From patchwork Thu Mar 16 18:15:54 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: John Moon X-Patchwork-Id: 13178186 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3DA52C6FD19 for ; Thu, 16 Mar 2023 18:17:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230525AbjCPSRR (ORCPT ); Thu, 16 Mar 2023 14:17:17 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42066 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230051AbjCPSRM (ORCPT ); Thu, 16 Mar 2023 14:17:12 -0400 Received: from mx0a-0031df01.pphosted.com (mx0a-0031df01.pphosted.com [205.220.168.131]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 95B38E1908; Thu, 16 Mar 2023 11:17:08 -0700 (PDT) Received: from pps.filterd (m0279865.ppops.net [127.0.0.1]) by mx0a-0031df01.pphosted.com (8.17.1.19/8.17.1.19) with ESMTP id 32GFkYuM017675; Thu, 16 Mar 2023 18:16:30 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=quicinc.com; h=from : to : cc : subject : date : message-id : in-reply-to : references : mime-version : content-type; s=qcppdkim1; bh=TD8cbj8mHAC/a/wgzikZZfBkwwR5ECfRox1vGjnzoJA=; b=KLMB/uOy33GYCxYRjW/0xAGll7E36oNa/ACPwM4rcvyBODP6B+IBl/u2kkodBngFbHru 7tvxiwjID0ndpmgpcwOJu+v6Xriga3MZW1ht/My+uM95Ul0DBvz2Xg72dFdxMZv2uw5/ YXOVJhDkmlYkH8oN6D3DiGdGWwehlKTJzMoPtNRlrL/RUzo3SARTgY9IrKT2MvR+wvDv kAXVZLCBsE6vHBlPB2+2mbg6cxkydgLR9/P945AE8rxj5aszdp65KioLUlpv8NX9+5kx WNWa0t8TcTj85mDTNJaDCik0kXC7Nbpf90rsL6yRUiYlIj+wxodn1cAszzYFX1QOkMIJ dg== Received: from nalasppmta05.qualcomm.com (Global_NAT1.qualcomm.com [129.46.96.20]) by mx0a-0031df01.pphosted.com (PPS) with ESMTPS id 3pc624gddt-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 16 Mar 2023 18:16:29 +0000 Received: from nalasex01c.na.qualcomm.com (nalasex01c.na.qualcomm.com [10.47.97.35]) by NALASPPMTA05.qualcomm.com (8.17.1.5/8.17.1.5) with ESMTPS id 32GIGRTi007111 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 16 Mar 2023 18:16:27 GMT Received: from hu-johmoo-lv.qualcomm.com (10.49.16.6) by nalasex01c.na.qualcomm.com (10.47.97.35) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.986.41; Thu, 16 Mar 2023 11:16:26 -0700 From: John Moon To: Masahiro Yamada , Nathan Chancellor , Nick Desaulniers , "Nicolas Schier" CC: John Moon , , , , , Greg Kroah-Hartman , Randy Dunlap , "Arnd Bergmann" , Bjorn Andersson , Todd Kjos , Matthias Maennich , Giuliano Procida , , , Jordan Crouse , Trilok Soni , Satya Durga Srinivasu Prabhala , Elliot Berman , "Guru Das Srinagesh" Subject: [PATCH v3 1/2] check-uapi: Introduce check-uapi.sh Date: Thu, 16 Mar 2023 11:15:54 -0700 Message-ID: <20230316181555.9327-2-quic_johmoo@quicinc.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20230316181555.9327-1-quic_johmoo@quicinc.com> References: <20230316181555.9327-1-quic_johmoo@quicinc.com> MIME-Version: 1.0 X-Originating-IP: [10.49.16.6] X-ClientProxiedBy: nalasex01c.na.qualcomm.com (10.47.97.35) To nalasex01c.na.qualcomm.com (10.47.97.35) X-QCInternal: smtphost X-Proofpoint-Virus-Version: vendor=nai engine=6200 definitions=5800 signatures=585085 X-Proofpoint-GUID: -yeJl9_0z-fHbZaPlCR3j4TJdVcmP6Lg X-Proofpoint-ORIG-GUID: -yeJl9_0z-fHbZaPlCR3j4TJdVcmP6Lg X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.254,Aquarius:18.0.942,Hydra:6.0.573,FMLib:17.11.170.22 definitions=2023-03-16_12,2023-03-16_01,2023-02-09_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 phishscore=0 adultscore=0 mlxlogscore=999 priorityscore=1501 spamscore=0 suspectscore=0 impostorscore=0 mlxscore=0 bulkscore=0 malwarescore=0 lowpriorityscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2303150002 definitions=main-2303160141 Precedence: bulk List-ID: X-Mailing-List: linux-kbuild@vger.kernel.org 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 --- - Default to checking all UAPI headers to avoid possible false negative brought up in v2 - Re-introduce ARCH environment variable to select which UAPIs under arch/*/include/uapi to check - Add "-m" flag to check only modified files - Add "-q" and "-v" flags to modify verbosity - Change "-r" flag to "-p" to represent a "past reference" - Added meaningful exit codes - Added check for minimum libdw version for use with clang - Fixed bug where some non-header files were being checked - Removed "scripts/unifdef" build as it was no longer needed scripts/check-uapi.sh | 564 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 564 insertions(+) create mode 100755 scripts/check-uapi.sh -- 2.17.1 diff --git a/scripts/check-uapi.sh b/scripts/check-uapi.sh new file mode 100755 index 000000000000..5d166dc9617d --- /dev/null +++ b/scripts/check-uapi.sh @@ -0,0 +1,564 @@ +#!