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, 201 insertions, 0 deletions

diff --git a/scripts/git-resolve.sh b/scripts/git-resolve.sh
new file mode 100755
index 000000000..e9b5940c0
--- /dev/null
+++ b/scripts/git-resolve.sh
@@ -0,0 +1,201 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# (c) 2025, Sasha Levin <sashal@kernel.org>
+
+usage() {
+	echo "Usage: $(basename "$0") [--selftest] [--force] <commit-id> [commit-subject]"
+	echo "Resolves a short git commit ID to its full SHA-1 hash, particularly useful for fixing references in commit messages."
+	echo ""
+	echo "Arguments:"
+	echo "  --selftest      Run self-tests"
+	echo "  --force         Try to find commit by subject if ID lookup fails"
+	echo "  commit-id       Short git commit ID to resolve"
+	echo "  commit-subject  Optional commit subject to help resolve between multiple matches"
+	exit 1
+}
+
+# Convert subject with ellipsis to grep pattern
+convert_to_grep_pattern() {
+	local subject="$1"
+	# First escape ALL regex special characters
+	local escaped_subject
+	escaped_subject=$(printf '%s\n' "$subject" | sed 's/[[\.*^$()+?{}|]/\\&/g')
+	# Also escape colons, parentheses, and hyphens as they are special in our context
+	escaped_subject=$(echo "$escaped_subject" | sed 's/[:-]/\\&/g')
+	# Then convert escaped ... sequence to .*?
+	escaped_subject=$(echo "$escaped_subject" | sed 's/\\\.\\\.\\\./.*?/g')
+	echo "^${escaped_subject}$"
+}
+
+git_resolve_commit() {
+	local force=0
+	if [ "$1" = "--force" ]; then
+		force=1
+		shift
+	fi
+
+	# Split input into commit ID and subject
+	local input="$*"
+	local commit_id="${input%% *}"
+	local subject=""
+
+	# Extract subject if present (everything after the first space)
+	if [[ "$input" == *" "* ]]; then
+		subject="${input#* }"
+		# Strip the ("...") quotes if present
+		subject="${subject#*(\"}"
+		subject="${subject%\")*}"
+	fi
+
+	# Get all possible matching commit IDs
+	local matches
+	readarray -t matches < <(git rev-parse --disambiguate="$commit_id" 2>/dev/null)
+
+	# Return immediately if we have exactly one match
+	if [ ${#matches[@]} -eq 1 ]; then
+		echo "${matches[0]}"
+		return 0
+	fi
+
+	# If no matches and not in force mode, return failure
+	if [ ${#matches[@]} -eq 0 ] && [ $force -eq 0 ]; then
+		return 1
+	fi
+
+	# If we have a subject, try to find a match with that subject
+	if [ -n "$subject" ]; then
+		# Convert subject with possible ellipsis to grep pattern
+		local grep_pattern
+		grep_pattern=$(convert_to_grep_pattern "$subject")
+
+		# In force mode with no ID matches, use git log --grep directly
+		if [ ${#matches[@]} -eq 0 ] && [ $force -eq 1 ]; then
+			# Use git log to search, but filter to ensure subject matches exactly
+			local match
+			match=$(git log --format="%H %s" --grep="$grep_pattern" --perl-regexp -10 | \
+					while read -r hash subject; do
+						if echo "$subject" | grep -qP "$grep_pattern"; then
+							echo "$hash"
+							break
+						fi
+					done)
+			if [ -n "$match" ]; then
+				echo "$match"
+				return 0
+			fi
+		else
+			# Normal subject matching for existing matches
+			for match in "${matches[@]}"; do
+				if git log -1 --format="%s" "$match" | grep -qP "$grep_pattern"; then
