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, 224 insertions, 0 deletions

diff --git a/scripts/bootgraph.pl b/scripts/bootgraph.pl
new file mode 100755
index 000000000..79c903292
--- /dev/null
+++ b/scripts/bootgraph.pl
@@ -0,0 +1,224 @@
+#!/usr/bin/env perl
+# SPDX-License-Identifier: GPL-2.0-only
+
+# Copyright 2008, Intel Corporation
+#
+# This file is part of the Linux kernel
+#
+# Authors:
+# 	Arjan van de Ven <arjan@linux.intel.com>
+
+
+#
+# This script turns a dmesg output into a SVG graphic that shows which
+# functions take how much time. You can view SVG graphics with various
+# programs, including Inkscape, The Gimp and Firefox.
+#
+#
+# For this script to work, the kernel needs to be compiled with the
+# CONFIG_PRINTK_TIME configuration option enabled, and with
+# "initcall_debug" passed on the kernel command line.
+#
+# usage:
+# 	dmesg | perl scripts/bootgraph.pl > output.svg
+#
+
+use strict;
+use Getopt::Long;
+my $header = 0;
+
+sub help {
+	my $text = << "EOM";
+Usage:
+1) dmesg | perl scripts/bootgraph.pl [OPTION] > output.svg
+2) perl scripts/bootgraph.pl -h
+
+Options:
+	-header	Insert kernel version and date
+EOM
+	my $std=shift;
+	if ($std == 1) {
+		print STDERR $text;
+	} else {
+		print $text;
+	}
+	exit;
+}
+
+GetOptions(
+	'h|help'	=>\&help,
+	'header'	=>\$header
+);
+
+my %start;
+my %end;
+my %type;
+my $done = 0;
+my $maxtime = 0;
+my $firsttime = 99999;
+my $count = 0;
+my %pids;
+my %pidctr;
+
+my $headerstep = 20;
+my $xheader = 15;
+my $yheader = 25;
+my $cyheader = 0;
+
+while (<>) {
+	my $line = $_;
+	if ($line =~ /([0-9\.]+)\] calling  ([a-zA-Z0-9\_\.]+)\+/) {
+		my $func = $2;
+		if ($done == 0) {
+			$start{$func} = $1;
+			$type{$func} = 0;
+			if ($1 < $firsttime) {
+				$firsttime = $1;
+			}
+		}
+		if ($line =~ /\@ ([0-9]+)/) {
+			$pids{$func} = $1;
+		}
+		$count = $count + 1;
+	}
+
+	if ($line =~ /([0-9\.]+)\] async_waiting @ ([0-9]+)/) {
+		my $pid = $2;
+		my $func;
+		if (!defined($pidctr{$pid})) {
+			$func = "wait_" . $pid . "_1";
+			$pidctr{$pid} = 1;
+		} else {
+			$pidctr{$pid} = $pidctr{$pid} + 1;
+			$func = "wait_" . $pid . "_" . $pidctr{$pid};
+		}
+		if ($done == 0) {
+			$start{$func} = $1;
+			$type{$func} = 1;
+			if ($1 < $firsttime) {
+				$firsttime = $1;
+			}
+		}
+		$pids{$func} = $pid;
+		$count = $count + 1;
+	}
+
+	if ($line =~ /([0-9\.]+)\] initcall ([a-zA-Z0-9\_\.]+)\+.*returned/) {
+		if ($done == 0) {
+			$end{$2} = $1;
+			$maxtime = $1;
+		}
+	}
+
+	if ($line =~ /([0-9\.]+)\] async_continuing @ ([0-9]+)/) {
+		my $pid = $2;
+		my $func =  "wait_" . $pid . "_" . $pidctr{$pid};
+		$end{$func} = $1;
+		$maxtime = $1;
+	}
+	if ($line =~ /Write protecting the/) {
+		$done = 1;
+	}
+	if ($line =~ /Freeing unused kernel memory/) {
+		$done = 1;
+	}
+}
+
+if ($count == 0) {
+    print STDERR <<END;
+No data found in the dmesg. Make sure that 'printk.time=1' and
+'initcall_debug' are passed on the kernel command line.
