[PATCH v7 0/3] Validating UAPI backwards compatibility

[PATCH v7 0/3] Validating UAPI backwards compatibility

[John Moon]

The kernel community has rigorously enforced a policy of backwards
compatibility in its userspace interfaces for a long time. This has
allowed user applications to enjoy stability across kernel upgrades
without recompiling. Our goal is to add tooling and documentation to
help kernel developers maintain this stability.

In terms of tooling, I've attached a couple of shell scripts we've been
internally to validate backwards compatibility of our UAPI headers.

The check-uapi.sh script uses libabigail's[1] tool abidiff[2] to compare a
modified header's ABI before and after a patch is applied. If an existing
UAPI is modified in a way that's not backwards compatibile, the script
exits non-zero. We use this script in our continuous integration system
to block changes that fail the check.

It generates output like this when a backwards incompatible change is
made to a UAPI header:

ABI differences detected in include/uapi/linux/bpf.h from HEAD~1 -> HEAD
    [C] 'struct bpf_insn' changed:
      type size hasn't changed
      2 data member changes:
        '__u8 dst_reg' offset changed from 8 to 12 (in bits) (by +4 bits)
        '__u8 src_reg' offset changed from 12 to 8 (in bits) (by -4 bits)

The check-module-params.sh script is quite a bit simpler. It basically
greps for module_param.* calls and compares their arguments before/after
a change is applied.

We wanted to share these scripts with the community and hopefully also
receive general feedback when it comes to tooling/policy surrounding
UAPI stability.

Since v6 of this patch, I also presented a talk at LPC[4] on this topic
in case anyone would like to review that. I've CC'd a few attendees who
participated in discussion during the presentation.

Previous discussion on v6 of this patch can be found here[5].

[1] https://sourceware.org/libabigail/manual/libabigail-overview.html
[2] https://sourceware.org/libabigail/manual/abidiff.html
[3] http://mirrors.kernel.org/sourceware/libabigail/libabigail-2.4.tar.xz
[4] https://www.youtube.com/watch?v=4ijcLgvmcek
[5] https://lore.kernel.org/all/20231027193016.27516-1-quic_johmoo@quicinc.com/T/#t

P.S. While at Qualcomm, Jordan Crouse <jorcrous@amazon.com> authored the
original version of the UAPI checker script. Thanks Jordan!

John Moon (3):
  check-uapi: Introduce check-uapi.sh
  docs: dev-tools: Add UAPI checker documentation
  check-module-params: Introduce check-module-params.sh

 Documentation/dev-tools/checkuapi.rst | 477 +++++++++++++++++++++
 Documentation/dev-tools/index.rst     |   1 +
 scripts/check-module-params.sh        | 371 +++++++++++++++++
 scripts/check-uapi.sh                 | 573 ++++++++++++++++++++++++++
 4 files changed, 1422 insertions(+)
 create mode 100644 Documentation/dev-tools/checkuapi.rst
 create mode 100755 scripts/check-module-params.sh
 create mode 100755 scripts/check-uapi.sh


base-commit: a39b6ac3781d46ba18193c9dbb2110f31e9bffe9
--
2.34.1

[PATCH v7 1/3] check-uapi: Introduce check-uapi.sh

[John Moon]

While the kernel community has been good at maintaining backwards
compatibility with kernel UAPIs, it would be helpful to have a tool
to check if a commit introduces changes that break backwards
compatibility.

To that end, introduce check-uapi.sh: a simple shell script that
checks for changes to UAPI headers using libabigail.

libabigail is "a framework which aims at helping developers and
software distributors to spot some ABI-related issues like interface
incompatibility in ELF shared libraries by performing a static
analysis of the ELF binaries at hand."

The script uses one of libabigail's tools, "abidiff", to compile the
changed header before and after the commit to detect any changes.

abidiff "compares the ABI of two shared libraries in ELF format. It
emits a meaningful report describing the differences between the two
ABIs."

The script also includes the ability to check the compatibility of
all UAPI headers across commits. This allows developers to inspect
the stability of the UAPIs over time.

Signed-off-by: John Moon <quic_johmoo@quicinc.com>
---
    - Applied minor code style suggestions from v6 review.

 scripts/check-uapi.sh | 573 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 573 insertions(+)
 create mode 100755 scripts/check-uapi.sh

