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

[Robin Jarry]

Mattias Rönnblom, Oct 06, 2024 at 11:47:
> OK, so it does change something, but not for the better, seemingly.
>
> meson.build now somehow has to distinguished between two different "errors":
> 1) One or more offending header files were found.
> 2) Any other kind of error (file not found, access control issues, 
> internal script error, etc).
>
> For 1), it should print a list of the offending header files.
>
> If you just set "check: true" in run_command(), and have the 
> chkextern.py script return non-zero on error, the offending header files 
> will not be printed on stdout.
>
> My guess would be that this complicating factor is the reason for this 
> pattern of not (in/from meson) depending on the script delegate exit 
> code, but rather the output.
>
> May I should rename the script to "scanextern.py" to better reflect that 
> a failure to find an issue is not an error (=non-zero exit code).

I think you need to change run_command() to custom_target(). I was 
thinking of this patch to be much simpler as follows:

diff --git a/buildtools/chkincs/check_extern_c.sh b/buildtools/chkincs/check_extern_c.sh
new file mode 100755
index 000000000000..96ace5ffd248
--- /dev/null
+++ b/buildtools/chkincs/check_extern_c.sh
@@ -0,0 +1,49 @@
+#!/bin/sh
+# SPDX-License-Identifier: BSD-3-Clause
+
+has_symbols() {
+	grep -Eq \
+		-e 'rte_[a-z0-9_]+\(' \
+		-e 'cmdline_[a-z0-9_]+\(' \
+		-e 'vt100_[a-z0-9_]+\(' \
+		-e 'rdline_[a-z0-9_]+\(' \
+		-e 'cirbuf_[a-z0-9_]+\(' \
+		-e 'pthread_[a-z0-9_]+\(' \
+		-e 'regcomp\(' \
+		-e 'count_cpu\(' \
+		-e '^extern[[:space:]]+[a-z0-9_]+[[:space:]]' \
+		"$1"
+}
+
+has_extern_c() {
+	grep -q 'extern "C"' "$1"
+}
+
+mode=$1
+shift
+ret=0
+
+case "$mode" in
+--missing)
+	for header in "$@"; do
+		if has_symbols "$header" && ! has_extern_c "$header"; then
+			echo "error: missing extern \"C\": $header" >&2
+			ret=1
+		fi
+	done
+	;;
+--redundant)
+	for header in "$@"; do
+		if ! has_symbols "$header" && has_extern_c "$header"; then
+			echo "error: missing extern \"C\": $header" >&2
+			exit 1
+		fi
+	done
+	;;
+*)
+	echo "error: unsupported mode '$mode'" >&2
+	ret=1
+esac
+
+exit $ret
diff --git a/buildtools/chkincs/meson.build b/buildtools/chkincs/meson.build
index f2dadcae18ef..b463845083eb 100644
--- a/buildtools/chkincs/meson.build
+++ b/buildtools/chkincs/meson.build
@@ -38,14 +38,11 @@ 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
-endif
+custom_target('check-extern-c',
+        command: files('check_extern_c.sh') + ['--missing', '@INPUT@'],
+        input: dpdk_chkinc_headers,
+        output: 'check-extern-c',
+        build_by_default: true)
 
 gen_cpp_files = generator(gen_c_file_for_header,
         output: '@BASENAME at .cpp',