/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] [-m] [-j N] [-l ERROR_LOG] [-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. -r v6.1). If unspecified or empty, + will use BASE_REF^1. Must be an ancestor of BASE_REF. + -m Check only UAPI headers modified between PAST_REF and BASE_REF for + backwards compatibility. + -j JOBS Number of checks to run in parallel (default: number of CPU cores). + -l ERROR_LOG Write error log to file (default: "\$KERNEL_SOURCE/abi_error_log.txt"). + -q Quiet operation (suppress all stdout, still print stderr). + -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: + $SUCCESS) Success + $FAIL_ABI) ABI difference detected + $FAIL_PREREQ) Prerequisite not met + $FAIL_COMPILE) Compilation error + $FAIL_ARCH) All modified files were for an architecture other than ARCH + $FAIL) General error +EOF +} + +readonly SUCCESS=0 +readonly FAIL_ABI=1 +readonly FAIL_PREREQ=2 +readonly FAIL_COMPILE=3 +readonly FAIL_ARCH=4 +readonly FAIL=5 + +# Print to stderr +eprintf() { + # shellcheck disable=SC2059 + printf "$@" >&2 +} + +# Print list of UAPI files to operate on +get_uapi_files() { + local -r check_all="$1" + local -r base_ref="$2" + local -r ref="$3" + local -r file_list="${tmp_dir}/file_list.txt" + + # Return already-processed list if it's available + if [ -s "$file_list" ]; then + cat "$file_list" + return 0 + fi + + if [ "$check_all" = "true" ]; then + # Print all of the UAPI header files at the commit in question + # Ignore the headers that we can't test. + # shellcheck disable=SC2086,SC2046 + git ls-tree --full-tree --name-only -r "${base_ref:-HEAD}" -- "${UAPI_DIRS[@]}" \ + | grep '.h$' \ + | sed -e 's/^/M\t/g' \ + | grep -v $({ get_no_header_list "$base_ref"; get_no_export_list; } | xargs -- printf '-e %s ') \ + > "$file_list" + else + if [ -z "$base_ref" ] || [ -z "$ref" ]; then + # shellcheck disable=SC2086 + git diff $GIT_ARGS > "$file_list" + else + # shellcheck disable=SC2086 + git diff "$ref" "$base_ref" $GIT_ARGS > "$file_list" + fi + + if mismatch_arch_files=$(grep -v "arch/${ARCH}" "$file_list" | grep -o "arch/.*\.h"); then + eprintf "warning - detected changes to following files, but can't check them with %s compiler:\n" "$ARCH" + for f in $mismatch_arch_files; do + eprintf " - %s\n" "$f" + sed -i -e "\|${f}|d" "$file_list" + printf "warning - could not perform ABI check on %s with %s compiler\n" "$f" "$ARCH" \ + >> "${tmp_dir}/arch_mismatches.error" + done + eprintf "\nFiltering them out and performing partial check on remaining files...\n" + if [ ! -s "$file_list" ]; then + eprintf "error - all files were filtered out, there's nothing to check!\n" + exit "$FAIL_ARCH" + fi + fi + fi + + if [ ! -s "$file_list" ]; then + return 1 + fi + + cat "$file_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 "$header" \ + - +} + +# Print the list of incompatible headers +get_no_header_list() { + local -r ref="${1:-HEAD}" + # Start with the usr/include/Makefile to get a list of the headers + # that don't compile using this method. + { + # shellcheck disable=SC2016 + printf 'all: ; @echo $(no-header-test)\n' + cat "usr/include/Makefile" + } | SRCARCH="$ARCH" make -f - | tr " " "\n" | grep -v "asm-generic" + + # The makefile also skips all asm-generic files, but prints "asm-generic/%" + # which won't match the files in this script, so just print all the asm-generic + # headers manually. + git ls-tree --full-tree --name-only -r "$ref" -- include/uapi/asm-generic \ + | grep '.h$' \ + | cut -d '/' -f 2- + + # Finally, print all the architecture-specific headers that are _not_ for the + # ARCH we're targeting + git ls-tree --full-tree --name-only -r "$ref" -- arch/*/include/uapi \ + | grep '.h$' \ + | grep -v "^arch/${ARCH}" +} + +# Print the list of headers that are not exported for this architecture +get_no_export_list() { + { + # shellcheck disable=SC2016 + printf 'all: ; @echo $(no-export-headers)\n' + cat "include/uapi/Kbuild" + } | SRCARCH="$ARCH" srctree="$KERNEL_SRC" make -f - | tr " " "\n" | sed '/^[[:space:]]*$/d' +} + +# Save the current git tree state, stashing if