diff --git a/scripts/check-uapi.sh b/scripts/check-uapi.sh
new file mode 100755
index 000000000000..876cb0543b7e
--- /dev/null
+++ b/scripts/check-uapi.sh
@@ -0,0 +1,573 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0-only
+# Script to check commits for UAPI backwards compatibility
+
+set -o errexit
+set -o pipefail
+
+print_usage() {
+	name=$(basename "$0")
+	cat << EOF
+$name - check for UAPI header stability across Git commits
+
+By default, the script will check to make sure the latest commit (or current
+dirty changes) did not introduce ABI changes when compared to HEAD^1. You can
+check against additional commit ranges with the -b and -p options.
+
+The script will not check UAPI headers for architectures other than the one
+defined in ARCH.
+
+Usage: $name [-b BASE_REF] [-p PAST_REF] [-j N] [-l ERROR_LOG] [-i] [-q] [-v]
+
+Options:
+    -b BASE_REF    Base git reference to use for comparison. If unspecified or empty,
+                   will use any dirty changes in tree to UAPI files. If there are no
+                   dirty changes, HEAD will be used.
+    -p PAST_REF    Compare BASE_REF to PAST_REF (e.g. -p v6.1). If unspecified or empty,
+                   will use BASE_REF^1. Must be an ancestor of BASE_REF. Only headers
+                   that exist on PAST_REF will be checked for compatibility.
+    -j JOBS        Number of checks to run in parallel (default: number of CPU cores).
+    -l ERROR_LOG   Write error log to file (default: no error log is generated).
+    -i             Ignore ambiguous changes that may or may not break UAPI compatibility.
+    -q             Quiet operation.
+    -v             Verbose operation (print more information about each header being checked).
+
+Environmental args:
+    ABIDIFF  Custom path to abidiff binary
+    CC       C compiler (default is "gcc")
+    ARCH     Target architecture for the UAPI check (default is host arch)
+
+Exit codes:
+    $SUCCESS) Success
+    $FAIL_ABI) ABI difference detected
+    $FAIL_PREREQ) Prerequisite not met
+EOF
+}
+
+readonly SUCCESS=0
+readonly FAIL_ABI=1
+readonly FAIL_PREREQ=2
+
+# Print to stderr
+eprintf() {
+	# shellcheck disable=SC2059
+	printf "$@" >&2
+}
+
+# Expand an array with a specific character (similar to Python string.join())
+join() {
+	local IFS="$1"
+	shift
+	printf "%s" "$*"
+}
+
+# Create abidiff suppressions
+gen_suppressions() {
+	# Common enum variant names which we don't want to worry about
+	# being shifted when new variants are added.
+	local -a enum_regex=(
+		".*_AFTER_LAST$"
+		".*_CNT$"
+		".*_COUNT$"
+		".*_END$"
+		".*_LAST$"
+		".*_MASK$"
+		".*_MAX$"
+		".*_MAX_BIT$"
+		".*_MAX_BPF_ATTACH_TYPE$"
+		".*_MAX_ID$"
+		".*_MAX_SHIFT$"
+		".*_NBITS$"
+		".*_NETDEV_NUMHOOKS$"
+		".*_NFT_META_IIFTYPE$"
+		".*_NL80211_ATTR$"
+		".*_NLDEV_NUM_OPS$"
+		".*_NUM$"
+		".*_NUM_ELEMS$"
+		".*_NUM_IRQS$"
+		".*_SIZE$"
+		".*_TLSMAX$"
+		"^MAX_.*"
+		"^NUM_.*"
+	)
+
+	# Common padding field names which can be expanded into
+	# without worrying about users.
+	local -a padding_regex=(
+		".*end$"
+		".*pad$"
+		".*pad[0-9]?$"
+		".*pad_[0-9]?$"
+		".*padding$"
+		".*padding[0-9]?$"
+		".*padding_[0-9]?$"
+		".*res$"
+		".*resv$"
+		".*resv[0-9]?$"
+		".*resv_[0-9]?$"
+		".*reserved$"
+		".*reserved[0-9]?$"
+		".*reserved_[0-9]?$"
+		".*rsvd[0-9]?$"
+		".*unused$"
+	)
+
+	cat << EOF
+[suppress_type]
+  type_kind = enum
+  changed_enumerators_regexp = $(join , "${enum_regex[@]}")
+EOF
+
+	for p in "${padding_regex[@]}"; do
+		cat << EOF
+[suppress_type]
+  type_kind = struct
+  has_data_member_inserted_at = offset_of_first_data_member_regexp(${p})
+EOF
+	done
+
+if [ "$IGNORE_AMBIGUOUS_CHANGES" = "true" ]; then
+	cat << EOF
+[suppress_type]
+  type_kind = struct
+  has_data_member_inserted_at = end
+  has_size_change = yes
+EOF
+fi
+}
+
+# Check if git tree is dirty
+tree_is_dirty() {
+	! git diff --quiet
+}
+
+# Get list of files installed in $ref
+get_file_list() {
+	local -r ref="$1"
+	local -r tree="$(get_header_tree "$ref")"
+
+	# Print all installed headers, filtering out ones that can't be compiled
+	find "$tree" -type f -name '*.h' -printf '%P\n' | grep -v -f "$INCOMPAT_LIST"
+}
+
+# Add to the list of incompatible headers
+add_to_incompat_list() {
+	local -r ref="$1"
+
+	# Start with the usr/include/Makefile to get a list of the headers
+	# that don't compile using this method.
+	if [ ! -f usr/include/Makefile ]; then
+		eprintf "error - no usr/include/Makefile present at %s\n" "$ref"
+		eprintf "Note: usr/include/Makefile was added in the v5.3 kernel release\n"
+		exit "$FAIL_PREREQ"
+	fi
+	{
+		# shellcheck disable=SC2016
+		printf 'all: ; @echo $(no-header-test)\n'
+		cat usr/include/Makefile
+	} | SRCARCH="$ARCH" make --always-make -f - | tr " " "\n" \
+	  | grep -v "asm-generic" >> "$INCOMPAT_LIST"
+
+	# The makefile also skips all asm-generic files, but prints "asm-generic/%"
+	# which won't work for our grep match. Instead, print something grep will match.
+	printf "asm-generic/.*\.h\n" >> "$INCOMPAT_LIST"
+}
+
+# Compile the simple test app
+do_compile() {
+	local -r inc_dir="$1"
+	local -r header="$2"
+	local -r out="$3"
+	printf "int main(void) { return 0; }\n" | \
+		"$CC" -c \
+		  -o "$out" \
+		  -x c \
+		  -O0 \
+		  -std=c90 \
+		  -fno-eliminate-unused-debug-types \
+		  -g \
+		  "-I${inc_dir}" \
+		  -include "$header" \
+		  -
+}
+
+# Run make headers_install
+run_make_headers_install() {
+	local -r ref="$1"
+        local -r install_dir="$(get_header_tree "$ref")"
+	make -j "$MAX_THREADS" ARCH="$ARCH" INSTALL_HDR_PATH="$install_dir" \
+		headers_install > /dev/null
+}
+
+# Install headers for both git refs
+install_headers() {
+	local -r base_ref="$1"
+	local -r past_ref="$2"
+
+	for ref in "$base_ref" "$past_ref"; do
+		printf "Installing user-facing UAPI headers from %s... " "${ref:-dirty tree}"
+		if [ -n "$ref" ]; then
+			git archive --format=tar --prefix="${ref}-archive/" "$ref" \
+				| (cd "$TMP_DIR" && tar xf -)
+			(
+				cd "${TMP_DIR}/${ref}-archive"
+				run_make_headers_install "$ref"
+				add_to_incompat_list "$ref" "$INCOMPAT_LIST"
+			)
+		else
+			run_make_headers_install "$ref"
+			add_to_incompat_list "$ref" "$INCOMPAT_LIST"
+		fi
+		printf "OK\n"
+	done
+	sort -u -o "$INCOMPAT_LIST" "$INCOMPAT_LIST"
+	sed -i -e '/^$/d' "$INCOMPAT_LIST"
+}
+
+# Print the path to the headers_install tree for a given ref
+get_header_tree() {
+	local -r ref="$1"
+	printf "%s" "${TMP_DIR}/${ref}/usr"
+}
+
+# Check file list for UAPI compatibility
+check_uapi_files() {
+	local -r base_ref="$1"
+	local -r past_ref="$2"
+	local -r abi_error_log="$3"
+
+	local passed=0;
+	local failed=0;
+	local -a threads=()
+	set -o errexit
+
+	printf "Checking changes to UAPI headers between %s and %s...\n" "$past_ref" "${base_ref:-dirty tree}"
+	# Loop over all UAPI headers that were installed by $past_ref (if they only exist on $base_ref,
+	# there's no way they're broken and no way to compare anyway)
+	while read -r file; do
+		if [ "${#threads[@]}" -ge "$MAX_THREADS" ]; then
+			if wait "${threads[0]}"; then
+				passed=$((passed + 1))
+			else
+				failed=$((failed + 1))
+			fi
+			threads=("${threads[@]:1}")
+		fi
+
+		check_individual_file "$base_ref" "$past_ref" "$file" &
+		threads+=("$!")
+	done < <(get_file_list "$past_ref")
+
+	for t in "${threads[@]}"; do
+		if wait "$t"; then
+			passed=$((passed + 1))
+		else
+			failed=$((failed + 1))
+		fi
+	done
+
+	if [ -n "$abi_error_log" ]; then
+		printf 'Generated by "%s %s" from git ref %s\n\n' \
+			"$0" "$*" "$(git rev-parse HEAD)" > "$abi_error_log"
+	fi
+
+	while read -r error_file; do
+		{
+			cat "$error_file"
+			printf "\n\n"
+		} | tee -a "${abi_error_log:-/dev/null}" >&2
+	done < <(find "$TMP_DIR" -type f -name '*.error' | sort)
+
+	total="$((passed + failed))"
+	if [ "$failed" -gt 0 ]; then
+		eprintf "error - %d/%d UAPI headers compatible with %s appear _not_ to be backwards compatible\n" \
+			"$failed" "$total" "$ARCH"
+		if [ -n "$abi_error_log" ]; then
+			eprintf "Failure summary saved to %s\n" "$abi_error_log"
+		fi
+	else
