linux-kernel - [PATCH -v3] checkpatch: Check for .byte-spelled insn opcodes documentation on x86

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Date:   Mon, 12 Oct 2020 16:23:06 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Joe Perches <joe@...ches.com>
Cc:     X86 ML <x86@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>,
        Andy Whitcroft <apw@...onical.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH -v3] checkpatch: Check for .byte-spelled insn opcodes
 documentation on x86

From: Borislav Petkov <bp@...e.de>

Instruction opcode bytes spelled using the gas directive .byte should
carry a comment above them stating which binutils version has added
support for the instruction mnemonic so that they can be replaced with
the mnemonic when that binutils version is equal or less than the
minimum-supported version by the kernel.

Add a check for that.

Requested-by: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Borislav Petkov <bp@...e.de>
---
 scripts/checkpatch.pl | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 504d2e431c60..e9ead600d685 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -408,6 +408,7 @@ our $Lval	= qr{$Ident(?:$Member)*};
 our $Int_type	= qr{(?i)llu|ull|ll|lu|ul|l|u};
 our $Binary	= qr{(?i)0b[01]+$Int_type?};
 our $Hex	= qr{(?i)0x[0-9a-f]+$Int_type?};
+our $Hex_byte	= qr{(?i)0x[0-9a-f]{1,2}};
 our $Int	= qr{[0-9]+$Int_type?};
 our $Octal	= qr{0[0-7]+$Int_type?};
 our $String	= qr{"[X\t]*"};
@@ -6858,6 +6859,18 @@ sub process {
 			WARN("DUPLICATED_SYSCTL_CONST",
 				"duplicated sysctl range checking value '$1', consider using the shared one in include/linux/sysctl.h\n" . $herecurr);
 		}
+
+# document which binutils version supports the actual insn mnemonic so that the naked opcode bytes can be replaced.
+# x86-only. Upper limit is rather arbitrary (max insn length on x86) but imposed so as to avoid perl aborts.
+		if ($realfile =~ m@...ch/x86/@ &&
+		    $rawline =~ /\s*\.byte\s+(?:$Hex_byte[,\s]*){1,15}/) {
+
+			my $comment = ctx_locate_comment($file ? 0 : $first_line, $linenr);
+			if ($comment !~ /binutils (?:version )*[0-9.]+/ms) {
+				WARN("MISSING_BINUTILS_VERSION",
+				     "Please consider documenting which binutils version supports these .byte-spelled insn opcodes by adding \"binutils version <num>\" in a comment above them.\n" . $herecurr);
+			}
+		}
 	}
 
 	# If we have no input at all, then there is nothing to report on
-- 
2.21.0

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette