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, 240 insertions, 0 deletions

diff --git a/scripts/config b/scripts/config
new file mode 100755
index 000000000..32428ea90
--- /dev/null
+++ b/scripts/config
@@ -0,0 +1,240 @@
+#!/usr/bin/env bash
+# SPDX-License-Identifier: GPL-2.0
+# Manipulate options in a .config file from the command line
+
+myname=${0##*/}
+
+# If no prefix forced, use the default CONFIG_
+CONFIG_="${CONFIG_-CONFIG_}"
+
+# We use an uncommon delimiter for sed substitutions
+SED_DELIM=$(echo -en "\001")
+
+usage() {
+	cat >&2 <<EOL
+Manipulate options in a .config file from the command line.
+Usage:
+$myname options command ...
+commands:
+	--enable|-e option   Enable option
+	--disable|-d option  Disable option
+	--module|-m option   Turn option into a module
+	--set-str option string
+	                     Set option to "string"
+	--set-val option value
+	                     Set option to value
+	--undefine|-u option Undefine option
+	--state|-s option    Print state of option (n,y,m,undef)
+
+	--enable-after|-E beforeopt option
+                             Enable option directly after other option
+	--disable-after|-D beforeopt option
+                             Disable option directly after other option
+	--module-after|-M beforeopt option
+                             Turn option into module directly after other option
+	--refresh            Refresh the config using old settings
+
+	commands can be repeated multiple times
+
+options:
+	--file config-file   .config file to change (default .config)
+	--keep-case|-k       Keep next symbols' case (don't upper-case it)
+
+$myname doesn't check the validity of the .config file. This is done at next
+make time.
+
+By default, $myname will upper-case the given symbol. Use --keep-case to keep
+the case of all following symbols unchanged.
+
+$myname uses 'CONFIG_' as the default symbol prefix. Set the environment
+variable CONFIG_ to the prefix to use. Eg.: CONFIG_="FOO_" $myname ...
+EOL
+	exit 1
+}
+
+checkarg() {
+	ARG="$1"
+	if [ "$ARG" = "" ] ; then
+		usage
+	fi
+	case "$ARG" in
+	${CONFIG_}*)
+		ARG="${ARG/${CONFIG_}/}"
+		;;
+	esac
+	if [ "$MUNGE_CASE" = "yes" ] ; then
+		ARG="`echo $ARG | tr a-z A-Z`"
+	fi
+}
+
+txt_append() {
+	local anchor="$1"
+	local insert="$2"
+	local infile="$3"
+
+	# sed append cmd: 'a\' + newline + text + newline
+	cmd="$(printf "a\\%b$insert" "\n")"
+
+	# We don't really need a backup file, but in-place editing with backup
+	# skipped is not portable due to different implementations parsing
+	# arguments in incompatible manners.
+	# Create a backup file anyway to ensure portability. The file will be
+	# deleted on exit.
+	sed -E -i.swp -e "/$anchor/$cmd" "$infile"
+	SED_EDITED=1
+}
+
+txt_subst() {
+	local before="$1"
+	local after="$2"
+	local infile="$3"
+
+	sed -E -i.swp -e "s$SED_DELIM$before$SED_DELIM$after$SED_DELIM" "$infile"
+	SED_EDITED=1
+}
+
+txt_delete() {
+	local text="$1"
+	local infile="$2"
+
+	sed -E -i.swp -e "/$text/d" "$infile"
+	SED_EDITED=1
+}
+
+set_var() {
+	local name=$1 new=$2 before=$3
+
+	name_re="^($name=.*|# $name is not set)"
+	before_re="^($before=|# $before is not set)"
+	if test -n "$before" && grep -Eq "$before_re" "$FN"; then
+		txt_append "$before_re" "$new" "$FN"
+	elif grep -Eq "$name_re" "$FN"; then
+		txt_subst "$name_re" "$new" "$FN"
+	else
+		echo "$new" >>"$FN"
+	fi
+}
+
+undef_var() {
+	local name=$1
+
+	txt_delete "^($name=|# $name is not set)" "$FN"
+}
+
+SED_EDITED=0
+on_exit() {
+	if [ "$SED_EDITED" -ge 1 ]; then
+		rm -f "$FN.swp"
+	fi
+}
+trap on_exit EXIT
+
+FN=.config
+CMDS=()
+while [[ $# -gt 0 ]]; do
+	if [ "$1" = "--file" ]; then
+		if [ "$2" = "" ]; then
+			usage
+		fi
+		FN="$2"
+		shift 2
+	else
+		CMDS+=("$1")
+		shift
+	fi
+done
+
+set -- "${CMDS[@]}"
+if [ "$1" = "" ] ; then
+	usage
+fi
+
+MUNGE_CASE=yes
+while [ "$1" != "" ] ; do
+	CMD="$1"
+	shift
+	case "$CMD" in
+	--keep-case|-k)
+		MUNGE_CASE=no
+		continue
+		;;
+	--refresh)
+		;;
+	--*-after|-E|-D|-M)
+		checkarg "$1"
+		A=$ARG
+		checkarg "$2"
+		B=$ARG
+		shift 2
+		;;
+	-*)
+		checkarg "$1"
+		shift
+		;;
+	esac
+	case "$CMD" in
+	--enable|-e)
+		set_var "${CONFIG_}$ARG" "${CONFIG_}$ARG=y"
+		;;
+
+	--disable|-d)
+		set_var "${CONFIG_}$ARG" "# ${CONFIG_}$ARG is not set"
+		;;
+
+	--module|-m)
+		set_var "${CONFIG_}$ARG" "${CONFIG_}$ARG=m"
+		;;
+
+	--set-str)
+		# sed swallows one level of escaping, so we need double-escaping
+		set_var "${CONFIG_}$ARG" "${CONFIG_}$ARG=\"${1//\"/\\\\\"}\""
+		shift
+		;;
+
+	--set-val)
+		set_var "${CONFIG_}$ARG" "${CONFIG_}$ARG=$1"
+		shift
+		;;
+	--undefine|-u)
+		undef_var "${CONFIG_}$ARG"
+		;;
+
+	--state|-s)
+		if grep -q "# ${CONFIG_}$ARG is not set" $FN ; then
+			echo n
+		else
+			V="$(grep "^${CONFIG_}$ARG=" $FN)"
+			if [ $? != 0 ] ; then
+				echo undef
+			else
+				V="${V/#${CONFIG_}$ARG=/}"
+				V="${V/#\"/}"
+				V="${V/%\"/}"
+				V="${V//\\\"/\"}"
+				echo "${V}"
+			fi
+		fi
+		;;
+
+	--enable-after|-E)
+		set_var "${CONFIG_}$B" "${CONFIG_}$B=y" "${CONFIG_}$A"
+		;;
+
+	--disable-after|-D)
+		set_var "${CONFIG_}$B" "# ${CONFIG_}$B is not set" "${CONFIG_}$A"
+		;;
+
+	--module-after|-M)
+		set_var "${CONFIG_}$B" "${CONFIG_}$B=m" "${CONFIG_}$A"
+		;;
+
+	--refresh)
+		yes "" | make oldconfig KCONFIG_CONFIG=$FN
+		;;
+
+	*)
+		echo "bad command: $CMD" >&2
+		usage
+		;;
+	esac
+done