needed +save_tree_state() { + printf "Saving current tree state... " + current_ref="$(git rev-parse HEAD)" + readonly current_ref + if ! git diff-index --quiet HEAD; then + unstash="true" + git stash push --quiet + fi + printf "OK\n" +} + +# Restore the git tree state, unstashing if needed +restore_tree_state() { + if [ -z "$current_ref" ]; then + return 0 + fi + + printf "Restoring current tree state... " + git checkout --quiet "$current_ref" + if [ "$unstash" = "true" ]; then + git stash pop --quiet + unstash="false" + fi + printf "OK\n" +} + +# Install headers for both git refs +install_headers() { + local -r check_all="$1" + local -r base_ref="$2" + local -r ref="$3" + + deviated_from_current_tree="false" + for inst_ref in "$base_ref" "$ref"; do + if [ -n "$inst_ref" ]; then + if [ "$deviated_from_current_tree" = "false" ]; then + save_tree_state + trap 'rm -rf "$tmp_dir"; restore_tree_state;' EXIT + deviated_from_current_tree="true" + fi + # This script ($0) is already loaded into memory at this point, + # so this operation is safe + git checkout --quiet "$(git rev-parse "$inst_ref")" + fi + + printf "Installing sanitized UAPI headers from %s... " "${inst_ref:-dirty tree}" + make ARCH="$ARCH" INSTALL_HDR_PATH="${tmp_dir}/${inst_ref}/usr" headers_install > /dev/null 2>&1 + printf "OK\n" + done + + restore_tree_state + trap 'rm -rf "$tmp_dir"' EXIT +} + +# Check file list for UAPI compatibility +check_uapi_files() { + local -r check_all="$1" + local -r base_ref="$2" + local -r ref="$3" + + install_headers "$check_all" "$base_ref" "$ref" + + local passed=0; + local failed=0; + local -a threads=() + + printf "Checking changes to UAPI headers between %s and %s\n" "$ref" "${base_ref:-dirty tree}" + while read -r status 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 "$base_ref" "$ref" "$status" "$file" & + threads+=("$!") + done < <(get_uapi_files "$check_all" "$base_ref" "$ref") + + for t in "${threads[@]}"; do + if wait "$t"; then + passed=$((passed + 1)) + else + failed=$((failed + 1)) + fi + done + + if [ "$check_all" = "true" ]; then + scope=$(printf "UAPI headers compatible with %s" "$ARCH") + else + scope=$(printf "UAPI headers modified between %s and %s" "$ref" "${base_ref:-dirty tree}") + fi + + total="$((passed + failed))" + if [ "$failed" -gt 0 ]; then + eprintf "error - %d/%d %s appear _not_ to be backwards compatible\n" "$failed" "$total" "$scope" + else + printf "All %d %s appear to be backwards compatible\n" "$total" "$scope" + fi + + if [ "$check_all" = "true" ]; then + printf "Note: UAPI headers for architectures other than %s were not checked\n" "$ARCH" + fi + + return "$failed" +} + +# Print the path to a given header in the tmp_dir +get_header() { + local -r ref="$1" + local -r arch="$2" + local -r base="$3" + + if [ -z "$arch" ]; then + printf "%s" "${tmp_dir}/${ref}/usr/${base}" + else + printf "%s" "${tmp_dir}/${ref}/usr/$(printf "%s" "$base" | cut -d '/' -f 3-)" + fi +} + +# Check an individual file for UAPI compatibility +check_individual_file() { + local -r base_ref="$1" + local -r ref="$2" + local -r status="$3" + local -r file="$4" + + local -r base=${file/uapi\//} + local -r uapi_arch="$(printf "%s" "$file" | grep -o 'arch/.*/uapi' | cut -d '/' -f 2)" + local -r base_header=$(get_header "$base_ref" "$uapi_arch" "$base") + local -r ref_header=$(get_header "$ref" "$uapi_arch" "$base") + local -r installed_base="$(printf "%s" "$base_header" | grep -o "usr/include/.*" | cut -d '/' -f 3-)" + + if [ "$status" = "D" ]; then + eprintf "error - UAPI header %s was incorrectly removed\n" "$file" | tee "${base_header}.error" + return 1 + fi + + # shellcheck disable=SC2076 + if [[ " $(get_no_header_list | xargs) " =~ " $installed_base " ]]; then + printf "warning - %s cannot be tested by this script (see usr/include/Makefile)\n" "$file" | tee "${base_header}.error" + return 1 + fi + + # shellcheck disable=SC2076 + if [[ " $(get_no_export_list | xargs) " =~ " $installed_base " ]]; then + printf "warning - %s is not exported by the %s architecture, so cannot be tested\n" "$file" "$ARCH" | tee "${base_header}.error" + return 1 + fi + + for h in "$base_header" "$ref_header"; do + if [ ! -f "$h" ]; then + eprintf "error - %s does not exist - cannot compare ABI\n" "$h" | tee "${h}.error" + return 1 + fi + done + + compare_abi "$file" "$base_header" "$ref_header" "$base_ref" "$ref" +} + +# Perform the A/B compilation and compare output ABI +compare_abi() { + local -r file="$1" + local -r base_header="$2" + local -r ref_header="$3" + local -r base_ref="$4" + local -r ref="$5" + local -r log="${tmp_dir}/log/$(basename "$file").log" + + mkdir -p "$(dirname "$log")" + + if ! do_compile "${tmp_dir}/${base_ref}/usr/include" "$base_header" "${base_header}.bin" 2> "$log"; then + eprintf "error - couldn't compile version of UAPI header %s at %s\n" "$file" "$base_ref" + cat "$log" >&2 + exit "$FAIL_COMPILE" + fi + + if ! do_compile "${tmp_dir}/${ref}/usr/include" "$ref_header" "${ref_header}.bin" 2> "$log"; then + eprintf "error - couldn't compile version of UAPI header %s at %s\n" "$file" "$ref" + cat "$log" >&2 + exit "$FAIL_COMPILE" + fi + + "$ABIDIFF" --non-reachable-types "${ref_header}.bin" "${base_header}.bin" > "$log" && ret="$?" || ret="$?" + if [ "$ret" -eq 0 ]; then + if [ "$VERBOSE" = "true" ]; then + printf "No ABI differences detected in %s from %s -> %s\n" "$file" "$ref" "${base_ref:-dirty tree}" + fi + else + # Bits in abidiff's return code can be used to determine the type of error + if [ $(("$ret" & 0x1)) -gt 0 ]; then + eprintf "error - abidiff did not run properly\n" + exit 1 + 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 + { + printf "!!! ABI differences detected in %s from %s -> %s !!!\n\n" "$file" "$ref" "${base_ref:-dirty tree}" + sed -e '/summary:/d' -e '/changed type/d' -e '/^$/d' -e 's/^/ /g' "$log" + + if ! cmp "$ref_header" "$base_header" > /dev/null 2>&1; then + printf "\nHeader file diff (after headers_install):\n" + diff -Naur "$ref_header" "$base_header" \ + | sed -e "s|${ref_header}|${ref}/${file}|g" \ + -e "s|${base_header}|${base_ref:-dirty}/${file}|g" + printf "\n" + else + printf "\n%s did not change between %s and %s...\n" "$file" "$ref" "${base_ref:-dirty tree}" + printf "It's possible a change to one of the headers it includes caused this error:\n" + grep '^#include' "$base_header" + printf "\n" + fi + } | tee "${base_header}.error" >&2 + return 1 + fi +} + +min_version_is_satisfied() { + local -r min_version="$1" + local -r version_installed="$2" + + printf "%s\n%s\n" "$min_version" "$version_installed" | sort -Vc > /dev/null 2>&1 +} + +# Make sure we have the tools we need +check_deps() { + ABIDIFF="${ABIDIFF:-abidiff}" + CC="${CC:-gcc}" + ARCH="${ARCH:-$(uname -m)}" + if [ "$ARCH" = "x86_64" ]; then + ARCH="x86" + fi + + local -r abidiff_min_version="1.7" + 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" + exit "$FAIL_PREREQ" + fi + + local -r abidiff_version="$("$ABIDIFF" --version | cut -d ' ' -f 2)" + if ! min_version_is_satisfied "$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" "$abidiff_min_version" + eprintf "See: https://sourceware.org/libabigail/manual/libabigail-overview.html\n" + exit "$FAIL_PREREQ" + fi + + if ! command -v "$CC" > /dev/null 2>&1; then + eprintf 'error - %s not found\n' "$CC" + exit "$FAIL_PREREQ" + fi + + if "$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" "$libdw_min_version_if_clang" + eprintf "See: https://sourceware.org/elfutils/\n" + exit "$FAIL_PREREQ" + 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" "$(find arch -maxdepth 1 -mindepth 1 -type d -printf '%f ' | fmt)" + exit "$FAIL_PREREQ" + fi +} + +run() { + local base_ref="$1" + local -r check_all="$2" + shift 2 + local -r orig_args="$*" + if [ -z "$KERNEL_SRC" ]; then + KERNEL_SRC="$(realpath "$(dirname "$0")"/..)" + fi + + cd "$KERNEL_SRC" + + abi_error_log="${abi_error_log:-${KERNEL_SRC}/abi_error_log.txt}" + + tmp_dir=$(mktemp -d) + trap 'rm -rf "$tmp_dir"' EXIT + + check_deps + + # Set of UAPI directories to check by default + UAPI_DIRS=(include/uapi arch/*/include/uapi) + GIT_ARGS="--name-status --no-renames --format= --diff-filter=a -- ${UAPI_DIRS[*]/%/\/*.h}" + + if ! git rev-parse --is-inside-work-tree > /dev/null 2>&1; then + eprintf "error - this script requires the kernel tree to be initialized with Git\n" + exit "$FAIL_PREREQ" + fi + + # If there are no dirty UAPI files, use HEAD as base_ref + # shellcheck disable=SC2086 + if [ -z "$base_ref" ] && git diff --exit-code $GIT_ARGS > /dev/null 2>&1; then + base_ref="HEAD" + fi + + if [ -z "$past_ref" ]; then + if [ -n "$base_ref" ]; then + past_ref="${base_ref}^1" + else + past_ref="HEAD" + fi + fi + + if [ -n "$past_ref" ] && ! git rev-parse --verify "$past_ref" > /dev/null 2>&1; then + printf 'error - invalid git reference "%s"\n' "$past_ref" + exit "$FAIL_PREREQ" + 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" "$base_ref" + exit "$FAIL_PREREQ" + fi + fi + + if [ "$check_all" != "true" ] && ! get_uapi_files "$check_all" "$base_ref" "$past_ref" > /dev/null; then + printf "No changes to UAPI headers were applied between %s and %s\n" "$past_ref" "$base_ref" + exit "$SUCCESS" + fi + + if ! check_uapi_files "$check_all" "$base_ref" "$past_ref"; then + eprintf "error - UAPI header ABI check failed\n" + { + printf 'Generated by "%s %s" from git ref %s\n\n' "$0" "$orig_args" "$(git rev-parse "HEAD")" + find "$tmp_dir" -type f -name '*.error' -exec cat {} + + } > "$abi_error_log" + eprintf "Failure summary saved to %s\n" "$abi_error_log" + exit "$FAIL_ABI" + fi +} + +main() { + MAX_THREADS=$(nproc) + VERBOSE="false" + local base_ref="" + local check_all="true" + local quiet="false" + while getopts "hb:p:mj:l:qv" opt; do + case $opt in + h) + print_usage + exit "$SUCCESS" + ;; + b) + base_ref="$OPTARG" + ;; + p) + past_ref="$OPTARG" + ;; + m) + check_all="false" + ;; + j) + MAX_THREADS="$OPTARG" + ;; + l) + abi_error_log="$OPTARG" + ;; + q) + quiet="true" + ;; + v) + VERBOSE="true" + ;; + *) + exit "$FAIL_PREREQ" + esac + done + + if [ "$quiet" = "true" ]; then + run "$base_ref" "$check_all" "$@" > /dev/null + else + run "$base_ref" "$check_all" "$@" + fi +} + +main "$@" From patchwork Thu Mar 16 18:15:55 2023 Content-Type: text/plain; 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Thu, 16 Mar 2023 18:16:28 GMT Received: from hu-johmoo-lv.qualcomm.com (10.49.16.6) by nalasex01c.na.qualcomm.com (10.47.97.35) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.986.41; Thu, 16 Mar 2023 11:16:27 -0700 From: John Moon To: Masahiro Yamada , Nathan Chancellor , Nick Desaulniers , "Nicolas Schier" CC: John Moon , , , , , Greg Kroah-Hartman , Randy Dunlap , "Arnd Bergmann" , Bjorn Andersson , Todd Kjos , Matthias Maennich , Giuliano Procida , , , Jordan Crouse , Trilok Soni , Satya Durga Srinivasu Prabhala , Elliot Berman , "Guru Das Srinagesh" Subject: [PATCH v3 2/2] docs: dev-tools: Add UAPI checker documentation Date: Thu, 16 Mar 2023 11:15:55 -0700 Message-ID: <20230316181555.9327-3-quic_johmoo@quicinc.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20230316181555.9327-1-quic_johmoo@quicinc.com> References: <20230316181555.9327-1-quic_johmoo@quicinc.com> MIME-Version: 1.0 X-Originating-IP: [10.49.16.6] X-ClientProxiedBy: nalasex01c.na.qualcomm.com (10.47.97.35) To nalasex01c.na.qualcomm.com (10.47.97.35) X-QCInternal: smtphost X-Proofpoint-Virus-Version: vendor=nai engine=6200 definitions=5800 signatures=585085 X-Proofpoint-GUID: 5I8CZOaFV21zfQ90meyyJseH5duDutbJ X-Proofpoint-ORIG-GUID: 5I8CZOaFV21zfQ90meyyJseH5duDutbJ X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.254,Aquarius:18.0.942,Hydra:6.0.573,FMLib:17.11.170.22 definitions=2023-03-16_10,2023-03-16_01,2023-02-09_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 mlxscore=0 adultscore=0 suspectscore=0 mlxlogscore=999 clxscore=1015 malwarescore=0 priorityscore=1501 bulkscore=0 phishscore=0 lowpriorityscore=0 impostorscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2303150002 definitions=main-2303160141 Precedence: bulk List-ID: X-Mailing-List: linux-kbuild@vger.kernel.org Add detailed documentation for scripts/check-uapi.sh. Signed-off-by: John Moon --- - Updated with new flags/usage - Added example of possible false negatives - Improved formatting Documentation/dev-tools/checkuapi.rst | 492 ++++++++++++++++++++++++++ Documentation/dev-tools/index.rst | 1 + 2 files changed, 493 insertions(+) create mode 100644 Documentation/dev-tools/checkuapi.rst -- 2.17.1 diff --git a/Documentation/dev-tools/checkuapi.rst b/Documentation/dev-tools/checkuapi.rst new file mode 100644 index 000000000000..0e257eff1526 --- /dev/null +++ b/Documentation/dev-tools/checkuapi.rst @@ -0,0 +1,492 @@ +.. 