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Date:   Fri, 14 Aug 2020 02:10:46 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Nathan Huckleberry <nhuck@...gle.com>,
        Tom Roeder <tmroeder@...gle.com>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] gen_compile_commands: wire up build rule to Makefile

On Thu, Aug 13, 2020 at 7:30 AM 'Nick Desaulniers' via Clang Built
Linux <clang-built-linux@...glegroups.com> wrote:
>
> On Wed, Aug 12, 2020 at 10:40 AM Masahiro Yamada <masahiroy@...nel.org> wrote:
> >
> > Currently, you need to explicitly run scripts/gen_compile_commands.py
> > to create compile_commands.json. It traverses the object tree
> > (you need to pass the -d option to deal with a separate output tree),
> > and parses all the .*.cmd file found.
> >
> > If you rebuild the kernel over again without 'make clean', stale
> > .*.cmd files from older builds will create invalid entries in
> > compile_commands.json.
>
> Definitely a problem; happy to see compile_commands.json added to
> `make clean` target, too.
>
> >
> > This commit wires up the compile_commands.json rule to the top
> > Makefile, and makes it parse .*.cmd files only from the current build
> > to avoid stale entries.
> >
> > It is possible to extract only relevant .*.cmd files by checking
> > $(KBUILD_VMLINUX_OBJS), $(KBUILD_VMLINUX_LIBS), and modules.order.
> > The objects or archives linked to vmlinux are listed in
> > $(KBUILD_VMLINUX_OBJS) or $(KBUILD_VMLINUX_LIBS). All the modules are
> > listed in modules.order.
> >
> > You can create compile_commands.json from Make:
> >
> >   $ make -j$(nproc) CC=clang compile_commands.json
> >
> > Of course, you can build vmlinux, modules, and compile_commands.json
> > all together in a single command:
> >
> >   $ make -j$(nproc) CC=clang all compile_commands.json
> >
> > It works also for M= builds. In this case, compile_commands.json
> > is created in the top directory of the external module.
> >
> > I hope this will be overall improvements, but it has a drawback;
> > the coverage of the compile_commands.json is reduced because only
> > the objects linked to vmlinux or modules are handled. For example,
> > the following C files are not included in compile_commands.json:
> >
> >  - Decompressor source files (arch/*/boot/compressed/)
> >  - VDSO source files
> >  - C files used to generate intermediates (e.g. kernel/bounds.c)
> >  - standalone host programs
>
> Oof, for an x86_64 defconfig, the difference in line count of
> compile_commands.json
> before: 12826


I think some lines of 'before'
are not so important.

Files suffixed with *.mod.c
are generated sources for modules.
There is no point to check them by Clang tools.


Some entries appear twice:

For example, 'before' contains two entries of
"file": "lib/cmdline.c"
Which entry is used by 'clang-tidy lib/cmdline.c',
the first one, the second one, or both?



Having said that, there is still a loss of more than 3%, yes.


> after: 12351
>
> That's a loss of 475 (3.7% of 12826) coverage. Is there something more
> we can do to preserve this functionality, while avoiding stale .cmd
> files?


I have no idea how to do this correctly.

> Is it that those aren't specified by `$(KBUILD_VMLINUX_OBJS)
> $(KBUILD_VMLINUX_LIBS)` ?

These variables contain only objects and archives
linked to vmlinux.




For example, VDSO is built as a prerequisite of
another object that wraps it.

See line 61 of arch/arm64/kernel/vdso/Makefile:
$(obj)/vdso.o : $(obj)/vdso.so


I do not know how to get the full list of active objects,
some of which are built on demand
in the dependency chain.


Idea 1)
Merge this series, and accept the loss.


Idea 2)
Add Makefile targets,
and also keep the previous work-flow.

When you run it from Make,
only objects for vmlinux and modules are handled.

When you need the full coverage, including non-kernel-space
sources, run scripts manually:

$ scripts/clang-tools/gen_compile_commands.py
$ scripts/clang-tools/run-clang-tools.py clang-tidy


Idea 3)
Give up supporting it from Makefile.
Instead, improve gen_scripts_commands.py
as a standalone program.


Maybe we can check whether the compiler is Clang or not.
We can run '<compiler> --version' and drop the
entry if it is GCC.

Usually, the compiler is the first word of
the "command" field in compile_commands.json,
but there are exceptions because
people may do CC="ccache clang".


If there are still stale entries causing troubles,
you need to run 'make clean', and rebuild the tree.


We were trying to have separate scripts,
gen_compile_commands.py and run-clang-tools.py,
and to add Makefile targets to run them in a row.

I think unifying the two scripts
might be handier.


Add two options, -t, -a,
to scripts/gen_compile_commands.py

If they are given,
scripts/gen_compilile_commands.py
generates compile_commands.json,
and immediately runs clang-tidy against it.


-t, --tidy
   Run 'clang-tidy -checks=-*,linuxkernel-*' after generating
compilation database
-a, --analyzer
   Run 'clang-tidy -checks=-*,clang-analyzer-*' after generating
compilation database


Both -a and -t are given,
it runs
'clang-tidy -checks=-*,linuxkernel-*,clang-analyzer-*'

This works more efficiently
if you want to check everything.


'make clang-tidy clang-analyzer'
will invoke clang-tidy twice for each file,
which is not very efficient.




