On 24/08/2022 10:19, Eyal Birger wrote:
> The helper value is ABI as defined by enum bpf_func_id.
> As bpf_helper_defs.h is used for the userpace part, it must be consistent
> with this enum.
>
> Before this change the comments order was used by the bpf_doc script in
> order to set the helper values defined in the helpers file.
>
> When adding new helpers it is very puzzling when the userspace application
> breaks in weird places if the comment is inserted instead of appended -
> because the generated helper ABI is incorrect and shifted.
>
> This commit sets the helper value to the enum value.
>
> In addition it is currently the practice to have the comments appended
> and kept in the same order as the enum. As such, add an assertion
> validating the comment order is consistent with enum value.
>
> In case a different comments ordering is desired, this assertion can
> be lifted.
>
> Signed-off-by: Eyal Birger <eyal.birger@xxxxxxxxx>
>
> ---
>
> v2: based on feedback from Quentin Monnet:
> - assert the current comment ordering
> - match only one FN in each line
> ---
> scripts/bpf_doc.py | 31 +++++++++++++++++++++----------
> 1 file changed, 21 insertions(+), 10 deletions(-)
>
> diff --git a/scripts/bpf_doc.py b/scripts/bpf_doc.py
> index f4f3e7ec6d44..80dfb230459d 100755
> --- a/scripts/bpf_doc.py
> +++ b/scripts/bpf_doc.py
> @@ -91,7 +91,7 @@ class HeaderParser(object):
> self.helpers = []
> self.commands = []
> self.desc_unique_helpers = set()
> - self.define_unique_helpers = []
> + self.define_unique_helpers = {}
> self.desc_syscalls = []
> self.enum_syscalls = []
>
> @@ -248,24 +248,24 @@ class HeaderParser(object):
> break
>
> def parse_define_helpers(self):
> - # Parse the number of FN(...) in #define __BPF_FUNC_MAPPER to compare
> - # later with the number of unique function names present in description.
> + # Parse FN(...) in #define __BPF_FUNC_MAPPER to compare later with the
> + # number of unique function names present in description and use the
> + # correct enumeration value.
> # Note: seek_to(..) discards the first line below the target search text,
> # resulting in FN(unspec) being skipped and not added to self.define_unique_helpers.
> self.seek_to('#define __BPF_FUNC_MAPPER(FN)',
> 'Could not find start of eBPF helper definition list')
> - # Searches for either one or more FN(\w+) defines or a backslash for newline
> - p = re.compile('\s*(FN\(\w+\))+|\\\\')
> - fn_defines_str = ''
> + # Searches for one FN(\w+) define or a backslash for newline
> + p = re.compile('\s*FN\((\w+)\)|\\\\')
> + i = 1 # 'unspec' is skipped as mentioned above
> while True:
> capture = p.match(self.line)
> if capture:
> - fn_defines_str += self.line
> + self.define_unique_helpers[capture.expand(r'bpf_\1')] = i
> + i += 1
> else:
> break
> self.line = self.reader.readline()
> - # Find the number of occurences of FN(\w+)
> - self.define_unique_helpers = re.findall('FN\(\w+\)', fn_defines_str)
>
> def run(self):
> self.parse_desc_syscall()
> @@ -608,6 +608,7 @@ class PrinterHelpers(Printer):
> def __init__(self, parser):
> self.elements = parser.helpers
> self.elem_number_check(parser.desc_unique_helpers, parser.define_unique_helpers, 'helper', '__BPF_FUNC_MAPPER')
> + self.define_unique_helpers = parser.define_unique_helpers
>
> type_fwds = [
> 'struct bpf_fib_lookup',
> @@ -796,7 +797,17 @@ class PrinterHelpers(Printer):
> comma = ', '
> print(one_arg, end='')
>
> - print(') = (void *) %d;' % len(self.seen_helpers))
> + helper_val = self.define_unique_helpers[proto['name']]
> +
> + # Assert helper description order is aligned with the enum value
Thanks! But this check should go in the parser, not in the printer. One
reason is that it won't show when generating the man page, with this
version; another reason is that it should return early and avoid
generating an incomplete, non-functional header if the assertion fails.
> + desc_val = len(self.seen_helpers)
> + if helper_val != desc_val:
> + print("Helper %s comment order (#%d) must be aligned with its enum "
> + "order (#%d)" % (proto['name'], desc_val, helper_val),
Please don't split the string on two lines, never mind if it goes over
80 characters. Makes it harder to grep otherwise.
Suggestion on the message: "with its enum order (<nb>)" -> "with its
position (<nb>) in enum bpf_func_id"?
> + file=sys.stderr)
> + sys.exit(1)
Can we raise an Exception instead of printing to stderr + exiting?
> +
> + print(') = (void *) %d;' % helper_val)
> print('')
>
> ##############################################################################
