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, 369 insertions, 0 deletions

diff --git a/tools/perf/util/mmap.c b/tools/perf/util/mmap.c
new file mode 100644
index 000000000..358e70c4f
--- /dev/null
+++ b/tools/perf/util/mmap.c
@@ -0,0 +1,369 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2011-2017, Red Hat Inc, Arnaldo Carvalho de Melo <acme@redhat.com>
+ *
+ * Parts came from evlist.c builtin-{top,stat,record}.c, see those files for further
+ * copyright notes.
+ */
+
+#include <sys/mman.h>
+#include <errno.h>
+#include <inttypes.h>
+#include <asm/bug.h>
+#include <linux/zalloc.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h> // sysconf()
+#include <perf/mmap.h>
+#ifdef HAVE_LIBNUMA_SUPPORT
+#include <numaif.h>
+#endif
+#include "cpumap.h"
+#include "debug.h"
+#include "event.h"
+#include "mmap.h"
+#include "../perf.h"
+#include <internal/lib.h> /* page_size */
+#include <linux/bitmap.h>
+
+#define MASK_SIZE 1023
+void mmap_cpu_mask__scnprintf(struct mmap_cpu_mask *mask, const char *tag)
+{
+	char buf[MASK_SIZE + 1];
+	size_t len;
+
+	len = bitmap_scnprintf(mask->bits, mask->nbits, buf, MASK_SIZE);
+	buf[len] = '\0';
+	pr_debug("%p: %s mask[%zd]: %s\n", mask, tag, mask->nbits, buf);
+}
+
+size_t mmap__mmap_len(struct mmap *map)
+{
+	return perf_mmap__mmap_len(&map->core);
+}
+
+int __weak auxtrace_mmap__mmap(struct auxtrace_mmap *mm __maybe_unused,
+			       struct auxtrace_mmap_params *mp __maybe_unused,
+			       void *userpg __maybe_unused,
+			       int fd __maybe_unused)
+{
+	return 0;
+}
+
+void __weak auxtrace_mmap__munmap(struct auxtrace_mmap *mm __maybe_unused)
+{
+}
+
+void __weak auxtrace_mmap_params__init(struct auxtrace_mmap_params *mp __maybe_unused,
+				       off_t auxtrace_offset __maybe_unused,
+				       unsigned int auxtrace_pages __maybe_unused,
+				       bool auxtrace_overwrite __maybe_unused)
+{
+}
+
+void __weak auxtrace_mmap_params__set_idx(struct auxtrace_mmap_params *mp __maybe_unused,
+					  struct evlist *evlist __maybe_unused,
+					  struct evsel *evsel __maybe_unused,
+					  int idx __maybe_unused)
+{
+}
+
+#ifdef HAVE_AIO_SUPPORT
+static int perf_mmap__aio_enabled(struct mmap *map)
+{
+	return map->aio.nr_cblocks > 0;
+}
+
+#ifdef HAVE_LIBNUMA_SUPPORT
+static int perf_mmap__aio_alloc(struct mmap *map, int idx)
+{
+	map->aio.data[idx] = mmap(NULL, mmap__mmap_len(map), PROT_READ|PROT_WRITE,
+				  MAP_PRIVATE|MAP_ANONYMOUS, 0, 0);
+	if (map->aio.data[idx] == MAP_FAILED) {
+		map->aio.data[idx] = NULL;
+		return -1;
+	}
+
+	return 0;
+}
+
+static void perf_mmap__aio_free(struct mmap *map, int idx)
+{
+	if (!map->aio.data || !map->aio.data[idx])
+		return;
+	munmap(map->aio.data[idx], mmap__mmap_len(map));
+	map->aio.data[idx] = NULL;
+}
+
+static int perf_mmap__aio_bind(struct mmap *map, int idx, struct perf_cpu cpu, int affinity)
+{
+	void *data;
+	size_t mmap_len;
+	unsigned long *node_mask;
+	unsigned long node_index;
+	int err = 0;
+
