kbuild: rust: keep Rust objects out of Clang LTO with inline helpersgrafted

Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit
`objtool` errors such as:

    vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a:
    can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd

The reason is that in such builds, the Clang invocation that compiles
the combined Rust plus helpers bitcode emits LLVM bitcode (again) --
the final code generation happens in the linker's LTO step, which the
`-mllvm` trap options passed to Clang do not reach.

This, in turn, means that unreachable traps are missing, and the
impossible paths do not merely fallthrough to the next symbol, but past
the end of their own section, since LTO builds place each function in
its own section.

Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always
emits machine code directly, with the traps in place.

Assisted-by: LLM
Cc: Gary Guo <gary@garyguo.net>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Matthew Maurer <mmaurer@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust")
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 432 insertions, 0 deletions

diff --git a/tools/perf/bench/sched-pipe.c b/tools/perf/bench/sched-pipe.c
new file mode 100644
index 000000000..eb20c6d73
--- /dev/null
+++ b/tools/perf/bench/sched-pipe.c
@@ -0,0 +1,432 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *
+ * sched-pipe.c
+ *
+ * pipe: Benchmark for pipe()
+ *
+ * Based on pipe-test-1m.c by Ingo Molnar <mingo@redhat.com>
+ *  http://people.redhat.com/mingo/cfs-scheduler/tools/pipe-test-1m.c
+ * Ported to perf by Hitoshi Mitake <mitake@dcl.info.waseda.ac.jp>
+ */
+#include <subcmd/parse-options.h>
+#include <api/fs/fs.h>
+#include "bench.h"
+#include "util/cgroup.h"
+
+#include <unistd.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <signal.h>
+#include <sys/wait.h>
+#include <string.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <assert.h>
+#include <poll.h>
+#include <sys/epoll.h>
+#include <sys/time.h>
+#include <sys/types.h>
+#include <sys/syscall.h>
+#include <linux/time64.h>
+
+#include <pthread.h>
+
+struct thread_data {
+	int			nr;
+	int			pipe_read;
+	int			pipe_write;
+	struct epoll_event      epoll_ev;
+	int			epoll_fd;
+	bool			cgroup_failed;
+	pthread_t		pthread;
+	char			*buf;
+};
+
+#define LOOPS_DEFAULT 1000000
+static	int			loops = LOOPS_DEFAULT;
+
+/* Use processes by default: */
+static bool			threaded;
+
+static bool			nonblocking;
+static unsigned int		write_size = sizeof(int);
+static char			*cgrp_names[2];
+static struct cgroup		*cgrps[2];
+
+static int parse_two_cgroups(const struct option *opt __maybe_unused,
+			     const char *str, int unset __maybe_unused)
+{
+	char *p = strdup(str);
+	char *q;
+	int ret = -1;
+
+	if (p == NULL) {
+		fprintf(stderr, "memory allocation failure\n");
+		return -1;
+	}
+
+	q = strchr(p, ',');
+	if (q == NULL) {
+		fprintf(stderr, "it should have two cgroup names: %s\n", p);
+		goto out;
+	}
+	*q = '\0';
+
+	cgrp_names[0] = strdup(p);
+	cgrp_names[1] = strdup(q + 1);
+
+	if (cgrp_names[0] == NULL || cgrp_names[1] == NULL) {
+		fprintf(stderr, "memory allocation failure\n");
+		goto out;
+	}
+	ret = 0;
+
+out:
+	free(p);
+	return ret;
+}
+
+static const struct option options[] = {
+	OPT_BOOLEAN('n', "nonblocking",	&nonblocking,	"Use non-blocking operations"),
+	OPT_INTEGER('l', "loop",	&loops,		"Specify number of loops"),
+	OPT_BOOLEAN('T', "threaded",	&threaded,	"Specify threads/process based task setup"),
+	OPT_UINTEGER('s', "write-size", &write_size,
+		     "Bytes per ping-pong write (default 4-bytes). Use larger values to exercise the pipe page-allocation path."),
+	OPT_CALLBACK('G', "cgroups", NULL, "SEND,RECV",
