From 5febf432df1cfa5b25d99b54c32103fafbdd0eb9 Mon Sep 17 00:00:00 2001 From: Miguel Ojeda Date: Sun, 16 Aug 2026 15:32:33 +0200 Subject: kbuild: rust: keep Rust objects out of Clang LTO with inline helpers Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit `objtool` errors such as: vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a: can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd The reason is that in such builds, the Clang invocation that compiles the combined Rust plus helpers bitcode emits LLVM bitcode (again) -- the final code generation happens in the linker's LTO step, which the `-mllvm` trap options passed to Clang do not reach. This, in turn, means that unreachable traps are missing, and the impossible paths do not merely fallthrough to the next symbol, but past the end of their own section, since LTO builds place each function in its own section. Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always emits machine code directly, with the traps in place. Assisted-by: LLM Cc: Gary Guo Cc: Boqun Feng Cc: Alice Ryhl Cc: Matthew Maurer Cc: Josh Poimboeuf Cc: Peter Zijlstra Cc: stable@vger.kernel.org Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust") Acked-by: Gary Guo Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org Signed-off-by: Miguel Ojeda --- tools/testing/selftests/splice/.gitignore | 3 + tools/testing/selftests/splice/Makefile | 5 + tools/testing/selftests/splice/config | 1 + .../selftests/splice/default_file_splice_read.c | 9 ++ .../selftests/splice/default_file_splice_read.sh | 8 ++ tools/testing/selftests/splice/settings | 1 + .../testing/selftests/splice/short_splice_read.sh | 133 +++++++++++++++++++++ tools/testing/selftests/splice/splice_read.c | 57 +++++++++ 8 files changed, 217 insertions(+) create mode 100644 tools/testing/selftests/splice/.gitignore create mode 100644 tools/testing/selftests/splice/Makefile create mode 100644 tools/testing/selftests/splice/config create mode 100644 tools/testing/selftests/splice/default_file_splice_read.c create mode 100755 tools/testing/selftests/splice/default_file_splice_read.sh create mode 100644 tools/testing/selftests/splice/settings create mode 100755 tools/testing/selftests/splice/short_splice_read.sh create mode 100644 tools/testing/selftests/splice/splice_read.c (limited to 'tools/testing/selftests/splice') diff --git a/tools/testing/selftests/splice/.gitignore b/tools/testing/selftests/splice/.gitignore new file mode 100644 index 000000000..be8266f5d --- /dev/null +++ b/tools/testing/selftests/splice/.gitignore @@ -0,0 +1,3 @@ +# SPDX-License-Identifier: GPL-2.0-only +default_file_splice_read +splice_read diff --git a/tools/testing/selftests/splice/Makefile b/tools/testing/selftests/splice/Makefile new file mode 100644 index 000000000..541cd826d --- /dev/null +++ b/tools/testing/selftests/splice/Makefile @@ -0,0 +1,5 @@ +# SPDX-License-Identifier: GPL-2.0 +TEST_PROGS := default_file_splice_read.sh short_splice_read.sh +TEST_GEN_PROGS_EXTENDED := default_file_splice_read splice_read + +include ../lib.mk diff --git a/tools/testing/selftests/splice/config b/tools/testing/selftests/splice/config new file mode 100644 index 000000000..058c92836 --- /dev/null +++ b/tools/testing/selftests/splice/config @@ -0,0 +1 @@ +CONFIG_TEST_LKM=m diff --git a/tools/testing/selftests/splice/default_file_splice_read.c b/tools/testing/selftests/splice/default_file_splice_read.c new file mode 100644 index 000000000..a3c6e5672 --- /dev/null +++ b/tools/testing/selftests/splice/default_file_splice_read.c @@ -0,0 +1,9 @@ +// SPDX-License-Identifier: GPL-2.0 +#define _GNU_SOURCE +#include + +int main(int argc, char **argv) +{ + splice(0, 0, 1, 0, 1<<30, 0); + return 0; +} diff --git a/tools/testing/selftests/splice/default_file_splice_read.sh b/tools/testing/selftests/splice/default_file_splice_read.sh new file mode 100755 index 000000000..490db5a2e --- /dev/null +++ b/tools/testing/selftests/splice/default_file_splice_read.sh @@ -0,0 +1,8 @@ +#!