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, 383 insertions, 0 deletions

diff --git a/tools/perf/tests/vmlinux-kallsyms.c b/tools/perf/tests/vmlinux-kallsyms.c
new file mode 100644
index 000000000..9396c8a77
--- /dev/null
+++ b/tools/perf/tests/vmlinux-kallsyms.c
@@ -0,0 +1,383 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/compiler.h>
+#include <linux/rbtree.h>
+#include <inttypes.h>
+#include <string.h>
+#include <ctype.h>
+#include <stdlib.h>
+#include "dso.h"
+#include "map.h"
+#include "symbol.h"
+#include <internal/lib.h> // page_size
+#include "tests.h"
+#include "debug.h"
+#include "machine.h"
+
+#define UM(x) map__unmap_ip(kallsyms_map, (x))
+
+static bool is_ignored_symbol(const char *name, char type)
+{
+	/* Symbol names that exactly match to the following are ignored.*/
+	static const char * const ignored_symbols[] = {
+		/*
+		 * Symbols which vary between passes. Passes 1 and 2 must have
+		 * identical symbol lists. The kallsyms_* symbols below are
+		 * only added after pass 1, they would be included in pass 2
+		 * when --all-symbols is specified so exclude them to get a
+		 * stable symbol list.
+		 */
+		"kallsyms_offsets",
+		"kallsyms_num_syms",
+		"kallsyms_names",
+		"kallsyms_markers",
+		"kallsyms_token_table",
+		"kallsyms_token_index",
+		/* Exclude linker generated symbols which vary between passes */
+		"_SDA_BASE_",		/* ppc */
+		"_SDA2_BASE_",		/* ppc */
+		NULL
+	};
+
+	/* Symbol names that begin with the following are ignored.*/
+	static const char * const ignored_prefixes[] = {
+		"$",			/* local symbols for ARM, MIPS, etc. */
+		".L",			/* local labels, .LBB,.Ltmpxxx,.L__unnamed_xx,.LASANPC, etc. */
+		"__crc_",		/* modversions */
+		"__efistub_",		/* arm64 EFI stub namespace */
+		"__kvm_nvhe_$",		/* arm64 local symbols in non-VHE KVM namespace */
+		"__kvm_nvhe_.L",	/* arm64 local symbols in non-VHE KVM namespace */
+		"__AArch64ADRPThunk_",	/* arm64 lld */
+		"__ARMV5PILongThunk_",	/* arm lld */
+		"__ARMV7PILongThunk_",
+		"__ThumbV7PILongThunk_",
+		"__LA25Thunk_",		/* mips lld */
+		"__microLA25Thunk_",
+		NULL
+	};
+
+	/* Symbol names that end with the following are ignored.*/
+	static const char * const ignored_suffixes[] = {
+		"_from_arm",		/* arm */
+		"_from_thumb",		/* arm */
+		"_veneer",		/* arm */
+		NULL
+	};
+
+	/* Symbol names that contain the following are ignored.*/
+	static const char * const ignored_matches[] = {
+		".long_branch.",	/* ppc stub */
+		".plt_branch.",		/* ppc stub */
+		NULL
+	};
+
+	const char * const *p;
+
+	for (p = ignored_symbols; *p; p++)
+		if (!strcmp(name, *p))
+			return true;
+
+	for (p = ignored_prefixes; *p; p++)
+		if (!strncmp(name, *p, strlen(*p)))
+			return true;
+
+	for (p = ignored_suffixes; *p; p++) {
+		int l = strlen(name) - strlen(*p);
+
+		if (l >= 0 && !strcmp(name + l, *p))
+			return true;
+	}
+
+	for (p = ignored_matches; *p; p++) {
+		if (strstr(name, *p))
+			return true;
+	}
+
+	if (type == 'U' || type == 'u')
+		return true;
+	/* exclude debugging symbols */
+	if (type == 'N' || type == 'n')
+		return true;
+
+	if (toupper(type) == 'A') {
+		/* Keep these useful absolute symbols */
+		if (strcmp(name, "__kernel_syscall_via_break") &&
+		    strcmp(name, "__kernel_syscall_via_epc") &&
+		    strcmp(name, "__kernel_sigtramp") &&
+		    strcmp(name, "__gp"))
+			return true;
+	}
+
+	return false;
+}
+
+struct test__vmlinux_matches_kallsyms_cb_args {
+	struct machine kallsyms;
+	struct map *vmlinux_map;
+	bool header_printed;
+};
+
+static int test__vmlinux_matches_kallsyms_cb1(struct map *map, void *data)
+{
+	struct test__vmlinux_matches_kallsyms_cb_args *args = data;
+	struct dso *dso = map__dso(map);
+	/*
+	 * If it is the kernel, kallsyms is always "[kernel.kallsyms]", while
+	 * the kernel will have the path for the vmlinux file being used, so use
+	 * the short name, less descriptive but the same ("[kernel]" in both
+	 * cases.
