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, 480 insertions, 0 deletions

diff --git a/tools/perf/util/trace-event-read.c b/tools/perf/util/trace-event-read.c
new file mode 100644
index 000000000..ecbbb93f0
--- /dev/null
+++ b/tools/perf/util/trace-event-read.c
@@ -0,0 +1,480 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2009, Steven Rostedt <srostedt@redhat.com>
+ */
+#include <dirent.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdarg.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/wait.h>
+#include <sys/mman.h>
+#include <event-parse.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <errno.h>
+
+#include "trace-event.h"
+#include "debug.h"
+#include "util.h"
+
+static int input_fd;
+
+static ssize_t trace_data_size;
+static bool repipe;
+
+static int __do_read(int fd, void *buf, int size)
+{
+	int rsize = size;
+
+	while (size) {
+		int ret = read(fd, buf, size);
+
+		if (ret <= 0)
+			return -1;
+
+		if (repipe) {
+			int retw = write(STDOUT_FILENO, buf, ret);
+
+			if (retw <= 0 || retw != ret) {
+				pr_debug("repiping input file");
+				return -1;
+			}
+		}
+
+		size -= ret;
+		buf += ret;
+	}
+
+	return rsize;
+}
+
+static int do_read(void *data, int size)
+{
+	int r;
+
+	r = __do_read(input_fd, data, size);
+	if (r <= 0) {
+		pr_debug("reading input file (size expected=%d received=%d)",
+			 size, r);
+		return -1;
+	}
+
+	trace_data_size += r;
+
+	return r;
+}
+
+/* If it fails, the next read will report it */
+static void skip(int size)
+{
+	char buf[BUFSIZ];
+	int r;
+
+	while (size) {
+		r = size > BUFSIZ ? BUFSIZ : size;
+		do_read(buf, r);
+		size -= r;
+	}
+}
+
+static unsigned int read4(struct tep_handle *pevent)
+{
+	unsigned int data;
+
+	if (do_read(&data, 4) < 0)
+		return 0;
+	return tep_read_number(pevent, &data, 4);
+}
+
+static unsigned long long read8(struct tep_handle *pevent)
+{
+	unsigned long long data;
+
+	if (do_read(&data, 8) < 0)
+		return 0;
+	return tep_read_number(pevent, &data, 8);
+}
+
+static char *read_string(void)
+{
+	char buf[BUFSIZ];
+	char *str = NULL;
+	int size = 0;
+	off_t r;
+	char c;
+
+	for (;;) {
+		r = read(input_fd, &c, 1);
+		if (r < 0) {
+			pr_debug("reading input file");
+			goto out;
+		}
+
+		if (!r) {
+			pr_debug("no data");
+			goto out;
+		}
+
+		if (repipe) {
+			int retw = write(STDOUT_FILENO, &c, 1);
+
+			if (retw <= 0 || retw != r) {
+				pr_debug("repiping input file string");
+				goto out;
+			}
+		}
+
+		buf[size++] = c;
+
+		if (!c)
+			break;
+	}
+
+	trace_data_size += size;
+
+	str = malloc(size);
+	if (str)
+		memcpy(str, buf, size);
+out:
+	return str;
+}
+
+static int read_proc_kallsyms(struct tep_handle *pevent)
+{
+	unsigned int size;
+
+	size = read4(pevent);
+	if (!size)
+		return 0;
+	/*
+	 * Just skip it, now that we configure libtraceevent to use the
+	 * tools/perf/ symbol resolver.
+	 *
+	 * We need to skip it so that we can continue parsing old perf.data
+	 * files, that contains this /proc/kallsyms payload.
+	 *
+	 * Newer perf.data files will have just the 4-bytes zeros "kallsyms
+	 * payload", so that older tools can continue reading it and interpret
+	 * it as "no kallsyms payload is present".
