Message-ID: <CAK7LNAT-AO9_Y-qunRvPbBYf7GZnoE6bxYKFNtcdKAKV8d_A+w@mail.gmail.com>
Date:   Thu, 6 Aug 2020 17:43:54 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Nathan Huckleberry <nhuck@...gle.com>
Cc:     Michal Marek <michal.lkml@...kovi.net>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Pirama Arumuga Nainar <pirama@...gle.com>,
        Bill Wendling <morbo@...gle.com>
Subject: Re: [PATCH v7] Makefile: Add clang-tidy and static analyzer support
 to makefile

On Tue, Jul 28, 2020 at 9:47 AM Nathan Huckleberry <nhuck@...gle.com> wrote:
>
> This patch adds clang-tidy and the clang static-analyzer as make
> targets. The goal of this patch is to make static analysis tools
> usable and extendable by any developer or researcher who is familiar
> with basic c++.
>
> The current static analysis tools require intimate knowledge of the
> internal workings of the static analysis. Clang-tidy and the clang
> static analyzers expose an easy to use api and allow users unfamiliar
> with clang to write new checks with relative ease.
>
> ===Clang-tidy===
>
> Clang-tidy is an easily extendable 'linter' that runs on the AST.
> Clang-tidy checks are easy to write and understand. A check consists of
> two parts, a matcher and a checker. The matcher is created using a
> domain specific language that acts on the AST
> (https://clang.llvm.org/docs/LibASTMatchersReference.html).  When AST
> nodes are found by the matcher a callback is made to the checker. The
> checker can then execute additional checks and issue warnings.
>
> Here is an example clang-tidy check to report functions that have calls
> to local_irq_disable without calls to local_irq_enable and vice-versa.
> Functions flagged with __attribute((annotation("ignore_irq_balancing")))
> are ignored for analysis. (https://reviews.llvm.org/D65828)
>
> ===Clang static analyzer===
>
> The clang static analyzer is a more powerful static analysis tool that
> uses symbolic execution to find bugs. Currently there is a check that
> looks for potential security bugs from invalid uses of kmalloc and
> kfree. There are several more general purpose checks that are useful for
> the kernel.
>
> The clang static analyzer is well documented and designed to be
> extensible.
> (https://clang-analyzer.llvm.org/checker_dev_manual.html)
> (https://github.com/haoNoQ/clang-analyzer-guide/releases/download/v0.1/clang-analyzer-guide-v0.1.pdf)
>
> The main draw of the clang tools is how accessible they are. The clang
> documentation is very nice and these tools are built specifically to be
> easily extendable by any developer. They provide an accessible method of
> bug-finding and research to people who are not overly familiar with the
> kernel codebase.
>
> Signed-off-by: Nathan Huckleberry <nhuck@...gle.com>
> ---
> Changes v6->v7
> * Fix issues with relative paths
> * Additional style fixes
>  MAINTAINERS                                   |  1 +
>  Makefile                                      |  3 +
>  scripts/clang-tools/Makefile.clang-tools      | 23 ++++++
>  .../{ => clang-tools}/gen_compile_commands.py |  0
>  scripts/clang-tools/run-clang-tools.py        | 74 +++++++++++++++++++
>  5 files changed, 101 insertions(+)
>  create mode 100644 scripts/clang-tools/Makefile.clang-tools
>  rename scripts/{ => clang-tools}/gen_compile_commands.py (100%)
>  create mode 100755 scripts/clang-tools/run-clang-tools.py
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 1d4aa7f942de..a444564e5572 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -4198,6 +4198,7 @@ W:        https://clangbuiltlinux.github.io/
>  B:     https://github.com/ClangBuiltLinux/linux/issues
>  C:     irc://chat.freenode.net/clangbuiltlinux
>  F:     Documentation/kbuild/llvm.rst
> +F:     scripts/clang-tools/
>  K:     \b(?i:clang|llvm)\b
>
>  CLEANCACHE API
> diff --git a/Makefile b/Makefile
> index fe0164a654c7..3e2df010b342 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -747,6 +747,7 @@ KBUILD_CFLAGS       += $(call cc-option,-fno-allow-store-data-races)
>
>  include scripts/Makefile.kcov
>  include scripts/Makefile.gcc-plugins
> +include scripts/clang-tools/Makefile.clang-tools
>
>  ifdef CONFIG_READABLE_ASM
>  # Disable optimizations that make assembler listings hard to read.
> @@ -1543,6 +1544,8 @@ help:
>         @echo  '  export_report   - List the usages of all exported symbols'
>         @echo  '  headerdep       - Detect inclusion cycles in headers'
>         @echo  '  coccicheck      - Check with Coccinelle'
> +       @echo  '  clang-analyzer  - Check with clang static analyzer'
> +       @echo  '  clang-tidy      - Check with clang-tidy'
>         @echo  ''
>         @echo  'Tools:'
>         @echo  '  nsdeps          - Generate missing symbol namespace dependencies'
> diff --git a/scripts/clang-tools/Makefile.clang-tools b/scripts/clang-tools/Makefile.clang-tools
> new file mode 100644
> index 000000000000..5c9d76f77595
> --- /dev/null
> +++ b/scripts/clang-tools/Makefile.clang-tools
> @@ -0,0 +1,23 @@
> +# SPDX-License-Identifier: GPL-2.0
> +#
> +# Copyright (C) Google LLC, 2020
> +#
> +# Author: Nathan Huckleberry <nhuck@...gle.com>
> +#
> +PHONY += clang-tidy
> +clang-tidy:
> +ifdef CONFIG_CC_IS_CLANG
> +       $(PYTHON3) scripts/clang-tools/gen_compile_commands.py
> +       $(PYTHON3) scripts/clang-tools/run-clang-tools.py clang-tidy compile_commands.json
> +else
> +       $(error clang-tidy requires CC=clang)
> +endif
> +
> +PHONY += clang-analyzer
> +clang-analyzer:
> +ifdef CONFIG_CC_IS_CLANG
> +       $(PYTHON3) scripts/clang-tools/gen_compile_commands.py
> +       $(PYTHON3) scripts/clang-tools/run-clang-tools.py clang-analyzer compile_commands.json
> +else
> +       $(error clang-analyzer requires CC=clang)
> +endif



You can unify the almost same two rules.

