Re: [PATCH 00/12] ARM: use adr_l/ldr_l macros for PC-relative references

[Nick Desaulniers <ndesaulniers@google.com>]

On Fri, Sep 18, 2020 at 1:44 PM Ard Biesheuvel <ardb@kernel.org> wrote:
>
> On Fri, 18 Sep 2020 at 22:03, Nick Desaulniers <ndesaulniers@google.com> wrote:
> >
> > On Wed, Sep 16, 2020 at 11:01 PM Ard Biesheuvel <ardb@kernel.org> wrote:
> > >
> > > On Thu, 17 Sep 2020 at 00:25, Nick Desaulniers <ndesaulniers@google.com> wrote:
> > > > Also, it looks like the GCC build of milbeaut_m10v_defconfig fails to
> > > > boot for me in QEMU; so maybe not just a Clang bug (or maybe, more
> > > > than one bug).  (or maybe one of my command line params to QEMU is
> > > > wrong).
> > > >
> > >
> > > I understand that this is actually an existing issue in -next, but in
> > > general, why would you expect to be able to boot
> > > milbeaut_m10v_defconfig on anything other than a Milbeaut MV10
> > > machine?
> >
> > We've been booting other configs in QEMU for a few years now, so I
> > don't see why yet another config would hurt.  Maybe there's some
> > hardware dependency, but I guess we'd find that out trying to boot it
> > in QEMU.  If it boots in QEMU, I guess not booting on metal wasn't so
> > bad?  Maybe this is considered an antipattern, but you can see how if
> > we've been getting away with it for years then that would lead to such
> > expectations.
> >
> > > (whatever it is) Or does QEMU emulate a milbeaut machine?
> >
> > $ qemu-system-arm -machine help
> >
> > doesn't print anything that looks like it, on initial glance.  Looks
> > like a socionext part:
> > https://www.socionext.com/en/pr/sn_pr20170105_01e.pdf
> >
> > > If
> > > not, better to stick with configs that are intended to boot on the
> > > QEMU machine emulation that you are using.
> >
> > I can see in our CI that we've been building+boot testing
> > multi_v5_defconfig, aspeed_g5_defconfig, and multi_v7_defconfig for a
> > while now without specifying any machine.  Is there a preferred
> > machine we should be using for those?  (It looks like qemu supports
> > ast2500-evb and ast2600-evb; is ARM1176 and ARMv6 core? Is that what
> > aspeed_g5 uses? Why is virt versioned? Ahhhh!!!!)
> >
>
> Milbeaut's serial output is on a "socionext,milbeaut-usio-uart" UART,
> and its defconfig does not include drivers for the PL011 or 8250/16550
> UARTs that you typically find on other boards. So how on earth would
> you expect to get any output at all if QEMU does not emulate this
> exact machine?

breakpoints in panic()/printk(), lx-dmesg in GDB via
CONFIG_GDB_SCRIPTS=y generally works. :^)

I guess one thing I don't understand is how to check what UART or what
the name of the tty device would be.  I can grep for
"socionext,milbeaut-usio-uart" and see where it's defined, but I never
would have/still don't know how to find that. Please teach me how to
fish.  I understand the point of DT, and see

arch/arm/boot/dts/milbeaut-m10v.dtsi
76:                     compatible = "socionext,milbeaut-usio-uart";

but the comment about ttyUSI0 is confusing to me; that identifier
doesn't appear anywhere else in the kernel sources.

I generally have the same problem trying to run Pixel kernels in QEMU;
I don't understand how to determine which serial driver is being used,
and what the tty device would be named.  So I just enable the PLO11
driver.

Only last week I found that trying to use a shell as init without any
serial output can result in the shell exiting, panicking the kernel,
which doesn't print over serial...goose chase...

> In general, if you use QEMU/mach-virt, the only defconfigs you should
> reasonably be testing are the ones that contain CONFIG_ARCH_VIRT=y.

Looks like then that would only be multi_v7_defconfig.  How do we
continue to verify we can boot ARMv6 or ARMv5 under virtualization?
There are such machines in QEMU, but then no defconfigs in the kernel.
-- 
Thanks,
~Nick Desaulniers