+					echo "$match"
+					return 0
+				fi
+			done
+		fi
+	fi
+
+	# No match found
+	return 1
+}
+
+run_selftest() {
+	local test_cases=(
+		'00250b5 ("MAINTAINERS: add new Rockchip SoC list")'
+		'0037727 ("KVM: selftests: Convert xen_shinfo_test away from VCPU_ID")'
+		'ffef737 ("net/tls: Fix skb memory leak when running kTLS traffic")'
+		'd3d7 ("cifs: Improve guard for excluding $LXDEV xattr")'
+		'dbef ("Rename .data.once to .data..once to fix resetting WARN*_ONCE")'
+		'12345678'  # Non-existent commit
+		'12345 ("I'\''m a dummy commit")'  # Valid prefix but wrong subject
+		'--force 99999999 ("net/tls: Fix skb memory leak when running kTLS traffic")'  # Force mode with non-existent ID but valid subject
+		'83be ("firmware: ... auto-update: fix poll_complete() ... errors")'  # Wildcard test
+		'--force 999999999999 ("firmware: ... auto-update: fix poll_complete() ... errors")'  # Force mode wildcard test
+	)
+
+	local expected=(
+		"00250b529313d6262bb0ebbd6bdf0a88c809f6f0"
+		"0037727b3989c3fe1929c89a9a1dfe289ad86f58"
+		"ffef737fd0372ca462b5be3e7a592a8929a82752"
+		"d3d797e326533794c3f707ce1761da7a8895458c"
+		"dbefa1f31a91670c9e7dac9b559625336206466f"
+		""  # Expect empty output for non-existent commit
+		""  # Expect empty output for wrong subject
+		"ffef737fd0372ca462b5be3e7a592a8929a82752"  # Should find commit by subject in force mode
+		"83beece5aff75879bdfc6df8ba84ea88fd93050e"  # Wildcard test
+		"83beece5aff75879bdfc6df8ba84ea88fd93050e"  # Force mode wildcard test
+	)
+
+	local expected_exit_codes=(
+		0
+		0
+		0
+		0
+		0
+		1  # Expect failure for non-existent commit
+		1  # Expect failure for wrong subject
+		0  # Should succeed in force mode
+		0  # Should succeed with wildcard
+		0  # Should succeed with force mode and wildcard
+	)
+
+	local failed=0
+
+	echo "Running self-tests..."
+	for i in "${!test_cases[@]}"; do
+		# Capture both output and exit code
+		local result
+		result=$(git_resolve_commit ${test_cases[$i]})  # Removed quotes to allow --force to be parsed
+		local exit_code=$?
+
+		# Check both output and exit code
+		if [ "$result" != "${expected[$i]}" ] || [ $exit_code != ${expected_exit_codes[$i]} ]; then
+			echo "Test case $((i+1)) FAILED"
+			echo "Input: ${test_cases[$i]}"
+			echo "Expected output: '${expected[$i]}'"
+			echo "Got output: '$result'"
+			echo "Expected exit code: ${expected_exit_codes[$i]}"
+			echo "Got exit code: $exit_code"
+			failed=1
+		else
+			echo "Test case $((i+1)) PASSED"
+		fi
+	done
+
+	if [ $failed -eq 0 ]; then
+		echo "All tests passed!"
+		exit 0
+	else
+		echo "Some tests failed!"
+		exit 1
+	fi
+}
+
+# Check for selftest
+if [ "$1" = "--selftest" ]; then
+	run_selftest
+	exit $?
+fi
+
+# Handle --force flag
+force=""
+if [ "$1" = "--force" ]; then
+	force="--force"
+	shift
+fi
+
+# Verify arguments
+if [ $# -eq 0 ]; then
+	usage
+fi
+
+# Skip validation in force mode
+if [ -z "$force" ]; then
+	# Validate that the first argument matches at least one git commit
+	if [ "$(git rev-parse --disambiguate="$1" 2>/dev/null | wc -l)" -eq 0 ]; then
+		echo "Error: '$1' does not match any git commit"
+		exit 1
+	fi
+fi
+
+git_resolve_commit $force "$@"
+exit $?