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    SubjectRe: Kernel-only deployments?
    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.

    I need to be arch-independent, but I will save off your solution,
    thank you!

    > If you want to do anything more complex, though -- you really want musl
    > or another lightweight libc instead. Glibc is utterly unfit for static
    > linking.

    Got it, thank you!

    Thanx, Paul

    > Meow!
    > --
    > ⢀⣴⠾⠻⢶⣦⠀ .globl _start↵.data↵rc: .ascii "/etc/init.d/rcS\0"↵.text↵_start
    > ⣾⠁⢰⠒⠀⣿⡁ mov $57,%rax↵syscall↵cmp $0,%rax↵jne child↵parent:↵mov $61,%rax
    > ⢿⡄⠘⠷⠚⠋⠀ mov $-1,%rdi↵xor %rsi,%rsi↵xor %rdx,%rdx↵syscall↵jmp parent↵child:
    > ⠈⠳⣄⠀⠀⠀⠀ mov $59,%rax↵mov $rc,%rdi↵xor %rsi,%rsi↵xor %rdx,%rdx↵syscall
    >

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