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Date:   Thu, 19 Jan 2023 14:56:07 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     "Erhard F." <erhard_f@mailbox.org>
Cc:     sandipan.das@amd.com, linux-kernel@vger.kernel.org
Subject: 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
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References: <20230119022303.177052e4@yea>
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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@amd.com>
> 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@amd.com>
>     Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
>     Link: https://lore.kernel.org/r/b75dbc32663cb395f0d701167e952c6a6b0445a3.1660211399.git.sandipan.das@amd.com
> 
>  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.