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, 122 insertions, 0 deletions

diff --git a/tools/perf/util/help-unknown-cmd.c b/tools/perf/util/help-unknown-cmd.c
new file mode 100644
index 000000000..a0a46e34f
--- /dev/null
+++ b/tools/perf/util/help-unknown-cmd.c
@@ -0,0 +1,122 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "cache.h"
+#include "config.h"
+#include <poll.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <subcmd/help.h>
+#include "../builtin.h"
+#include "levenshtein.h"
+#include <linux/zalloc.h>
+
+static int autocorrect;
+
+static int perf_unknown_cmd_config(const char *var, const char *value,
+				   void *cb __maybe_unused)
+{
+	if (!strcmp(var, "help.autocorrect"))
+		return perf_config_int(&autocorrect, var,value);
+
+	return 0;
+}
+
+static int levenshtein_compare(const void *p1, const void *p2)
+{
+	const struct cmdname *const *c1 = p1, *const *c2 = p2;
+	const char *s1 = (*c1)->name, *s2 = (*c2)->name;
+	int l1 = (*c1)->len;
+	int l2 = (*c2)->len;
+	return l1 != l2 ? l1 - l2 : strcmp(s1, s2);
+}
+
+static int add_cmd_list(struct cmdnames *cmds, struct cmdnames *old)
+{
+	unsigned int i, nr = cmds->cnt + old->cnt;
+	void *tmp;
+
+	if (nr > cmds->alloc) {
+		/* Choose bigger one to alloc */
+		if (alloc_nr(cmds->alloc) < nr)
+			cmds->alloc = nr;
+		else
+			cmds->alloc = alloc_nr(cmds->alloc);
+		tmp = realloc(cmds->names, cmds->alloc * sizeof(*cmds->names));
+		if (!tmp)
+			return -1;
+		cmds->names = tmp;
+	}
+	for (i = 0; i < old->cnt; i++)
+		cmds->names[cmds->cnt++] = old->names[i];
+	zfree(&old->names);
+	old->cnt = 0;
+	return 0;
+}
+
+const char *help_unknown_cmd(const char *cmd, struct cmdnames *main_cmds)
+{
+	unsigned int i, n = 0, best_similarity = 0;
+	struct cmdnames other_cmds;
+
+	memset(&other_cmds, 0, sizeof(other_cmds));
+
+	perf_config(perf_unknown_cmd_config, NULL);
+
+	load_command_list("perf-", main_cmds, &other_cmds);
+
+	if (add_cmd_list(main_cmds, &other_cmds) < 0) {
+		fprintf(stderr, "ERROR: Failed to allocate command list for unknown command.\n");
+		goto end;
+	}
+	qsort(main_cmds->names, main_cmds->cnt,
+	      sizeof(main_cmds->names), cmdname_compare);
+	uniq(main_cmds);
+
+	if (main_cmds->cnt) {
+		/* This reuses cmdname->len for similarity index */
+		for (i = 0; i < main_cmds->cnt; ++i) {
+			main_cmds->names[i]->len =
+				levenshtein(cmd, main_cmds->names[i]->name,
+					/*swap_penalty=*/0,
+					/*substition_penality=*/2,
+					/*insertion_penality=*/1,
+					/*deletion_penalty=*/1);
+		}
+		qsort(main_cmds->names, main_cmds->cnt,
+		      sizeof(*main_cmds->names), levenshtein_compare);
+
+		best_similarity = main_cmds->names[0]->len;
+		n = 1;
+		while (n < main_cmds->cnt && best_similarity == main_cmds->names[n]->len)
+			++n;
+	}
+
+	if (autocorrect && n == 1) {
+		const char *assumed = main_cmds->names[0]->name;
+
+		main_cmds->names[0] = NULL;
+		clean_cmdnames(&other_cmds);
+		fprintf(stderr, "WARNING: You called a perf program named '%s', "
+			"which does not exist.\n"
+			"Continuing under the assumption that you meant '%s'\n",
+			cmd, assumed);
+		if (autocorrect > 0) {
+			fprintf(stderr, "in %0.1f seconds automatically...\n",
+				(float)autocorrect/10.0);
+			poll(NULL, 0, autocorrect * 100);
+		}
+		return assumed;
+	}
+
+	fprintf(stderr, "perf: '%s' is not a perf-command. See 'perf --help'.\n", cmd);
+
+	if (main_cmds->cnt && best_similarity < 6) {
+		fprintf(stderr, "\nDid you mean %s?\n",
+			n < 2 ? "this": "one of these");
+
+		for (i = 0; i < n; i++)
+			fprintf(stderr, "\t%s\n", main_cmds->names[i]->name);
+	}
+end:
+	clean_cmdnames(&other_cmds);
+	return NULL;
+}