+		printf "All %d UAPI headers compatible with %s appear to be backwards compatible\n" \
+			"$total" "$ARCH"
+	fi
+
+	return "$failed"
+}
+
+# Check an individual file for UAPI compatibility
+check_individual_file() {
+	local -r base_ref="$1"
+	local -r past_ref="$2"
+	local -r file="$3"
+
+	local -r base_header="$(get_header_tree "$base_ref")/${file}"
+	local -r past_header="$(get_header_tree "$past_ref")/${file}"
+
+	if [ ! -f "$base_header" ]; then
+		mkdir -p "$(dirname "$base_header")"
+		printf "==== UAPI header %s was removed between %s and %s ====" \
+			"$file" "$past_ref" "$base_ref" \
+				> "${base_header}.error"
+		return 1
+	fi
+
+	compare_abi "$file" "$base_header" "$past_header" "$base_ref" "$past_ref"
+}
+
+# Perform the A/B compilation and compare output ABI
+compare_abi() {
+	local -r file="$1"
+	local -r base_header="$2"
+	local -r past_header="$3"
+	local -r base_ref="$4"
+	local -r past_ref="$5"
+	local -r log="${TMP_DIR}/log/${file}.log"
+	local -r error_log="${TMP_DIR}/log/${file}.error"
+
+	mkdir -p "$(dirname "$log")"
+
+	if ! do_compile "$(get_header_tree "$base_ref")/include" "$base_header" "${base_header}.bin" 2> "$log"; then
+		{
+			warn_str=$(printf "==== Could not compile version of UAPI header %s at %s ====\n" \
+				"$file" "$base_ref")
+			printf "%s\n" "$warn_str"
+			cat "$log"
+			printf -- "=%.0s" $(seq 0 ${#warn_str})
+		} > "$error_log"
+		return 1
+	fi
+
+	if ! do_compile "$(get_header_tree "$past_ref")/include" "$past_header" "${past_header}.bin" 2> "$log"; then
+		{
+			warn_str=$(printf "==== Could not compile version of UAPI header %s at %s ====\n" \
+				"$file" "$past_ref")
+			printf "%s\n" "$warn_str"
+			cat "$log"
+			printf -- "=%.0s" $(seq 0 ${#warn_str})
+		} > "$error_log"
+		return 1
+	fi
+
+	local ret=0
+	"$ABIDIFF" --non-reachable-types \
+		--suppressions "$SUPPRESSIONS" \
+		"${past_header}.bin" "${base_header}.bin" > "$log" || ret="$?"
+	if [ "$ret" -eq 0 ]; then
+		if [ "$VERBOSE" = "true" ]; then
+			printf "No ABI differences detected in %s from %s -> %s\n" \
+				"$file" "$past_ref" "$base_ref"
+		fi
+	else
+		# Bits in abidiff's return code can be used to determine the type of error
+		if [ $((ret & 0x2)) -gt 0 ]; then
+			eprintf "error - abidiff did not run properly\n"
+			exit 1
+		fi
+
+		if [ "$IGNORE_AMBIGUOUS_CHANGES" = "true" ] && [ "$ret" -eq 4 ]; then
+			return 0
+		fi
+
+		# If the only changes were additions (not modifications to existing APIs), then
+		# there's no problem. Ignore these diffs.
+		if grep "Unreachable types summary" "$log" | grep -q "0 removed" &&
+		   grep "Unreachable types summary" "$log" | grep -q "0 changed"; then
+			return 0
+		fi
+
+		{
+			warn_str=$(printf "==== ABI differences detected in %s from %s -> %s ====" \
+				"$file" "$past_ref" "$base_ref")
+			printf "%s\n" "$warn_str"
+			sed  -e '/summary:/d' -e '/changed type/d' -e '/^$/d' -e 's/^/  /g' "$log"
+			printf -- "=%.0s" $(seq 0 ${#warn_str})
+			if cmp "$past_header" "$base_header" > /dev/null 2>&1; then
+				printf "\n%s did not change between %s and %s...\n" "$file" "$past_ref" "${base_ref:-dirty tree}"
+				printf "It's possible a change to one of the headers it includes caused this error:\n"
+				grep '^#include' "$base_header"
+				printf "\n"
+			fi
+		} > "$error_log"
+
+		return 1
+	fi
+}
+
+# Check that a minimum software version number is satisfied
+min_version_is_satisfied() {
+	local -r min_version="$1"
+	local -r version_installed="$2"
+
+	printf "%s\n%s\n" "$min_version" "$version_installed" \
+		| sort -Vc > /dev/null 2>&1
+}
+
+# Make sure we have the tools we need and the arguments make sense
+check_deps() {
+	ABIDIFF="${ABIDIFF:-abidiff}"
+	CC="${CC:-gcc}"
+	ARCH="${ARCH:-$(uname -m)}"
+	if [ "$ARCH" = "x86_64" ]; then
+		ARCH="x86"
+	fi
+
+	local -r abidiff_min_version="2.4"
+	local -r libdw_min_version_if_clang="0.171"
+
+	if ! command -v "$ABIDIFF" > /dev/null 2>&1; then
+		eprintf "error - abidiff not found!\n"
+		eprintf "Please install abigail-tools version %s or greater\n" "$abidiff_min_version"
+		eprintf "See: https://sourceware.org/libabigail/manual/libabigail-overview.html\n"
+		return 1
+	fi
+
+	local -r abidiff_version="$("$ABIDIFF" --version | cut -d ' ' -f 2)"
+	if ! min_version_is_satisfied "$abidiff_min_version" "$abidiff_version"; then
+		eprintf "error - abidiff version too old: %s\n" "$abidiff_version"
+		eprintf "Please install abigail-tools version %s or greater\n" "$abidiff_min_version"
+		eprintf "See: https://sourceware.org/libabigail/manual/libabigail-overview.html\n"
+		return 1
+	fi
+
+	if ! command -v "$CC" > /dev/null 2>&1; then
+		eprintf 'error - %s not found\n' "$CC"
+		return 1
+	fi
+
+	if "$CC" --version | grep -q clang; then
+		local -r libdw_version="$(ldconfig -v 2>/dev/null | grep -v SKIPPED | grep -m 1 -o 'libdw-[0-9]\+.[0-9]\+' | cut -c 7-)"
+		if ! min_version_is_satisfied "$libdw_min_version_if_clang" "$libdw_version"; then
+			eprintf "error - libdw version too old for use with clang: %s\n" "$libdw_version"
+			eprintf "Please install libdw from elfutils version %s or greater\n" "$libdw_min_version_if_clang"
+			eprintf "See: https://sourceware.org/elfutils/\n"
+			return 1
+		fi
+	fi
+
+	if [ ! -d "arch/${ARCH}" ]; then
+		eprintf 'error - ARCH "%s" is not a subdirectory under arch/\n' "$ARCH"
+		eprintf "Please set ARCH to one of:\n%s\n" "$(find arch -maxdepth 1 -mindepth 1 -type d -printf '%f ' | fmt)"
+		return 1
+	fi
+
+	if ! git rev-parse --is-inside-work-tree > /dev/null 2>&1; then
+		eprintf "error - this script requires the kernel tree to be initialized with Git\n"
+		return 1
+	fi
+
+	if ! git rev-parse --verify "$past_ref" > /dev/null 2>&1; then
+		printf 'error - invalid git reference "%s"\n' "$past_ref"
+		return 1
+	fi
+
+	if [ -n "$base_ref" ]; then
+		if ! git merge-base --is-ancestor "$past_ref" "$base_ref" > /dev/null 2>&1; then
+			printf 'error - "%s" is not an ancestor of base ref "%s"\n' "$past_ref" "$base_ref"
+			return 1
+		fi
+		if [ "$(git rev-parse "$base_ref")" = "$(git rev-parse "$past_ref")" ]; then
+			printf 'error - "%s" and "%s" are the same reference\n' "$past_ref" "$base_ref"
+			return 1
+		fi
+	fi
+}
+
+run() {
+	local base_ref="$1"
+	local past_ref="$2"
+	local abi_error_log="$3"
+	shift 3
+
+	if [ -z "$KERNEL_SRC" ]; then
+		KERNEL_SRC="$(realpath "$(dirname "$0")"/..)"
+	fi
+
+	cd "$KERNEL_SRC"
+
+	if [ -z "$base_ref" ] && ! tree_is_dirty; then
+		base_ref=HEAD
+	fi
+
+	if [ -z "$past_ref" ]; then
+		if [ -n "$base_ref" ]; then
+			past_ref="${base_ref}^1"
+		else
+			past_ref=HEAD
+		fi
+	fi
+
+	if ! check_deps; then
+		exit "$FAIL_PREREQ"
+	fi
+
+	TMP_DIR=$(mktemp -d)
+	readonly TMP_DIR
+	trap 'rm -rf "$TMP_DIR"' EXIT
+
+	readonly INCOMPAT_LIST="${TMP_DIR}/incompat_list.txt"
+	touch "$INCOMPAT_LIST"
+
+	readonly SUPPRESSIONS="${TMP_DIR}/suppressions.txt"
+	gen_suppressions > "$SUPPRESSIONS"
+
+	# Run make install_headers for both refs
+	install_headers "$base_ref" "$past_ref"
+
+	# Check for any differences in the installed header trees
+	if diff -r -q "$(get_header_tree "$base_ref")" "$(get_header_tree "$past_ref")" > /dev/null 2>&1; then
+		printf "No changes to UAPI headers were applied between %s and %s\n" "$past_ref" "${base_ref:-dirty tree}"
+		exit "$SUCCESS"
+	fi
+
+	if ! check_uapi_files "$base_ref" "$past_ref" "$abi_error_log"; then
+		exit "$FAIL_ABI"
+	fi
+}
+
+main() {
+	MAX_THREADS=$(nproc)
+	VERBOSE="false"
+	IGNORE_AMBIGUOUS_CHANGES="false"
+	quiet="false"
+	local base_ref=""
+	while getopts "hb:p:j:l:iqv" opt; do
+		case $opt in
+		h)
+			print_usage
+			exit "$SUCCESS"
+			;;
+		b)
+			base_ref="$OPTARG"
+			;;
+		p)
+			past_ref="$OPTARG"
+			;;
+		j)
+			MAX_THREADS="$OPTARG"
+			;;
+		l)
+			abi_error_log="$OPTARG"
+			;;
+		i)
+			IGNORE_AMBIGUOUS_CHANGES="true"
+			;;
+		q)
+			quiet="true"
+			VERBOSE="false"
+			;;
+		v)
+			VERBOSE="true"
+			quiet="false"
+			;;
+		*)
+			exit "$FAIL_PREREQ"
+		esac
+	done
+
+	if [ "$quiet" = "true" ]; then
+		exec > /dev/null 2>&1
+	fi
+
+	run "$base_ref" "$past_ref" "$abi_error_log" "$@"
+}
+
+main "$@"
--
2.34.1