+	if (affinity != PERF_AFFINITY_SYS && cpu__max_node() > 1) {
+		int node;
+
+		data = map->aio.data[idx];
+		mmap_len = mmap__mmap_len(map);
+		node = cpu__get_node(cpu);
+		/* -1 sign-extends to ULONG_MAX, wrapping bitmap_zalloc(0) and OOB __set_bit */
+		if (node < 0)
+			return 0;
+		node_index = node;
+		node_mask = bitmap_zalloc(node_index + 1);
+		if (!node_mask) {
+			pr_err("Failed to allocate node mask for mbind: error %m\n");
+			return -1;
+		}
+		__set_bit(node_index, node_mask);
+		if (mbind(data, mmap_len, MPOL_BIND, node_mask, node_index + 1 + 1, 0)) {
+			pr_err("Failed to bind [%p-%p] AIO buffer to node %lu: error %m\n",
+				data, data + mmap_len, node_index);
+			err = -1;
+		}
+		bitmap_free(node_mask);
+	}
+
+	return err;
+}
+#else /* !HAVE_LIBNUMA_SUPPORT */
+static int perf_mmap__aio_alloc(struct mmap *map, int idx)
+{
+	map->aio.data[idx] = malloc(mmap__mmap_len(map));
+	if (map->aio.data[idx] == NULL)
+		return -1;
+
+	return 0;
+}
+
+static void perf_mmap__aio_free(struct mmap *map, int idx)
+{
+	if (!map->aio.data)
+		return;
+	zfree(&(map->aio.data[idx]));
+}
+
+static int perf_mmap__aio_bind(struct mmap *map __maybe_unused, int idx __maybe_unused,
+		struct perf_cpu cpu __maybe_unused, int affinity __maybe_unused)
+{
+	return 0;
+}
+#endif
+
+static int perf_mmap__aio_mmap(struct mmap *map, struct mmap_params *mp)
+{
+	int delta_max, i, prio, ret;
+
+	map->aio.nr_cblocks = mp->nr_cblocks;
+	if (map->aio.nr_cblocks) {
+		map->aio.aiocb = calloc(map->aio.nr_cblocks, sizeof(struct aiocb *));
+		if (!map->aio.aiocb) {
+			pr_debug2("failed to allocate aiocb for data buffer, error %m\n");
+			return -1;
+		}
+		map->aio.cblocks = calloc(map->aio.nr_cblocks, sizeof(struct aiocb));
+		if (!map->aio.cblocks) {
+			pr_debug2("failed to allocate cblocks for data buffer, error %m\n");
+			return -1;
+		}
+		map->aio.data = calloc(map->aio.nr_cblocks, sizeof(void *));
+		if (!map->aio.data) {
+			pr_debug2("failed to allocate data buffer, error %m\n");
+			return -1;
+		}
+		delta_max = sysconf(_SC_AIO_PRIO_DELTA_MAX);
+		for (i = 0; i < map->aio.nr_cblocks; ++i) {
+			ret = perf_mmap__aio_alloc(map, i);
+			if (ret == -1) {
+				pr_debug2("failed to allocate data buffer area, error %m");
+				return -1;
+			}
+			ret = perf_mmap__aio_bind(map, i, map->core.cpu, mp->affinity);
+			if (ret == -1)
+				return -1;
+			/*
+			 * Use cblock.aio_fildes value different from -1
+			 * to denote started aio write operation on the
+			 * cblock so it requires explicit record__aio_sync()
+			 * call prior the cblock may be reused again.
+			 */
+			map->aio.cblocks[i].aio_fildes = -1;
+			/*
+			 * Allocate cblocks with priority delta to have
+			 * faster aio write system calls because queued requests
+			 * are kept in separate per-prio queues and adding
+			 * a new request will iterate thru shorter per-prio
+			 * list. Blocks with numbers higher than
+			 *  _SC_AIO_PRIO_DELTA_MAX go with priority 0.