> >  clean-dirs := $(KBUILD_EXTMOD)
> > -clean: rm-files := $(KBUILD_EXTMOD)/Module.symvers $(KBUILD_EXTMOD)/modules.nsdeps
> > +clean: rm-files := $(KBUILD_EXTMOD)/Module.symvers $(KBUILD_EXTMOD)/modules.nsdeps \
> > +       $(KBUILD_EXTMOD)/compile_commands.json
>
> So the `clean` target doesn't make use of `CLEAN_FILES`? It looks like
> there's some duplication there?  Oh, this is dependent on
> !KBUILD_EXTMOD, and is a new `clean` target. Do I understand that
> correctly?

Correct.

We can move CLEAN_FILES to a common part
so external module builds can use it.

> >      """
> >      usage = 'Creates a compile_commands.json database from kernel .cmd files'
> >      parser = argparse.ArgumentParser(description=usage)
> >
> > -    directory_help = ('Path to the kernel source directory to search '
> > -                      '(defaults to the working directory)')
> > -    parser.add_argument('-d', '--directory', type=str, help=directory_help)
> > +    ar_help = 'command used for parsing .a archives'
> > +    parser.add_argument('-a', '--ar', type=str, default='ar', help=ar_help)
>
> Might be nice to warn if run with no arguments? In case someone does:
> $ ./scripts/clang-tools/gen_compile_commands.py

Right.

nargs='+' seems to work.



> > +    # Collect objects compiled for vmlinux or modules
> > +    objects = []
> > +    for file in files:
> > +        if file.endswith('.o'):
> > +            # Some objects (head-y) are linked to vmlinux directly
> > +            objects.append(file)
> > +        elif file.endswith('.a'):
> > +            # Most of built-in objects are linked via built-in.a or lib.a.
> > +            # Use 'ar -t' to get the list of the contained objects.
> > +            objects += subprocess.check_output([ar, '-t', file]).decode().split()
> > +        elif file.endswith('modules.order'):
> > +           # modules.order lists all the modules.
> > +            with open(file) as f:
>
> `file` is another builtin (or at least was in Python2), perhaps `filename`?
>
> > +                for line in f:
> > +                    ko = line.rstrip()
> > +                    base, ext = os.path.splitext(ko)
> > +                    if ext != '.ko':
> > +                        sys.exit('{}: mobule path must end with .ko'.format(ko))
> > +                    mod = base + '.mod'
> > +                   # The first line of *.mod lists the objects that
> > +                   # compose the module.
>
> This comment and the one above it uses tabs for indentation vs spaces
> for the rest of the file.  I use
> https://github.com/nickdesaulniers/dotfiles/blob/a90865a9ea48bbefa0082f7508607fdeb361e801/.vimrc#L37-L43
> to help me catch these.

Awesome. Copied to mine.



> > +                    with open(mod) as mod_f:
> > +                        objects += mod_f.readline().split()
> > +        else:
> > +            sys.exit('{}: unknown file type'.format(file))
>
> Consider breaking up this one long function into multiple, perhaps the
> above could just return `objects`?



I thought that returning a big list causes needless memory-copy.
If we do not need to be worried too much,
I can make it a helper function.


>
> >
> >      compile_commands = []
> > -    for dirpath, _, filenames in os.walk(directory):
> > -        for filename in filenames:
> > -            if not filename_matcher.match(filename):
> > -                continue
> > -            filepath = os.path.join(dirpath, filename)
> > -
> > -            with open(filepath, 'rt') as f:
> > -                line = f.readline()
> > -                result = line_matcher.match(line)
> > -                if result:
> > -                    try:
> > -                        entry = process_line(directory, dirpath,
> > -                                             result.group(1), result.group(2))
> > -                        compile_commands.append(entry)
> > -                    except ValueError as err:
> > -                        logging.info('Could not add line from %s: %s',
> > -                                     filepath, err)
> > +    cwd = os.getcwd()
> > +    for object in objects:
> > +        dir, notdir = os.path.split(object)
>
> `object` is a builtin Class in python.  I'm not sure if it's quite
> considered a keyword, but maybe a different identifier would be nicer,
> like `object_file` or something?


Not a keyword, but 'object' is a class, yes.
Not sure about 'file'.


$ python
Python 3.8.2 (default, Jul 16 2020, 14:00:26)
[GCC 9.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import keyword
>>> keyword.iskeyword("import")
True
>>> keyword.iskeyword("if")
True
>>> keyword.iskeyword("file")
False
>>> keyword.iskeyword("object")
False
>>> object
<class 'object'>
>>> file
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'file' is not defined
>>>


If this is a problem, I can rename it.




> > +        cmd_file = os.path.join(dir, '.' + notdir + '.cmd')
> > +        with open(cmd_file, 'rt') as f:
> > +            line = f.readline()
> > +            result = line_matcher.match(line)
>
> ^ combine statements.

OK.


> > +            if result:
> > +                entry = process_line(cwd, result.group(1), result.group(2))
> > +                compile_commands.append(entry)
> >
> >      with open(output, 'wt') as f:
> >          json.dump(compile_commands, f, indent=2, sort_keys=True)
> >
> > -    count = len(compile_commands)
> > -    if count < _LOW_COUNT_THRESHOLD:
> > -        logging.warning(
> > -            'Found %s entries. Have you compiled the kernel?', count)
> > -
> > -
> >  if __name__ == '__main__':
> >      main()
> > --
> > 2.25.1
> >
>
> Thank you for your assistance and help enabling these tools.
>
> --
> Thanks,
> ~Nick Desaulniers
>
> --
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--
Best Regards
Masahiro Yamada

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