[PATCH v7 2/3] docs: dev-tools: Add UAPI checker documentation

[John Moon]

Add detailed documentation for scripts/check-uapi.sh.

Signed-off-by: John Moon <quic_johmoo@quicinc.com>
---
 Documentation/dev-tools/checkuapi.rst | 477 ++++++++++++++++++++++++++
 Documentation/dev-tools/index.rst     |   1 +
 2 files changed, 478 insertions(+)
 create mode 100644 Documentation/dev-tools/checkuapi.rst

diff --git a/Documentation/dev-tools/checkuapi.rst b/Documentation/dev-tools/checkuapi.rst
new file mode 100644
index 000000000000..9072f21b50b0
--- /dev/null
+++ b/Documentation/dev-tools/checkuapi.rst
@@ -0,0 +1,477 @@
+.. SPDX-License-Identifier: GPL-2.0-only
+
+============
+UAPI Checker
+============
+
+The UAPI checker (``scripts/check-uapi.sh``) is a shell script which
+checks UAPI header files for userspace backwards-compatibility across
+the git tree.
+
+Options
+=======
+
+This section will describe the options with which ``check-uapi.sh``
+can be run.
+
+Usage::
+
+    check-uapi.sh [-b BASE_REF] [-p PAST_REF] [-j N] [-l ERROR_LOG] [-i] [-q] [-v]
+
+Available options::
+
+    -b BASE_REF    Base git reference to use for comparison. If unspecified or empty,
+                   will use any dirty changes in tree to UAPI files. If there are no
+                   dirty changes, HEAD will be used.
+    -p PAST_REF    Compare BASE_REF to PAST_REF (e.g. -p v6.1). If unspecified or empty,
+                   will use BASE_REF^1. Must be an ancestor of BASE_REF. Only headers
+                   that exist on PAST_REF will be checked for compatibility.
+    -j JOBS        Number of checks to run in parallel (default: number of CPU cores).
+    -l ERROR_LOG   Write error log to file (default: no error log is generated).
+    -i             Ignore ambiguous changes that may or may not break UAPI compatibility.
+    -q             Quiet operation.
+    -v             Verbose operation (print more information about each header being checked).
+
+Environmental args::
+
+    ABIDIFF  Custom path to abidiff binary
+    CC       C compiler (default is "gcc")
+    ARCH     Target architecture of C compiler (default is host arch)
+
+Exit codes::
+
+    0) Success
+    1) ABI difference detected
+    2) Prerequisite not met
+
+Examples
+========
+
+Basic Usage
+-----------
+
+First, let's try making a change to a UAPI header file that obviously
+won't break userspace::
+
+    cat << 'EOF' | patch -l -p1
+    --- a/include/uapi/linux/acct.h
+    +++ b/include/uapi/linux/acct.h
+    @@ -21,7 +21,9 @@
+     #include <asm/param.h>
+     #include <asm/byteorder.h>
+
+    -/*
+    +#define FOO
+    +
+    +/*
+      *  comp_t is a 16-bit "floating" point number with a 3-bit base 8
+      *  exponent and a 13-bit fraction.
+      *  comp2_t is 24-bit with 5-bit base 2 exponent and 20 bit fraction
+    diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
+    EOF
+
+Now, let's use the script to validate::
+
+    % ./scripts/check-uapi.sh
+    Installing user-facing UAPI headers from dirty tree... OK
+    Installing user-facing UAPI headers from HEAD... OK
+    Checking changes to UAPI headers between HEAD and dirty tree...
+    All 912 UAPI headers compatible with x86 appear to be backwards compatible
+
+Let's add another change that *might* break userspace::
+
+    cat << 'EOF' | patch -l -p1
+    --- a/include/uapi/linux/bpf.h
+    +++ b/include/uapi/linux/bpf.h
+    @@ -74,7 +74,7 @@ struct bpf_insn {
+            __u8    dst_reg:4;      /* dest register */
+            __u8    src_reg:4;      /* source register */
+            __s16   off;            /* signed offset */
+    -       __s32   imm;            /* signed immediate constant */
+    +       __u32   imm;            /* unsigned immediate constant */
+     };
+
+     /* Key of an a BPF_MAP_TYPE_LPM_TRIE entry */
+    EOF
+
+The script will catch this::
+
+    % ./scripts/check-uapi.sh
+    Installing user-facing UAPI headers from dirty tree... OK
+    Installing user-facing UAPI headers from HEAD... OK
+    Checking changes to UAPI headers between HEAD and dirty tree...
+    ==== ABI differences detected in include/linux/bpf.h from HEAD -> dirty tree ====
+        [C] 'struct bpf_insn' changed:
+          type size hasn't changed
+          1 data member change:
+            type of '__s32 imm' changed:
+              typedef name changed from __s32 to __u32 at int-ll64.h:27:1
+              underlying type 'int' changed:
+                type name changed from 'int' to 'unsigned int'
+                type size hasn't changed
+    ==================================================================================
+
+    error - 1/912 UAPI headers compatible with x86 appear _not_ to be backwards compatible
+
+In this case, the script is reporting the type change because it could
+break a userspace program that passes in a negative number. Now, let's
+say you know that no userspace program could possibly be using a negative
+value in ``imm``, so changing to an unsigned type there shouldn't hurt
+anything. You can pass the ``-i`` flag to the script to ignore changes
+in which the userspace backwards compatibility is ambiguous::
+
+    % ./scripts/check-uapi.sh -i
+    Installing user-facing UAPI headers from dirty tree... OK
+    Installing user-facing UAPI headers from HEAD... OK
+    Checking changes to UAPI headers between HEAD and dirty tree...
+    All 912 UAPI headers compatible with x86 appear to be backwards compatible
+
+Now, let's make a similar change that *will* break userspace::
+
+    cat << 'EOF' | patch -l -p1
+    --- a/include/uapi/linux/bpf.h
+    +++ b/include/uapi/linux/bpf.h
+    @@ -71,8 +71,8 @@ enum {
+
+     struct bpf_insn {
+            __u8    code;           /* opcode */
+    -       __u8    dst_reg:4;      /* dest register */
+            __u8    src_reg:4;      /* source register */
+    +       __u8    dst_reg:4;      /* dest register */
+            __s16   off;            /* signed offset */
+            __s32   imm;            /* signed immediate constant */
+     };
+    EOF
+
+Since we're re-ordering an existing struct member, there's no ambiguity,
+and the script will report the breakage even if you pass ``-i``::
+
+    % ./scripts/check-uapi.sh -i
+    Installing user-facing UAPI headers from dirty tree... OK
+    Installing user-facing UAPI headers from HEAD... OK
+    Checking changes to UAPI headers between HEAD and dirty tree...
+    ==== ABI differences detected in include/linux/bpf.h from HEAD -> dirty tree ====
+        [C] 'struct bpf_insn' changed:
+          type size hasn't changed
+          2 data member changes:
+            '__u8 dst_reg' offset changed from 8 to 12 (in bits) (by +4 bits)
+            '__u8 src_reg' offset changed from 12 to 8 (in bits) (by -4 bits)
+    ==================================================================================
+
+    error - 1/912 UAPI headers compatible with x86 appear _not_ to be backwards compatible
+
+Let's commit the breaking change, then commit the innocuous change::
+
+    % git commit -m 'Breaking UAPI change' include/uapi/linux/bpf.h
+    [detached HEAD f758e574663a] Breaking UAPI change
+     1 file changed, 1 insertion(+), 1 deletion(-)
+    % git commit -m 'Innocuous UAPI change' include/uapi/linux/acct.h
+    [detached HEAD 2e87df769081] Innocuous UAPI change
+     1 file changed, 3 insertions(+), 1 deletion(-)
+
+Now, let's run the script again with no arguments::
+
+    % ./scripts/check-uapi.sh
+    Installing user-facing UAPI headers from HEAD... OK
+    Installing user-facing UAPI headers from HEAD^1... OK
+    Checking changes to UAPI headers between HEAD^1 and HEAD...
+    All 912 UAPI headers compatible with x86 appear to be backwards compatible
+
+It doesn't catch any breaking change because, by default, it only
+compares ``HEAD`` to ``HEAD^1``. The breaking change was committed on
+``HEAD~2``. If we wanted the search scope to go back further, we'd have to
+use the ``-p`` option to pass a different past reference. In this case,
+let's pass ``-p HEAD~2`` to the script so it checks UAPI changes between
+``HEAD~2`` and ``HEAD``::
+
+    % ./scripts/check-uapi.sh -p HEAD~2
+    Installing user-facing UAPI headers from HEAD... OK
+    Installing user-facing UAPI headers from HEAD~2... OK
+    Checking changes to UAPI headers between HEAD~2 and HEAD...
+    ==== ABI differences detected in include/linux/bpf.h from HEAD~2 -> HEAD ====
+        [C] 'struct bpf_insn' changed:
+          type size hasn't changed
+          2 data member changes:
+            '__u8 dst_reg' offset changed from 8 to 12 (in bits) (by +4 bits)
+            '__u8 src_reg' offset changed from 12 to 8 (in bits) (by -4 bits)
+    ==============================================================================
+
+    error - 1/912 UAPI headers compatible with x86 appear _not_ to be backwards compatible
+
+Alternatively, we could have also run with ``-b HEAD~``. This would set the
+base reference to ``HEAD~`` so then the script would compare it to ``HEAD~^1``.
+
+Architecture-specific Headers
+-----------------------------
+
+Consider this change::
+
+    cat << 'EOF' | patch -l -p1
+    --- a/arch/arm64/include/uapi/asm/sigcontext.h
+    +++ b/arch/arm64/include/uapi/asm/sigcontext.h
+    @@ -70,6 +70,7 @@ struct sigcontext {
+     struct _aarch64_ctx {
+            __u32 magic;
+            __u32 size;
+    +       __u32 new_var;
+     };
+
+     #define FPSIMD_MAGIC   0x46508001
+    EOF
+
+This is a change to an arm64-specific UAPI header file. In this example, I'm
+running the script from an x86 machine with an x86 compiler, so, by default,
+the script only checks x86-compatible UAPI header files::
+
+    % ./scripts/check-uapi.sh
+    Installing user-facing UAPI headers from dirty tree... OK
+    Installing user-facing UAPI headers from HEAD... OK
+    No changes to UAPI headers were applied between HEAD and dirty tree
+
+With an x86 compiler, we can't check header files in ``arch/arm64``, so the
+script doesn't even try.
+
+If we want to check the header file, we'll have to use an arm64 compiler and
+set ``ARCH`` accordingly::
+
+    % CC=aarch64-linux-gnu-gcc ARCH=arm64 ./scripts/check-uapi.sh
