Date:   Wed, 8 Jul 2020 12:10:54 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Nathan Huckleberry <nhuck@...gle.com>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Tom Roeder <tmroeder@...gle.com>,
        Bill Wendling <morbo@...gle.com>,
        Pirama Arumuga Nainar <pirama@...gle.com>
Subject: Re: [PATCH v2] Makefile: Add clang-tidy and static analyzer support
 to makefile

On Wed, Jul 8, 2020 at 11:21 AM 'Nathan Huckleberry' via Clang Built
Linux <clang-built-linux@...glegroups.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 V1 -> V2:
> * Remove dependencies on GNU Parallel
> * * Clang-tidy/analyzer now invoked directly from python
> Link: https://lkml.org/lkml/2019/8/6/941
>
>  Makefile                                      |  3 +
>  scripts/clang-tools/Makefile.clang-tools      | 23 ++++++
>  .../{ => clang-tools}/gen_compile_commands.py |  0

+ Tom for the rename.

I think we should add scripts/clang-tools/ to MAINTAINERS under
CLANG/LLVM SUPPORT:
```
diff --git a/MAINTAINERS b/MAINTAINERS
index c87b94e6b2f6..42602231929c 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4211,6 +4211,7 @@ 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
```
that way we get cc'ed properly on proposed changes (should folks use
scripts/get_maintainer.pl).

>  scripts/clang-tools/run-clang-tools.py        | 77 +++++++++++++++++++
>  4 files changed, 103 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/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..e09dc1a8efff
> --- /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)

s/Clang/clang/ to match the case of the target.

> +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 static-analyzer compile_commands.json
> +else
> +       $(error Clang-analyzer requires CC=clang)

s/Clang/clang/ to match the case of the target.

> +endif
> 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..d429a150e23a
> --- /dev/null
> +++ b/scripts/clang-tools/run-clang-tools.py
> @@ -0,0 +1,77 @@
> +#!/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 logging
> +import multiprocessing
> +import os
> +import re
> +import subprocess
> +
> +def parse_arguments():
> +  """Set up and parses command-line arguments.
> +  Returns:
> +    args: Dict of parsed args
> +      Has keys 'file' and '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', 'static-analyzer'],
> +                      help=type_help)
> +  file_path_help = ('Path to the compilation database to parse')
> +  parser.add_argument('file',  type=str, help=file_path_help)

I don't know if the kernel has a preferred style for Python, but I
think it would be good to be consistent in the use of single vs double
quotes for strings.  My preference is for double quotes, but I don't
know enough about the various PEPs for style or if the kernel has a
preferred style for these.

+ Bill who knows a bit about Python style.

> +
> +  args = parser.parse_args()
> +
> +  return args
> +
> +def init(l,t):
> +  global lock
> +  global analysis_type
> +  lock = l
> +  analysis_type = t

Is this canonical Python?  Maybe wrap these functions into methods of
an object you construct, that way you can assign these as instance
variables against `self`, rather than using global variables.

> +
> +def run_analysis(entry):
> +  filename = entry['file']
> +  p = None
> +  if(analysis_type == "clang-tidy"):
> +    p = subprocess.run(["clang-tidy", "-p", os.getcwd(),
> +                        "-checks=-*,linuxkernel-*", filename],
> +                       stdout=subprocess.PIPE, stderr=subprocess.PIPE)
> +  if(analysis_type == "static-analyzer"):
> +    p = subprocess.run(["clang-tidy", "-p", os.getcwd(),
> +                        "-checks=-*,clang-analyzer-*", filename],
> +                       stdout=subprocess.PIPE, stderr=subprocess.PIPE)

When you have a fair amount of duplication between two branches of an
if/else (for instance, same method invocation and number of
parameters, just slight differences in parameter values), consider if
you can use a ternary to simplify or make the code more concise. That
would also help avoid initializing `p` to `None`:

checks = "-checks=-*,linuxkernel-*" if analysis_type == "clang-tidy"
else "-checks=-*,clang-analyzer-*"
p = subprocess.run(["clang-tidy", "-p", os.getcwd(), checks,
    stdout=subprocess.PIPE, stderr=subprocess.PIPE]

then maybe do some validation of the analysis_type when validating
command line arguments earlier.

> +  lock.acquire()
> +  print(entry['file'])
> +  os.write(1, p.stdout)
> +  os.write(2, p.stderr)

Please use sys.stdout and sys.stderr rather than magic constants for
their file descriptors.

> +  lock.release()
> +
> +
> +def main():
> +  args = parse_arguments()
> +  filename = args.file
> +
> +  #Read JSON data into the datastore variable
> +  if filename:

Isn't there a way to make command line arguments required with
Argparse? In that case, would you still need the conditional?

> +    with open(filename, 'r') as f:
> +      datastore = json.load(f)
> +
> +      lock = multiprocessing.Lock()
> +      pool = multiprocessing.Pool(initializer=init, initargs=(lock,args.type,))
> +      pool.map(run_analysis,datastore)

Please use a space to separate parameters in a parameter list.

> +
> +if __name__ == '__main__':
> +    main()

So rather than call a function named main, you could simply construct
an object, then call a method on it or have the constructor simply
kick off the analysis (essentially a mix of `main` and `init`).

-- 
Thanks,
~Nick Desaulniers

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