Re: [Xen-devel] [PATCH v3] gcov: add new interface and 3.4 and 4.7 format support

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 12.10.16 at 15:44, <konrad.wilk@xxxxxxxxxx> wrote:
> On Wed, Oct 12, 2016 at 07:31:52AM -0600, Jan Beulich wrote:
>> >>> On 12.10.16 at 15:23, <konrad.wilk@xxxxxxxxxx> wrote:
>> >>  And then - how is all of this supposed to be working in conjucntion
>> >> with live patching, where the patch may have been created by yet
>> >> another compiler version?
>> > 
>> > Uh, I hope one does not create a livepatch patch with another compiler 
>> > version!
>> > 
>> > Let me put on the TODO to make livepatch-build-tools check gcc against
>> > compile.h so that one does not try this.
>> 
>> What's wrong with mixing compiler versions in general?
> 
> Besides scaring me?

What is it that scares you?

> The one issue we had encountered was with compilers generating random named
> symbols for the switch tables. Those end up being called "CSWTCH.XYZ"
> where the XYZ depends on the position of the moon along with how many
> goats you have sacrificied to the altar of GCC gods.
> 
> Older compilers don't neccessarily do it, newer ones do, and every time
> you build an livepatch the naming is different. Frustrating.

But this would mean you don't just depend on gcc version, but even
on the specific build (as the numbering you refer to may change with
whatever patches a distro applies on top of the upstream tarball, as
well as perhaps with configure and build options).

Jan


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