Re: [PATCH v2 05/28] docs: kdoc_re: add a C tokenizer

Mauro Carvalho Chehab
2026-03-17T07:59:37Z

On Mon, 16 Mar 2026 17:01:11 -0600
Jonathan Corbet <corbet@lwn.net> wrote:

> On Thu, 12 Mar 2026 15:54:25 +0100, Mauro Carvalho Chehab <mchehab+huawei@kernel.org> wrote:
> > Handling C code purely using regular expressions doesn't work well.
> >
> > Add a C tokenizer to help doing it the right way.
> >
> > The tokenizer was written using as basis the Python re documentation
> > tokenizer example from:
> > https://docs.python.org/3/library/re.html#writing-a-tokenizer
> >
> > Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
> > Message-ID: <c63ad36c81fe043e9e33ca55630414893f127413.1773074166.git.mchehab+huawei@kernel.org>
> > Message-ID: <8541ffa469647db1a7154f274fb2d55b4c127dcb.1773326442.git.mchehab+huawei@kernel.org>
>
> This is a combined effort to review this patch and to try out "b4 review",
> we'll see how it goes :).
>
> > diff --git a/tools/lib/python/kdoc/kdoc_re.py b/tools/lib/python/kdoc/kdoc_re.py
> > index 085b89a4547c0..7bed4e9a88108 100644
> > --- a/tools/lib/python/kdoc/kdoc_re.py
> > +++ b/tools/lib/python/kdoc/kdoc_re.py
> > @@ -141,6 +141,240 @@ class KernRe:
> > [ ... skip 4 lines ... ]
> > +
> > + @staticmethod
> > + def __str__(val):
> > + """Return the name of an enum value"""
> > + return TokType._name_by_val.get(val, f"UNKNOWN({val})")
> > +
>
> What is this class supposed to do?

This __str__() method ensures that, when printing a CToken object,
the name will be displayed, instead of a number. This is really
useful when debugging.

See, if I add a print:

<snip>
--- a/tools/lib/python/kdoc/kdoc_parser.py
+++ b/tools/lib/python/kdoc/kdoc_parser.py
@@ -87,6 +87,7 @@ def trim_private_members(text):
"""

tokens = CTokenizer(text)
+ print(tokens.tokens)
return str(tokens)

</snip>

the tokens will appear as names at the output:

$ ./scripts/kernel-doc -none er.c
[CToken(CToken.ENUM, "enum", 0, (0, 0, 0)), CToken(CToken.SPACE, " ", 4, (0, 0, 0)), CToken(CToken.NAME, "dmub_abm_ace_curve_type", 5, (0, 0, 0)), CToken(CToken.SPACE, " ", 28, (0, 0, 0)), CToken(CToken.BEGIN, "{", 29, (0, 0, 1)), CToken(CToken.SPACE, " ", 30, (0, 0, 1)), CToken(CToken.COMMENT, "/**
* ACE curve as defined by the SW layer. */", 31, (0, 0, 1)), CToken(CToken.SPACE, " ", 86, (0, 0, 1)), CToken(CToken.NAME, "ABM_ACE_CURVE_TYPE__SW", 87, (0, 0, 1)), CToken(CToken.SPACE, " ", 109, (0, 0, 1)), CToken(CToken.OP, "=", 110, (0, 0, 1)), CToken(CToken.SPACE, " ", 111, (0, 0, 1)), CToken(CToken.NUMBER, "0", 112, (0, 0, 1)), CToken(CToken.PUNC, ",", 113, (0, 0, 1)), CToken(CToken.SPACE, " ", 114, (0, 0, 1)), CToken(CToken.COMMENT, "/**
* ACE curve as defined by the SW to HW translation interface layer. */", 115, (0, 0, 1)), CToken(CToken.SPACE, " ", 198, (0, 0, 1)), CToken(CToken.NAME, "ABM_ACE_CURVE_TYPE__SW_IF", 199, (0, 0, 1)), CToken(CToken.SPACE, " ", 224, (0, 0, 1)), CToken(CToken.OP, "=", 225, (0, 0, 1)), CToken(CToken.SPACE, " ", 226, (0, 0, 1)), CToken(CToken.NUMBER, "1", 227, (0, 0, 1)), CToken(CToken.PUNC, ",", 228, (0, 0, 1)), CToken(CToken.SPACE, " ", 229, (0, 0, 1)), CToken(CToken.END, "}", 230, (0, 0, 0)), CToken(CToken.PUNC, ";", 231, (0, 0, 0))]

>
> > [ ... skip 27 lines ... ]
> > + _name_by_val = {v: k for k, v in dict(vars()).items() if isinstance(v, int)}
> > +
> > + # Dict to convert from string to an enum-like integer value.
> > + _name_to_val = {k: v for v, k in _name_by_val.items()}
> > +
> > + @staticmethod
>
> This stuff strikes me as a bit overdone; _name_to_val is really just the
> variable list for the class, right?

