Re: [PATCH] linux-user/arm: Reset CPSR_E when entering a signal handler

[Peter Maydell <peter.maydell@linaro.org>]

On Sat, 16 May 2020 at 05:12, Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> On 5/15/20 2:25 PM, Peter Maydell wrote:
> >> You also need to call arm_rebuild_hflags() after modifying CPSR_E
> >> otherwise the change doesn't take effect.
> >
> > Hmm. I was expecting cpsr_write() to take care of that if we
> > updated a cpsr flag that was in the hflags, but it looks like
> > the rebuild_hflags() is in the HELPER() wrapper but not in
> > cpsr_write() itself. Richard, does anything go wrong if
> > cpsr_write() proper does the hflags rebuild ?
>
> We wind up rebuilding hflags multiple times, is all.
>
> Most of the time we call cpsr_write we also do something else that also
> requires a rebuild.  So we do it once after all updates.

The downside is that it leaves a trap which makes it really
easy to introduce bugs where hflags aren't rebuilt: as
a caller of cpsr_write() I don't really want to have to
care which cpsr flags happen to be in the hflags or not,
and it's particularly awkward that simply fixing which
flags belong in CPSR_USER suddenly means that a call
that happened to be OK before is now buggy.

thanks
-- PMM