Re: CVS commit: src/sys/arch

[Maxime Villard <max%m00nbsd.net@localhost>]

Le 18/08/2017 à 20:52, matthew green a écrit :
> "Maxime Villard" writes:
> > Module Name:	src
> > Committed By:	maxv
> > Date:		Fri Aug 18 10:28:53 UTC 2017
> >
> > Modified Files:
> > 	src/sys/arch/amd64/conf: kern.ldscript
> > 	src/sys/arch/i386/conf: kern.ldscript kern.ldscript.4MB
> >
> > Log Message:
> > Fill the .text padding with 0xcc (int3), in such a way that any jump into
> > this area will automatically fault. The alignment within the section is
> > necessary, in order to fill strictly all of the padding (took me a while
> > to figure this out); but it does not change the kernel size.
> >
> > Greatly inspired from FreeBSD, but for some reason they decided not to
> > apply the alignment.
>
> it's really a pity that we have almost _2MB_ of basically wasted
> space in the kernel.  there's really no good reason for it.  it's
> not as if ELF files are incapable of expressing discontiguous
> sections separately without zero or other filling.  the int3
> filling could be done at run time.
>
> you didn't introduce this issue, but you did add 1MB of wastage
> a while back now.  can you please look at fixing this?

I already know how to fix it, change max-page-size to 0x1000. But it causes
the kernel to have three PT_LOAD sections, and the bootloader expects only
two. Fixing the bootloader is more complicated, because several things are
shared between architectures.

> it both slows boot and fills my boot disk/partition.

(filling in the padding at run time is slower than having it done in the
kernel statically.)

Maxime