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. + +The script can produce false positives in some cases, so developers are +encouraged to use their best judgement when interpreting the results. Please +refer to kernel documentation on the topic of IOCTL stability for more +information (Documentation/process/botching-up-ioctls.rst). + +Options +======= + +This section will describe the options ``check-uapi.sh`` can be run with. + +Usage:: + + ./scripts/check-uapi.sh [-b BASE_REF] [-p PAST_REF] [-m] [-j N] [-l ERROR_LOG] [-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. -r v6.1). If unspecified or empty, + will use BASE_REF^1. Must be an ancestor of BASE_REF. + -m Check only UAPI headers modified between PAST_REF and BASE_REF for + backwards compatibility. + -j JOBS Number of checks to run in parallel (default: number of CPU cores). + -l ERROR_LOG Write error log to file (default: "$KERNEL_SOURCE/abi_error_log.txt"). + -q Quiet operation (suppress all stdout, still print stderr). + -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 + 3) Compilation error + 4) All modified files were for an architecture other than ARCH + 5) General error + +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 + #include + + -/* + +#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 sanitized UAPI headers from dirty tree... OK + Saving current tree state... OK + Installing sanitized UAPI headers from HEAD... OK + Restoring current tree state... OK + Checking changes to UAPI headers between HEAD and dirty tree + All 888 UAPI headers compatible with x86 appear to be backwards compatible + Note: UAPI headers for architectures other than x86 were not checked + +Let's add another change that *would* break userspace:: + + cat << 'EOF' | patch -l -p1 + --- a/include/uapi/linux/bpf.h 2023-02-28 13:32:36.505591077 -0800 + +++ b/include/uapi/linux/bpf.h 2023-02-28 13:32:57.033494020 -0800 + @@ -73,7 +73,7 @@ + __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 should catch this incompatibility:: + + % ./scripts/check-uapi.sh + Installing sanitized UAPI headers from dirty tree... OK + Saving current tree state... OK + Installing sanitized UAPI headers from HEAD... OK + Restoring current tree state... OK + Checking changes to UAPI headers between HEAD and dirty tree + !!! ABI differences detected in include/uapi/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 + + Header file diff (after headers_install): + --- HEAD/include/uapi/linux/bpf.h 2023-03-15 16:05:39.601082143 -0700 + +++ dirty/include/uapi/linux/bpf.h 2023-03-15 16:05:37.669092565 -0700 + @@ -73,7 +73,7 @@ + __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 */ + + error - 1/888 UAPI headers compatible with x86 appear _not_ to be backwards compatible + Note: UAPI headers for architectures other than x86 were not checked + error - UAPI header ABI check failed + +The script finds the ABI breakage and reports it (along with a diff of the +offending file). + +Let's commit the breaking change, then commit the good 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 + Saving current tree state... OK + Installing sanitized UAPI headers from HEAD... OK + Installing sanitized UAPI headers from HEAD^1... OK + Restoring current tree state... OK + Checking changes to UAPI headers between HEAD^1 and HEAD + All 888 UAPI headers compatible with x86 appear to be backwards compatible + Note: UAPI headers for architectures other than x86 were not checked + +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 to compare to. 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 + Saving current tree state... OK + Installing sanitized UAPI headers from HEAD... OK + Installing sanitized UAPI headers from HEAD~2... OK + Restoring current tree state... OK + Checking changes to UAPI headers between HEAD~2 and HEAD + !!! ABI differences detected in include/uapi/linux/bpf.h from HEAD~2 -> HEAD !!! + + [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 + + Header file diff (after headers_install): + --- HEAD~2/include/uapi/linux/bpf.h 2023-03-15 16:10:39.495462638 -0700 + +++ HEAD/include/uapi/linux/bpf.h 2023-03-15 16:10:38.919465752 -0700 + @@ -73,7 +73,7 @@ + __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 */ + + error - 1/888 UAPI headers compatible with x86 appear _not_ to be backwards compatible + Note: UAPI headers for architectures other than x86 were not checked + error - UAPI header ABI check failed + +Alternatively, you could have also ran 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 works with x86-compatible UAPI header files:: + + % ./scripts/check-uapi.sh + Installing