Re: [PATCH for-4.15] xen: Bump the minimum version of GCC supported to 4.9 (5.1 on arm64)

[Julien Grall <julien@xen.org>]

Hi Roger,

On 07/03/2021 10:57, Roger Pau Monné wrote:
> On Sat, Mar 06, 2021 at 09:41:48PM +0000, Julien Grall wrote:
>> From: Julien Grall <jgrall@amazon.com>
>>
>> Compilers older than 4.8 have known codegen issues which can lead to
>> silent miscompilation:
>>
>> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145
>>
>> Furthermore, pre-4.9 GCC have known bugs (including things like
>> internal compiler errors on Arm) which would require workaround (I
>> haven't checked if we have any in Xen).
>>
>> The minimum version of GCC to build the hypervisor is now raised to 4.9.
> 
> The README entry doesn't differentiate between tools and hypervisor
> GCC version, can the bug above also manifest in toolstack code?

I guess it can manifest in the firmware (e.g. hvmloader, rombios). It 
looks rather unlikely in the userspace tools as we seem to barely use 
volatile.

For the Arm64 bug [1], I think it can also show up when receiving a signal.

> 
> I don't think it makes much sense to have diverging requirements for
> tools vs hypervisor builds, but if the bug(s) can also manifest in
> toolstack code we might want to add a GCC version check to
> tools/configure.ac.

Agree. I can add check in ./configure for the toolstack.

Cheers,

[1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63293

-- 
Julien Grall