linux-kernel - Re: [PATCH v2 0/4] Enable measuring the kernel's Source-based Code Coverage and MC/DC with Clang

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Message-ID: <20241009031738.2851980-1-wentaoz5@illinois.edu>
Date: Tue,  8 Oct 2024 22:17:38 -0500
From: Wentao Zhang <wentaoz5@...inois.edu>
To: nathan@...nel.org
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Subject: Re: [PATCH v2 0/4] Enable measuring the kernel's Source-based Code Coverage and MC/DC with Clang

On 2024-10-03 18:29, Nathan Chancellor wrote:
> ...
>>> I was able to successfully build that same configuration and setup with
>>> my primary workstation, which is much beefier. Unfortunately, the
>>> resulting kernel did not boot with my usual VM testing setup. I will see
>>> if I can narrow down a particular configuration option that causes this
>>> tomorrow because I did a test with defconfig +
>>> CONFIG_LLVM_COV_PROFILE_ALL and it booted fine. Perhaps some other
>>> option that is not compatible with this? I'll follow up with more
>>> information as I have it.
>>
>> Good to hear that you've run it and thanks for reporting the booting issue.
>> You may send me the config if appropriate and I'll also take a look.
> 
> I seem to have narrowed down it to a few different configurations on top
> of x86_64_defconfig but I will include the full bad configuration as an
> attachment just in case anything else is relevant.
> 
> $ echo 'CONFIG_LLVM_COV_KERNEL=y
> CONFIG_LLVM_COV_PROFILE_ALL=y' >kernel/configs/llvm_cov.config
> 
> $ echo CONFIG_FORTIFY_SOURCE=y >kernel/configs/fortify_source.config
> 
> $ echo CONFIG_AMD_MEM_ENCRYPT=y >arch/x86/configs/amd_mem_encrypt.config
> 

Chuck and I can confirm the issue is reproducible these options, and we
are still looking into it. Thanks for catching this!

> ...
> 
> Another thing I noticed with this series is there is no entries added to
> MAINTAINERS. Who is going to be responsible for maintaining this code?
> 

We are going to add the following as the fifth patch in v3:

diff --git a/MAINTAINERS b/MAINTAINERS
index a097afd76..55438cb90 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -13262,6 +13262,12 @@ F:	include/net/llc*
 F:	include/uapi/linux/llc.h
 F:	net/llc/

+LLVM-COV BASED KERNEL PROFILING
+M:	Wentao Zhang <wentaoz5@...inois.edu>
+M:	Chuck Wolber <chuck.wolber@...ing.com>
+S:	Maintained
+F:	kernel/llvm-cov/
+
 LM73 HARDWARE MONITOR DRIVER
 M:	Guillaume Ligneul <guillaume.ligneul@...il.com>
 L:	linux-hwmon@...r.kernel.org

Other than the booting issue, v3 is ready and being tested locally.

Thanks,
Wentao

> Cheers,
> Nathan