Hi, On Wed, Aug 24, 2005 at 02:41:44PM +0100, Paul Brook wrote: > > Probably more important is to make sure none constant data structures > > are done on the stack. There is no good reason why any code page > > should be read-write. > > Huh? this is nonsense.
Uhoh, I seem to have managed to stir up a veritable hornet's net with my patch... > Making global data readonly is a small win because it means it can be shared > by multiple instances of the same application. Yup. > Moving global RW data onto the stack isn't neccly a win. Most systems have a > relatively small limit on stack size, so putting large objects on the stack > is a bad idea. Indeed. Witness e.g. Linux's optional kernel stack reduction to 4k and the problems that ensued. > Contrary to popular belief the "const" qualifier on pointers has absolutely > no > effect on optimization. It's simply a debugging aid so the compiler will > generate an error if you accidentally assign to it. It's perfectly legal to > cast a (const char *) to a (char *) then dereference and write to it, > provided the object the object it points to is modifiable. I was thinking just that: that constifying stuff at most gives a very small compiler gain, but most probably just nothing (some people reported some rather weak 1.4% performance gain somewhere!? Statistical noise...). Since you say it's nothing I'm strongly inclined to believe it... Well, it's not only a compiler debugging aid, but also a runtime debugging aid, since random (attempted) .rodata page corruption should SEGV in that case. Andreas Mohr _______________________________________________ Qemu-devel mailing list Qemu-devel@nongnu.org http://lists.nongnu.org/mailman/listinfo/qemu-devel
