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, 146 insertions, 0 deletions

diff --git a/tools/perf/perf-archive.sh b/tools/perf/perf-archive.sh
new file mode 100755
index 000000000..7977e9b0a
--- /dev/null
+++ b/tools/perf/perf-archive.sh
@@ -0,0 +1,146 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# perf archive
+# Arnaldo Carvalho de Melo <acme@redhat.com>
+
+PERF_DATA=perf.data
+PERF_SYMBOLS=perf.symbols
+PERF_ALL=perf.all
+ALL=0
+UNPACK=0
+
+while [ $# -gt 0 ] ; do
+	if [ $1 == "--all" ]; then
+		ALL=1
+		shift
+	elif [ $1 == "--unpack" ]; then
+		UNPACK=1
+		shift
+	elif [ $1 == "--exclude-buildids" ]; then
+		EXCLUDE_BUILDIDS="$2"
+		if [ ! -e "$EXCLUDE_BUILDIDS" ]; then
+			echo "Provided exclude-buildids file $EXCLUDE_BUILDIDS does not exist"
+			exit 1
+		fi
+		shift 2
+	else
+		PERF_DATA=$1
+		UNPACK_TAR=$1
+		shift
+	fi
+done
+
+if [ $UNPACK -eq 1 ]; then
+	if [ ! -z "$UNPACK_TAR" ]; then					# tar given as an argument
+		if [ ! -e "$UNPACK_TAR" ]; then
+			echo "Provided file $UNPACK_TAR does not exist"
+			exit 1
+		fi
+		TARGET="$UNPACK_TAR"
+	else																# search for perf tar in the current directory
+		TARGET=`find . -regex "\./perf.*\.tar\.bz2"`
+		TARGET_NUM=`echo -n "$TARGET" | grep -c '^'`
+
+		if [ -z "$TARGET" ] || [ $TARGET_NUM -gt 1 ]; then
+			echo -e "Error: $TARGET_NUM files found for unpacking:\n$TARGET"
+			echo "Provide the requested file as an argument"
+			exit 1
+		else
+			echo "Found target file for unpacking: $TARGET"
+		fi
+	fi
+
+	if [[ "$TARGET" =~ (\./)?$PERF_ALL.*.tar.bz2 ]]; then				# perf tar generated by --all option
+		TAR_CONTENTS=`tar tvf "$TARGET" | tr -s " " | cut -d " " -f 6`
+		VALID_TAR=`echo "$TAR_CONTENTS" | grep "$PERF_SYMBOLS.tar.bz2" | wc -l`		# check if it contains a sub-tar perf.symbols
+		if [ $VALID_TAR -ne 1 ]; then
+			echo "Error: $TARGET file is not valid (contains zero or multiple sub-tar files with debug symbols)"
+			exit 1
+		fi
+
+		INTERSECT=`comm -12 <(ls) <(echo "$TAR_CONTENTS") | tr "\n" " "`	# check for overwriting
+		if [ ! -z "$INTERSECT" ]; then										# prompt if file(s) already exist in the current directory
+			echo "File(s) ${INTERSECT::-1} already exist in the current directory."
+			while true; do
+				read -p 'Do you wish to overwrite them? ' yn
+				case $yn in
+					[Yy]* ) break;;
+					[Nn]* ) exit 1;;
+					* ) echo "Please answer yes or no.";;
+				esac
+			done
+		fi
+
+		# unzip the perf.data file in the current working directory	and debug symbols in ~/.debug directory
+		tar xvf $TARGET && tar xvf $PERF_SYMBOLS.tar.bz2 -C ~/.debug
+
+	else																# perf tar generated by perf archive (contains only debug symbols)
+		tar xvf $TARGET -C ~/.debug
+	fi
+	exit 0
+fi
+
+#
+# PERF_BUILDID_DIR environment variable set by perf
+# path to buildid directory, default to $HOME/.debug
+#
+if [ -z $PERF_BUILDID_DIR ]; then
+	PERF_BUILDID_DIR=~/.debug/
+else
+        # append / to make substitutions work
+        PERF_BUILDID_DIR=$PERF_BUILDID_DIR/
+fi
+
+BUILDIDS=$(mktemp /tmp/perf-archive-buildids.XXXXXX)
+
+#
+# EXCLUDE_BUILDIDS is an optional file that contains build-ids to be excluded from the
+# archive. It is a list of build-ids, one per line, without any leading or trailing spaces.
+# If the file is empty, all build-ids will be included in the archive. To create a exclude-
+# buildids file, you can use the following command:
+# 	perf buildid-list -i perf.data --with-hits | grep -v "^ " > exclude_buildids.txt
+# You can edit the file to remove the lines that you want to keep in the archive, then:
+# 	perf archive --exclude-buildids exclude_buildids.txt
+#
+if [ -s "$EXCLUDE_BUILDIDS" ]; then
+	perf buildid-list -i $PERF_DATA --with-hits | grep -v "^ " | grep -Fv -f $EXCLUDE_BUILDIDS > $BUILDIDS
+	if [ ! -s "$BUILDIDS" ] ; then
+		echo "perf archive: no build-ids found after applying exclude-buildids file"
+		rm $BUILDIDS || true
+		exit 1
+	fi
+else
+	perf buildid-list -i $PERF_DATA --with-hits | grep -v "^ " > $BUILDIDS
+	if [ ! -s "$BUILDIDS" ] ; then
+		echo "perf archive: no build-ids found"
+		rm $BUILDIDS || true
+		exit 1
+	fi
+fi
+
+MANIFEST=$(mktemp /tmp/perf-archive-manifest.XXXXXX)
+PERF_BUILDID_LINKDIR=$(readlink -f $PERF_BUILDID_DIR)/
+
+cut -d ' ' -f 1 $BUILDIDS | \
+while read build_id ; do
+	linkname=$PERF_BUILDID_DIR.build-id/${build_id:0:2}/${build_id:2}
+	filename=$(readlink -f $linkname)
+	echo ${linkname#$PERF_BUILDID_DIR} >> $MANIFEST
+	echo ${filename#$PERF_BUILDID_LINKDIR} >> $MANIFEST
+done
+
+if [ $ALL -eq 1 ]; then						# pack perf.data file together with tar containing debug symbols
+	HOSTNAME=$(hostname)
+	DATE=$(date '+%Y%m%d-%H%M%S')
+	tar cjf $PERF_SYMBOLS.tar.bz2 -C $PERF_BUILDID_DIR -T $MANIFEST
+	tar cjf	$PERF_ALL-$HOSTNAME-$DATE.tar.bz2 $PERF_DATA $PERF_SYMBOLS.tar.bz2
+	rm $PERF_SYMBOLS.tar.bz2 $MANIFEST $BUILDIDS || true
+else										# pack only the debug symbols
+	tar cjf $PERF_DATA.tar.bz2 -C $PERF_BUILDID_DIR -T $MANIFEST
+	rm $MANIFEST $BUILDIDS || true
+fi
+
+echo -e "Now please run:\n"
+echo -e "$ perf archive --unpack\n"
+echo "or unpack the tar manually wherever you need to run 'perf report' on."
+exit 0