serial hang in qemu-system-ppc64 -M pseries

[Rob Landley]

On 4/27/22 10:27, Thomas Huth wrote:
> On 26/04/2022 12.26, Rob Landley wrote:
>> When I cut and paste 80-ish characters of text into the Linux serial console, it
>> reads 16 characters and stops. When I hit space, it reads another 16 characters,
>> and if I keep at it will eventually catch up without losing data. If I type,
>> every character shows up immediately.
> 
> That "16" certainly comes from VTERM_BUFSIZE in hw/char/spapr_vty.c in the 
> QEMU sources, I think.
> 
>> (On other qemu targets and kernels I can cut and paste an entire uuencoded
>> binary and it goes through just fine in one go, but this target hangs with big
>> pastes until I hit keys.)
>> 
>> Is this a qemu-side bug, or a kernel-side bug?
>> 
>> Kernel config attached (linux 5.18-rc3 or thereabouts), qemu invocation is:
>> 
>> qemu-system-ppc64 -M pseries -vga none -nographic -no-reboot -m 256 -kernel
>> vmlinux -initrd powerpc64leroot.cpio.gz -append "panic=1 HOST=powerpc64le
>> console=hvc0"
> 
> Which version of QEMU are you using?

$ qemu-system-ppc64 --version
QEMU emulator version 6.2.92 (v6.2.0-rc2)
Copyright (c) 2003-2021 Fabrice Bellard and the QEMU Project developers

>From november. I can pull and rebuild but it'll take a bit. (Hopefully
rebuilding would fix the need to echo -e '\e[?7h' afterwards to undo the "bash
command line history marches up the screen because qemu's x86 bios disabled line
wrap and then left it that way" issue...)

> Which frontend (GTK or terminal?) ... 

The above command line has -nographic, forcing terminal. Running ldd on the
binary doesn't pull up anything gtk. (It pulls up libncursesw though.)

If you want to reproduce my test locally:

wget https://landley.net/toybox/downloads/binaries/mkroot/0.8.5/powerpc64le.tgz
tar xvzf powerpc64le.tgz
cd powerpc64le
./qemu-*.sh

Then paste something longer than 16 characters at the eventual command prompt
once the kernel finishes booting.

If you want to reproduce it all from source:

git clone https://github.com/landley/toybox
cd toybox && mkdir ccc && cd ccc
wget
https://landley.net/toybox/downloads/binaries/toolchains/latest/powerpc64le-linux-musl-cross.tar.xz
-O - | tar xv
cd ..
CROSS=powerpc64le LINUX=~/linux scripts/mkroot.sh
cd root/powerpc64le
./qemu-*.sh

This assumes your linux kernel source directory is in ~/linux of course, and
that qemu-system-ppc64 is in the $PATH...

> this rings a distant bell, but I thought we had fixed these issues long ago 
> in the past... e.g.:
>
> https://yhbt.net/lore/all/1380113886-16845-10-git-send-email-mdroth@linux.vnet.ibm.com/
> 
> https://git.qemu.org/?p=qemu.git;a=commitdiff;h=8a273cbe53221d28

The qemu I'm running is newer than 2016. :)

Most targets are fine with this: I cut and paste entire uuencoded binaries into
the serial console as an easy way to insert a file into an initramfs. It can
usually take multiple megabytes without dropping a character, so you just
"uudecode" enter, and then paste.

Even my 32 bit powerpc target works fine with this. (Although -M g3beige is a
very different machine from -M pseries...)

Alas this target (and sh4 -m r2d) stop at 16 chars. (On sh4 the extra is
discarded, not delivered progressively as more interrupts are generated.)

> ... but maybe my memory also just fails and this has never been properly fixed.
> 
>   Thomas

Rob