On Thursday 21 November 2002 18:44, Martin J. Bligh wrote:
> > The conventional wisdom is that compiling x86 without frame pointer
> > results in smaller code. It turns out to be the opposite, compiling
> > with frame pointers results in a smaller kernel. gcc version 3.2
> > 20020822 (Red Hat Linux Rawhide 3.2-4).
>
> I looked at 2.5.47 (with a splattering of performance patches) using
> gcc 2.95.4 (Debian Woody), on a 16-way NUMA-Q, and did some kernel
> compile testing. The times to do the tests were almost identical
> (within error noise), but the kernel was indeed smaller
>
> text data bss dec hex filename
> 1873293 396231 459388 2728912 29a3d0 2.5.47-mjb1/vmlinux
> 1427355 396875 455356 2279586 22c8a2 2.5.47-mjb1-frameptr/vmlinux
>
> Wow ... that's quite some difference ;-)
I also tried it, but it is not that big a difference:
text data bss dec hex filename flags
1991125 306324 270484 2567933 272efd vmlinux -fomit-frame-pointer
1981477 306324 270484 2558285 27094d vmlinux
1990965 306324 270484 2567773 272e5d vmlinux -momit-leaf-frame-pointer
this was with gcc 2.95.3 and binutils 2.12 on my lfs system
Rudmer
>
> > I use -momit-leaf-frame-pointer for optimization in some own
> > projects, instead of the "-fomit-frame-pointer". For me, this
> > results in better codesize/speed compared to both "-fomit-frame-pointer"
> > or no option at all. Actually gcc-2.95 seems to support this feature
> > as well, but it never made it into the 2.95 docs...
>
> I tried this, but it seemed to be the same as -fomit-frame-pointer
> (on 2.95 at least).
>
> Given that omitting the -fomit-frame-pointer makes a smaller kernel,
> that's easier to debug, I'd say this is a good thing to do unless someone
> can get *negative* benchmark results.
>
> M.
>
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