checkpatch: add warning for pr_* and dev_* macros without a trailing newline

Add a new check in scripts/checkpatch.pl to detect usage of pr_(level) and
dev_(level) macros (for both C and Rust) when the string literal does not
end with '\n'.  Missing trailing newlines can lead to incomplete log lines
that do not appear properly in dmesg or in console output.  To show an
example of this working after applying the patch we can run the script on
the commit that likely motivated this need/issue:

  ./scripts/checkpatch.pl --strict -g "f431c5c581fa1"

Also, the patch is able to handle correctly if there is a printing call
without a newline which then has a newline printed via pr_cont for both
Rust and C alike.  If there is no newline printed and the patch ends or
there is another pr_* call before a newline with pr_cont is printed it
will show a warning.  Not implemented for dev_cont because it is not clear
to me if that is used at all.

One false warning that will be generated due to this change is in case we
have a patch that modifies a `pr_* call without a newline` which has a
pr_cont with a newline following it.  In this case there will be a warning
but because the patch does not include the following pr_cont it will warn
there is nothing creating a newline.  I have modified the warning to be
softer due to this known problem.

I have tested with comments, whitespace, differen orders of pr_* calls and
pr_cont and the only case that I suspect to be a problem is the one
outlined above.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Alban Kurti <[email protected]>
Suggested-by: Miguel Ojeda <[email protected]>
Closes: Rust-for-Linux#1140
Cc: Alex Gaynor <[email protected]>
Cc: Alice Ryhl <[email protected]>
Cc: Andreas Hindborg <[email protected]>
Cc: Andy Whitcroft <[email protected]>
Cc: Benno Lossin <[email protected]>
Cc: Björn Roy Baron <[email protected]>
Cc: Boqun Feng <[email protected]>
Cc: Dwaipayan Ray <[email protected]>
Cc: Gary Guo <[email protected]>
Cc: Joe Perches <[email protected]>
Cc: Lukas Bulwahn <[email protected]>
Cc: Trevor Gross <[email protected]>
Cc: Charalampos Mitrodimas <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: albankurti

scripts/checkpatch.pl

@@ -77,6 +77,8 @@
 
 my %maybe_linker_symbol; # for externs in c exceptions, when seen in *vmlinux.lds.h
 
+my $pending_log = undef;
+
 sub help {
 	my ($exitcode) = @_;
 
@@ -3878,6 +3880,91 @@ sub process {
 			}
 		}
 
+# check for pr_* and dev_* logs without a newline for C and Rust files to avoid missing log messages
+  my $pr_cont_pattern = qr{
+      \b
+      pr_cont!?
+      \s*
+      \(
+      \s*
+      "([^"]*)"
+      [^)]*
+      \)
+  }x;
+  my $log_macro_pattern = qr{
+      \b
+      (
+          pr_(?:emerg|alert|crit|err|warn|notice|info|debug)
+        | dev_(?:emerg|alert|crit|err|warn|notice|info|dbg)
+      )
+      (!?)
+      \s*
+      \(
+      \s*
+      "([^"]*)"
+  }x;
+
+  if ($realfile =~ /\.(?:c|h|rs)$/) {
+      if ($rawline =~ /^\+/) {
+          my $cleanline = $rawline;
+          $cleanline =~ s/^[+\s]+//;
+          $cleanline =~ s/\r?$//;
+          $cleanline =~ s{/\*.*?\*/}{}g;
+          $cleanline =~ s{//.*}{}g;
+
+          if ($pending_log) {
+              if ($cleanline =~ /$pr_cont_pattern/) {
+                  my $cont_string_arg = $1;
+                  if ($cont_string_arg =~ /\\n$/) {
+                      $pending_log = undef;
+                  }
+              } elsif ($cleanline =~ /$log_macro_pattern/) {
+                  WARN($pending_log->{lang} . "_LOG_NO_NEWLINE",
+                       "Possible usage of $pending_log->{macro_call} without a trailing newline.\n" .
+                       $pending_log->{herecurr});
+
+                  $pending_log = undef;
+
+                  my $macro_call  = $1;
+                  my $maybe_excl  = $2;
+                  my $string_arg  = $3;
+                  $string_arg =~ s/\s+$//;
+
+                  if ($realfile =~ /\.rs$/ && $maybe_excl ne '!') {
+                      return;
+                  }
+
+                  if ($string_arg !~ /\\n$/ && $string_arg !~ /\n$/) {
+                      $pending_log = {
+                          macro_call => $macro_call,
+                          herecurr => $herecurr,
+                          lang => ($realfile =~ /\.rs$/) ? "Rust" : "C",
+                      };
+                  }
+              }
+          } else {
+              if ($cleanline =~ /$log_macro_pattern/) {
+                  my $macro_call = $1;
+                  my $maybe_excl = $2;
+                  my $string_arg = $3;
+                  $string_arg =~ s/\s+$//;
+
+                  if ($realfile =~ /\.rs$/ && $maybe_excl ne '!') {
+                      return;
+                  }
+
+                  if ($string_arg !~ /\\n$/ && $string_arg !~ /\n$/) {
+                      $pending_log = {
+                          macro_call => $macro_call,
+                          herecurr   => $herecurr,
+                          lang       => ($realfile =~ /\.rs$/) ? "Rust" : "C",
+                      };
+                  }
+              }
+          }
+      }
+  }
+
 # check for .L prefix local symbols in .S files
 		if ($realfile =~ /\.S$/ &&
 		    $line =~ /^\+\s*(?:[A-Z]+_)?SYM_[A-Z]+_(?:START|END)(?:_[A-Z_]+)?\s*\(\s*\.L/) {
@@ -7670,6 +7757,15 @@ sub process {
 		}
 	}
 
+# pending log means a pr_* without an ending newline has not
+# been followed by a pr_cont call with a newline at the end
+  if ($pending_log) {
+    WARN($pending_log->{lang} . "_LOG_NO_NEWLINE",
+      "Usage of $pending_log->{macro_call} without a trailing newline.\n" .
+      $pending_log->{herecurr});
+    $pending_log = undef;
+  }
+
 	# If we have no input at all, then there is nothing to report on
 	# so just keep quiet.
 	if ($#rawlines == -1) {