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, 380 insertions, 0 deletions

diff --git a/tools/perf/util/namespaces.c b/tools/perf/util/namespaces.c
new file mode 100644
index 000000000..01502570b
--- /dev/null
+++ b/tools/perf/util/namespaces.c
@@ -0,0 +1,380 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *
+ * Copyright (C) 2017 Hari Bathini, IBM Corporation
+ */
+
+#include "namespaces.h"
+#include "event.h"
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <sched.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+#include <asm/bug.h>
+#include <linux/kernel.h>
+#include <linux/zalloc.h>
+
+static const char *perf_ns__names[] = {
+	[NET_NS_INDEX]		= "net",
+	[UTS_NS_INDEX]		= "uts",
+	[IPC_NS_INDEX]		= "ipc",
+	[PID_NS_INDEX]		= "pid",
+	[USER_NS_INDEX]		= "user",
+	[MNT_NS_INDEX]		= "mnt",
+	[CGROUP_NS_INDEX]	= "cgroup",
+};
+
+const char *perf_ns__name(unsigned int id)
+{
+	if (id >= ARRAY_SIZE(perf_ns__names))
+		return "UNKNOWN";
+	return perf_ns__names[id];
+}
+
+struct namespaces *namespaces__new(struct perf_record_namespaces *event)
+{
+	struct namespaces *namespaces;
+	u64 link_info_size = ((event ? event->nr_namespaces : NR_NAMESPACES) *
+			      sizeof(struct perf_ns_link_info));
+
+	namespaces = zalloc(sizeof(struct namespaces) + link_info_size);
+	if (!namespaces)
+		return NULL;
+
+	namespaces->end_time = -1;
+
+	if (event)
+		memcpy(namespaces->link_info, event->link_info, link_info_size);
+
+	return namespaces;
+}
+
+void namespaces__free(struct namespaces *namespaces)
+{
+	free(namespaces);
+}
+
+static int nsinfo__get_nspid(pid_t *tgid, pid_t *nstgid, bool *in_pidns, const char *path)
+{
+	FILE *f = NULL;
+	char *statln = NULL;
+	size_t linesz = 0;
+	char *nspid;
+
+	f = fopen(path, "r");
+	if (f == NULL)
+		return -1;
+
+	while (getline(&statln, &linesz, f) != -1) {
+		/* Use tgid if CONFIG_PID_NS is not defined. */
+		if (strstr(statln, "Tgid:") != NULL) {
+			*tgid = (pid_t)strtol(strrchr(statln, '\t'), NULL, 10);
+			*nstgid = *tgid;
+		}
+
+		if (strstr(statln, "NStgid:") != NULL) {
+			nspid = strrchr(statln, '\t');
+			*nstgid = (pid_t)strtol(nspid, NULL, 10);
+			/*
+			 * If innermost tgid is not the first, process is in a different
+			 * PID namespace.
+			 */
+			*in_pidns = (statln + sizeof("NStgid:") - 1) != nspid;
+			break;
+		}
+	}
+
+	fclose(f);
+	free(statln);
+	return 0;
+}
+
+int nsinfo__init(struct nsinfo *nsi)
+{
+	char oldns[PATH_MAX];
+	char spath[PATH_MAX];
+	char *newns = NULL;
+	struct stat old_stat;
+	struct stat new_stat;
+	int rv = -1;
+
+	if (snprintf(oldns, PATH_MAX, "/proc/self/ns/mnt") >= PATH_MAX)
+		return rv;
+
+	if (asprintf(&newns, "/proc/%d/ns/mnt", nsinfo__pid(nsi)) == -1)
+		return rv;
+
+	if (stat(oldns, &old_stat) < 0)
+		goto out;
+
+	if (stat(newns, &new_stat) < 0)
+		goto out;
+
+	/* Check if the mount namespaces differ, if so then indicate that we
+	 * want to switch as part of looking up dso/map data.
+	 */
+	if (old_stat.st_ino != new_stat.st_ino) {
+		RC_CHK_ACCESS(nsi)->need_setns = true;
+		RC_CHK_ACCESS(nsi)->mntns_path = newns;
+		newns = NULL;
+	}
+
+	/* If we're dealing with a process that is in a different PID namespace,
+	 * attempt to work out the innermost tgid for the process.
