Commit 15d4734c authored by Jim Cromie's avatar Jim Cromie Committed by Andrew Morton
Browse files

checkpatch: qualify do-while-0 advice 

Add a paragraph of advice qualifying the general do-while-0 advice, noting
3 possible misguidings.  reduce one ERROR to WARN, for the case I actually
encountered.

And add 'static_assert' to named exceptions, along with some additional
comments about named exceptions vs (detection of) declarative construction
primitives (union, struct, [], etc).

Link: https://lkml.kernel.org/r/20250325235156.663269-3-jim.cromie@gmail.com


Signed-off-by: default avatarJim Cromie <jim.cromie@gmail.com>
Cc: Andy Whitcroft <apw@canonical.com>
Cc: Joe Perches <joe@perches.com>
Cc: Dwaipayan Ray <dwaipayanray1@gmail.com>
Cc: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Cc: Louis Chauvet <louis.chauvet@bootlin.com>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent df3d5274

scripts/checkpatch.pl

+27 −6
Original line number Diff line number Diff line
@@ -151,6 +151,24 @@ EOM 
	exit($exitcode);

}



my $DO_WHILE_0_ADVICE = q{

   do {} while (0) advice is over-stated in a few situations:



   The more obvious case is macros, like MODULE_PARM_DESC, invoked at

   file-scope, where C disallows code (it must be in functions).  See

   $exceptions if you have one to add by name.



   More troublesome is declarative macros used at top of new scope,

   like DECLARE_PER_CPU.  These might just compile with a do-while-0

   wrapper, but would be incorrect.  Most of these are handled by

   detecting struct,union,etc declaration primitives in $exceptions.



   Theres also macros called inside an if (block), which "return" an

   expression.  These cannot do-while, and need a ({}) wrapper.



   Enjoy this qualification while we work to improve our heuristics.

};



sub uniq {

	my %seen;

	return grep { !$seen{$_}++ } @_;
@@ -5883,9 +5901,9 @@ sub process { 
			}

		}



# multi-statement macros should be enclosed in a do while loop, grab the

# first statement and ensure its the whole macro if its not enclosed

# in a known good container

# Usually multi-statement macros should be enclosed in a do {} while

# (0) loop.  Grab the first statement and ensure its the whole macro

# if its not enclosed in a known good container

		if ($realfile !~ m@/vmlinux.lds.h$@ &&

		    $line =~ /^.\s*\#\s*define\s*$Ident(\()?/) {

			my $ln = $linenr;
@@ -5938,10 +5956,13 @@ sub process { 


			my $exceptions = qr{

				$Declare|

				# named exceptions

				module_param_named|

				MODULE_PARM_DESC|

				DECLARE_PER_CPU|

				DEFINE_PER_CPU|

				static_assert|

				# declaration primitives

				__typeof__\(|

				union|

				struct|
@@ -5976,11 +5997,11 @@ sub process { 
					ERROR("MULTISTATEMENT_MACRO_USE_DO_WHILE",

					      "Macros starting with if should be enclosed by a do - while loop to avoid possible if/else logic defects\n" . "$herectx");

				} elsif ($dstat =~ /;/) {

					ERROR("MULTISTATEMENT_MACRO_USE_DO_WHILE",

					      "Macros with multiple statements should be enclosed in a do - while loop\n" . "$herectx");

					WARN("MULTISTATEMENT_MACRO_USE_DO_WHILE",

					      "Non-declarative macros with multiple statements should be enclosed in a do - while loop\n" . "$herectx\nBUT SEE:\n$DO_WHILE_0_ADVICE");

				} else {

					ERROR("COMPLEX_MACRO",

					      "Macros with complex values should be enclosed in parentheses\n" . "$herectx");

					      "Macros with complex values should be enclosed in parentheses\n" . "$herectx\nBUT SEE:\n$DO_WHILE_0_ADVICE");

				}



			}