sanitized UAPI headers from dirty tree... OK + Saving current tree state... OK + Installing sanitized UAPI headers from HEAD... OK + Restoring current tree state... OK + Checking changes to UAPI headers between HEAD and dirty tree + All 888 UAPI headers compatible with x86 appear to be backwards compatible + Note: UAPI headers for architectures other than x86 were not checked + +With an x86 compiler, we can't check header files in ``arch/arm64``, so the +script doesn't even try. You can pass the ``-m`` to force the script to look at +modified files, but in this case, you'll run into an issue:: + + % ./scripts/check-uapi.sh -m + warning - detected changes to following files, but can't check them with x86 compiler: + - arch/arm64/include/uapi/asm/sigcontext.h + + Filtering them out and performing partial check on remaining files... + error - all files were filtered out, there's nothing to check! + +The script will attempt filtering out files that don't work with ``ARCH``, but +if it filters all of the files out, it bails out. + +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 sanitized UAPI headers from dirty tree... OK + Saving current tree state... OK + Installing sanitized UAPI headers from HEAD... OK + Restoring current tree state... OK + Checking changes to UAPI headers between HEAD and dirty tree + !!! ABI differences detected in arch/arm64/include/uapi/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) + + Header file diff (after headers_install): + --- HEAD/arch/arm64/include/uapi/asm/sigcontext.h 2023-03-15 16:15:46.613800573 -0700 + +++ dirty/arch/arm64/include/uapi/asm/sigcontext.h 2023-03-15 16:15:44.765810584 -0700 + @@ -70,6 +70,7 @@ + struct _aarch64_ctx { + __u32 magic; + __u32 size; + + __u32 new_var; + }; + + #define FPSIMD_MAGIC 0x46508001 + + error - 1/858 UAPI headers compatible with arm64 appear _not_ to be backwards compatible + Note: UAPI headers for architectures other than arm64 were not checked + error - UAPI header ABI check failed + +We can see with ``ARCH`` and ``CC`` set properly for the file, the ABI change +is reported properly. + + +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``. Now, let's see what we get +when we run the script with ``-m`` to only check for modified files:: + + % ./scripts/check-uapi.sh -m + Installing sanitized UAPI headers from dirty tree... OK + Saving current tree state... OK + Installing sanitized UAPI headers from HEAD... OK + Restoring current tree state... OK + Checking changes to UAPI headers between HEAD and dirty tree + All 1 UAPI headers modified between HEAD and dirty tree appear to be backwards compatible + +With the ``-m`` flag, the script will only check the ABI compatibility of +modified files. It reports back that there aren't any ABI issues with +``types.h``. However, other UAPI headers in the tree may be broken by this +change! + +When you run *without* the ``-m`` flag, *all* headers are checked:: + + % ./scripts/check-uapi.sh + Installing sanitized UAPI headers from dirty tree... OK + Saving current tree state... OK + Installing sanitized UAPI headers from HEAD... OK + Restoring current tree state... OK + Checking changes to UAPI headers between HEAD and dirty tree + !!! ABI differences detected in include/uapi/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/uapi/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 + #include + + error - 1/888 UAPI headers compatible with x86 appear _not_ to be backwards compatible + Note: UAPI headers for architectures other than x86 were not checked + error - UAPI header ABI check failed + +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``. + +To make sure issues like this are caught, it's recommended **not** to run with +the ``-m`` flag when doing formal validation checks (such as in a continuous +integration system). + + +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 + Saving current tree state... OK + Installing sanitized UAPI headers from v6.1... OK + Installing sanitized UAPI headers from v6.0... OK + Restoring current tree state... OK + Checking changes to UAPI headers between v6.0 and v6.1 + --- snip --- + error - 89/888 UAPI headers compatible with x86 appear _not_ to be backwards compatible + Note: UAPI headers for architectures other than x86 were not checked + error - UAPI header ABI check failed + +You'll