1#!/usr/bin/python3
2# SPDX-License-Identifier: GPL-2.0-only
3#
4# Copyright (C) 2018-2019 Netronome Systems, Inc.
5
6# In case user attempts to run with Python 2.
7from __future__ import print_function
8
9import argparse
10import re
11import sys, os
12
13class NoHelperFound(BaseException):
14    pass
15
16class ParsingError(BaseException):
17    def __init__(self, line='<line not provided>', reader=None):
18        if reader:
19            BaseException.__init__(self,
20                                   'Error at file offset %d, parsing line: %s' %
21                                   (reader.tell(), line))
22        else:
23            BaseException.__init__(self, 'Error parsing line: %s' % line)
24
25class Helper(object):
26    """
27    An object representing the description of an eBPF helper function.
28    @proto: function prototype of the helper function
29    @desc: textual description of the helper function
30    @ret: description of the return value of the helper function
31    """
32    def __init__(self, proto='', desc='', ret=''):
33        self.proto = proto
34        self.desc = desc
35        self.ret = ret
36
37    def proto_break_down(self):
38        """
39        Break down helper function protocol into smaller chunks: return type,
40        name, distincts arguments.
41        """
42        arg_re = re.compile('((\w+ )*?(\w+|...))( (\**)(\w+))?$')
43        res = {}
44        proto_re = re.compile('(.+) (\**)(\w+)\(((([^,]+)(, )?){1,5})\)$')
45
46        capture = proto_re.match(self.proto)
47        res['ret_type'] = capture.group(1)
48        res['ret_star'] = capture.group(2)
49        res['name']     = capture.group(3)
50        res['args'] = []
51
52        args    = capture.group(4).split(', ')
53        for a in args:
54            capture = arg_re.match(a)
55            res['args'].append({
56                'type' : capture.group(1),
57                'star' : capture.group(5),
58                'name' : capture.group(6)
59            })
60
61        return res
62
63class HeaderParser(object):
64    """
65    An object used to parse a file in order to extract the documentation of a
66    list of eBPF helper functions. All the helpers that can be retrieved are
67    stored as Helper object, in the self.helpers() array.
68    @filename: name of file to parse, usually include/uapi/linux/bpf.h in the
69               kernel tree
70    """
71    def __init__(self, filename):
72        self.reader = open(filename, 'r')
73        self.line = ''
74        self.helpers = []
75
76    def parse_helper(self):
77        proto    = self.parse_proto()
78        desc     = self.parse_desc()
79        ret      = self.parse_ret()
80        return Helper(proto=proto, desc=desc, ret=ret)
81
82    def parse_proto(self):
83        # Argument can be of shape:
84        #   - "void"
85        #   - "type  name"
86        #   - "type *name"
87        #   - Same as above, with "const" and/or "struct" in front of type
88        #   - "..." (undefined number of arguments, for bpf_trace_printk())
89        # There is at least one term ("void"), and at most five arguments.
90        p = re.compile(' \* ?((.+) \**\w+\((((const )?(struct )?(\w+|\.\.\.)( \**\w+)?)(, )?){1,5}\))$')
91        capture = p.match(self.line)
92        if not capture:
93            raise NoHelperFound
94        self.line = self.reader.readline()
95        return capture.group(1)
96
97    def parse_desc(self):
98        p = re.compile(' \* ?(?:\t| {5,8})Description$')
99        capture = p.match(self.line)
100        if not capture:
101            # Helper can have empty description and we might be parsing another
102            # attribute: return but do not consume.
103            return ''
104        # Description can be several lines, some of them possibly empty, and it
105        # stops when another subsection title is met.
106        desc = ''
107        while True:
108            self.line = self.reader.readline()
109            if self.line == ' *\n':
110                desc += '\n'
111            else:
112                p = re.compile(' \* ?(?:\t| {5,8})(?:\t| {8})(.*)')
113                capture = p.match(self.line)
114                if capture:
115                    desc += capture.group(1) + '\n'
116                else:
117                    break
118        return desc
119
120    def parse_ret(self):
121        p = re.compile(' \* ?(?:\t| {5,8})Return$')
122        capture = p.match(self.line)
123        if not capture:
124            # Helper can have empty retval and we might be parsing another
125            # attribute: return but do not consume.
126            return ''
127        # Return value description can be several lines, some of them possibly
128        # empty, and it stops when another subsection title is met.
129        ret = ''
130        while True:
131            self.line = self.reader.readline()
132            if self.line == ' *\n':
133                ret += '\n'
134            else:
135                p = re.compile(' \* ?(?:\t| {5,8})(?:\t| {8})(.*)')
136                capture = p.match(self.line)
137                if capture:
138                    ret += capture.group(1) + '\n'
139                else:
140                    break
141        return ret
142
143    def run(self):
144        # Advance to start of helper function descriptions.
