On Tue, Jul 22, 2014 at 08:24:30PM +0300, Timo Teras wrote: > On Tue, 22 Jul 2014 13:07:15 -0400 > "Cathey, Jim" <jcat...@ciena.com> wrote: > > > >Am I missing something here? There is no structure, just a > > >character pointer. If you leave off "static" it will be compiled as > > >an instruction that pushes a constant onto the stack, by any/every > > >compiler. > > > > Which is probably _larger_ code than just referring to something > > stored in the .text/.data segment. It's copying something that is > > found in text/data into the stack space, then referring to that > > address thereafter. The compiler has to do: > > > > Copy A->B > > Then use &B. > > > > -vs- > > > > Use &A. > > > > You do this when you want the ability to modify B. > > If A is fixed and inviolate, you mark it static const > > and be done with it. What this turns into, exactly, > > depends upon your compiler, CPU, and ABI, but I can't > > think of any case where the extra copy is going to > > turn out _better_ than the simpler case. > > Usage of 'static' depends whether it's "const char *" or "const > char[]". When defining "const char *" static does not make sense, as > in theory it should enforce *also* the pointer value to go to .rodata > (the string literal of course goes there too). So you might end up > wasting one extra pointer in .rodata. > > OTOH, with "const char[]" you definitely want the "static" as other > wise you'd end up with the copy described above. > > I only suggested removing 'static' since I had it a pointer. The latest > patch has array, and thus is static.
I agree that using a static const array is the best approach here, and that with a *single* pointer, making a static object to hold the pointer rather than just an automatic const-qualified variable is a pessimization, if anything. However static const pointers are useful when they're arrays of pointers, or part of structures, etc., but their usefulness is limited except with static linking and non-PIE main programs, since they'll need relocations for PIC/PIE which would throw them out of rodata. Rich _______________________________________________ busybox mailing list busybox@busybox.net http://lists.busybox.net/mailman/listinfo/busybox