/bin/sh +# SPDX-License-Identifier: GPL-2.0 +n=`./default_file_splice_read &2 + echo "$title ..." >&2 + + set +e + "$@" + rc=$? + set -e + + case "$rc" in + 0) + echo "ok: $title succeeded" >&2 + ;; + 1) + echo "FAIL: $title should work" >&2 + ret=$(( ret + 1 )) + ;; + *) + echo "FAIL: something else went wrong" >&2 + ret=$(( ret + 1 )) + ;; + esac +} + +expect_failure() +{ + title="$1" + shift + + echo "" >&2 + echo "$title ..." >&2 + + set +e + "$@" + rc=$? + set -e + + case "$rc" in + 0) + echo "FAIL: $title unexpectedly worked" >&2 + ret=$(( ret + 1 )) + ;; + 1) + echo "ok: $title correctly failed" >&2 + ;; + *) + echo "FAIL: something else went wrong" >&2 + ret=$(( ret + 1 )) + ;; + esac +} + +do_splice() +{ + filename="$1" + bytes="$2" + expected="$3" + report="$4" + + out=$("$DIR"/splice_read "$filename" "$bytes" | cat) + if [ "$out" = "$expected" ] ; then + echo " matched $report" >&2 + return 0 + else + echo " no match: '$out' vs $report" >&2 + return 1 + fi +} + +test_splice() +{ + filename="$1" + + echo " checking $filename ..." >&2 + + full=$(cat "$filename") + rc=$? + if [ $rc -ne 0 ] ; then + return 2 + fi + + two=$(echo "$full" | grep -m1 . | cut -c-2) + + # Make sure full splice has the same contents as a standard read. + echo " splicing 4096 bytes ..." >&2 + if ! do_splice "$filename" 4096 "$full" "full read" ; then + return 1 + fi + + # Make sure a partial splice see the first two characters. + echo " splicing 2 bytes ..." >&2 + if ! do_splice "$filename" 2 "$two" "'$two'" ; then + return 1 + fi + + return 0 +} + +### /proc/$pid/ has no splice interface; these should all fail. +expect_failure "proc_single_open(), seq_read() splice" test_splice /proc/$$/limits +expect_failure "special open(), seq_read() splice" test_splice /proc/$$/comm + +### /proc/sys/ has a splice interface; these should all succeed. +expect_success "proc_handler: proc_dointvec_minmax() splice" test_splice /proc/sys/fs/nr_open +expect_success "proc_handler: proc_dostring() splice" test_splice /proc/sys/kernel/modprobe +expect_success "proc_handler: special read splice" test_splice /proc/sys/kernel/version + +### /sys/ has no splice interface; these should all fail. +if ! [ -d /sys/module/test_module/sections ] ; then + expect_success "test_module kernel module load" modprobe test_module +fi +expect_success "kernfs attr splice" test_splice /sys/module/test_module/coresize +expect_success "kernfs binattr splice" test_splice /sys/module/test_module/sections/.init.text + +exit $ret diff --git a/tools/testing/selftests/splice/splice_read.c b/tools/testing/selftests/splice/splice_read.c new file mode 100644 index 000000000..46dae6a25 --- /dev/null +++ b/tools/testing/selftests/splice/splice_read.c @@ -0,0 +1,57 @@ +// SPDX-License-Identifier: GPL-2.0 +#define _GNU_SOURCE +#include +#include +#include +#include +#include +#include +#include +#include + +int main(int argc, char *argv[]) +{ + int fd; + size_t size; + ssize_t spliced; + + if (argc < 2) { + fprintf(stderr, "Usage: %s INPUT [BYTES]\n", argv[0]); + return EXIT_FAILURE; + } + + fd = open(argv[1], O_RDONLY); + if (fd < 0) { + perror(argv[1]); + return EXIT_FAILURE; + } + + if (argc == 3) + size = atol(argv[2]); + else { + struct stat statbuf; + + if (fstat(fd, &statbuf) < 0) { + perror(argv[1]); + return EXIT_FAILURE; + } + + if (statbuf.st_size > INT_MAX) { + fprintf(stderr, "%s: Too big\n", argv[1]); + return EXIT_FAILURE; + } + + size = statbuf.st_size; + } + + /* splice(2) file to stdout. */ + spliced = splice(fd, NULL, STDOUT_FILENO, NULL, + size, SPLICE_F_MOVE); + if (spliced < 0) { + perror("splice"); + return EXIT_FAILURE; + } + + close(fd); + return EXIT_SUCCESS; +} -- cgit v1.3.1