Those two vars are a kind of magic: they create two dictionaries:

- _name_by_val converts a token integer into a string;
- _name_to_val converts a string to an integer.

I opted to use this approach for a couple of reasons:

1. using tok.kind == "BEGIN" (and similar) everywhere is harder to
maintain, as python won't check for typos. Now, if one writes:
CToken.BEGHIN, an error will be raised;

2. the cost to convert from string to int is O(1), so not much
a performance issue at the conversion;

3. using an integer on all checks should make the code faster as
it doesn't require a loop to check the string.

>
> > [ ... skip 30 lines ... ]
> > + f"{self.brace_level}, {self.paren_level}, {self.bracket_level})"
> > +
> > +#: Tokens to parse C code.
> > +TOKEN_LIST = [
> > + (CToken.COMMENT, r"//[^\n]*|/\*[\s\S]*?\*/"),
> > +
>
> So these aren't "tokens", this is a list of regexes; how is it intended
> to be used?

Right. I could have named it better, like RE_TOKEN_LIST, or
TOKEN_REGEX, as at the original example, which came from Python
documentation for "re" module:

https://docs.python.org/3/library/re.html#writing-a-tokenizer

basically, we have the token type as the first element at the tuple,
and regex as the second one.

When regex matches, the CToken will be filed with kind=tuple[0].

the loop:
for match in re.finditer(TOKEN_LIST, code):

will parse the entire C code source, in order, converting it into
a token list. So, a file like this:

/**
* enum dmub_abm_ace_curve_type - ACE curve type.
*/
enum dmub_abm_ace_curve_type {
/**
* ACE curve as defined by the SW layer.
*/
ABM_ACE_CURVE_TYPE__SW = 0,
/**
* ACE curve as defined by the SW to HW translation interface layer.
*/
ABM_ACE_CURVE_TYPE__SW_IF = 1,
};

will become (I used pprint here to better align the tokens):

[CToken(CToken.ENUM, "enum", 0, (0, 0, 0)),
CToken(CToken.SPACE, " ", 4, (0, 0, 0)),
CToken(CToken.NAME, "dmub_abm_ace_curve_type", 5, (0, 0, 0)),
CToken(CToken.SPACE, " ", 28, (0, 0, 0)),
CToken(CToken.BEGIN, "{", 29, (0, 0, 1)),
CToken(CToken.SPACE, " ", 30, (0, 0, 1)),
CToken(CToken.COMMENT, "/**
* ACE curve as defined by the SW layer. */", 31, (0, 0, 1)),
CToken(CToken.SPACE, " ", 86, (0, 0, 1)),
CToken(CToken.NAME, "ABM_ACE_CURVE_TYPE__SW", 87, (0, 0, 1)),
CToken(CToken.SPACE, " ", 109, (0, 0, 1)),
CToken(CToken.OP, "=", 110, (0, 0, 1)),
CToken(CToken.SPACE, " ", 111, (0, 0, 1)),
CToken(CToken.NUMBER, "0", 112, (0, 0, 1)),
CToken(CToken.PUNC, ",", 113, (0, 0, 1)),
CToken(CToken.SPACE, " ", 114, (0, 0, 1)),
CToken(CToken.COMMENT, "/**
* ACE curve as defined by the SW to HW translation interface layer. */", 115, (0, 0, 1)),
CToken(CToken.SPACE, " ", 198, (0, 0, 1)),
CToken(CToken.NAME, "ABM_ACE_CURVE_TYPE__SW_IF", 199, (0, 0, 1)),
CToken(CToken.SPACE, " ", 224, (0, 0, 1)),
CToken(CToken.OP, "=", 225, (0, 0, 1)),
CToken(CToken.SPACE, " ", 226, (0, 0, 1)),
CToken(CToken.NUMBER, "1", 227, (0, 0, 1)),
CToken(CToken.PUNC, ",", 228, (0, 0, 1)),
CToken(CToken.SPACE, " ", 229, (0, 0, 1)),
CToken(CToken.END, "}", 230, (0, 0, 0)),
CToken(CToken.PUNC, ";", 231, (0, 0, 0))]

>
> > + (CToken.STRING, r'"(?:\\.|[^"\\])*"'),
> > + (CToken.CHAR, r"'(?:\\.|[^'\\])'"),
> > +
> > + (CToken.NUMBER, r"0[xX][0-9a-fA-F]+[uUlL]*|0[0-7]+[uUlL]*|"
>
> How does "[\s\S]*" differ from plain old "*" ?

