Currently bpf_helper_defs.h is auto-generated using function documentation
present in bpf.h. If the documentation for the helper is missing
or doesn't follow a specific format for e.g. if a function is documented
as:
 * long bpf_kallsyms_lookup_name( const char *name, int name_sz, int flags, u64 *res )
instead of
 * long bpf_kallsyms_lookup_name(const char *name, int name_sz, int flags, u64 *res)
(notice the extra space at the start and end of function arguments)
then that helper is not dumped in the auto-generated header and results in
an invalid call during eBPF runtime, even if all the code specific to the
helper is correct.

This patch checks the number of functions documented within the header file
with those present as part of #define __BPF_FUNC_MAPPER and generates a
warning in the header file if they don't match. It is not needed with the
currently documented upstream functions, but can help in debugging
when developing new helpers when there might be missing or misformatted
documentation.

Signed-off-by: Usama Arif <redacted>
---
 scripts/bpf_doc.py | 46 ++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 44 insertions(+), 2 deletions(-)

diff --git a/scripts/bpf_doc.py b/scripts/bpf_doc.py
index a6403ddf5de7..736bd853155b 100755
--- a/scripts/bpf_doc.py
+++ b/scripts/bpf_doc.py

@@ -87,6 +87,8 @@ class HeaderParser(object):
         self.line = ''
         self.helpers = []
         self.commands = []
+        self.desc_unique_helpers = set()
+        self.define_unique_helpers = []

     def parse_element(self):
         proto    = self.parse_symbol()

@@ -193,19 +195,41 @@ class HeaderParser(object):
             except NoSyscallCommandFound:
                 break

-    def parse_helpers(self):
+    def parse_desc_helpers(self):
         self.seek_to('* Start of BPF helper function descriptions:',
                      'Could not find start of eBPF helper descriptions list')
         while True:
             try:
                 helper = self.parse_helper()
                 self.helpers.append(helper)
+                proto = helper.proto_break_down()
+                if proto['name'] not in self.desc_unique_helpers:
+                    self.desc_unique_helpers.add(proto['name'])
             except NoHelperFound:
                 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
+        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 = ''
+        while True:
+            capture = p.match(self.line)
+            if capture:
+                fn_defines_str += self.line
+            else:
+                break
+            self.line = self.reader.readline()
+        # Find the number of occurences of FN(\w+)
+        self.define_unique_helpers = len(re.findall('FN\(\w+\)', fn_defines_str))
+
     def run(self):
         self.parse_syscall()
-        self.parse_helpers()
+        self.parse_desc_helpers()
+        self.parse_define_helpers()
         self.reader.close()

 ###############################################################################

@@ -509,6 +533,8 @@ class PrinterHelpers(Printer):
     """
     def __init__(self, parser):
         self.elements = parser.helpers
+        self.desc_unique_helpers = parser.desc_unique_helpers
+        self.define_unique_helpers = parser.define_unique_helpers

     type_fwds = [
             'struct bpf_fib_lookup',

@@ -628,6 +654,22 @@ class PrinterHelpers(Printer):
 /* Forward declarations of BPF structs */'''

         print(header)
+
+        nr_desc_unique_helpers = len(self.desc_unique_helpers)
+        nr_define_unique_helpers = len(self.define_unique_helpers)