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Re: [PATCH 0/2] Fixups for fcf-protection


  • To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Jason Andryuk <jandryuk@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
  • From: Stefan Bader <stefan.bader@xxxxxxxxxxxxx>
  • Date: Wed, 13 May 2020 07:41:15 +0200
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  • Cc: Wei Liu <wl@xxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
  • Delivery-date: Wed, 13 May 2020 05:41:40 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 12.05.20 20:47, Andrew Cooper wrote:
> On 12/05/2020 08:17, Stefan Bader wrote:
>> On 12.05.20 05:39, Jason Andryuk wrote:
>>> Two patches to fix building with a cf-protection toolchain.  The first
>>> handles the case where the compiler fails to run with "error:
>>> ‘-mindirect-branch’ and ‘-fcf-protection’ are not compatible".
>>>
>>> The second fixes a runtime error that prevented Xen booting in legacy
>>> mode.
>> That might be better than just disabling fcf-protection as well (which was 
>> done
>> in Ubuntu lacking a better solution).
> 
> It is a GCC bug
> 
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93654
> 
> Fixed for 10, and 9.4

Ah, thanks. And yes, should have reported sooner but, as always, one runs into
those things while in a hurry, with not enough time. We were glad to have
something that did work somehow.

> 
>>
>> Not sure it was already hit but that additional .note section breaks the 
>> build
>> of the emulator as generated headers become gigantic:
>>
>> https://git.launchpad.net/ubuntu/+source/xen/tree/debian/patches/1001-strip-note-gnu-property.patch?h=ubuntu/focal
> 
> 4.6G of notes?!?  That is surely a toolchain bug.

No, sorry if that was unclear. The .notes themselves are just about some Kb or
so per object file. Problem is that each object file gets converted into a hex
array header file. And this does multiply the resulting header file sizes.
So the .h files generated are 4.6G in size. And there were a couple of those,
all included into one .c file. Which ended in the compiler running out of memory
on a 32GB system.

> 
> ~Andrew
> 




 


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