Re: [PATCH 0/7] RFC: coverage deduplication for KCOV

[Alexander Potapenko]

> We've conducted an experiment running syz-testbed [3] on 10 syzkaller
> instances for 24 hours.  Out of those 10 instances, 5 were enabling the
> kcov_deduplicate flag from [4], which makes use of the KCOV_UNIQUE_ENABLE
> ioctl, reserving 4096 words (262144 bits) for the bitmap and leaving 520192
> words for the trace collection.
>
> Below are the average stats from the runs.
>
> kcov_deduplicate=false:
>   corpus: 52176
>   coverage: 302658
>   cover overflows: 225288
>   comps overflows: 491
>   exec total: 1417829
>   max signal: 318894
>
> kcov_deduplicate=true:
>   corpus: 52581
>   coverage: 304344
>   cover overflows: 986
>   comps overflows: 626
>   exec total: 1484841
>   max signal: 322455
>
> [1] https://lore.kernel.org/linux-arm-kernel/20250114-kcov-v1-5-004294b931a2@xxxxxxxxxxx/T/
> [2] https://clang.llvm.org/docs/SanitizerCoverage.html
> [3] https://github.com/google/syzkaller/tree/master/tools/syz-testbed
> [4] https://github.com/ramosian-glider/linux/pull/7
Ouch, this should have been:
  [4] https://github.com/ramosian-glider/syzkaller/tree/kcov_dedup-new

I will update the link in v2.
>
>
> Alexander Potapenko (7):
>   kcov: apply clang-format to kcov code
>   kcov: factor out struct kcov_state
>   kcov: x86: introduce CONFIG_KCOV_ENABLE_GUARDS
>   kcov: add `trace` and `trace_size` to `struct kcov_state`
>   kcov: add ioctl(KCOV_UNIQUE_ENABLE)
>   x86: objtool: add support for R_X86_64_REX_GOTPCRELX
>   mm/kasan: define __asan_before_dynamic_init, __asan_after_dynamic_init
>
>  Documentation/dev-tools/kcov.rst  |  43 +++
>  MAINTAINERS                       |   1 +
>  arch/x86/include/asm/elf.h        |   1 +
>  arch/x86/kernel/module.c          |   8 +
>  arch/x86/kernel/vmlinux.lds.S     |   1 +
>  arch/x86/um/asm/elf.h             |   1 +
>  include/asm-generic/vmlinux.lds.h |  14 +-
>  include/linux/kcov-state.h        |  46 +++
>  include/linux/kcov.h              |  60 ++--
>  include/linux/sched.h             |  16 +-
>  include/uapi/linux/kcov.h         |   1 +
>  kernel/kcov.c                     | 453 +++++++++++++++++++-----------
>  lib/Kconfig.debug                 |  16 ++
>  mm/kasan/generic.c                |  18 ++
>  mm/kasan/kasan.h                  |   2 +
>  scripts/Makefile.kcov             |   4 +
>  scripts/module.lds.S              |  23 ++
>  tools/objtool/arch/x86/decode.c   |   1 +
>  tools/objtool/check.c             |   1 +
>  19 files changed, 508 insertions(+), 202 deletions(-)
>  create mode 100644 include/linux/kcov-state.h
>
> --
> 2.49.0.604.gff1f9ca942-goog
>


--
Alexander Potapenko
Software Engineer

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