+	 */
+	struct map *pair = maps__find_by_name(args->kallsyms.kmaps,
+					(dso__kernel(dso) ? dso__short_name(dso) : dso__name(dso)));
+
+	if (pair) {
+		map__set_priv(pair);
+		map__put(pair);
+	} else {
+		if (!args->header_printed) {
+			pr_info("WARN: Maps only in vmlinux:\n");
+			args->header_printed = true;
+		}
+		map__fprintf(map, stderr);
+	}
+	return 0;
+}
+
+static int test__vmlinux_matches_kallsyms_cb2(struct map *map, void *data)
+{
+	struct test__vmlinux_matches_kallsyms_cb_args *args = data;
+	struct map *pair;
+	u64 mem_start = map__unmap_ip(args->vmlinux_map, map__start(map));
+	u64 mem_end = map__unmap_ip(args->vmlinux_map, map__end(map));
+
+	pair = maps__find(args->kallsyms.kmaps, mem_start);
+
+	if (pair != NULL && !map__priv(pair) && map__start(pair) == mem_start) {
+		struct dso *dso = map__dso(map);
+
+		if (!args->header_printed) {
+			pr_info("WARN: Maps in vmlinux with a different name in kallsyms:\n");
+			args->header_printed = true;
+		}
+
+		pr_info("WARN: %" PRIx64 "-%" PRIx64 " %" PRIx64 " %s in kallsyms as",
+			map__start(map), map__end(map), map__pgoff(map), dso__name(dso));
+		if (mem_end != map__end(pair))
+			pr_info(":\nWARN: *%" PRIx64 "-%" PRIx64 " %" PRIx64,
+				map__start(pair), map__end(pair), map__pgoff(pair));
+		pr_info(" %s\n", dso__name(dso));
+		map__set_priv(pair);
+	}
+	map__put(pair);
+	return 0;
+}
+
+static int test__vmlinux_matches_kallsyms_cb3(struct map *map, void *data)
+{
+	struct test__vmlinux_matches_kallsyms_cb_args *args = data;
+
+	if (!map__priv(map)) {
+		if (!args->header_printed) {
+			pr_info("WARN: Maps only in kallsyms:\n");
+			args->header_printed = true;
+		}
+		map__fprintf(map, stderr);
+	}
+	return 0;
+}
+
+static int test__vmlinux_matches_kallsyms(struct test_suite *test __maybe_unused,
+					int subtest __maybe_unused)
+{
+	int err = TEST_FAIL;
+	struct rb_node *nd;
+	struct symbol *sym;
+	struct map *kallsyms_map;
+	struct machine vmlinux = { 0 };
+	struct maps *maps;
+	u64 mem_start, mem_end;
+	struct test__vmlinux_matches_kallsyms_cb_args args;
+
+	/*
+	 * Step 1:
+	 *
+	 * Init the machines that will hold kernel, modules obtained from
+	 * both vmlinux + .ko files and from /proc/kallsyms split by modules.
+	 */
+	if (machine__init(&args.kallsyms, "", HOST_KERNEL_ID))
+		goto out;
+	if (machine__init(&vmlinux, "", HOST_KERNEL_ID))
+		goto out;
+
+	maps = machine__kernel_maps(&vmlinux);
+
+	/*
+	 * Step 2:
+	 *
+	 * Create the kernel maps for kallsyms and the DSO where we will then
+	 * load /proc/kallsyms. Also create the modules maps from /proc/modules
+	 * and find the .ko files that match them in /lib/modules/`uname -r`/.
+	 */
+	if (machine__create_kernel_maps(&args.kallsyms) < 0) {
+		pr_debug("machine__create_kernel_maps failed");
+		err = TEST_SKIP;
+		goto out;
+	}
+
+	/*
+	 * Step 3:
+	 *
+	 * Load and split /proc/kallsyms into multiple maps, one per module.
+	 * Do not use kcore, as this test was designed before kcore support
+	 * and has parts that only make sense if using the non-kcore code.
+	 * XXX: extend it to stress the kcorre code as well, hint: the list
+	 * of modules extracted from /proc/kcore, in its current form, can't
+	 * be compacted against the list of modules found in the "vmlinux"
+	 * code and with the one got from /proc/modules from the "kallsyms" code.
+	 */
+	if (machine__load_kallsyms(&args.kallsyms, "/proc/kallsyms") <= 0) {
+		pr_debug("machine__load_kallsyms failed");
+		err = TEST_SKIP;
+		goto out;
+	}
+
+	/*
+	 * Step 4:
+	 *
+	 * kallsyms will be internally on demand sorted by name so that we can
+	 * find the reference relocation * symbol, i.e. the symbol we will use
+	 * to see if the running kernel was relocated by checking if it has the
+	 * same value in the vmlinux file we load.
