximum number phases allowed. The default is 20.
DESCRIPTION
The cord command rearranges procedures in an executable object file to
maximize efficiency in a machine's cache. By rearranging the procedures
properly, you can reduce the instruction cache miss rates. The cord
command does not attempt to determine the correct ordering; it must be
given a reorder-file containing the desired procedure order. The
reorder file is generated by the ftoc program, which in turn generates
a reorder file from a set of profile feedback files (see prof(1)).
Processed lines in the reorder file are called procedure lines. Each
procedure line must be on a separate source line. Each procedure line
must contain the source name of the file, followed by a blank, followed
by a qualified procedure name. Nested procedures must be qualified x.y,
where x is the outer procedure. A newline or blank can follow the pro‐
cedure name:
foo.c bar (everything else following is ignored)
Lines beginning with # are comments, lines beginning with $ are consid‐
ered cord directive lines. The only directive currently understood is
$phase. This directive will consider the rest of the file (until the
end of file or next $phase) as a new phase of the program and will
order the procedures accordingly. A procedure may appear in more than
one phase, resulting in more than one copy of it in the final binary.
First, cord will try to relocate procedure references to a copy of the
procedure belonging to the requesting phase; otherwise, it will relo‐
cate the references to a random copy.
Use the -cord option to a compiler driver like cc(1) rather than exe‐
cute cord directly. The cord options can be specified with -Wc,cor‐
darg0,cordarg1,.... If you have to run cord by hand, you may want to
run it once with the driver using the -v option on a simple program.
This will enable you to see the exact passes and the arguments involved
in using cord.
Warning
Since cord works from an input list of procedures generated from pro‐
file output, the resulting binary is data dependent. In other words, it
may only perform well on the same input data that generated the profile
information, and may perform worse than the original binary on other
data. Furthermore, if the hot areas in the cache do not fit well into
one cachepage, performance can degrade.
SEE ALSO
Commands: cc(1), ftoc(1), ld(1), prof(1)
Programmer's Guide
cord(1)
