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

[Richard Henderson <richard.henderson@linaro.org>]

On 5/16/20 5:58 AM, Peter Maydell wrote:
> 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.

I don't see any way around that.

As I said, if we put the rebuild in cpsr_write, then we should also rearrange
the code that calls cpsr_write to assume that's where the rebuild gets done.


r~