xstr(1)
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XSTR(1) NetBSD General Commands Manual XSTR(1)
NAME
xstr -- extract strings from C programs to implement shared strings
SYNOPSIS
xstr [-cv] [-l array] [-] [file ...]
DESCRIPTION
xstr maintains a file strings into which strings in component parts of a
large program are hashed. These strings are replaced with references to
this common area. This serves to implement shared constant strings, most
useful if they are also read-only.
Available options:
- xstr reads from the standard input.
-c xstr will extract the strings from the C source file or the
standard input (-), replacing string references by expres-
sions of the form (&xstr[number]) for some number. An
appropriate declaration of xstr is prepended to the file.
The resulting C text is placed in the file x.c, to then be
compiled. The strings from this file are placed in the
strings data base if they are not there already. Repeated
strings and strings which are suffixes of existing strings
do not cause changes to the data base.
-l array Specify the named array in program references to abstracted
strings. The default array name is xstr.
-v Be verbose.
After all components of a large program have been compiled, a file xs.c
declaring the common xstr space can be created by a command of the form:
$ xstr
The file xs.c should then be compiled and loaded with the rest of the
program. If possible, the array can be made read-only (shared) saving
space and swap overhead.
xstr can also be used on a single file. The following command creates
files x.c and xs.c as before, without using or affecting any strings file
in the same directory:
$ xstr name
It may be useful to run xstr after the C preprocessor if any macro defi-
nitions yield strings or if there is conditional code which contains
strings which may not, in fact, be needed. An appropriate command
sequence for running xstr after the C preprocessor is:
$ cc -E name.c | xstr -c -
$ cc -c x.c
$ mv x.o name.o
xstr does not touch the file strings unless new items are added, thus
make(1) can avoid remaking xs.o unless truly necessary.
FILES
strings Data base of strings
x.c Massaged C source
xs.c C source for definition of array `xstr'
/tmp/xs* Temp file when `xstr name' doesn't touch strings
SEE ALSO
mkstr(1)
HISTORY
The xstr command appeared in 3.0BSD.
BUGS
If a string is a suffix of another string in the data base, but the
shorter string is seen first by xstr both strings will be placed in the
data base, when just placing the longer one there will do.
xstr does not parse the file properly so it does not know not to process:
char var[] = "const";
into:
char var[] = (&xstr[N]);
These must be changed manually into an appropriate initialization for the
string, or use the following ugly hack.
Also, xstr cannot initialize structures and unions that contain strings.
Those can be fixed by changing from:
struct foo {
int i;
char buf[10];
} = {
1, "foo"
};
to:
struct foo {
int i;
char buf[10];
} = {
1, { 'f', 'o', 'o', '\0' }
};
The real problem in both cases above is that the compiler knows the size
of the literal constant so that it can perform the initialization
required, but when xstr changes the literal string to a pointer refer-
ence, the size information is lost. It would require a real parser to do
this right, so the obvious solution is to fix the program manually to
compile, or even better rely on the compiler and the linker to merge
strings appropriately.
Finally, xstr is not very useful these days because most of the string
merging is done automatically by the compiler and the linker, provided
that the strings are identical and read-only.
NetBSD 7.0 July 23, 2004 NetBSD 7.0
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