+	 */
+	if (snprintf(spath, PATH_MAX, "/proc/%d/status", nsinfo__pid(nsi)) >= PATH_MAX)
+		goto out;
+
+	rv = nsinfo__get_nspid(&RC_CHK_ACCESS(nsi)->tgid, &RC_CHK_ACCESS(nsi)->nstgid,
+			       &RC_CHK_ACCESS(nsi)->in_pidns, spath);
+
+out:
+	free(newns);
+	return rv;
+}
+
+static struct nsinfo *nsinfo__alloc(void)
+{
+	struct nsinfo *res;
+	RC_STRUCT(nsinfo) *nsi;
+
+	nsi = calloc(1, sizeof(*nsi));
+	if (ADD_RC_CHK(res, nsi))
+		refcount_set(&nsi->refcnt, 1);
+
+	return res;
+}
+
+struct nsinfo *nsinfo__new(pid_t pid)
+{
+	struct nsinfo *nsi;
+
+	if (pid == 0)
+		return NULL;
+
+	nsi = nsinfo__alloc();
+	if (!nsi)
+		return NULL;
+
+	RC_CHK_ACCESS(nsi)->pid = pid;
+	RC_CHK_ACCESS(nsi)->tgid = pid;
+	RC_CHK_ACCESS(nsi)->nstgid = pid;
+	nsinfo__clear_need_setns(nsi);
+	RC_CHK_ACCESS(nsi)->in_pidns = false;
+	/* Init may fail if the process exits while we're trying to look at its
+	 * proc information. In that case, save the pid but don't try to enter
+	 * the namespace.
+	 */
+	if (nsinfo__init(nsi) == -1)
+		nsinfo__clear_need_setns(nsi);
+
+	return nsi;
+}
+
+static const char *nsinfo__mntns_path(const struct nsinfo *nsi)
+{
+	return RC_CHK_ACCESS(nsi)->mntns_path;
+}
+
+struct nsinfo *nsinfo__copy(const struct nsinfo *nsi)
+{
+	struct nsinfo *nnsi;
+
+	if (nsi == NULL)
+		return NULL;
+
+	nnsi = nsinfo__alloc();
+	if (!nnsi)
+		return NULL;
+
+	RC_CHK_ACCESS(nnsi)->pid = nsinfo__pid(nsi);
+	RC_CHK_ACCESS(nnsi)->tgid = nsinfo__tgid(nsi);
+	RC_CHK_ACCESS(nnsi)->nstgid = nsinfo__nstgid(nsi);
+	RC_CHK_ACCESS(nnsi)->need_setns = nsinfo__need_setns(nsi);
+	RC_CHK_ACCESS(nnsi)->in_pidns = nsinfo__in_pidns(nsi);
+	if (nsinfo__mntns_path(nsi)) {
+		RC_CHK_ACCESS(nnsi)->mntns_path = strdup(nsinfo__mntns_path(nsi));
+		if (!RC_CHK_ACCESS(nnsi)->mntns_path) {
+			nsinfo__put(nnsi);
+			return NULL;
+		}
+	}
+
+	return nnsi;
+}
+
+static refcount_t *nsinfo__refcnt(struct nsinfo *nsi)
+{
+	return &RC_CHK_ACCESS(nsi)->refcnt;
+}
+
+static void nsinfo__delete(struct nsinfo *nsi)
+{
+	if (nsi) {
+		WARN_ONCE(refcount_read(nsinfo__refcnt(nsi)) != 0, "nsinfo refcnt unbalanced\n");
+		zfree(&RC_CHK_ACCESS(nsi)->mntns_path);
+		RC_CHK_FREE(nsi);
+	}
+}
+
+struct nsinfo *nsinfo__get(struct nsinfo *nsi)
+{
+	struct nsinfo *result;
+
+	if (RC_CHK_GET(result, nsi))
+		refcount_inc(nsinfo__refcnt(nsi));
+
+	return result;
+}
+
+void nsinfo__put(struct nsinfo *nsi)
+{
+	if (nsi && refcount_dec_and_test(nsinfo__refcnt(nsi)))
+		nsinfo__delete(nsi);
+	else
+		RC_CHK_PUT(nsi);
+}
+
