On Wed, 17 May 2023 at 23:42, Nick Desaulniers ndesaulniers@google.com wrote:
On Wed, May 17, 2023 at 8:21 AM Naresh Kamboju naresh.kamboju@linaro.org wrote:
Linux next-20230517 build with clang nightly for i386 boot fails intermittently.
Keyword: intermittently. That will make tracking this down fun.
Our CI also hit a boot failure on tip/master with the same splat: https://github.com/ClangBuiltLinux/continuous-integration2/actions/runs/4998... Though the CI pulled down a SHA 0932447780e1f9a43bf68ef7fe3d9b41b46d58fc which looks weird on https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?id=09324...
Notice: this object is not reachable from any branch.
That this failed in -next and -tip in the same way makes me wonder if something affecting this is coming in via -tip? Maybe the splat looks familiar to x86 folks?
I haven't been able to reproduce locally when my machine is relatively load-less. If I do a kernel build in the background, I was able to get QEMU to hang, but without any splat. That was using tip/master @ f81d8f759e7f.
Naresh, when you say "intermittent" do you have any data on the relative frequency of this boot failure? (Also, please make sure to use llvm@lists.linux.dev in the future; we moved mailing lists years ago).
Noted: It is reproducible only 3 times out of 100 runs.
Looks like our CI report linked above has an additional splat though via apply_alternatives and optimize_nops.
[ 0.166742] Code: Unable to access opcode bytes at 0x36.
Peter, that smells like perhaps either: commit b6c881b248ef ("x86/alternative: Complicate optimize_nops() some more") commit 6c480f222128 ("x86/alternative: Rewrite optimize_nops() some")
Looks like BP committed them May 11; maybe just recently they were merged into tip/master?
- i386: boot/clang-nightly-lkftconfig - failed
- Naresh