Le 04/11/2021 à 12:11, Peter Maydell a écrit :
On Wed, 3 Nov 2021 at 13:27, Jean-Christophe DUBOIS<j...@tribudubois.net>
wrote:
I have a little application that is designed to work on the i.MX6UL processor.
I developed it and tested it on the mcimx6ul-evk platform emulated by Qemu.
This application used to work "flawlessly" on Qemu 5.0.50 and is working on
Qemu 6.0.0 (available as a pre-built package on the latest Ubuntu).
But when I try to run the exact same command line on a Qemu version I compile
myself from main/latest of github (Qemu 6.1.50), my application fails to start.
So a little background:
My application expects to start in "secure" state and supervisor mode (which is
the default state of i.MX6UL when booting barebone [without u-boot]).
From this state the application tries to get to "non secure" / hypervisor mode which imply going to the
"secure" / monitor state before being able to drop to "non secure" / hypervisor. To do so is runs a "smc
0" operand (from "secure" / supervisor).
This "smc" instruction is processed "as expected" by Qemu 5.0.50 and Qemu 6.0.0 (getting to
"secure" / monitor mode) but on Qemu 6.1.50 (latest from github) it is as if the smc operand was a no-op. It
doesn't trigger any exception and the processor just get to the next instruction after the "smc" instruction.
So I am a bit puzzled.
Is there something that changed in Qemu (since Qemu 6.0.0) when it comes to the
"secure" world/state?
Is there some additional command line parameters to use (I search in the
documentation but without luck) to get secure world behavior ?
Is it necessary to "adapt" the emulated platform (i.MX6UL/mcimx6ul-evk) in some way (it looks like
the "virt" machine with "secure=on" does work for arm platform)?
Could you try doing a bisect to find the QEMU commit that caused
your guest to stop working ?
OK, I did the bisect and the commit that break the i.MX6UL behavior for
my program is commit 9fcd15b9193e819b6cc2fd0a45e3506148812bb4 (arm: tcg:
Adhere to SMCCC 1.3 section 5.2).
Before it the SMC instruction would trigger a monitor exception.
After it the SMC instruction is acting like a no-op.
Thanks
JC
thanks
-- PMM