notice that the script did detect 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: false +positives. + +False Positives +=============== + +The UAPI checker is very aggressive in detecting ABI changes, so some false +positives may appear. For example, if you check all UAPI headers between v6.0 +and v6.1, many breakages will be flagged. Run the following:: + + ./scripts/check-uapi.sh -b v6.1 -p v6.0 + +The errors will be logged to ``abi_error_log.txt``. Here, we'll find examples +of several types of false positives. + +Enum Expansion +-------------- + +:: + + !!! ABI differences detected in include/uapi/linux/openvswitch.h from v6.0 -> v6.1 !!! + + [C] 'enum ovs_datapath_attr' changed: + type size hasn't changed + 1 enumerator insertion: + 'ovs_datapath_attr::OVS_DP_ATTR_IFINDEX' value '9' + 1 enumerator change: + 'ovs_datapath_attr::__OVS_DP_ATTR_MAX' from value '9' to '10' at openvswitch.h.current:85:1 + +In this case, an enum was expanded. Consequently, the "MAX" value was +incremented. This is not considered a breaking change because it's assumed +userspace programs are using the MAX value in a sane fashion. + +Expanding Into Reserved/Padding Fields +-------------------------------------- + +:: + + !!! ABI differences detected in include/uapi/linux/perf_event.h from v6.0 -> v6.1 !!! + + [C] 'struct perf_branch_entry' changed: + type size hasn't changed + 3 data member insertions: + '__u64 spec', at offset 152 (in bits) at perf_event.h.current:1420:1 + '__u64 new_type', at offset 154 (in bits) at perf_event.h.current:1421:1 + '__u64 priv', at offset 158 (in bits) at perf_event.h.current:1422:1 + 1 data member change: + '__u64 reserved' offset changed from 152 to 161 (in bits) (by +9 bits) + +In this case, a reserved field was expanded into. Previously, the reserved +field occupied 40 bits in the struct. After the change, three new members +were added that took up 9 bits, so the size of the reserved field was +reduced to 31. + +As the size of the struct did not change and none of the fields a userspace +program could have been using were removed/changed/relocated, this change is +not considered breaking. + +Removals For Refactoring +------------------------ + +There is not an example of this in the v6.0 -> v6.1 span, but try:: + + % ./scripts/check-uapi.sh -b d759be8953febb6e5b5376c7d9bbf568864c6e2d -m + warning - detected changes to following files, but can't check them with x86 compiler: + - arch/alpha/include/uapi/asm/poll.h + - arch/ia64/include/uapi/asm/poll.h + + Filtering them out and performing partial check on remaining files... + Saving current tree state... OK + Installing sanitized UAPI headers from d759be8953febb6e5b5376c7d9bbf568864c6e2d... OK + Installing sanitized UAPI headers from d759be8953febb6e5b5376c7d9bbf568864c6e2d^1... OK + Restoring current tree state... OK + Checking changes to UAPI headers between d759be8953febb6e5b5376c7d9bbf568864c6e2d^1 and d759be8953febb6e5b5376c7d9bbf568864c6e2d + error - UAPI header arch/x86/include/uapi/asm/poll.h was incorrectly removed + error - 1/1 UAPI headers modified between d759be8953febb6e5b5376c7d9bbf568864c6e2d^1 and d759be8953febb6e5b5376c7d9bbf568864c6e2d appear _not_ to be backwards compatible + error - UAPI header ABI check failed + +In this case, the commit was a cleanup/refactoring change that does not impact +UAPIs. Unfortunately, the script is not smart enough to see this and raises the +alarm because UAPI headers were removed. + +Summary +------- + +There may be other examples of false positives that are not listed here. + +In the future, as tooling improves, we may be able to filter out more of these +false positives. There may also be additional examples of false positives not +listed here. Use your best judgement, and ideally a unit test in userspace, to +test your UAPI changes! + +False Negatives +=============== + +The script can report false negatives when running with ``-m``. This occurs +when a change is made to a header file which causes a break in a separate header +file that includes it. + +For this reason, it's recommended not to run with the ``-m`` option unless you +know the modified files are not being included elsewhere. + +For an example of this behavior, please see the Cross-Dependency Breakage +example above. 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