+ checkpatch-special-case-extern-struct-in-c.patch added to mm-nonmm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: checkpatch: special case extern struct in .c
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     checkpatch-special-case-extern-struct-in-c.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/checkpatch-special-case-extern-struct-in-c.patch

This patch will later appear in the mm-nonmm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Jim Cromie <jim.cromie@gmail.com>
Subject: checkpatch: special case extern struct in .c
Date: Mon, 7 Aug 2023 21:30:18 -0600

"externs should be avoided in .c files" needs an exception for linker
symbols, like those that mark the start, stop of many kernel sections.

Since checkpatch already checks REALNAME to avoid looking at fragments
changing vmlinux.lds.h, add a new else-if block to look at them
instead.  As a simple heuristic, treat all words (in the patch-line)
as possible symbols, to screen later warnings.

For my test case, the possible-symbols included BOUNDED_BY (a macro),
which is extra, but not troublesome - these are just to screen
WARNINGS that might be issued on later fragments (changing .c files)

Where the WARN is issued, precede it with an else-if block to catch
one common extern-in-c use case: "extern struct foo bar[]".  Here we
can at least issue a softer warning, after checking for a match with a
maybe-linker-symbol parsed earlier from the patch.

Though heuristic, it worked for my test-case, allowing both start__,
stop__ $symbol's (wo the prefixes specifically named).  I've coded it
narrowly, it can be expanded later to cover any other expressions.

It does require that the externs in .c's have the additions to
vmlinux.lds.h in the same patch.  And requires vmlinux.lds.h before .c
fragments.

Link: https://lkml.kernel.org/r/20230808033019.21911-2-jim.cromie@gmail.com
Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 scripts/checkpatch.pl |   20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

--- a/scripts/checkpatch.pl~checkpatch-special-case-extern-struct-in-c
+++ a/scripts/checkpatch.pl
@@ -74,6 +74,8 @@ my $git_command ='export LANGUAGE=en_US.
 my $tabsize = 8;
 my ${CONFIG_} = "CONFIG_";
 
+my %maybe_linker_symbol; # for externs in c exceptions, when seen in *vmlinux.lds.h
+
 sub help {
 	my ($exitcode) = @_;
 
@@ -6051,6 +6053,9 @@ sub process {
 
 # check for line continuations outside of #defines, preprocessor #, and asm
 
+		} elsif ($realfile =~ m@/vmlinux.lds.h$@) {
+		    $line =~ s/(\w+)/$maybe_linker_symbol{$1}++/ge;
+		    #print "REAL: $realfile\nln: $line\nkeys:", sort keys %maybe_linker_symbol;
 		} else {
 			if ($prevline !~ /^..*\\$/ &&
 			    $line !~ /^\+\s*\#.*\\$/ &&		# preprocessor
@@ -7120,6 +7125,21 @@ sub process {
 			}
 
 		} elsif ($realfile =~ /\.c$/ && defined $stat &&
+		    $stat =~ /^\+extern struct\s+(\w+)\s+(\w+)\[\];/)
+		{
+			my ($st_type, $st_name) = ($1, $2);
+
+			for my $s (keys %maybe_linker_symbol) {
+			    #print "Linker symbol? $st_name : $s\n";
+			    goto LIKELY_LINKER_SYMBOL
+				if $st_name =~ /$s/;
+			}
+			WARN("AVOID_EXTERNS",
+			     "found a file-scoped extern type:$st_type name:$st_name in .c file\n"
+			     . "is this a linker symbol ?\n" . $herecurr);
+		  LIKELY_LINKER_SYMBOL:
+
+		} elsif ($realfile =~ /\.c$/ && defined $stat &&
 		    $stat =~ /^.\s*extern\s+/)
 		{
 			WARN("AVOID_EXTERNS",
_

Patches currently in -mm which might be from jim.cromie@gmail.com are

checkpatch-special-case-extern-struct-in-c.patch
checkpatch-reword-long-line-warning-about-commit-msg.patch