PHONY += clang-tidy clang-analyzer
clang-tidy clang-analyzer:
ifdef CONFIG_CC_IS_CLANG
        $(PYTHON3) scripts/clang-tools/gen_compile_commands.py
        $(PYTHON3) scripts/clang-tools/run-clang-tools.py $@
compile_commands.json
else
        $(error $@ requires CC=clang)
endif




But, before we proceed, please tell me
what this check is intended for.





Case 1)
Build the kernel with CC=clang,
and then run clang-tidy without CC=clang.

$ make CC=clang defconfig
$ make CC=clang -j$(nproc)
$ make clang-tidy

scripts/clang-tools/Makefile.clang-tools:13: *** clang-tidy requires
CC=clang.  Stop.




Case 2)
Build the kernel using GCC,
and then run clang-tidy with CC=clang.

$ make defconfig
$ make -j$(nproc)
$ make CC=clang clang-tidy

This patch happily runs clang-tidy
although compile_commands.json
contains GCC commands.





So, it checks if you have passed CC=clang
to "make clang-tidy", where I do not see
any user of the $(CC) variable.

It does not care whether you have built
the kernel with GCC or Clang.



What happens if you run clang-tidy against
compile_commands.json that contains GCC
commands?


I also care about stale commands
in compile_commands.json.


gen_compile_commands.py creates compile_commands.json
based on *.cmd files it found.

If you rebuild the kernel for various settings
using GCC/clang without "make clean",
stale .*.cmd files will grow.

compile_commands.json will pick up commands
from older compilation, i.e. the end up with
the mixture of GCC/Clang commands.

So, I'd like to know how clang-tidy handles
the GCC commands from compile_commands.json





> diff --git a/scripts/gen_compile_commands.py b/scripts/clang-tools/gen_compile_commands.py
> similarity index 100%
> rename from scripts/gen_compile_commands.py
> rename to scripts/clang-tools/gen_compile_commands.py
> diff --git a/scripts/clang-tools/run-clang-tools.py b/scripts/clang-tools/run-clang-tools.py
> new file mode 100755
> index 000000000000..fa7655c7cec0
> --- /dev/null
> +++ b/scripts/clang-tools/run-clang-tools.py
> @@ -0,0 +1,74 @@
> +#!/usr/bin/env python
> +# SPDX-License-Identifier: GPL-2.0
> +#
> +# Copyright (C) Google LLC, 2020
> +#
> +# Author: Nathan Huckleberry <nhuck@...gle.com>
> +#
> +"""A helper routine run clang-tidy and the clang static-analyzer on
> +compile_commands.json.
> +"""
> +
> +import argparse
> +import json
> +import multiprocessing
> +import os
> +import subprocess
> +import sys
> +
> +
> +def parse_arguments():
> +    """Set up and parses command-line arguments.
> +    Returns:
> +        args: Dict of parsed args
> +        Has keys: [path, type]
> +    """
> +    usage = """Run clang-tidy or the clang static-analyzer on a
> +        compilation database."""
> +    parser = argparse.ArgumentParser(description=usage)
> +
> +    type_help = "Type of analysis to be performed"
> +    parser.add_argument("type",
> +                        choices=["clang-tidy", "clang-analyzer"],
> +                        help=type_help)
> +    path_help = "Path to the compilation database to parse"
> +    parser.add_argument("path", type=str, help=path_help)
> +
> +    return parser.parse_args()
> +
> +
> +def init(l, a):
> +    global lock
> +    global args
> +    lock = l
> +    args = a
> +
> +
> +def run_analysis(entry):
> +    # Disable all checks, then re-enable the ones we want
> +    checks = "-checks=-*,"
> +    if args.type == "clang-tidy":
> +        checks += "linuxkernel-*"
> +    else:
> +        checks += "clang-analyzer-*"
> +    p = subprocess.run(["clang-tidy", "-p", args.path, checks, entry["file"]],
> +                       stdout=subprocess.PIPE,
> +                       stderr=subprocess.STDOUT,
> +                       cwd=entry["directory"])
> +    with lock:
> +        sys.stderr.buffer.write(p.stdout)
> +
> +
> +def main():
> +    args = parse_arguments()
> +
> +    lock = multiprocessing.Lock()
> +    pool = multiprocessing.Pool(initializer=init, initargs=(lock, args))
> +    # Read JSON data into the datastore variable
> +    with open(args.path, "r") as f:
> +        datastore = json.load(f)
> +        pool.map(run_analysis, datastore)
> +
> +
> +if __name__ == "__main__":
> +    main()
> --
> 2.28.0.rc0.142.g3c755180ce-goog
>


-- 
Best Regards
Masahiro Yamada

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