patch

software 1. A temporary addition to a piece of code, usually

as a quick-and-dirty remedy to an existing bug or

misfeature. A patch may or may not work, and may or may not

eventually be incorporated permanently into the program.

Distinguished from a diff or mod by the fact that a patch

is generated by more primitive means than the rest of the

program; the classical examples are instructions modified by

using the front panel switches, and changes made directly to

the binary executable of a program originally written in an

HLL. Compare one-line fix.

2. To insert a patch into a piece of code.

3. [in the Unix world] A diff.

4. A set of modifications to binaries to be applied by a

patching program. IBM systems often receive updates to the

operating system in the form of absolute hexadecimal

patches. If you have modified your OS, you have to

disassemble these back to the source code. The patches

might later be corrected by other patches on top of them

(patches were said to "grow scar tissue"). The result was

often a convoluted patch space and headaches galore.

There is a classic story of a tiger team penetrating a

secure military computer that illustrates the danger inherent

in binary patches (or, indeed, any patches that you can't - or

don't - inspect and examine before installing). They couldn't

find any trap doors or any way to penetrate security of

IBM's OS, so they made a site visit to an IBM office

(remember, these were official military types who were

purportedly on official business), swiped some IBM stationery,

and created a fake patch. The patch was actually the trapdoor

they needed. The patch was distributed at about the right

time for an IBM patch, had official stationery and all

accompanying documentation, and was dutifully installed. The

installation manager very shortly thereafter learned something

about proper procedures.

5. Larry Wall's "patch" utility, which automatically applies

a patch to a set of source code or other text files. It

accepts input in any of the four forms output by the Unix

diff utility and uses many helpful heuristics to determine

how to apply them.

Diff and patch are the standard way of producing and applying

updates to Unix files ditributed via Usenet and the

Internet, both have been ported to other operatingsystems.

See your nearest GNU archive site.

[Jargon File]

(1996-06-04)