linux-kernel - Re: [PATCH v3 0/3] gcov: add Clang support

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Message-Id: <7c7b4521-d747-d064-0506-4e3d6746877e@linux.ibm.com>
Date:   Tue, 5 Mar 2019 15:29:51 +0100
From:   Peter Oberparleiter <oberpar@...ux.ibm.com>
To:     Tri Vo <trong@...roid.com>
Cc:     ghackmann@...roid.com, ndesaulniers@...gle.com,
        linux-kernel@...r.kernel.org, kernel-team@...roid.com,
        yamada.masahiro@...ionext.com,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v3 0/3] gcov: add Clang support

On 23.01.2019 00:37, Tri Vo wrote:
> This patch series adds Clang supoprt for gcov.
> 
> Patch 1 refactors existing code in preparation for Clang support.
> Patch 2 implements necessary LLVM runtime hooks and gcov kernel interfaces.
> Patch 3 updates documentation.

Thanks for the updates! I've provided suggestions for some minor
improvements in my other review e-mails.

With those changes applied, the patch set is in my opinion ready for
inclusion into the mainline kernel. My suggestion would be to re-post
the resulting version while putting Andrew Morton on CC as gcov changes
are typically integrated via his tree.

Also I've successfully re-tested this patch set version on s390 using
GCC 7.3.0 to ensure that the existing GCC support is still working.
Unfortunately I wasn't able to test the Clang version due to some
compile problems on s390 (unrelated to this patch set).

If you haven't done so, I would like to suggest to run the following
tests with the Clang gcov-kernel version that should catch problems in
some corner cases:

1. Unload a module, then use llvm-cov on the associated coverage file.

   Expectation: correct llvm-cov output including coverage of module
   exit code.

2. Unload a module, modify its source, re-compile it and load it again,
   then use llvm-cov on the associated coverage file.

   Expectation: kernel message "discarding saved data", correct llvm-cov
   output with no coverage of module exit code.

3. Unload a module, then reset all coverage data by writing to
   /sys/kernel/debug/gcov/reset.

   Expectation: all coverage files associated with the module are
   removed from debugfs.

-- 
Peter Oberparleiter
Linux on Z Development - IBM Germany