+bool nsinfo__need_setns(const struct nsinfo *nsi)
+{
+	return RC_CHK_ACCESS(nsi)->need_setns;
+}
+
+void nsinfo__clear_need_setns(struct nsinfo *nsi)
+{
+	RC_CHK_ACCESS(nsi)->need_setns = false;
+}
+
+pid_t nsinfo__tgid(const struct nsinfo  *nsi)
+{
+	return RC_CHK_ACCESS(nsi)->tgid;
+}
+
+pid_t nsinfo__nstgid(const struct nsinfo  *nsi)
+{
+	return RC_CHK_ACCESS(nsi)->nstgid;
+}
+
+pid_t nsinfo__pid(const struct nsinfo  *nsi)
+{
+	return RC_CHK_ACCESS(nsi)->pid;
+}
+
+bool nsinfo__in_pidns(const struct nsinfo *nsi)
+{
+	return RC_CHK_ACCESS(nsi)->in_pidns;
+}
+
+void nsinfo__set_in_pidns(struct nsinfo *nsi)
+{
+	RC_CHK_ACCESS(nsi)->in_pidns = true;
+}
+
+void nsinfo__mountns_enter(struct nsinfo *nsi,
+				  struct nscookie *nc)
+{
+	char curpath[PATH_MAX];
+	int oldns = -1;
+	int newns = -1;
+	char *oldcwd = NULL;
+
+	if (nc == NULL)
+		return;
+
+	nc->oldns = -1;
+	nc->newns = -1;
+
+	if (!nsi || !nsinfo__need_setns(nsi))
+		return;
+
+	if (!getcwd(curpath, sizeof(curpath)))
+		return;
+
+	oldcwd = strdup(curpath);
+	if (!oldcwd)
+		return;
+
+	oldns = open("/proc/self/ns/mnt", O_RDONLY);
+	if (oldns < 0)
+		goto errout;
+
+	newns = open(nsinfo__mntns_path(nsi), O_RDONLY);
+	if (newns < 0)
+		goto errout;
+
+	if (setns(newns, CLONE_NEWNS) < 0)
+		goto errout;
+
+	nc->oldcwd = oldcwd;
+	nc->oldns = oldns;
+	nc->newns = newns;
+	return;
+
+errout:
+	free(oldcwd);
+	if (oldns > -1)
+		close(oldns);
+	if (newns > -1)
+		close(newns);
+}
+
+void nsinfo__mountns_exit(struct nscookie *nc)
+{
+	if (nc == NULL || nc->oldns == -1 || nc->newns == -1 || !nc->oldcwd)
+		return;
+
+	setns(nc->oldns, CLONE_NEWNS);
+
+	if (nc->oldcwd) {
+		WARN_ON_ONCE(chdir(nc->oldcwd));
+		zfree(&nc->oldcwd);
+	}
+
+	if (nc->oldns > -1) {
+		close(nc->oldns);
+		nc->oldns = -1;
+	}
+
+	if (nc->newns > -1) {
+		close(nc->newns);
+		nc->newns = -1;
+	}
+}
+
+char *nsinfo__realpath(const char *path, struct nsinfo *nsi)
+{
+	char *rpath;
+	struct nscookie nsc;
+
+	nsinfo__mountns_enter(nsi, &nsc);
+	rpath = realpath(path, NULL);
+	nsinfo__mountns_exit(&nsc);
+
+	return rpath;
+}
+
+int nsinfo__stat(const char *filename, struct stat *st, struct nsinfo *nsi)
+{
+	int ret;
+	struct nscookie nsc;
+
+	nsinfo__mountns_enter(nsi, &nsc);
+	ret = stat(filename, st);
+	nsinfo__mountns_exit(&nsc);
+
+	return ret;
+}
+
+bool nsinfo__is_in_root_namespace(void)
+{
+	pid_t tgid = 0, nstgid = 0;
+	bool in_pidns = false;
+
+	nsinfo__get_nspid(&tgid, &nstgid, &in_pidns, "/proc/self/status");
+	return !in_pidns;
+}