fs.py --generate-dtb Linux kernel boot simulation fails for aarch64 with "Exiting @ tick because simulate() limit reached"

[cirosantilli2]

https://www.mail-archive.com/gem5-users@gem5.org/msg15539.html

I had both aarch64 and arm working with --dtb-file using: https://github.com/cirosantilli/linux-kernel-module-cheat/tree/0678bd82ac61f0decce3480fef798bd5edbfd0c3#gem5

But now I've learnt about the awesome --generate-dtb option, which would make my setup simpler, and I'd like to use it.

If I replace my --dtb-file with --generate-dtb on an arm simulation, it all worked fine and Linux booted.

However, for a very analogous boot of aarch64 nothing shows on the terminal and gem5 exits with an error.

gem5 revision: 49f96e7b77925837aa5bc84d4c3453ab5f07408e (current master)

full gem5 command line:

M5_PATH='/work/linux-kernel-module-cheat/out/common/gem5/system' \
 '/work/linux-kernel-module-cheat/out/common/gem5/build/ARM/gem5.opt' \
--debug-file=trace.txt \
 -d '/work/linux-kernel-module-cheat/out/aarch64/gem5/m5out' \
'/work/linux-kernel-module-cheat/gem5/gem5/configs/example/fs.py' \
--disk-image='/work/linux-kernel-module-cheat/out/aarch64/buildroot/images/rootfs.ext2' \
--kernel='/work/linux-kernel-module-cheat/out/aarch64/buildroot/build/linux-custom/vmlinux' \
--mem-size='256MB' \
--num-cpus='1' \
--script='/work/linux-kernel-module-cheat/data/readfile' \
 --command-line='earlyprintk=pl011,0x1c090000 console=ttyAMA0 lpj=19988480 rw loglevel=8 mem=256MB root=/dev/sda console_msg_format=syslog nokaslr norandmaps printk.devkmsg=on printk.time=y' \
--generate-dtb \
--machine-type=VExpress_GEM5_V1 \

It boots correctly however I use instead of --generate-dtb:

--dtb-file='/work/linux-kernel-module-cheat/out/common/gem5/system/arm/dt/armv8_gem5_v1_1cpu.dtb' \

Error message:

**** REAL SIMULATION ****
warn: Existing EnergyCtrl, but no enabled DVFSHandler found.
info: Entering event queue @ 0.  Starting simulation...
warn: SCReg: Access to unknown device dcc0:site0:pos0:fn7:dev0
warn: Tried to read RealView I/O at offset 0x60 that doesn't exist
warn: Tried to read RealView I/O at offset 0x48 that doesn't exist
warn: Tried to write RVIO at offset 0xa8 (data 0) that doesn't exist
Exiting @ tick 18446744073709551615 because simulate() limit reached

[cdunham]

Hi Ciro,
You are probably experiencing this problem because the simulated CPU enters a wait state (e.g. via WFI/WFE on Arm) but without any simulated (or otherwise, i.e. user provided) I/O activity, no event ever gets scheduled and time immediately proceeds to its maximum value, resulting in this message.

To avoid this, you need to activate time_sync_enable on the Root object (see src/sim/Root.py:73-75). You will find that this can be enabled using the --timesync argument to fs.py.

Regards,
Curtis

[cdunham]

Ah I see you mention nothing shows on the terminal. Possibly you are running into another issue first.

[cirosantilli2]

@cdunham thanks for the tip, if I pass --timesync it does not exit anymore with limit reached but rather appears to hang without any output on terminal. Let me know if you manage to reproduce, or have a working aarch64 setup.

[cirosantilli2]

Can't reproduce anymore on a5bc2291391b0497fdc60fdc960e07bcecebfb8f.