+END
+	help(1);
+    exit 1;
+}
+
+print "<?xml version=\"1.0\" standalone=\"no\"?> \n";
+print "<svg width=\"2000\" height=\"100%\" version=\"1.1\" xmlns=\"http://www.w3.org/2000/svg\">\n";
+
+
+if ($header) {
+	my $version = `uname -a`;
+	my $date = `date`;
+	print "<text transform=\"translate($xheader,$yheader)\">Kernel version: $version</text>\n";
+	$cyheader = $yheader+$headerstep;
+	print "<text transform=\"translate($xheader,$cyheader)\">Date: $date</text>\n";
+}
+
+my @styles;
+
+$styles[0] = "fill:rgb(0,0,255);fill-opacity:0.5;stroke-width:1;stroke:rgb(0,0,0)";
+$styles[1] = "fill:rgb(0,255,0);fill-opacity:0.5;stroke-width:1;stroke:rgb(0,0,0)";
+$styles[2] = "fill:rgb(255,0,20);fill-opacity:0.5;stroke-width:1;stroke:rgb(0,0,0)";
+$styles[3] = "fill:rgb(255,255,20);fill-opacity:0.5;stroke-width:1;stroke:rgb(0,0,0)";
+$styles[4] = "fill:rgb(255,0,255);fill-opacity:0.5;stroke-width:1;stroke:rgb(0,0,0)";
+$styles[5] = "fill:rgb(0,255,255);fill-opacity:0.5;stroke-width:1;stroke:rgb(0,0,0)";
+$styles[6] = "fill:rgb(0,128,255);fill-opacity:0.5;stroke-width:1;stroke:rgb(0,0,0)";
+$styles[7] = "fill:rgb(0,255,128);fill-opacity:0.5;stroke-width:1;stroke:rgb(0,0,0)";
+$styles[8] = "fill:rgb(255,0,128);fill-opacity:0.5;stroke-width:1;stroke:rgb(0,0,0)";
+$styles[9] = "fill:rgb(255,255,128);fill-opacity:0.5;stroke-width:1;stroke:rgb(0,0,0)";
+$styles[10] = "fill:rgb(255,128,255);fill-opacity:0.5;stroke-width:1;stroke:rgb(0,0,0)";
+$styles[11] = "fill:rgb(128,255,255);fill-opacity:0.5;stroke-width:1;stroke:rgb(0,0,0)";
+
+my $style_wait = "fill:rgb(128,128,128);fill-opacity:0.5;stroke-width:0;stroke:rgb(0,0,0)";
+
+my $mult = 1950.0 / ($maxtime - $firsttime);
+my $threshold2 = ($maxtime - $firsttime) / 120.0;
+my $threshold = $threshold2/10;
+my $stylecounter = 0;
+my %rows;
+my $rowscount = 1;
+my @initcalls = sort { $start{$a} <=> $start{$b} } keys(%start);
+
+foreach my $key (@initcalls) {
+	my $duration = $end{$key} - $start{$key};
+
+	if ($duration >= $threshold) {
+		my ($s, $s2, $s3, $e, $w, $y, $y2, $style);
+		my $pid = $pids{$key};
+
+		if (!defined($rows{$pid})) {
+			$rows{$pid} = $rowscount;
+			$rowscount = $rowscount + 1;
+		}
+		$s = ($start{$key} - $firsttime) * $mult;
+		$s2 = $s + 6;
+		$s3 = $s + 1;
+		$e = ($end{$key} - $firsttime) * $mult;
+		$w = $e - $s;
+
+		$y = $rows{$pid} * 150;
+		$y2 = $y + 4;
+
+		$style = $styles[$stylecounter];
+		$stylecounter = $stylecounter + 1;
+		if ($stylecounter > 11) {
+			$stylecounter = 0;
+		};
+
+		if ($type{$key} == 1) {
+			$y = $y + 15;
+			print "<rect x=\"$s\" width=\"$w\" y=\"$y\" height=\"115\" style=\"$style_wait\"/>\n";
+		} else {
+			print "<rect x=\"$s\" width=\"$w\" y=\"$y\" height=\"145\" style=\"$style\"/>\n";
+			if ($duration >= $threshold2) {
+				print "<text transform=\"translate($s2,$y2) rotate(90)\">$key</text>\n";
+			} else {
+				print "<text transform=\"translate($s3,$y2) rotate(90)\" font-size=\"3pt\">$key</text>\n";
+			}
+		}
+	}
+}
+
+
+# print the time line on top
+my $time = $firsttime;
+my $step = ($maxtime - $firsttime) / 15;
+while ($time < $maxtime) {
+	my $s3 = ($time - $firsttime) * $mult;
+	my $tm = int($time * 100) / 100.0;
+	print "<text transform=\"translate($s3,89) rotate(90)\">$tm</text>\n";
+	$time = $time + $step;
+}
+
+print "</svg>\n";