Geert Uytterhoeven wrote:
> My idea was to replace empty and most simple functions by predefined dummy(),
> dummy_zeros(), dummy_ones() and dummy_einval() functions, so they appear only
> once in a kernel image. But is it worth the effort?
I've often thought about the same thing.
One problem would be to get it to compile without warnings, since these
functions have all different prototypes. Unfortunately ANSI won't let
you say:
void dummy(...) {}
For filling in function pointers you can do:
void _dummy(void) {}
#define dummy ((void *)_dummy)
But now you'll get an error if you try calling dummy directly (then again,
why would you?)
I think a much neater solution would be to postulate that gcc will generally
always produce identical code for these functions (is that true? I assume
register state will alwaus be the same each time for a non-inlined function!).
Then you could hack up the toolchain to make a md5sum of all the functions
assembly code and then merge the duplicates. That way you might even pick
up a couple slightly more complicated variants.
You can even get crazier than this. You could look for pieces of the tails
of functions that match (with no jumps across) and then shorten functions
by jumping into the middle of a function with the right ending. Note
that this would be hard to get right and would likely screw up a modern
CPUs ability to match call/return's, so probably not worth it :-)
It would be interesting to try to apply a similar merge on rodata sections...
I wonder how much blood could be wrung from that stone.
Anyway, are there any students out there looking for a thesis project? ;-)
-Mitch
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This archive was generated by hypermail 2b29 : Sat Jul 15 2000 - 21:00:11 EST