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CORD(1-SysV) RISC/os Reference Manual CORD(1-SysV)
NAME
cord - rearranges procedures in an executable file to facil-
itate better cache mapping.
SYNOPSIS
cord [-v] [-o outfile] [-f] [-c cachesize] [-p maxphases]
obj_file reorder_file
DESCRIPTION
The cord command rearranges procedures in an exectable
object file to maximize efficiency in a machine's cache. By
rearranging the procedures properly, we end up reducing the
instruction cache miss rates. cord does not attempt to
determine the correct ordering, but is 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 pro-
cedure name. Nested procedures must be qualified x.y where
x is the outer procedure. A newline or blank can follow the
procedure name:
foo.c bar (everything else following is ignored)
Lines beginning with # are comments, lines beginning with $
are considered cord directive lines. The only directive
currently understood is $phase. This directive will con-
sider 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 relocate the references
to a random copy.
We suggest you use the -cord option to a compiler driver
like cc(1) rather than execute cord directly. cord options
can be specified with -Wz,cordarg0,cordarg1,.... If you
have to run cord by hand, you may want to run it once with
the driver using the -v flag on a simple program. This will
enable you to see the exact passes and the arguments
involved in using cord.
obj is an executable object file with its relocation infor-
mation intact. This can be achieved by passing the -r -z -d
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CORD(1-SysV) RISC/os Reference Manual CORD(1-SysV)
options to the linker, ld(1). The linker option -r main-
tains relocation information in the object file, but will
not make it a ZMAGIC file (hence -z). It also will not
allocate common variables (hence -d) as it would without the
option.
WARNING: Since cord works from an input list of procedures
generated from profile output, the resulting binary is data
dependent. In other words, it may only preform well on the
same input data that generated the profile information, and
may preform worse than the original binary on other data.
Furthermore, if the hot areas in the cache don't fit well
into one cachepage, performance can degrade.
The cord command accepts these options:
-v Print verbose information. This includes listing
those procedures considered part of other pro-
cedures and cannot be rearranged (these are basi-
cally assembler procedures that may contain rela-
tive branches to other procedures rather than
relocatable ones). The listing also lists those
procedures in the flipped area (if any) and a map-
ping of old location to new.
-f Flip the first cachepage size procedures. The
assumption when cord was written was that pro-
cedures would be reordered by procedure density
(cycles/byte). This option ensures that the den-
sest part of each page following the first
cachepage would conflict with the least-dense part
of the first cachepage.
-c cachesize
Specify the cachesize (in bytes) of the machine on
which you want to execute. This only affects the
-f option. If not specified, 65536 is used.
-o outputfile
Specifies the output file. If not specified, a.out
is used.
-p phasemax
specifies the maximum number phases allowed. The
default is 20.
SEE ALSO
cc(1), ftoc(1), ld(1), prof(1).
RISCompiler Programmer's Guide
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