+	 */
+	kallsyms_map = machine__kernel_map(&args.kallsyms);
+
+	/*
+	 * Step 5:
+	 *
+	 * Now repeat step 2, this time for the vmlinux file we'll auto-locate.
+	 */
+	if (machine__create_kernel_maps(&vmlinux) < 0) {
+		pr_info("machine__create_kernel_maps failed");
+		goto out;
+	}
+
+	args.vmlinux_map = machine__kernel_map(&vmlinux);
+
+	/*
+	 * Step 6:
+	 *
+	 * Locate a vmlinux file in the vmlinux path that has a buildid that
+	 * matches the one of the running kernel.
+	 *
+	 * While doing that look if we find the ref reloc symbol, if we find it
+	 * we'll have its ref_reloc_symbol.unrelocated_addr and then
+	 * maps__reloc_vmlinux will notice and set proper ->[un]map_ip routines
+	 * to fixup the symbols.
+	 */
+	if (machine__load_vmlinux_path(&vmlinux) <= 0) {
+		pr_info("Couldn't find a vmlinux that matches the kernel running on this machine, skipping test\n");
+		err = TEST_SKIP;
+		goto out;
+	}
+
+	err = 0;
+	/*
+	 * Step 7:
+	 *
+	 * Now look at the symbols in the vmlinux DSO and check if we find all of them
+	 * in the kallsyms dso. For the ones that are in both, check its names and
+	 * end addresses too.
+	 */
+	map__for_each_symbol(args.vmlinux_map, sym, nd) {
+		struct symbol *pair, *first_pair;
+
+		sym  = rb_entry(nd, struct symbol, rb_node);
+
+		if (sym->start == sym->end)
+			continue;
+
+		mem_start = map__unmap_ip(args.vmlinux_map, sym->start);
+		mem_end = map__unmap_ip(args.vmlinux_map, sym->end);
+
+		first_pair = machine__find_kernel_symbol(&args.kallsyms, mem_start, NULL);
+		pair = first_pair;
+
+		if (pair && UM(pair->start) == mem_start) {
+next_pair:
+			if (arch__compare_symbol_names(sym->name, pair->name) == 0) {
+				/*
+				 * kallsyms don't have the symbol end, so we
+				 * set that by using the next symbol start - 1,
+				 * in some cases we get this up to a page
+				 * wrong, trace_kmalloc when I was developing
+				 * this code was one such example, 2106 bytes
+				 * off the real size. More than that and we
+				 * _really_ have a problem.
+				 */
+				s64 skew = mem_end - UM(pair->end);
+				if (llabs(skew) >= page_size)
+					pr_debug("WARN: %#" PRIx64 ": diff end addr for %s v: %#" PRIx64 " k: %#" PRIx64 "\n",
+						 mem_start, sym->name, mem_end,
+						 UM(pair->end));
+
+				/*
+				 * Do not count this as a failure, because we
+				 * could really find a case where it's not
+				 * possible to get proper function end from
+				 * kallsyms.
+				 */
+				continue;
+			} else {
+				pair = machine__find_kernel_symbol_by_name(&args.kallsyms,
+									   sym->name, NULL);
+				if (pair) {
+					if (UM(pair->start) == mem_start)
+						goto next_pair;
+
+					pr_debug("WARN: %#" PRIx64 ": diff name v: %s k: %s\n",
+						 mem_start, sym->name, pair->name);
+				} else {
+					pr_debug("WARN: %#" PRIx64 ": diff name v: %s k: %s\n",
+						 mem_start, sym->name, first_pair->name);
+				}
+
+				continue;
+			}
+		} else if (mem_start == map__end(args.kallsyms.vmlinux_map)) {
+			/*
+			 * Ignore aliases to _etext, i.e. to the end of the kernel text area,
+			 * such as __indirect_thunk_end.
+			 */
+			continue;
+		} else if (is_ignored_symbol(sym->name, symbol__type(sym))) {
+			/*
+			 * Ignore hidden symbols, see scripts/kallsyms.c for the details
+			 */
+			continue;
+		} else {
+			pr_debug("ERR : %#" PRIx64 ": %s not on kallsyms\n",
+				 mem_start, sym->name);
+		}
+
+		err = -1;
+	}
+
+	if (verbose <= 0)
+		goto out;
+
+	args.header_printed = false;
+	maps__for_each_map(maps, test__vmlinux_matches_kallsyms_cb1, &args);
+
+	args.header_printed = false;
+	maps__for_each_map(maps, test__vmlinux_matches_kallsyms_cb2, &args);
+
+	args.header_printed = false;
+	maps = machine__kernel_maps(&args.kallsyms);
+	maps__for_each_map(maps, test__vmlinux_matches_kallsyms_cb3, &args);
+
+out:
+	machine__exit(&args.kallsyms);
+	machine__exit(&vmlinux);
+	return err;
+}
+
+DEFINE_SUITE("vmlinux symtab matches kallsyms", vmlinux_matches_kallsyms);