145        offset = self.reader.read().find('* Start of BPF helper function descriptions:')
146        if offset == -1:
147            raise Exception('Could not find start of eBPF helper descriptions list')
148        self.reader.seek(offset)
149        self.reader.readline()
150        self.reader.readline()
151        self.line = self.reader.readline()
152
153        while True:
154            try:
155                helper = self.parse_helper()
156                self.helpers.append(helper)
157            except NoHelperFound:
158                break
159
160        self.reader.close()
161        print('Parsed description of %d helper function(s)' % len(self.helpers),
162              file=sys.stderr)
163
164###############################################################################
165
166class Printer(object):
167    """
168    A generic class for printers. Printers should be created with an array of
169    Helper objects, and implement a way to print them in the desired fashion.
170    @helpers: array of Helper objects to print to standard output
171    """
172    def __init__(self, helpers):
173        self.helpers = helpers
174
175    def print_header(self):
176        pass
177
178    def print_footer(self):
179        pass
180
181    def print_one(self, helper):
182        pass
183
184    def print_all(self):
185        self.print_header()
186        for helper in self.helpers:
187            self.print_one(helper)
188        self.print_footer()
189
190class PrinterRST(Printer):
191    """
192    A printer for dumping collected information about helpers as a ReStructured
193    Text page compatible with the rst2man program, which can be used to
194    generate a manual page for the helpers.
195    @helpers: array of Helper objects to print to standard output
196    """
197    def print_header(self):
198        header = '''\
199.. Copyright (C) All BPF authors and contributors from 2014 to present.
200.. See git log include/uapi/linux/bpf.h in kernel tree for details.
201..
202.. %%%LICENSE_START(VERBATIM)
203.. Permission is granted to make and distribute verbatim copies of this
204.. manual provided the copyright notice and this permission notice are
205.. preserved on all copies.
206..
207.. Permission is granted to copy and distribute modified versions of this
208.. manual under the conditions for verbatim copying, provided that the
209.. entire resulting derived work is distributed under the terms of a
210.. permission notice identical to this one.
211..
212.. Since the Linux kernel and libraries are constantly changing, this
213.. manual page may be incorrect or out-of-date.  The author(s) assume no
214.. responsibility for errors or omissions, or for damages resulting from
215.. the use of the information contained herein.  The author(s) may not
216.. have taken the same level of care in the production of this manual,
217.. which is licensed free of charge, as they might when working
218.. professionally.
219..
220.. Formatted or processed versions of this manual, if unaccompanied by
221.. the source, must acknowledge the copyright and authors of this work.
222.. %%%LICENSE_END
223..
224.. Please do not edit this file. It was generated from the documentation
225.. located in file include/uapi/linux/bpf.h of the Linux kernel sources
226.. (helpers description), and from scripts/bpf_helpers_doc.py in the same
227.. repository (header and footer).
228
229===========
230BPF-HELPERS
231===========
232-------------------------------------------------------------------------------
233list of eBPF helper functions
234-------------------------------------------------------------------------------
235
236:Manual section: 7
237
238DESCRIPTION
239===========
240
241The extended Berkeley Packet Filter (eBPF) subsystem consists in programs
242written in a pseudo-assembly language, then attached to one of the several
243kernel hooks and run in reaction of specific events. This framework differs
244from the older, "classic" BPF (or "cBPF") in several aspects, one of them being
245the ability to call special functions (or "helpers") from within a program.
246These functions are restricted to a white-list of helpers defined in the
247kernel.
248
249These helpers are used by eBPF programs to interact with the system, or with
250the context in which they work. For instance, they can be used to print
251debugging messages, to get the time since the system was booted, to interact
252with eBPF maps, or to manipulate network packets. Since there are several eBPF
253program types, and that they do not run in the same context, each program type
254can only call a subset of those helpers.
255
256Due to eBPF conventions, a helper can not have more than five arguments.
257
258Internally, eBPF programs call directly into the compiled helper functions
259without requiring any foreign-function interface. As a result, calling helpers
260introduces no overhead, thus offering excellent performance.
261
262This document is an attempt to list and document the helpers available to eBPF
263developers. They are sorted by chronological order (the oldest helpers in the
264kernel at the top).
265
266HELPERS
267=======
268'''
269        print(header)
270
271    def print_footer(self):
272        footer = '''
273EXAMPLES
274========
275
276Example usage for most of the eBPF helpers listed in this manual page are
277available within the Linux kernel sources, at the following locations:
278
279* *samples/bpf/*
280* *tools/testing/selftests/bpf/*
281
282LICENSE
283=======
284
285eBPF programs can have an associated license, passed along with the bytecode
286instructions to the kernel when the programs are loaded. The format for that
287string is identical to the one in use for kernel modules (Dual licenses, such
288as "Dual BSD/GPL", may be used). Some helper functions are only accessible to
289programs that are compatible with the GNU Privacy License (GPL).