+    Installing user-facing UAPI headers from dirty tree... OK
+    Installing user-facing UAPI headers from HEAD... OK
+    Checking changes to UAPI headers between HEAD and dirty tree...
+    ==== ABI differences detected in include/asm/sigcontext.h from HEAD -> dirty tree ====
+        [C] 'struct _aarch64_ctx' changed:
+          type size changed from 64 to 96 (in bits)
+          1 data member insertion:
+            '__u32 new_var', at offset 64 (in bits) at sigcontext.h:73:1
+        -- snip --
+        [C] 'struct zt_context' changed:
+          type size changed from 128 to 160 (in bits)
+          2 data member changes (1 filtered):
+            '__u16 nregs' offset changed from 64 to 96 (in bits) (by +32 bits)
+            '__u16 __reserved[3]' offset changed from 80 to 112 (in bits) (by +32 bits)
+    =======================================================================================
+
+    error - 1/884 UAPI headers compatible with arm64 appear _not_ to be backwards compatible
+
+We can see with ``ARCH`` and ``CC`` set properly for the file, the ABI
+change is reported properly. Also notice that the total number of UAPI
+header files checked by the script changes. This is because the number
+of headers installed for arm64 platforms is different than x86.
+
+Cross-Dependency Breakages
+--------------------------
+
+Consider this change::
+
+    cat << 'EOF' | patch -l -p1
+    --- a/include/uapi/linux/types.h
+    +++ b/include/uapi/linux/types.h
+    @@ -52,7 +52,7 @@ typedef __u32 __bitwise __wsum;
+     #define __aligned_be64 __be64 __attribute__((aligned(8)))
+     #define __aligned_le64 __le64 __attribute__((aligned(8)))
+
+    -typedef unsigned __bitwise __poll_t;
+    +typedef unsigned short __bitwise __poll_t;
+
+     #endif /*  __ASSEMBLY__ */
+     #endif /* _UAPI_LINUX_TYPES_H */
+    EOF
+
+Here, we're changing a ``typedef`` in ``types.h``. This doesn't break
+a UAPI in ``types.h``, but other UAPIs in the tree may break due to
+this change::
+
+    % ./scripts/check-uapi.sh
+    Installing user-facing UAPI headers from dirty tree... OK
+    Installing user-facing UAPI headers from HEAD... OK
+    Checking changes to UAPI headers between HEAD and dirty tree...
+    ==== ABI differences detected in include/linux/eventpoll.h from HEAD -> dirty tree ====
+        [C] 'struct epoll_event' changed:
+          type size changed from 96 to 80 (in bits)
+          2 data member changes:
+            type of '__poll_t events' changed:
+              underlying type 'unsigned int' changed:
+                type name changed from 'unsigned int' to 'unsigned short int'
+                type size changed from 32 to 16 (in bits)
+            '__u64 data' offset changed from 32 to 16 (in bits) (by -16 bits)
+    ========================================================================================
+    include/linux/eventpoll.h did not change between HEAD and dirty tree...
+    It's possible a change to one of the headers it includes caused this error:
+    #include <linux/fcntl.h>
+    #include <linux/types.h>
+
+Note that the script noticed the failing header file did not change,
+so it assumes one of its includes must have caused the breakage. Indeed,
+we can see ``linux/types.h`` is used from ``eventpoll.h``.
+
+UAPI Header Removals
+--------------------
+
+Consider this change::
+
+    cat << 'EOF' | patch -l -p1
+    diff --git a/include/uapi/asm-generic/Kbuild b/include/uapi/asm-generic/Kbuild
+    index ebb180aac74e..a9c88b0a8b3b 100644
+    --- a/include/uapi/asm-generic/Kbuild
+    +++ b/include/uapi/asm-generic/Kbuild
+    @@ -31,6 +31,6 @@ mandatory-y += stat.h
+     mandatory-y += statfs.h
+     mandatory-y += swab.h
+     mandatory-y += termbits.h
+    -mandatory-y += termios.h
+    +#mandatory-y += termios.h
+     mandatory-y += types.h
+     mandatory-y += unistd.h
+    EOF
+
+This script removes a UAPI header file from the install list. Let's run
+the script::
+
+    % ./scripts/check-uapi.sh
+    Installing user-facing UAPI headers from dirty tree... OK
+    Installing user-facing UAPI headers from HEAD... OK
+    Checking changes to UAPI headers between HEAD and dirty tree...
+    ==== UAPI header include/asm/termios.h was removed between HEAD and dirty tree ====
+
+    error - 1/912 UAPI headers compatible with x86 appear _not_ to be backwards compatible
+
+Removing a UAPI header is considered a breaking change, and the script
+will flag it as such.
+
+Checking Historic UAPI Compatibility
+------------------------------------
+
+You can use the ``-b`` and ``-p`` options to examine different chunks of your
+git tree. For example, to check all changed UAPI header files between tags
+v6.0 and v6.1, you'd run::
+
+    % ./scripts/check-uapi.sh -b v6.1 -p v6.0
+    Installing user-facing UAPI headers from v6.1... OK
+    Installing user-facing UAPI headers from v6.0... OK
+    Checking changes to UAPI headers between v6.0 and v6.1...
+
+    --- snip ---
+    error - 37/907 UAPI headers compatible with x86 appear _not_ to be backwards compatible
+
+Note: Before v5.3, a header file needed by the script is not present,
+so the script is unable to check changes before then.
+
+You'll notice that the script detected many UAPI changes that are not
+backwards compatible. Knowing that kernel UAPIs are supposed to be stable
+forever, this is an alarming result. This brings us to the next section:
+caveats.
+
+Caveats
+=======
+
+The UAPI checker makes no assumptions about the author's intention, so some
+types of changes may be flagged even though they intentionally break UAPI.
+
+Removals For Refactoring or Deprecation
+---------------------------------------
+
+Sometimes drivers for very old hardware are removed, such as in this example::
+
+    % ./scripts/check-uapi.sh -b ba47652ba655
+    Installing user-facing UAPI headers from ba47652ba655... OK
+    Installing user-facing UAPI headers from ba47652ba655^1... OK
+    Checking changes to UAPI headers between ba47652ba655^1 and ba47652ba655...
+    ==== UAPI header include/linux/meye.h was removed between ba47652ba655^1 and ba47652ba655 ====
+
+    error - 1/910 UAPI headers compatible with x86 appear _not_ to be backwards compatible
+
+The script will always flag removals (even if they're intentional).
+
+Struct Expansions
+-----------------
+
+Depending on how a structure is handled in kernelspace, a change which
+expands a struct could be non-breaking.
+
+If a struct is used as the argument to an ioctl, then the kernel driver
+must be able to handle ioctl commands of any size. Beyond that, you need
+to be careful when copying data from the user. Say, for example, that
+``struct foo`` is changed like this::
+
+    struct foo {
+        __u64 a; /* added in version 1 */
+    +   __u32 b; /* added in version 2 */
+    +   __u32 c; /* added in version 2 */
+    }
+
+By default, the script will flag this kind of change for further review::
+
+    [C] 'struct foo' changed:
+      type size changed from 64 to 128 (in bits)
+      2 data member insertions:
+        '__u32 b', at offset 64 (in bits)
+        '__u32 c', at offset 96 (in bits)
+
+However, it is possible that this change was made safely.
+
+If a userspace program was built with version 1, it will think
+``sizeof(struct foo)`` is 8. That size will be encoded in the
+ioctl value that gets sent to the kernel. If the kernel is built
+with version 2, it will think the ``sizeof(struct foo)`` is 16.
+
+The kernel can use the ``_IOC_SIZE`` macro to get the size encoded
+in the ioctl code that the user passed in and then use
+``copy_struct_from_user()`` to safely copy the value::
+
+    int handle_ioctl(unsigned long cmd, unsigned long arg)
+    {
+        switch _IOC_NR(cmd) {
+        0x01: {
+            struct foo my_cmd;  /* size 16 in the kernel */
+
+            ret = copy_struct_from_user(&my_cmd, arg, sizeof(struct foo), _IOC_SIZE(cmd));
+            ...
+
+``copy_struct_from_user`` will zero the struct in the kernel and then copy
+only the bytes passed in from the user (leaving new members zeroized).
+If the user passed in a larger struct, the extra members are ignored.
+
+If you know this situation is accounted for in the kernel code, you can
+pass ``-i`` to the script, and struct expansions like this will be ignored.
+
+Flex Array Migration
+--------------------
+
+While the script handles expansion into an existing flex array, it does
+still flag initial migration to flex arrays from 1-element fake flex
+arrays. For example::
+
+    struct foo {
+          __u32 x;
+    -     __u32 flex[1]; /* fake flex */
+    +     __u32 flex[];  /* real flex */
+    };
+
+This change would be flagged by the script::
+
+    [C] 'struct foo' changed:
+      type size changed from 64 to 32 (in bits)
+      1 data member change:
+        type of '__u32 flex[1]' changed:
+          type name changed from '__u32[1]' to '__u32[]'
+          array type size changed from 32 to 'unknown'
+          array type subrange 1 changed length from 1 to 'unknown'
+
+At this time, there's no way to filter these types of changes, so be
+aware of this possible false positive.
+
+Summary
+-------
+
+While many types of false positives are filtered out by the script,
+it's possible there are some cases where the script flags a change
+which does not break UAPI. It's also possible a change which *does*
+break userspace would not be flagged by this script. While the script
+has been run on much of the kernel history, there could still be corner
+cases that are not accounted for.
+
+The intention is for this script to be used as a quick check for
+maintainers or automated tooling, not as the end-all authority on
+patch compatibility. It's best to remember: use your best judgment
+(and ideally a unit test in userspace) to make sure your UAPI changes
+are backwards-compatible!
diff --git a/Documentation/dev-tools/index.rst b/Documentation/dev-tools/index.rst
index 6b0663075dc0..0876f5a2cf55 100644
--- a/Documentation/dev-tools/index.rst
+++ b/Documentation/dev-tools/index.rst
@@ -34,6 +34,7 @@ Documentation/dev-tools/testing-overview.rst
    kselftest
    kunit/index
    ktap
+   checkuapi
 
