[PATCH v12 1/7] buildtools/chkincs: relax C linkage requirement

["Mattias Rönnblom" <mattias.ronnblom@ericsson.com>]

Relax chkincs requirement of all DPDK header files having to contain
'extern "C"'.

Instructing a C++ toolchain to use C linkage is only necessarily if the
header file declares symbols (i.e., functions or global variables).

With this change, chkincs tries to find if any functions or references
to global variables are declared in the header file, and if not, no C
linkage is required.

Signed-off-by: Mattias Rönnblom <mattias.ronnblom@ericsson.com>

--

PATCH v11:
 * Detect functions from the Windows POSIX wrappers, to avoid false
   positives for redundant 'extern "C"'.
---
 buildtools/chkincs/chkextern.py | 88 +++++++++++++++++++++++++++++++++
 buildtools/chkincs/meson.build  | 14 +++---
 2 files changed, 95 insertions(+), 7 deletions(-)
 create mode 100755 buildtools/chkincs/chkextern.py

diff --git a/buildtools/chkincs/chkextern.py b/buildtools/chkincs/chkextern.py
new file mode 100755
index 0000000000..5374ce1c72
--- /dev/null
+++ b/buildtools/chkincs/chkextern.py
@@ -0,0 +1,88 @@
+#! /usr/bin/env python3
+# SPDX-License-Identifier: BSD-3-Clause
+# Copyright(c) 2024 Ericsson AB
+
+import sys
+import re
+
+def strip_cpp(header):
+    no_cpp = ""
+    header = header.replace("\\\n", " ")
+
+    for line in header.split("\n"):
+        if re.match(r'^\s*#.*', line) is None and len(line) > 0:
+            no_cpp += "%s\n" % line
+
+    return no_cpp
+
+
+def strip_comments(header):
+    no_c_comments = re.sub(r'/\*.*?\*/', '', header, flags=re.DOTALL)
+    no_cxx_comments = re.sub(r'//.*', '', no_c_comments)
+    return no_cxx_comments
+
+
+def strip(header):
+    header = strip_comments(header)
+    header = strip_cpp(header)
+    return header
+
+
+def has_extern_c(header):
+    return header.find('extern "C"') != -1
+
+
+def has_vars(header):
+    return re.search(r'^extern\s+[a-z0-9_]+\s.*;', header, flags=re.MULTILINE) is not None
+
+
+FUNCTION_RES = [
+    r'rte_[a-z0-9_]+\(',
+    r'cmdline_[a-z0-9_]+\(',
+    r'vt100_[a-z0-9_]+\(',
+    r'rdline_[a-z0-9_]+\(',
+    r'cirbuf_[a-z0-9_]+\(',
+    # Windows UNIX compatibility
+    r'pthread_[a-z0-9_]+\(',
+    r'regcomp\(',
+    r'count_cpu\('
+]
+
+
+def has_functions(header):
+    for function_re in FUNCTION_RES:
+        if re.search(function_re, header) is not None:
+            return True
+    return False
+
+
+def has_symbols(header):
+    return has_functions(header) or has_vars(header)
+
+
+def chk_missing(filename):
+    header = open(filename).read()
+    if has_symbols(header) and not has_extern_c(header):
+        print(filename)
+
+
+def chk_redundant(filename):
+    header = open(filename).read()
+    if not has_symbols(header) and has_extern_c(header):
+        print(filename)
+
+if len(sys.argv) < 3:
+    print("%s missing|redundant <header-file> ..." % sys.argv[0])
+    sys.exit(1)
+
+op = sys.argv[1]
+headers = sys.argv[2:]
+
+for header in headers:
+    if op == 'missing':
+        chk_missing(header)
+    elif op == 'redundant':
+        chk_redundant(header)
+    else:
+        print("Unknown operation.")
+        sys.exit(1)
diff --git a/buildtools/chkincs/meson.build b/buildtools/chkincs/meson.build
index f2dadcae18..762f85efe5 100644
--- a/buildtools/chkincs/meson.build
+++ b/buildtools/chkincs/meson.build
@@ -38,13 +38,13 @@ if not add_languages('cpp', required: false)
 endif
 
 # check for extern C in files, since this is not detected as an error by the compiler
-grep = find_program('grep', required: false)
-if grep.found()
-    errlist = run_command([grep, '--files-without-match', '^extern "C"', dpdk_chkinc_headers],
-            check: false, capture: true).stdout().split()
-    if errlist != []
-        error('Files missing C++ \'extern "C"\' guards:\n- ' + '\n- '.join(errlist))
-    endif
+chkextern = find_program('chkextern.py')
+
+missing_extern_headers = run_command(chkextern, 'missing', dpdk_chkinc_headers,
+      capture: true, check: true).stdout().split()
+
+if missing_extern_headers != []
+    error('Files missing C++ \'extern "C"\' guards:\n- ' + '\n- '.join(missing_extern_headers))
 endif
 
 gen_cpp_files = generator(gen_c_file_for_header,
-- 
2.43.0