Re: [bisected] clang 15 built kernel fails to boot, stuck at "Loading Linux 6.1.1 ...", gcc 12 built kernel with same config boots fine

[Peter Zijlstra]

On Thu, Jan 19, 2023 at 02:56:08PM +0100, Peter Zijlstra wrote:
> On Thu, Jan 19, 2023 at 02:23:03AM +0100, Erhard F. wrote:
> > Hi!
> > 
> > I did a kernel bisect for an issue I originally posted on https://github.com/ClangBuiltLinux/linux/issues/1774
> > 
> > It is about kernel 6.1.x not booting on my machines when built with clang. A gcc built kernel with the same config just works fine. Turns out kernel v6.2-rc4 and earlier v6.2-rc are still affected.
> > 
> > I did a kernel bisect which revealed this commit:
> > 
> >  # git bisect bad
> > 706460a96fc654e80b6bed1f562b00d2ce9f2f4d is the first bad commit
> > commit 706460a96fc654e80b6bed1f562b00d2ce9f2f4d
> > Author: Sandipan Das <sandipan.das@xxxxxxx>
> > Date:   Thu Aug 11 17:59:51 2022 +0530
> > 
> >     perf/x86/amd/core: Add generic branch record interfaces
> >     
> >     AMD processors that are capable of recording branches support either Branch
> >     Sampling (BRS) or Last Branch Record (LBR). In preparation for adding Last
> >     Branch Record Extension Version 2 (LbrExtV2) support, introduce new static
> >     calls which act as gateways to call into the feature-dependent functions
> >     based on what is available on the processor.
> >     
> >     Signed-off-by: Sandipan Das <sandipan.das@xxxxxxx>
> >     Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> >     Link: https://lore.kernel.org/r/b75dbc32663cb395f0d701167e952c6a6b0445a3.1660211399.git.sandipan.das@xxxxxxx
> > 
> >  arch/x86/events/amd/core.c | 34 ++++++++++++++++++++++------------
> >  1 file changed, 22 insertions(+), 12 deletions(-)
> 
> Using: v6.2-rc4-67-g7287904c8771
> 
> I have an AMD Interlagos and after bringing it back to live/up-to-date I
> can't seem to even boot your .config in qemu/kvm irrespective of
> GCC/Clang.
> 
> When I build defconfig+kvm_guest.config both GCC-12 and clang-15 boot
> just fine in qemu/kvm.

Furthermore, testing localyesconfig based off Debian's
config-6.1.0-1-amd64 boots fine using both GCC-12 and clang-15 as host
kernels on that machine.