Re: Kernel-only deployments?

Paul E. McKenney
2018-08-23T20:39:46Z

On Thu, Aug 23, 2018 at 12:16:04PM -0700, Josh Triplett wrote:
> On Thu, Aug 23, 2018 at 08:54:17PM +0200, Adam Borowski wrote:
> > On Thu, Aug 23, 2018 at 10:43:59AM -0700, Paul E. McKenney wrote:
> > > The mkinitramfs approach results in about 40MB of initrd, and dracut
> > > about 10MB. Most of this is completely useless for rcutorture, which
> > > isn't interested in mounting filesystems, opening devices, and almost
> > > all of the other interesting things that mkinitramfs and dracut enable.
> > >
> > > Those who know me will not be at all surprised to learn that I went
> > > overboard making the resulting initrd as small as possible. I started
> > > by throwing out everything not absolutely needed by the dash and sleep
> > > binaries, which got me down to about 2.5MB, 1.8MB of which was libc.
> > > This situation of course prompted me to create an initrd containing
> > > a statically linked binary named "init" and absolutely nothing else
> > > (not even /dev or /tmp directories), which weighs in at not quite 800KB.
> > > This is a great improvement over 10MB, to say nothing of 40MB, but 800KB
> > > for a C-language "for" loop containing nothing more than a single call to
> > > sleep()?
> >
> > .globl _start
> > .data
> > req: .8byte 999999999, 999999999
> > .text
> > _start:
> > mov $35, %rax # syscall: nanosleep
> > mov $req, %rdi
> > xor %rsi, %rsi
> > syscall
> > jmp _start
> >
> >
> > as sl.s -o sl.o
> > ld sl.o -o init
> >
> > 'Ere you go, no libc needed. If your arch is not amd64, just say so.
>
> "pause" ($34) would also suffice, and would not require an argument or a
> .data section.

Cute! ;-)

Thanx, Paul