Messages in this thread | | | Date | Fri, 20 Jan 2023 11:20:53 +0530 | 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 | From | Sandipan Das <> |
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On 1/19/2023 8:48 PM, Peter Zijlstra wrote: > 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@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. >>
I had a similar experience on a system with an AMD EPYC 7713. Both guest and bare-metal boot failed.
>> 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. >
With the combination of defconfig+kvm_guest.config+localyesconfig, the only thing that made a difference was the compiler optimization choice. The kernel boots up with CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE=y but not with CONFIG_CC_OPTIMIZE_FOR_SIZE=y. Both Clang 15 and 16 kernel builds are affected.
- Sandipan
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