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Re: [Qemu-arm] [Qemu-devel] [PATCH] target/arm: Allow to switch from MON

From: Alexander Graf
Subject: Re: [Qemu-arm] [Qemu-devel] [PATCH] target/arm: Allow to switch from MON->HYP on AArch32
Date: Wed, 9 Jan 2019 18:14:10 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0

On 01/09/2019 05:59 PM, Peter Maydell wrote:
On Wed, 9 Jan 2019 at 16:52, Peter Maydell <address@hidden> wrote:
On Wed, 9 Jan 2019 at 15:26, Alexander Graf <address@hidden> wrote:
In U-boot, we switch from S-SVC -> MON -> HYP when we want to enter
HYP mode. This dance seems to work ok (hence it's there in the code
base), but breaks with current QEMU.
PS: it would be helpful if the commit message said how u-boot
is trying to go from Mon to Hyp -- some ways to try to do
this are OK, and some are not, so whether it's supposed to
work or not depends on what u-boot is actually doing...

I don't fully understand all of it to be honest :). But the code is here:


What I managed to understand so far is that it goes to MON using the smc #0 call and then changes SPSR so that on return (movs pc) the mode will be different.

But please double check whether this is supposed to work - I don't find mode switching on ARM terribly intuitive ;).


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