+		     "Put sender and receivers in given cgroups",
+		     parse_two_cgroups),
+	OPT_END()
+};
+
+static const char * const bench_sched_pipe_usage[] = {
+	"perf bench sched pipe <options>",
+	NULL
+};
+
+static int enter_cgroup(int nr)
+{
+	char buf[32];
+	int fd, len, ret;
+	int saved_errno;
+	struct cgroup *cgrp;
+	pid_t pid;
+
+	if (cgrp_names[nr] == NULL)
+		return 0;
+
+	if (cgrps[nr] == NULL) {
+		cgrps[nr] = cgroup__new(cgrp_names[nr], /*do_open=*/true);
+		if (cgrps[nr] == NULL)
+			goto err;
+	}
+	cgrp = cgrps[nr];
+
+	if (threaded)
+		pid = syscall(__NR_gettid);
+	else
+		pid = getpid();
+
+	snprintf(buf, sizeof(buf), "%d\n", pid);
+	len = strlen(buf);
+
+	/* try cgroup v2 interface first */
+	if (threaded)
+		fd = openat(cgrp->fd, "cgroup.threads", O_WRONLY);
+	else
+		fd = openat(cgrp->fd, "cgroup.procs", O_WRONLY);
+
+	/* try cgroup v1 if failed */
+	if (fd < 0 && errno == ENOENT)
+		fd = openat(cgrp->fd, "tasks", O_WRONLY);
+
+	if (fd < 0)
+		goto err;
+
+	ret = write(fd, buf, len);
+	close(fd);
+
+	if (ret != len) {
+		printf("Cannot enter to cgroup: %s\n", cgrp->name);
+		return -1;
+	}
+	return 0;
+
+err:
+	saved_errno = errno;
+	printf("Failed to open cgroup file in %s\n", cgrp_names[nr]);
+
+	if (saved_errno == ENOENT) {
+		char mnt[PATH_MAX];
+
+		if (cgroupfs_find_mountpoint(mnt, sizeof(mnt), "perf_event") == 0)
+			printf(" Hint: create the cgroup first, like 'mkdir %s/%s'\n",
+			       mnt, cgrp_names[nr]);
+	} else if (saved_errno == EACCES && geteuid() > 0) {
+		printf(" Hint: try to run as root\n");
+	}
+
+	return -1;
+}
+
+static void exit_cgroup(int nr)
+{
+	cgroup__put(cgrps[nr]);
+	free(cgrp_names[nr]);
+}
+
+/* Sleep until @fd is writable, so we don't busy-spin on EWOULDBLOCK. */
+static inline void wait_writable(int fd)
+{
+	struct pollfd pfd = {
+		.fd	= fd,
+		.events	= POLLOUT,
+	};
+
+	poll(&pfd, 1, -1);
+}
+
+/*
+ * Loop on short read()/write(): the kernel may return fewer bytes than
+ * requested, retry on EINTR, and in non-blocking mode wait via poll()
+ * when the writer transiently hits EWOULDBLOCK while the peer is still
+ * draining a full pipe (capacity is sized to write_size).
+ */
+static inline int write_pipe(struct thread_data *td)
+{
+	unsigned int done = 0;
+	int ret;
+
+	while (done < write_size) {
+		ret = write(td->pipe_write, td->buf + done, write_size - done);
+		if (ret < 0) {
+			if (errno == EINTR)
+				continue;
+			if (nonblocking && errno == EWOULDBLOCK) {
+				wait_writable(td->pipe_write);
+				continue;
+			}
+			return ret;
+		}
+		done += ret;
+	}
+	return done;
+}
+
+static inline int read_pipe(struct thread_data *td)
+{
+	unsigned int done = 0;
+	int ret;
+
+	while (done < write_size) {
+		if (nonblocking) {
+			ret = epoll_wait(td->epoll_fd, &td->epoll_ev, 1, -1);
+			if (ret < 0) {
+				if (errno == EINTR)
+					continue;
+				return ret;
+			}
+		}
+		ret = read(td->pipe_read, td->buf + done, write_size - done);
+		if (ret < 0) {
+			if (errno == EINTR)
+				continue;
+			if (nonblocking && errno == EWOULDBLOCK)
+				continue;
+			return ret;
+		}
+		if (ret == 0)
+			return done;
+		done += ret;
+	}
+	return done;
+}
+
+static void *worker_thread(void *__tdata)
+{
+	struct thread_data *td = __tdata;
+	int i, ret;
+
+	ret = enter_cgroup(td->nr);
+	if (ret < 0) {
+		td->cgroup_failed = true;
+		return NULL;
+	}
+
+	if (nonblocking) {
+		td->epoll_ev.events = EPOLLIN;
+		td->epoll_fd = epoll_create(1);
+		BUG_ON(td->epoll_fd < 0);
+		BUG_ON(epoll_ctl(td->epoll_fd, EPOLL_CTL_ADD, td->pipe_read, &td->epoll_ev) < 0);
+	}
+
+	for (i = 0; i < loops; i++) {
+		ret = write_pipe(td);
+		BUG_ON(ret != (int)write_size);
+		ret = read_pipe(td);
+		BUG_ON(ret != (int)write_size);
+	}
+
+	return NULL;
+}
+
