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

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

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?

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.

It maybe that newer versions of GCC are more predictable about this
naming.

Maybe Martin can share some of his experience? CC-ing him.

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