[Skiboot] [PATCH 2/2] external/mambo: Error out if kernel is too large

[Oliver]

On Mon, Mar 25, 2019 at 3:51 PM Russell Currey <ruscur at russell.cc> wrote:
>
> On Mon, 2019-03-25 at 15:49 +1100, Oliver wrote:
> > On Mon, Mar 25, 2019 at 3:39 PM Russell Currey <ruscur at russell.cc>
> > wrote:
> > > If you're trying to boot a gigantic kernel in mambo (which you can
> > > reproduce by building a kernel with CONFIG_MODULES=n) you'll get
> > > misleading errors like:
> > >
> > > WARNING: 0: (0): [0:0]: Invalid/unsupported instr
> > > 0x00000000[INVALID]
> > > WARNING: 0: (0):  PC(EA): 0x0000000030000010
> > > PC(RA):0x0000000030000010 MSR: 0x9000000000000000 LR:
> > > 0x0000000000000000
> > > WARNING: 0: (0):  numInstructions = 0
> > > WARNING: 1: (1): [0:0]: Invalid/unsupported instr
> > > 0x00000000[INVALID]
> > > WARNING: 1: (1):  PC(EA): 0x0000000000000E40
> > > PC(RA):0x0000000000000E40 MSR: 0x9000000000000000 LR:
> > > 0x0000000000000000
> > > WARNING: 1: (1):  numInstructions = 1
> > > WARNING: 1: (1): Interrupt to 0x0000000000000E40 from
> > > 0x0000000000000E40
> > > INFO: 1: (2): ** Execution stopped: Continuous Interrupt,
> > > Instruction caused exception,  **
> > >
> > > So add an error to skiboot.tcl to warn the user before this
> > > happens.
> > > Making PAYLOAD_ADDR further back is one way to do this but if
> > > there's a
> > > less gross way to generally work around this very niche problem, I
> > > can
> > > suggest that instead.
> > >
> > > Signed-off-by: Russell Currey <ruscur at russell.cc>
> > > ---
> > >  external/mambo/skiboot.tcl | 4 ++++
> > >  1 file changed, 4 insertions(+)
> > >
> > > diff --git a/external/mambo/skiboot.tcl
> > > b/external/mambo/skiboot.tcl
> > > index 096f1c34..7a939bfb 100644
> > > --- a/external/mambo/skiboot.tcl
> > > +++ b/external/mambo/skiboot.tcl
> > > @@ -552,6 +552,10 @@ mysim memory fread $mconf(boot_load)
> > > $boot_size $mconf(boot_image)
> > >  set payload_size [file size $mconf(payload)]
> > >  mysim memory fread $mconf(payload_addr) $payload_size
> > > $mconf(payload)
> > >
> > > +if { $payload_size > [expr $mconf(boot_load) -
> > > $mconf(payload_addr)] } {
> > > +       error "vmlinux is too large, consider adjusting
> > > PAYLOAD_ADDR"
> > > +}
> >
> > Can we just load the kernel at zero? 768MB really ought to be enough
> > for anyone...
>
> I didn't change the address since I don't know why it is the way it is
> currently.  Even so we should keep the error just in case some mad lad
> makes a gigabyte kernel.

Oh sure, I was just wondering why we don't do that currently.
Actually, come to think of it, it's probably because if you load a
zImage won't have space to extract the vmlinux into.

<bikeshed> maybe mention in the error message that it's overlapping
the skiboot image instead of saying "lolnope"</bikeshed>

>
> >
> > > +
> > >  # Flatten it
> > >  epapr::of2dtb mysim $mconf(epapr_dt_addr)
> > >
> > > --
> > > 2.21.0
> > >
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>