 
 .. only::  subproject and html
-- 
2.34.1

[PATCH v7 3/3] check-module-params: Introduce check-module-params.sh

[John Moon]

One part of maintaining backwards compatibility with older
userspace programs is avoiding changes to module parameters.

To that end, add a script (check-module-params.sh) which
performs a simple check of module parameter changes across
git references.

For example, if this module parameter:

module_param(max_nullfunc_tries, int, 0644);

...restricted its mode parameter:

module_param(max_nullfunc_tries, int, 0600);

The script would flag the change:

Module parameter "max_nullfunc_tries" in net/mac80211/mlme.c changed!
  Original args: int,0644
       New args: int,0600

Signed-off-by: John Moon <quic_johmoo@quicinc.com>
---
    - Added ability to filter out equivalent permission changes
      (e.g. S_IRUGO -> 0444 is now considered compatible).
    - Added flag to avoid filtering out equivalent permission changes
      in case user doesn't have/want a host compiler.
    - Added flag to skip flagging module param removals as this may
      be too noisy in some cases.
    - Fixed typos in log naming.

 scripts/check-module-params.sh | 371 +++++++++++++++++++++++++++++++++
 1 file changed, 371 insertions(+)
 create mode 100755 scripts/check-module-params.sh

diff --git a/scripts/check-module-params.sh b/scripts/check-module-params.sh
new file mode 100755
index 000000000000..990b271a8dbf
--- /dev/null
+++ b/scripts/check-module-params.sh
@@ -0,0 +1,371 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0-only
+# Script to check commits for UAPI backwards compatibility
+
+set -o errexit
+set -o pipefail
+
+print_usage() {
+	name=$(basename "$0")
+	cat << EOF
+$name - check for module parameter stability across git commits.
+
+By default, the script will check to make sure the latest commit (or current
+dirty changes) did not introduce changes when compared to HEAD^1. You can
+check against additional commit ranges with the -b and -p options.
+
+Usage: $name [-b BASE_REF] [-p PAST_REF] [-j N] [-l ERROR_LOG] [-P] [-R] [-q]
+
+Options:
+    -b BASE_REF    Base git reference to use for comparison. If unspecified or empty,
+                   will use any dirty changes in tree. If there are no dirty changes,
+                   HEAD will be used.
+    -p PAST_REF    Compare BASE_REF to PAST_REF (e.g. -p v6.1). If unspecified or empty,
+                   will use BASE_REF^1. Must be an ancestor of BASE_REF. Only headers
+                   that exist on PAST_REF will be checked for compatibility.
+    -j JOBS        Number of checks to run in parallel (default: number of CPU cores).
+    -l ERROR_LOG   Write error log to file (default: no error log is generated).
+    -P             Flag all changes to permissions (even if they're compatible). This
+                   option negates the need for a host C compiler.
+    -R             Skip flagging parameter removals.
+    -q             Quiet operation (suppress stdout, still print stderr).
+
+Environmental args:
+    HOSTCC   C compiler for permission conversion to octal (default is "gcc")
+
+Exit codes:
+    $SUCCESS) Success
+    $FAILURE) Module param differences detected
+EOF
+}
+
+readonly SUCCESS=0
+readonly FAILURE=1
+
+# Print to stderr
+eprintf() {
+	# shellcheck disable=SC2059
+	printf "$@" >&2
+}
+
+# Check if git tree is dirty
+tree_is_dirty() {
+	! git diff --quiet
+}
+
+file_module_params_unmodified() {
+	local file="$1"
+	local base_ref="$2"
+	local past_ref="$3"
+	local base_params_file="${TMP_DIR}/${file}.base"
+	local past_params_file="${TMP_DIR}/${file}.past"
+	local error_log="${TMP_DIR}/${file}.error"
+
+	local -r awk_cmd='/^ *module_param.*\(/,/.*\);/'
+
+	mkdir -p "$(dirname "$error_log")"
+	git show "${past_ref}:${file}" 2> /dev/null \
+		| awk "$awk_cmd" > "$past_params_file" || true
+
+	if [ -z "$base_ref" ]; then
+		awk "$awk_cmd" "${KERNEL_SRC}/${file}" \
+			> "$base_params_file" 2> /dev/null || true
+	else
+		git show "${base_ref}:${file}" 2> /dev/null \
+			| awk "$awk_cmd" > "$base_params_file" || true
+	fi
+
+	# Ignore files that don't exist at the past ref or don't have module params
+	if [ ! -s "$past_params_file" ]; then
+		return 255 # Special return code for "no-op"
+	fi
+
+	# Process the param data to come up with an associative array of param names to param data
+	# For example:
+	#   module_param_call(foo, set_result, get_result, NULL, 0600);
+	#
+	# is processed into:
+	#   pre_change_params[foo]="set_result,get_result,NULL,0600"
+	local -A pre_change_params
+	local param_name
+	local param_params
+
+	while read -r mod_param_args; do
+		param_name="$(echo "$mod_param_args" | cut -d ',' -f 1)"
+		param_params="$(echo "$mod_param_args" | cut -d ',' -f 2-)"
+
+		pre_change_params[$param_name]=$param_params
+	done < <(tr -d '\t\n ' < "$past_params_file" | tr ';' '\n' | perl -lne '/\((.*)\)/ && print $1')
+
+	local -A post_change_params
+	while read -r mod_param_args; do
+		param_name="$(echo "$mod_param_args" | cut -d ',' -f 1)"
+		param_params="$(echo "$mod_param_args" | cut -d ',' -f 2-)"
+
+		post_change_params[$param_name]=$param_params
+	done < <(tr -d '\t\n ' < "$base_params_file" | tr ';' '\n' | perl -lne '/\((.*)\)/ && print $1')
+
+	#for param in "${!pre_change_params[@]}"; do
+	#	echo "$param: ${pre_change_params[${param}]}"
+	#done
+
+	# Flag any module param changes that:
+	#  - Remove/rename a parameter
+	#  - Change the arguments of the parameter
+	local incompat_param_changes=0
+	local pre
+	local post
+	for param_name in "${!pre_change_params[@]}"; do
+		pre="${pre_change_params[$param_name]}"
+		if [ ! "${post_change_params[$param_name]+set}" ]; then
+			if [ "$SKIP_PARAM_REMOVALS" = "true" ]; then
+				continue
+			fi
+			{
+				printf "Module parameter \"%s\" in %s removed!\n" "$param_name" "$file"
+				printf "  Original args: %s\n" "$pre"
+			} > "$error_log"