+			 */
+			prio = delta_max - i;
+			map->aio.cblocks[i].aio_reqprio = prio >= 0 ? prio : 0;
+		}
+	}
+
+	return 0;
+}
+
+static void perf_mmap__aio_munmap(struct mmap *map)
+{
+	int i;
+
+	for (i = 0; i < map->aio.nr_cblocks; ++i)
+		perf_mmap__aio_free(map, i);
+	if (map->aio.data)
+		zfree(&map->aio.data);
+	zfree(&map->aio.cblocks);
+	zfree(&map->aio.aiocb);
+}
+#else /* !HAVE_AIO_SUPPORT */
+static int perf_mmap__aio_enabled(struct mmap *map __maybe_unused)
+{
+	return 0;
+}
+
+static int perf_mmap__aio_mmap(struct mmap *map __maybe_unused,
+			       struct mmap_params *mp __maybe_unused)
+{
+	return 0;
+}
+
+static void perf_mmap__aio_munmap(struct mmap *map __maybe_unused)
+{
+}
+#endif
+
+void mmap__munmap(struct mmap *map)
+{
+	bitmap_free(map->affinity_mask.bits);
+	map->affinity_mask.bits = NULL;
+	map->affinity_mask.nbits = 0;
+
+	zstd_fini(&map->zstd_data);
+
+	perf_mmap__aio_munmap(map);
+	if (map->data != NULL) {
+		munmap(map->data, mmap__mmap_len(map));
+		map->data = NULL;
+	}
+	auxtrace_mmap__munmap(&map->auxtrace_mmap);
+}
+
+static void build_node_mask(int node, struct mmap_cpu_mask *mask)
+{
+	int idx, nr_cpus;
+	struct perf_cpu cpu;
+	struct perf_cpu_map *cpu_map = cpu_map__online();
+
+	if (!cpu_map)
+		return;
+
+	nr_cpus = perf_cpu_map__nr(cpu_map);
+	for (idx = 0; idx < nr_cpus; idx++) {
+		cpu = perf_cpu_map__cpu(cpu_map, idx); /* map c index to online cpu index */
+		if (cpu__get_node(cpu) == node)
+			__set_bit(cpu.cpu, mask->bits);
+	}
+	perf_cpu_map__put(cpu_map);
+}
+
+static int perf_mmap__setup_affinity_mask(struct mmap *map, struct mmap_params *mp)
+{
+	map->affinity_mask.nbits = cpu__max_cpu().cpu;
+	map->affinity_mask.bits = bitmap_zalloc(map->affinity_mask.nbits);
+	if (!map->affinity_mask.bits)
+		return -1;
+
+	if (mp->affinity == PERF_AFFINITY_NODE && cpu__max_node() > 1)
+		build_node_mask(cpu__get_node(map->core.cpu), &map->affinity_mask);
+	else if (mp->affinity == PERF_AFFINITY_CPU)
+		__set_bit(map->core.cpu.cpu, map->affinity_mask.bits);
+
+	return 0;
+}
+
+int mmap__mmap(struct mmap *map, struct mmap_params *mp, int fd, struct perf_cpu cpu)
+{
+	if (perf_mmap__mmap(&map->core, &mp->core, fd, cpu)) {
+		pr_debug2("failed to mmap perf event ring buffer, error %d\n",
+			  errno);
+		return -1;
+	}
+
+	if (mp->affinity != PERF_AFFINITY_SYS &&
+		perf_mmap__setup_affinity_mask(map, mp)) {
+		pr_debug2("failed to alloc mmap affinity mask, error %d\n",
+			  errno);
+		return -1;
+	}
+
+	if (verbose == 2)
+		mmap_cpu_mask__scnprintf(&map->affinity_mask, "mmap");
+
+	map->core.flush = mp->flush;
+
+	if (zstd_init(&map->zstd_data, mp->comp_level)) {
+		pr_debug2("failed to init mmap compressor, error %d\n", errno);
+		return -1;
+	}
+
+	if (mp->comp_level && !perf_mmap__aio_enabled(map)) {
+		map->data = mmap(NULL, mmap__mmap_len(map), PROT_READ|PROT_WRITE,
+				 MAP_PRIVATE|MAP_ANONYMOUS, 0, 0);
+		if (map->data == MAP_FAILED) {
+			pr_debug2("failed to mmap data buffer, error %d\n",
+					errno);
+			map->data = NULL;
+			return -1;
+		}
+	}
+
+	if (auxtrace_mmap__mmap(&map->auxtrace_mmap,
+				&mp->auxtrace_mp, map->core.base, fd))
+		return -1;
+
+	return perf_mmap__aio_mmap(map, mp);
+}
+
+int perf_mmap__push(struct mmap *md, void *to,
+		    int push(struct mmap *map, void *to, void *buf, size_t size))
+{
+	u64 head = perf_mmap__read_head(&md->core);
+	unsigned char *data = md->core.base + page_size;
+	unsigned long size;
+	void *buf;
+	int rc = 0;
+
+	rc = perf_mmap__read_init(&md->core);
+	if (rc < 0)
+		return (rc == -EAGAIN) ? 1 : -1;
+
+	size = md->core.end - md->core.start;
+
+	if ((md->core.start & md->core.mask) + size != (md->core.end & md->core.mask)) {
+		buf = &data[md->core.start & md->core.mask];
+		size = md->core.mask + 1 - (md->core.start & md->core.mask);
+		md->core.start += size;
+
+		if (push(md, to, buf, size) < 0) {
+			rc = -1;
+			goto out;
+		}
+	}
+
+	buf = &data[md->core.start & md->core.mask];
+	size = md->core.end - md->core.start;
+	md->core.start += size;
+
+	if (push(md, to, buf, size) < 0) {
+		rc = -1;
+		goto out;
+	}
+
+	md->core.prev = head;
+	perf_mmap__consume(&md->core);
+out:
+	return rc;
+}