They are not identical, as "*" doesn't match "\n". As the tokenizer
also picks "\n" on several cases, like on comments, r"\s\S" works
better.

> > [ ... skip 15 lines ... ]
> > + (CToken.STRUCT, r"\bstruct\b"),
> > + (CToken.UNION, r"\bunion\b"),
> > + (CToken.ENUM, r"\benum\b"),
> > + (CToken.TYPEDEF, r"\bkinddef\b"),
> > +
> > + (CToken.NAME, r"[A-Za-z_][A-Za-z0-9_]*"),
>

> "-" and "!" never need to be escaped.

"-" usually needs to be escaped, because it can be a range. I had
some troubles with the parser due to the lack of escapes, so I
ended being conservative.

( I'm finding a little bit hard to follow your comments...
Here, for instance, "!" is not at CToken.NAME regex.
Did b4 review place your comment at the wrong place? )

>
> > +
> > + (CToken.SPACE, r"[\s]+"),
> > +
> > + (CToken.MISMATCH,r"."),
> > +]
> > +
>
> "kinddef" ?

Should be "typedef".

This was due to a "sed s,type,kind," I applied to avoid using
"type" for the token type, as, when I started integrating it
with kdoc_re, it became confusing.

I'll fix at the next respin.

>
> > +#: Handle C continuation lines.
> > +RE_CONT = KernRe(r"\\\n")
> > +
> > +RE_COMMENT_START = KernRe(r'/\*\s*')
> > +
>
> Don't need the [brackets] here

where?

>
> > [ ... skip 6 lines ... ]
> > +
> > + When converted to string, it drops comments and handle public/private
> > + values, respecting depth.
> > + """
> > +
> > + # This class is inspired and follows the basic concepts of:
>
> That seems weird, why don't you just initialize it here?

Hard to tell what you're referring to. Maybe this:

RE_SCANNER = fill_re_scanner(TOKEN_LIST)

The rationale is that I don't want to re-create this every time,
as this is const.

>
> > [ ... skip 14 lines ... ]
> > + source = RE_CONT.sub("", source)
> > +
> > + brace_level = 0
> > + paren_level = 0
> > + bracket_level = 0
> > +
>
> Do you mean "iterator" here?

If you mean the typo at _tokenize() help text, yes:

interactor -> iterator

>
> > [ ... skip 33 lines ... ]
> > + in this particular case, it makes sense, as we can pick the name
> > + when matching a code via re_scanner().
> > + """
> > + global re_scanner
> > +
> > + if not re_scanner:
>
> Putting __init__() first is fairly standard, methinks.

class CTokenizer __init__() module calls _tokenize() method on it.

My personal preference is to have the caller methods before the methods
that actually call them, even inside a class, where the order doesn't
matter - or even in C, when we have an include with all prototypes.

But if you prefer, I can reorder it.

> > [ ... skip 15 lines ... ]
> > +
> > + for tok in self.tokens:
> > + if tok.kind == CToken.BEGIN:
> > + show_stack.append(show_stack[-1])
> > +
> > + elif tok.kind == CToken.END:
>
> I still don't understand why you do this here - this is all constant, right?

This one I didn't get to what part of the code you're referring to.

All constants on this code are using upper case names. They are:

- TOKEN_LIST (which should probably be named as TOKEN_REGEX_LIST).
- CToken enum-like names (BEGIN, END, OP, NAME, ...)
- three regexes (RE_COUNT, RE_COMMENT_START, RE_SCANNER)

See, what the tokenizer does is a linear transformation from a C
source string into a token list.

So, for each instance, its content will change. Also, when we apply
CMatch logic, its content will also change.

>
> > + prev = show_stack[-1]
> > + if len(show_stack) > 1:
> > + show_stack.pop()
> > +
> > + if not prev and show_stack[-1]:
>
> So you create a nice iterator structure, then just put it all together into a
> list anyway?

Not sure what you meant here.

The end result of the tokenizer is a list of tokens, in the order
they appear at the source code.

To be able to handle public/private and do code transforms, using it
as a list is completely fine.

Now, if we want to use the tokenizer to parse things like:

typedef struct ca_descr_info {
unsigned int num;
unsigned int type;
} ca_descr_info_t;

Then having iterators to parse tokens on both directions
would be great, as the typedef identifier is at the end.

Thanks,
Mauro