+			incompat_param_changes=$((incompat_param_changes + 1))
+			continue
+		fi
+
+		post="${post_change_params[$param_name]}"
+		if [ "$pre" != "$post" ]; then
+			if [ "$SKIP_SAFE_PERM_CHANGES" = "true" ] && perm_change_is_safe "$pre" "$post"; then
+				continue
+			fi
+			{
+				printf "Module parameter \"%s\" in %s changed!\n" "$param_name" "$file"
+				printf "  Original args: %s\n" "$pre"
+				printf "       New args: %s\n" "$post"
+			} > "$error_log"
+			incompat_param_changes=$((incompat_param_changes + 1))
+			continue
+		fi
+	done
+
+	if [ "$incompat_param_changes" -gt 0 ]; then
+		return 1
+	fi
+}
+
+perm_change_is_safe() {
+	local -r pre="$1"
+	local -r post="$2"
+
+	# Assume that the permission arg is always the last one.
+	pre_perm_arg=$(echo "$pre" | grep -o '[^,]*$')
+	post_perm_arg=$(echo "$post" | grep -o '[^,]*$')
+
+	# If the non-permission arguments are different, then
+	# don't even bother checking the permission arg.
+	if [ "${pre/,${pre_perm_arg}/}" != "${post/,${post_perm_arg}/}" ]; then
+		return 1
+	fi
+
+	# Convert both to octal representation to compare
+	pre_perm_arg_octal=$(get_octal_val "$pre_perm_arg")
+	post_perm_arg_octal=$(get_octal_val "$post_perm_arg")
+
+	if [ "$pre_perm_arg_octal" = "$post_perm_arg_octal" ]; then
+		return 0
+	else
+		return 1
+	fi
+}
+
+get_octal_val() {
+	local -r input="$1"
+
+	# Save needing to recompile for input we've seen before
+	local -r input_hash="$(echo "$input" | md5sum | cut -d ' ' -f 1)"
+
+	local -r prog="${TMP_DIR}/get_octal_val_${input_hash}"
+	local -r stat="include/linux/stat.h"
+
+	if [ ! -x "$prog" ]; then
+		cat << EOF > "${prog}.c"
+#include <stdio.h>
+#include <sys/stat.h>
+
+$(grep '#define *S_IRWXUGO' "$stat")
+$(grep '#define *S_IALLUGO' "$stat")
+$(grep '#define *S_IRUGO' "$stat")
+$(grep '#define *S_IWUGO' "$stat")
+$(grep '#define *S_IXUGO' "$stat")
+
+int main(void) { printf("%04o\\n", $input); };
+EOF
+		"${HOSTCC:-gcc}" -o "$prog" "${prog}.c"
+	fi
+
+	"$prog"
+}
+run() {
+	local base_ref="$1"
+	local past_ref="$2"
+	local param_error_log="$3"
+
+	diff_args=("$past_ref")
+	if [ -n "$base_ref" ]; then
+		diff_args+=("$base_ref")
+	fi
+
+	local -a threads=()
+	local passed=0
+	local failed=0
+	printf "Checking files between %s and %s for module parameter compatibility...\n" \
+		"$past_ref" "$base_ref"
+	while read -r modified_file; do
+		if [ "${#threads[@]}" -ge "$MAX_THREADS" ]; then
+			wait "${threads[0]}" && ret="$?" || ret="$?"
+			if [ "$ret" -eq 0 ]; then
+				passed=$((passed + 1))
+			elif [ "$ret" -eq 1 ]; then
+				failed=$((failed + 1))
+			fi
+			threads=("${threads[@]:1}")
+		fi
+
+		file_module_params_unmodified "$modified_file" "$base_ref" "$past_ref" &
+		threads+=("$!")
+	done < <(git diff --diff-filter=MCD --name-only "${diff_args[@]}" -- '*.c' '*.h')
+
+	for t in "${threads[@]}"; do
+		wait "$t" && ret="$?" || ret="$?"
+		if [ "$ret" -eq 0 ]; then
+			passed=$((passed + 1))
+		elif [ "$ret" -eq 1 ]; then
+			failed=$((failed + 1))
+		fi
+	done
+
+	total=$((passed + failed))
+	if [ "$total" -eq 0 ]; then
+		printf "No files with module parameters modified between %s and %s\n" \
+			"$past_ref" "${base_ref:-dirty tree}"
+		exit "$SUCCESS"
+	fi
+
+	if [ -n "$param_error_log" ]; then
+		printf 'Generated by "%s %s" from git ref %s\n\n' \
+			"$0" "$*" "$(git rev-parse HEAD)" > "$param_error_log"
+	fi
+
+	while read -r error_file; do
+		{
+			cat "$error_file"
+			printf "\n\n"
+		} | tee -a "${param_error_log:-/dev/null}" >&2
+	done < <(find "$TMP_DIR" -type f -name '*.error' | sort)
+
+	if [ "$failed" -gt 0 ]; then
+		eprintf "error - %d/%d files with modules parameters appear _not_ to be backwards compatible\n" \
+			"$failed" "$total"
+		if [ -n "$param_error_log" ]; then
+			eprintf "Failure summary saved to %s\n" "$param_error_log"
+		fi
+	else
+		printf "All %d files with module_parameters checked appear to be backwards compatible\n" \
+			"$total"
+	fi
+
+	exit "$failed"
+}
+
+# Make sure the git refs we have make sense
+check_refs() {
+	if ! git rev-parse --is-inside-work-tree > /dev/null 2>&1; then
+		eprintf "error - this script requires the kernel tree to be initialized with Git\n"
+		return 1
+	fi
+
+	if ! git rev-parse --verify "$past_ref" > /dev/null 2>&1; then
+		printf 'error - invalid git reference "%s"\n' "$past_ref"
+		return 1
+	fi
+
+	if [ -n "$base_ref" ]; then
+		if ! git merge-base --is-ancestor "$past_ref" "$base_ref" > /dev/null 2>&1; then
+			printf 'error - "%s" is not an ancestor of base ref "%s"\n' "$past_ref" "$base_ref"
+			return 1
+		fi
+		if [ "$(git rev-parse "$base_ref")" = "$(git rev-parse "$past_ref")" ]; then
+			printf 'error - "%s" and "%s" are the same reference\n' "$past_ref" "$base_ref"
+			return 1
+		fi
+	fi
+}
+
+main() {
+	MAX_THREADS=$(nproc)
+	SKIP_SAFE_PERM_CHANGES="true"
+	SKIP_PARAM_REMOVALS="false"
+	quiet="false"
+	local base_ref=""
+	while getopts "hb:p:j:l:PRq" opt; do
+		case $opt in
+		h)
+			print_usage
+			exit "$SUCCESS"
+			;;
+		b)
+			base_ref="$OPTARG"
+			;;
+		p)
+			past_ref="$OPTARG"
+			;;
+		j)
+			MAX_THREADS="$OPTARG"
+			;;
+		l)
+			param_error_log="$OPTARG"
+			;;
+		P)
+			SKIP_SAFE_PERM_CHANGES="false"
+			;;
+		R)
+			SKIP_PARAM_REMOVALS="true"
+			;;
+		q)
+			quiet="true"
+			;;
+		*)
+			exit "$FAILURE"
+		esac
+	done
+
+	if [ "$quiet" = "true" ]; then
+		exec > /dev/null 2>&1
+	fi
+
+	if [ -z "$KERNEL_SRC" ]; then
+		KERNEL_SRC="$(realpath "$(dirname "$0")"/..)"
+	fi
+
+	cd "$KERNEL_SRC"
+
+	if [ -z "$base_ref" ] && ! tree_is_dirty; then
+		base_ref=HEAD
+	fi
+
+	if [ -z "$past_ref" ]; then
+		if [ -n "$base_ref" ]; then
+			past_ref="${base_ref}^1"
+		else
+			past_ref=HEAD
+		fi
+	fi
+
+	if ! check_refs; then
+		exit "$FAILURE"
+	fi
+
+	TMP_DIR=$(mktemp -d)
+	readonly TMP_DIR
+	trap 'rm -rf "$TMP_DIR"' EXIT
+
+	run "$base_ref" "$past_ref" "$param_error_log"
+}
+
+main "$@"
--
2.34.1

