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, 208 insertions, 0 deletions

diff --git a/tools/bootconfig/test-bootconfig.sh b/tools/bootconfig/test-bootconfig.sh
new file mode 100755
index 000000000..fc69f815c
--- /dev/null
+++ b/tools/bootconfig/test-bootconfig.sh
@@ -0,0 +1,208 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-only
+
+echo "Boot config test script"
+
+if [ -d "$1" ]; then
+  TESTDIR=$1
+else
+  TESTDIR=.
+fi
+BOOTCONF=${TESTDIR}/bootconfig
+ALIGN=4
+
+INITRD=`mktemp ${TESTDIR}/initrd-XXXX`
+TEMPCONF=`mktemp ${TESTDIR}/temp-XXXX.bconf`
+OUTFILE=`mktemp ${TESTDIR}/tempout-XXXX`
+NG=0
+
+cleanup() {
+  rm -f $INITRD $TEMPCONF $OUTFILE
+  exit $NG
+}
+
+trap cleanup EXIT TERM
+
+NO=1
+
+xpass() { # pass test command
+  echo "test case $NO ($*)... "
+  if ! ($@ && printf "\t\t[OK]\n"); then
+     printf "\t\t[NG]\n"; NG=$((NG + 1))
+  fi
+  NO=$((NO + 1))
+}
+
+xfail() { # fail test command
+  echo "test case $NO ($*)... "
+  if ! (! $@ && printf "\t\t[OK]\n"); then
+     printf "\t\t[NG]\n"; NG=$((NG + 1))
+  fi
+  NO=$((NO + 1))
+}
+
+echo "Basic command test"
+xpass $BOOTCONF $INITRD
+
+echo "Delete command should success without bootconfig"
+xpass $BOOTCONF -d $INITRD
+
+dd if=/dev/zero of=$INITRD bs=4096 count=1
+printf "key = value;" > $TEMPCONF
+bconf_size=$(wc -c < $TEMPCONF)
+initrd_size=$(wc -c < $INITRD)
+
+echo "Apply command test"
+xpass $BOOTCONF -a $TEMPCONF $INITRD
+new_size=$(wc -c < $INITRD)
+
+echo "Show command test"
+xpass $BOOTCONF $INITRD
+
+echo "File size check"
+total_size=$(expr $bconf_size + $initrd_size + 9 + 12 + $ALIGN - 1 )
+total_size=$(expr $total_size / $ALIGN)
+total_size=$(expr $total_size \* $ALIGN)
+xpass test $new_size -eq $total_size
+
+echo "Apply command repeat test"
+xpass $BOOTCONF -a $TEMPCONF $INITRD
+
+echo "File size check"
+xpass test $new_size -eq $(wc -c < $INITRD)
+
+echo "Delete command check"
+xpass $BOOTCONF -d $INITRD
+
+echo "File size check"
+new_size=$(wc -c < $INITRD)
+xpass test $new_size -eq $initrd_size
+
+echo "No error messge while applying"
+dd if=/dev/zero of=$INITRD bs=4096 count=1
+printf " \0\0\0 \0\0\0" >> $INITRD
+$BOOTCONF -a $TEMPCONF $INITRD > $OUTFILE 2>&1
+xfail grep -i "failed" $OUTFILE
+xfail grep -i "error" $OUTFILE
+
+echo "Max node number check"
+
+awk '
+BEGIN {
+  for (i = 0; i < 26; i += 1)
+      printf("%c\n", 65 + i % 26)
+  for (i = 26; i < 8192; i += 1)
+      printf("%c%c%c\n", 65 + i % 26, 65 + (i / 26) % 26, 65 + (i / 26 / 26))
+}
+' > $TEMPCONF
+xpass $BOOTCONF -a $TEMPCONF $INITRD
+
+printf "badnode\n" >> $TEMPCONF
+xfail $BOOTCONF -a $TEMPCONF $INITRD
+
+echo "Max filesize check"
+
+# Max size is 32767 (including terminal byte)
+printf "data = \"" > $TEMPCONF
+dd if=/dev/urandom bs=768 count=32 | base64 -w0 >> $TEMPCONF
+printf "\"\n" >> $TEMPCONF
+xfail $BOOTCONF -a $TEMPCONF $INITRD
+
+dd if=$TEMPCONF of=$OUTFILE bs=1 count=32764
+cp $OUTFILE $TEMPCONF
+printf "\"\n" >> $TEMPCONF	# add 2 bytes + terminal ('\"\n\0')
+xpass $BOOTCONF -a $TEMPCONF $INITRD
+
+echo "Adding same-key values"
+cat > $TEMPCONF << EOF
+key = bar, baz
+key += qux
+EOF
+echo > $INITRD
+
+xpass $BOOTCONF -a $TEMPCONF $INITRD
+$BOOTCONF $INITRD > $OUTFILE
+xpass grep -q "bar" $OUTFILE
+xpass grep -q "baz" $OUTFILE
+xpass grep -q "qux" $OUTFILE
+
+echo "Override same-key values"
+cat > $TEMPCONF << EOF
+key = bar, baz
+key := qux
+EOF
+echo > $INITRD
+
+xpass $BOOTCONF -a $TEMPCONF $INITRD
+$BOOTCONF $INITRD > $OUTFILE
+xfail grep -q "bar" $OUTFILE
+xfail grep -q "baz" $OUTFILE
+xpass grep -q "qux" $OUTFILE
+
+echo "Double/single quotes test"
+printf "key = '\"string\"';" > $TEMPCONF
+$BOOTCONF -a $TEMPCONF $INITRD
+$BOOTCONF $INITRD > $TEMPCONF
+cat $TEMPCONF
+xpass grep \'\"string\"\' $TEMPCONF
+
+echo "Repeat same-key tree"
+cat > $TEMPCONF << EOF
+foo
+bar
+foo { buz }
+EOF
+echo > $INITRD
+
+xpass $BOOTCONF -a $TEMPCONF $INITRD
+$BOOTCONF $INITRD > $OUTFILE
+xpass grep -q "bar" $OUTFILE
+
+
+echo "Remove/keep tailing spaces"
+cat > $TEMPCONF << EOF
+foo = val     # comment
+bar = "val2 " # comment
+EOF
+echo > $INITRD
+
+xpass $BOOTCONF -a $TEMPCONF $INITRD
+$BOOTCONF $INITRD > $OUTFILE
+xfail grep -q 'val[[:space:]]' $OUTFILE
+xpass grep -q 'val2[[:space:]]' $OUTFILE
+
+echo "Showing correct line:column of no closing brace"
+cat > $TEMPCONF << EOF
+foo {
+bar {
+}
+EOF
+$BOOTCONF -a $TEMPCONF $INITRD 2> $OUTFILE
+xpass grep -q "1:1" $OUTFILE
+
+echo "=== expected failure cases ==="
+for i in samples/bad-* ; do
+  xfail $BOOTCONF -a $i $INITRD
+done
+
+echo "=== expected success cases ==="
+for i in samples/good-* ; do
+  xpass $BOOTCONF -a $i $INITRD
+  x="samples/exp-"`basename $i`
+  $BOOTCONF $i > $TEMPCONF
+  xpass diff $x $TEMPCONF
+done
+
+
+echo
+echo "=== Summary ==="
+echo "# of Passed: $(expr $NO - $NG - 1)"
+echo "# of Failed: $NG"
+
+echo
+if [ $NG -eq 0 ]; then
+	echo "All tests passed"
+else
+	echo "$NG tests failed"
+	exit 1
+fi