[Toybox] Impact of global struct size

[enh]

On Thu, Jan 4, 2024 at 10:05 AM Rob Landley <rob at landley.net> wrote:
>
> On 1/3/24 12:19, Mouse wrote:
> >> (The line between PIE and dynamic linking confuses even me.  How does
> >> static PIE relocate itself?
> >
> > It may not.  It could get relocated by in-kernel ASLR or the like.
> > Also, I think PIE isn't relevant, or certainly isn't _as_ relevant, to
> > the final executable; my impression is that it's more important for
> > library code, so it doesn't need fixups.  These are less important for
> > static executables, since the fixups there happen once, at link time,
> > whereas for a .so the fixups happen at runtime and reduce the
> > text-segment sharing that is one of the benefits of shared objects.
>
> I want https://www.muppetlabs.com/~breadbox/software/tiny/teensy.html but a
> walkthrough for the kernel's ELF loader. (I've had to walk through it MYSELF
> several times, but I didn't do writeups afterwards so forgot it all.)

(yeah, and the one i've done for that and for the libc side of things
were both just google-internal talks, so there's no record of them
anywhere :-( )

i've been meaning to tell you, apropos something you said on your blog
about ARG_MAX (for xargs?), that the kernel changed how that works
recently... see
https://android.googlesource.com/platform/bionic/+/main/tests/unistd_test.cpp#1128
for more detail and links.

> I suppose I should start by reading his dynamic version:
>
> https://www.muppetlabs.com/~breadbox/software/tiny/somewhat.html
>
> >> Luckily X11 has "detach and restart" plumbing that lets it reopen a
> >> process's network pipe without killing the window or the process,
> >
> > ...?  When did it grow that, and where can I find out more about it?
>
> Um... A) Before Scale 2011, B) ask Kir Kolyshkin? He said it was something old.
> (I think the program can just detect that the connection closed and dial out to
> the server again, opening a new window and repopulating it? It's just most
> programs don't bother.)
>
> What OpenVZ was doing was
>
> A) tell the container to create a giant multi-process coredump file that had
> every process in the container in one big file (but don't STOP anything, just
> checkpoint the live running stuff racily).
>
> B) rsync the filesystem and coredump over to the new machine.
>
> C) Suspend the container (all processes) and re-write the big coredump file.
>
> D) rsync everything AGAIN (fast because not much changed)
>
> E) do TCP/IP connection hijacking so the new machine inherits the old open
> connections (you don't have to predict sequence numbers the other side sends
> you, don't forget to broadcast an ARP update so the packets go to the new
> ethernet address):
>
> https://www.idc-online.com/technical_references/pdfs/data_communications/TCP_Sequence_Prediction_Attack.pdf
>
> F) Resume the new container in the new filesystem.
>
> He had an animated X11 window (screensaver) that paused for 1/3 of a second
> while migrating from machine to machine. His demo involved plugging in a cat 5
> to the new machine, migrating to it, and unplugging the old one's network cable.
>
> This was in 2011. I assume vanilla Linux has caught up by now, but there was
> quite the laundry list at the time...
>
> Rob
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