Re: [PATCH v7 3/3] check-module-params: Introduce check-module-params.sh

[Christoph Hellwig]

On Mon, Dec 11, 2023 at 06:02:59PM -0800, John Moon wrote:
> One part of maintaining backwards compatibility with older
> userspace programs is avoiding changes to module parameters.

Really?  I don't think module parameters are a UAPI in the traditional
sense.  Now if you break a heavily used one you got to fix it, but
applying strict stability guarantees on module options which are not
availble to normal users or even normal programs doesn't make a whole
lot of sense.

Re: [PATCH v7 3/3] check-module-params: Introduce check-module-params.sh

[John Moon]

On 12/11/2023 11:41 PM, Christoph Hellwig wrote:
> On Mon, Dec 11, 2023 at 06:02:59PM -0800, John Moon wrote:
>> One part of maintaining backwards compatibility with older
>> userspace programs is avoiding changes to module parameters.
> 
> Really?  I don't think module parameters are a UAPI in the traditional
> sense.  

Agreed, they're not UAPI in the traditional sense. But, we're trying to 
establish tooling to help the community stabilize all interfaces that 
cross the kernel <-> userspace boundary and module params do fall into 
that bucket.

> Now if you break a heavily used one you got to fix it, but
> applying strict stability guarantees on module options which are not
> availble to normal users or even normal programs doesn't make a whole
> lot of sense.
> 

True, but unfortunately we don't have any heuristic to determine if a 
param is "heavily used". However, in this rev, we added the ability to 
parse the permissions of a module param, so we could add a filter which 
does not flag change/removal of params with 0{0,4,6}000 permissions.

It's also obviously fine if the community has no interest in the script. 
We just wanted to share it as we find it to be a useful supplement to 
our code reviews and thought maintainers may find it useful as well.

Cheers,
John

Re: [PATCH v7 1/3] check-uapi: Introduce check-uapi.sh

[Masahiro Yamada]

On Tue, Dec 12, 2023 at 11:04 AM John Moon <quic_johmoo@quicinc.com> wrote:
>
> While the kernel community has been good at maintaining backwards
> compatibility with kernel UAPIs, it would be helpful to have a tool
> to check if a commit introduces changes that break backwards
> compatibility.
>
> To that end, introduce check-uapi.sh: a simple shell script that
> checks for changes to UAPI headers using libabigail.
>
> libabigail is "a framework which aims at helping developers and
> software distributors to spot some ABI-related issues like interface
> incompatibility in ELF shared libraries by performing a static
> analysis of the ELF binaries at hand."
>
> The script uses one of libabigail's tools, "abidiff", to compile the
> changed header before and after the commit to detect any changes.
>
> abidiff "compares the ABI of two shared libraries in ELF format. It
> emits a meaningful report describing the differences between the two
> ABIs."
>
> The script also includes the ability to check the compatibility of
> all UAPI headers across commits. This allows developers to inspect
> the stability of the UAPIs over time.
>
> Signed-off-by: John Moon <quic_johmoo@quicinc.com>
> ---
>     - Applied minor code style suggestions from v6 review.




The code looks OK. I think it should work as designed.

Line 197 is inconsistently indented by spaces instead of a space,
but I can fix it up locally.


I just thought requiring target commits as positional parameters
("check-uapi.sh treeA treeB" just like "git diff treeA treeB")
might be intuitive, but I guess everything is specified
by a short option is a design. I can live with that.



I will wait a few days, and if there is nothing more,
I will pick up 1/3 and 2/3.




-- 
Best Regards
Masahiro Yamada

Re: [PATCH v7 3/3] check-module-params: Introduce check-module-params.sh

[Masahiro Yamada]

On Wed, Dec 13, 2023 at 1:58 AM John Moon <quic_johmoo@quicinc.com> wrote:
>
> On 12/11/2023 11:41 PM, Christoph Hellwig wrote:
> > On Mon, Dec 11, 2023 at 06:02:59PM -0800, John Moon wrote:
> >> One part of maintaining backwards compatibility with older
> >> userspace programs is avoiding changes to module parameters.
> >
> > Really?  I don't think module parameters are a UAPI in the traditional
> > sense.
>
> Agreed, they're not UAPI in the traditional sense. But, we're trying to
> establish tooling to help the community stabilize all interfaces that
> cross the kernel <-> userspace boundary and module params do fall into
> that bucket.
>
> > Now if you break a heavily used one you got to fix it, but
> > applying strict stability guarantees on module options which are not
> > availble to normal users or even normal programs doesn't make a whole
> > lot of sense.
> >
>
> True, but unfortunately we don't have any heuristic to determine if a
> param is "heavily used". However, in this rev, we added the ability to
> parse the permissions of a module param, so we could add a filter which
> does not flag change/removal of params with 0{0,4,6}000 permissions.
>
> It's also obviously fine if the community has no interest in the script.
> We just wanted to share it as we find it to be a useful supplement to
> our code reviews and thought maintainers may find it useful as well.
>
> Cheers,
> John


I am with Christoph.

This tool detects some changes and removals, but I think
the community intentionally changed them.

To merge this tool in the mainline,
I need more people who are interested in this.




-- 
Best Regards
Masahiro Yamada

Re: [PATCH v7 1/3] check-uapi: Introduce check-uapi.sh

[John Moon]

On 12/22/2023 9:50 AM, Masahiro Yamada wrote:
> On Tue, Dec 12, 2023 at 11:04 AM John Moon <quic_johmoo@quicinc.com> wrote:
> 
> The code looks OK. I think it should work as designed.
> 
> Line 197 is inconsistently indented by spaces instead of a space,
> but I can fix it up locally.
> 
> 
> I just thought requiring target commits as positional parameters
> ("check-uapi.sh treeA treeB" just like "git diff treeA treeB")
> might be intuitive, but I guess everything is specified
> by a short option is a design. I can live with that.
> 
> 
> 
> I will wait a few days, and if there is nothing more,
> I will pick up 1/3 and 2/3.
> 
> 

Thank you Masahiro! If anyone else has comments please let me know.

Cheers,
John