290
291In order to use such helpers, the eBPF program must be loaded with the correct
292license string passed (via **attr**) to the **bpf**\ () system call, and this
293generally translates into the C source code of the program containing a line
294similar to the following:
295
296::
297
298	char ____license[] __attribute__((section("license"), used)) = "GPL";
299
300IMPLEMENTATION
301==============
302
303This manual page is an effort to document the existing eBPF helper functions.
304But as of this writing, the BPF sub-system is under heavy development. New eBPF
305program or map types are added, along with new helper functions. Some helpers
306are occasionally made available for additional program types. So in spite of
307the efforts of the community, this page might not be up-to-date. If you want to
308check by yourself what helper functions exist in your kernel, or what types of
309programs they can support, here are some files among the kernel tree that you
310may be interested in:
311
312* *include/uapi/linux/bpf.h* is the main BPF header. It contains the full list
313  of all helper functions, as well as many other BPF definitions including most
314  of the flags, structs or constants used by the helpers.
315* *net/core/filter.c* contains the definition of most network-related helper
316  functions, and the list of program types from which they can be used.
317* *kernel/trace/bpf_trace.c* is the equivalent for most tracing program-related
318  helpers.
319* *kernel/bpf/verifier.c* contains the functions used to check that valid types
320  of eBPF maps are used with a given helper function.
321* *kernel/bpf/* directory contains other files in which additional helpers are
322  defined (for cgroups, sockmaps, etc.).
323
324Compatibility between helper functions and program types can generally be found
325in the files where helper functions are defined. Look for the **struct
326bpf_func_proto** objects and for functions returning them: these functions
327contain a list of helpers that a given program type can call. Note that the
328**default:** label of the **switch ... case** used to filter helpers can call
329other functions, themselves allowing access to additional helpers. The
330requirement for GPL license is also in those **struct bpf_func_proto**.
331
332Compatibility between helper functions and map types can be found in the
333**check_map_func_compatibility**\ () function in file *kernel/bpf/verifier.c*.
334
335Helper functions that invalidate the checks on **data** and **data_end**
336pointers for network processing are listed in function
337**bpf_helper_changes_pkt_data**\ () in file *net/core/filter.c*.
338
339SEE ALSO
340========
341
342**bpf**\ (2),
343**cgroups**\ (7),
344**ip**\ (8),
345**perf_event_open**\ (2),
346**sendmsg**\ (2),
347**socket**\ (7),
348**tc-bpf**\ (8)'''
349        print(footer)
350
351    def print_proto(self, helper):
352        """
353        Format function protocol with bold and italics markers. This makes RST
354        file less readable, but gives nice results in the manual page.
355        """
356        proto = helper.proto_break_down()
357
358        print('**%s %s%s(' % (proto['ret_type'],
359                              proto['ret_star'].replace('*', '\\*'),
360                              proto['name']),
361              end='')
362
363        comma = ''
364        for a in proto['args']:
365            one_arg = '{}{}'.format(comma, a['type'])
366            if a['name']:
367                if a['star']:
368                    one_arg += ' {}**\ '.format(a['star'].replace('*', '\\*'))
369                else:
370                    one_arg += '** '
371                one_arg += '*{}*\\ **'.format(a['name'])
372            comma = ', '
373            print(one_arg, end='')
374
375        print(')**')
376
377    def print_one(self, helper):
378        self.print_proto(helper)
379
380        if (helper.desc):
381            print('\tDescription')
382            # Do not strip all newline characters: formatted code at the end of
383            # a section must be followed by a blank line.
384            for line in re.sub('\n$', '', helper.desc, count=1).split('\n'):
385                print('{}{}'.format('\t\t' if line else '', line))
386
387        if (helper.ret):
388            print('\tReturn')
389            for line in helper.ret.rstrip().split('\n'):
390                print('{}{}'.format('\t\t' if line else '', line))
391
392        print('')
393
394###############################################################################
395
396# If script is launched from scripts/ from kernel tree and can access
397# ../include/uapi/linux/bpf.h, use it as a default name for the file to parse,
398# otherwise the --filename argument will be required from the command line.
399script = os.path.abspath(sys.argv[0])
400linuxRoot = os.path.dirname(os.path.dirname(script))
401bpfh = os.path.join(linuxRoot, 'include/uapi/linux/bpf.h')
402
403argParser = argparse.ArgumentParser(description="""
404Parse eBPF header file and generate documentation for eBPF helper functions.
405The RST-formatted output produced can be turned into a manual page with the
406rst2man utility.
407""")
408if (os.path.isfile(bpfh)):
409    argParser.add_argument('--filename', help='path to include/uapi/linux/bpf.h',
410                           default=bpfh)
411else:
412    argParser.add_argument('--filename', help='path to include/uapi/linux/bpf.h')
413args = argParser.parse_args()
414
415# Parse file.
416headerParser = HeaderParser(args.filename)
417headerParser.run()
418
419# Print formatted output to standard output.
420printer = PrinterRST(headerParser.helpers)
421printer.print_all()
422