kbuild: rust: keep Rust objects out of Clang LTO with inline helpersgrafted

Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit
`objtool` errors such as:

    vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a:
    can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd

The reason is that in such builds, the Clang invocation that compiles
the combined Rust plus helpers bitcode emits LLVM bitcode (again) --
the final code generation happens in the linker's LTO step, which the
`-mllvm` trap options passed to Clang do not reach.

This, in turn, means that unreachable traps are missing, and the
impossible paths do not merely fallthrough to the next symbol, but past
the end of their own section, since LTO builds place each function in
its own section.

Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always
emits machine code directly, with the traps in place.

Assisted-by: LLM
Cc: Gary Guo <gary@garyguo.net>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Matthew Maurer <mmaurer@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust")
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 178 insertions, 0 deletions

diff --git a/scripts/cleanfile b/scripts/cleanfile
new file mode 100755
index 000000000..c00c69b91
--- /dev/null
+++ b/scripts/cleanfile
@@ -0,0 +1,178 @@
+#!/usr/bin/env perl
+# SPDX-License-Identifier: GPL-2.0
+#
+# Clean a text file -- or directory of text files -- of stealth whitespace.
+# WARNING: this can be a highly destructive operation.  Use with caution.
+#
+
+use warnings;
+use bytes;
+use File::Basename;
+
+# Default options
+$max_width = 79;
+
+# Clean up space-tab sequences, either by removing spaces or
+# replacing them with tabs.
+sub clean_space_tabs($)
+{
+    no bytes;			# Tab alignment depends on characters
+
+    my($li) = @_;
+    my($lo) = '';
+    my $pos = 0;
+    my $nsp = 0;
+    my($i, $c);
+
+    for ($i = 0; $i < length($li); $i++) {
+	$c = substr($li, $i, 1);
+	if ($c eq "\t") {
+	    my $npos = ($pos+$nsp+8) & ~7;
+	    my $ntab = ($npos >> 3) - ($pos >> 3);
+	    $lo .= "\t" x $ntab;
+	    $pos = $npos;
+	    $nsp = 0;
+	} elsif ($c eq "\n" || $c eq "\r") {
+	    $lo .= " " x $nsp;
+	    $pos += $nsp;
+	    $nsp = 0;
+	    $lo .= $c;
+	    $pos = 0;
+	} elsif ($c eq " ") {
+	    $nsp++;
+	} else {
+	    $lo .= " " x $nsp;
+	    $pos += $nsp;
+	    $nsp = 0;
+	    $lo .= $c;
+	    $pos++;
+	}
+    }
+    $lo .= " " x $nsp;
+    return $lo;
+}
+
+# Compute the visual width of a string
+sub strwidth($) {
+    no bytes;			# Tab alignment depends on characters
+
+    my($li) = @_;
+    my($c, $i);
+    my $pos = 0;
+    my $mlen = 0;
+
+    for ($i = 0; $i < length($li); $i++) {
+	$c = substr($li,$i,1);
+	if ($c eq "\t") {
+	    $pos = ($pos+8) & ~7;
+	} elsif ($c eq "\n") {
+	    $mlen = $pos if ($pos > $mlen);
+	    $pos = 0;
+	} else {
+	    $pos++;
+	}
+    }
+
+    $mlen = $pos if ($pos > $mlen);
+    return $mlen;
+}
+
+$name = basename($0);
+
+@files = ();
+
+while (defined($a = shift(@ARGV))) {
+    if ($a =~ /^-/) {
+	if ($a eq '-width' || $a eq '-w') {
+	    $max_width = shift(@ARGV)+0;
+	} else {
+	    print STDERR "Usage: $name [-width #] files...\n";
+	    exit 1;
+	}
+    } else {
+	push(@files, $a);
+    }
+}
+
+foreach $f ( @files ) {
+    print STDERR "$name: $f\n";
+
+    if (! -f $f) {
+	print STDERR "$f: not a file\n";
+	next;
+    }
+
+    if (!open(FILE, '+<', $f)) {
+	print STDERR "$name: Cannot open file: $f: $!\n";
+	next;
+    }
+
+    binmode FILE;
+
+    # First, verify that it is not a binary file; consider any file
+    # with a zero byte to be a binary file.  Is there any better, or
+    # additional, heuristic that should be applied?
+    $is_binary = 0;
+
+    while (read(FILE, $data, 65536) > 0) {
+	if ($data =~ /\0/) {
+	    $is_binary = 1;
+	    last;
+	}
+    }
+
+    if ($is_binary) {
+	print STDERR "$name: $f: binary file\n";
+	next;
+    }
+
+    seek(FILE, 0, 0);
+
+    $in_bytes = 0;
+    $out_bytes = 0;
+    $blank_bytes = 0;
+
+    @blanks = ();
+    @lines  = ();
+    $lineno = 0;
+
+    while ( defined($line = <FILE>) ) {
+	$lineno++;
+	$in_bytes += length($line);
+	$line =~ s/[ \t\r]*$//;		# Remove trailing spaces
+	$line = clean_space_tabs($line);
+
+	if ( $line eq "\n" ) {
+	    push(@blanks, $line);
+	    $blank_bytes += length($line);
+	} else {
+	    push(@lines, @blanks);
+	    $out_bytes += $blank_bytes;
+	    push(@lines, $line);
+	    $out_bytes += length($line);
+	    @blanks = ();
+	    $blank_bytes = 0;
+	}
+
+	$l_width = strwidth($line);
+	if ($max_width && $l_width > $max_width) {
+	    print STDERR
+		"$f:$lineno: line exceeds $max_width characters ($l_width)\n";
+	}
+    }
+
+    # Any blanks at the end of the file are discarded
+
+    if ($in_bytes != $out_bytes) {
+	# Only write to the file if changed
+	seek(FILE, 0, 0);
+	print FILE @lines;
+
+	if ( !defined($where = tell(FILE)) ||
+	     !truncate(FILE, $where) ) {
+	    die "$name: Failed to truncate modified file: $f: $!\n";
+	}
+    }
+
+    close(FILE);
+}