Re: [PATCH 1/3] x86/EFI: Fix detection of buildid

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Fri, 6 Jun 2025, Jan Beulich wrote:
> > But the argument I'm going to make this this:  Why do you want a check,
> > even if you can find a correct one (and as said before, I cannot)?
> > 
> > This function is run exactly once.  We've excluded "nothing given by the
> > toolchain", and excluded "what the toolchain gave us was not the
> > expected ELF note".  The only thing left (modulo toolchain bugs) is the
> > CodeView region, and if it's not a valid CodeView region then we've
> > wasted a handful of cycles.
> 
> Two reasons: Having code which cannot possibly do anything useful isn't
> good. Misra calls the latest the body of the inner if() "unreachable code"
> and objects to the presence of such in a build. (I'm pretty sure Eclair
> wouldn't spot it, but that doesn't eliminate this being a violation of
> the respective rule.)

As far as I can tell this code can be reachable simply by having an
appropriate test with Xen booted via a non-EFI method and a CodeView
record being present. No code changes to Xen needed.


> And then, based on your reasoning above, why don't you also drop the
> #ifdef CONFIG_X86?

Because while theoretically possible, today there is not a single test
that would allow us to trigger this code on ARM. We would need to change
Xen to do it first.