+/*
+ * On a custom write_size, resize the pipes so a single payload fits.
+ */
+static int resize_pipes(int wfd1, int wfd2)
+{
+	int r1, r2;
+
+	if (write_size <= sizeof(int))
+		return 0;
+
+	r1 = fcntl(wfd1, F_SETPIPE_SZ, write_size);
+	r2 = fcntl(wfd2, F_SETPIPE_SZ, write_size);
+	if (r1 < 0 || r2 < 0 ||
+	    (unsigned int)r1 < write_size ||
+	    (unsigned int)r2 < write_size) {
+		fprintf(stderr,
+			"--write-size %u exceeds /proc/sys/fs/pipe-max-size\n",
+			write_size);
+		return -1;
+	}
+	return 0;
+}
+
+int bench_sched_pipe(int argc, const char **argv)
+{
+	struct thread_data threads[2] = {};
+	struct thread_data *td;
+	int pipe_1[2], pipe_2[2];
+	struct timeval start, stop, diff;
+	unsigned long long result_usec = 0;
+	int nr_threads = 2;
+	int t;
+
+	/*
+	 * why does "ret" exist?
+	 * discarding returned value of read(), write()
+	 * causes error in building environment for perf
+	 */
+	int __maybe_unused ret, wait_stat, flags = 0;
+	pid_t pid, retpid __maybe_unused;
+
+	argc = parse_options(argc, argv, options, bench_sched_pipe_usage, 0);
+
+	/*
+	 * The error paths below return early without closing the pipes or
+	 * freeing the cgroup state. That is fine: bench_sched_pipe() runs
+	 * once and the process exits right after it returns, so these are
+	 * not real leaks.
+	 */
+	if (write_size == 0 || write_size > INT_MAX) {
+		fprintf(stderr, "--write-size must be in 1..%d\n", INT_MAX);
+		return -1;
+	}
+
+	if (nonblocking)
+		flags |= O_NONBLOCK;
+
+	BUG_ON(pipe2(pipe_1, flags));
+	BUG_ON(pipe2(pipe_2, flags));
+
+	if (resize_pipes(pipe_1[1], pipe_2[1]) < 0)
+		return -1;
+
+	for (t = 0; t < nr_threads; t++) {
+		threads[t].buf = calloc(1, write_size);
+		BUG_ON(!threads[t].buf);
+	}
+
+	gettimeofday(&start, NULL);
+
+	for (t = 0; t < nr_threads; t++) {
+		td = threads + t;
+
+		td->nr = t;
+
+		if (t == 0) {
+			td->pipe_read = pipe_1[0];
+			td->pipe_write = pipe_2[1];
+		} else {
+			td->pipe_write = pipe_1[1];
+			td->pipe_read = pipe_2[0];
+		}
+	}
+
+	if (threaded) {
+		for (t = 0; t < nr_threads; t++) {
+			td = threads + t;
+
+			ret = pthread_create(&td->pthread, NULL, worker_thread, td);
+			BUG_ON(ret);
+		}
+
+		for (t = 0; t < nr_threads; t++) {
+			td = threads + t;
+
+			ret = pthread_join(td->pthread, NULL);
+			BUG_ON(ret);
+		}
+	} else {
+		pid = fork();
+		assert(pid >= 0);
+
+		if (!pid) {
+			worker_thread(threads + 0);
+			exit(0);
+		} else {
+			worker_thread(threads + 1);
+		}
+
+		retpid = waitpid(pid, &wait_stat, 0);
+		assert((retpid == pid) && WIFEXITED(wait_stat));
+	}
+
+	gettimeofday(&stop, NULL);
+	timersub(&stop, &start, &diff);
+
+	for (t = 0; t < nr_threads; t++)
+		free(threads[t].buf);
+
+	exit_cgroup(0);
+	exit_cgroup(1);
+
+	if (threads[0].cgroup_failed || threads[1].cgroup_failed)
+		return 0;
+
+	switch (bench_format) {
+	case BENCH_FORMAT_DEFAULT:
+		printf("# Executed %d pipe operations between two %s\n\n",
+			loops, threaded ? "threads" : "processes");
+
+		result_usec = diff.tv_sec * USEC_PER_SEC;
+		result_usec += diff.tv_usec;
+
+		printf(" %14s: %lu.%03lu [sec]\n\n", "Total time",
+		       (unsigned long) diff.tv_sec,
+		       (unsigned long) (diff.tv_usec / USEC_PER_MSEC));
+
+		printf(" %14lf usecs/op\n",
+		       (double)result_usec / (double)loops);
+		printf(" %14d ops/sec\n",
+		       (int)((double)loops /
+			     ((double)result_usec / (double)USEC_PER_SEC)));
+		break;
+
+	case BENCH_FORMAT_SIMPLE:
+		printf("%lu.%03lu\n",
+		       (unsigned long) diff.tv_sec,
+		       (unsigned long) (diff.tv_usec / USEC_PER_MSEC));
+		break;
+
+	default:
+		/* reaching here is something disaster */
+		fprintf(stderr, "Unknown format:%d\n", bench_format);
+		exit(1);
+		break;
+	}
+
+	return 0;
+}