Re: [PATCH v1 2/3] linux-user: deal with address wrap for ARM_COMMPAGE on 32 bit

[Alex Bennée]

Aleksandar Markovic <address@hidden> writes:

> сре, 27. мај 2020. у 14:05 Aleksandar Markovic
> <address@hidden> је написао/ла:
>>
>> сре, 27. мај 2020. у 12:07 Alex Bennée <address@hidden> је написао/ла:
>> >
>> > We rely on the pointer to wrap when accessing the high address of the
>> > COMMPAGE so it lands somewhere reasonable. However on 32 bit hosts we
>> > cannot afford just to map the entire 4gb address range. The old mmap
>> > trial and error code handled this by just checking we could map both
>> > the guest_base and the computed COMMPAGE address.
>> >
>> > We can't just manipulate loadaddr to get what we want so we introduce
>> > an offset which pgb_find_hole can apply when looking for a gap for
>> > guest_base that ensures there is space left to map the COMMPAGE
>> > afterwards.
>> >
>> > This is arguably a little inefficient for the one 32 bit
>> > value (kuser_helper_version) we need to keep there given all the
>> > actual code entries are picked up during the translation phase.
>> >
>> > Fixes: ee94743034b
>> > Bug: https://bugs.launchpad.net/qemu/+bug/1880225
>>
>> For the scenario in this bug report, for today's master, before and after
>> applying this patch:
>>
>
> I am not sure how significant is this info, but I executed the test
> without applying patch 1/3, so only 2/3 was applied in the case
> "AFTER".

That is expected. The other fix only affects binaries run inside a
/proc-less chroot and the final patch is a test case for COMMPAGE
support.

-- 
Alex Bennée