+	 */
+	lseek(input_fd, size, SEEK_CUR);
+	trace_data_size += size;
+	return 0;
+}
+
+static int read_ftrace_printk(struct tep_handle *pevent)
+{
+	unsigned int size;
+	char *buf;
+
+	/* it can have 0 size */
+	size = read4(pevent);
+	if (!size)
+		return 0;
+
+	buf = malloc(size + 1);
+	if (buf == NULL)
+		return -1;
+
+	if (do_read(buf, size) < 0) {
+		free(buf);
+		return -1;
+	}
+
+	buf[size] = '\0';
+
+	parse_ftrace_printk(pevent, buf, size);
+
+	free(buf);
+	return 0;
+}
+
+static int read_header_files(struct tep_handle *pevent)
+{
+	unsigned long long size;
+	char *header_page;
+	char buf[BUFSIZ];
+	int ret = 0;
+
+	if (do_read(buf, 12) < 0)
+		return -1;
+
+	if (memcmp(buf, "header_page", 12) != 0) {
+		pr_debug("did not read header page");
+		return -1;
+	}
+
+	size = read8(pevent);
+
+	header_page = malloc(size);
+	if (header_page == NULL)
+		return -1;
+
+	if (do_read(header_page, size) < 0) {
+		pr_debug("did not read header page");
+		free(header_page);
+		return -1;
+	}
+
+	if (!tep_parse_header_page(pevent, header_page, size,
+				   tep_get_long_size(pevent))) {
+		/*
+		 * The commit field in the page is of type long,
+		 * use that instead, since it represents the kernel.
+		 */
+		tep_set_long_size(pevent, tep_get_header_page_size(pevent));
+	}
+	free(header_page);
+
+	if (do_read(buf, 13) < 0)
+		return -1;
+
+	if (memcmp(buf, "header_event", 13) != 0) {
+		pr_debug("did not read header event");
+		return -1;
+	}
+
+	size = read8(pevent);
+	skip(size);
+
+	return ret;
+}
+
+static int read_ftrace_file(struct tep_handle *pevent, unsigned long long size)
+{
+	int ret;
+	char *buf;
+
+	buf = malloc(size);
+	if (buf == NULL) {
+		pr_debug("memory allocation failure\n");
+		return -1;
+	}
+
+	ret = do_read(buf, size);
+	if (ret < 0) {
+		pr_debug("error reading ftrace file.\n");
+		goto out;
+	}
+
+	ret = parse_ftrace_file(pevent, buf, size);
+	if (ret < 0)
+		pr_debug("error parsing ftrace file.\n");
+out:
+	free(buf);
+	return ret;
+}
+
+static int read_event_file(struct tep_handle *pevent, char *sys,
+			   unsigned long long size)
+{
+	int ret;
+	char *buf;
+
+	buf = malloc(size);
+	if (buf == NULL) {
+		pr_debug("memory allocation failure\n");
+		return -1;
+	}
+
+	ret = do_read(buf, size);
+	if (ret < 0)
+		goto out;
+
+	ret = parse_event_file(pevent, buf, size, sys);
+	if (ret < 0)
+		pr_debug("error parsing event file.\n");
+out:
+	free(buf);
+	return ret;
+}
+
+static int read_ftrace_files(struct tep_handle *pevent)
+{
+	unsigned long long size;
+	int count;
+	int i;
+	int ret;
+
+	count = read4(pevent);
+
+	for (i = 0; i < count; i++) {
+		size = read8(pevent);
+		ret = read_ftrace_file(pevent, size);
+		if (ret)
+			return ret;
+	}
+	return 0;
+}
+
+static int read_event_files(struct tep_handle *pevent)
+{
+	unsigned long long size;
+	char *sys;
+	int systems;
+	int count;
+	int i,x;
+	int ret;
+
+	systems = read4(pevent);
+
+	for (i = 0; i < systems; i++) {
+		sys = read_string();
+		if (sys == NULL)
+			return -1;
+
+		count = read4(pevent);
+
+		for (x=0; x < count; x++) {
+			size = read8(pevent);
+			ret = read_event_file(pevent, sys, size);
+			if (ret) {
+				free(sys);
+				return ret;
+			}
+		}
+		free(sys);
+	}
+	return 0;
+}
+
+static int read_saved_cmdline(struct tep_handle *pevent)
+{
+	unsigned long long size;
+	char *buf;
+	int ret;
+
+	/* it can have 0 size */
+	size = read8(pevent);
+	if (!size)
+		return 0;
+
+	buf = malloc(size + 1);
+	if (buf == NULL) {
+		pr_debug("memory allocation failure\n");
+		return -1;
+	}
+
+	ret = do_read(buf, size);
+	if (ret < 0) {
+		pr_debug("error reading saved cmdlines\n");
+		goto out;
+	}
+	buf[ret] = '\0';
+
+	parse_saved_cmdline(pevent, buf, size);
+	ret = 0;
+out:
+	free(buf);
+	return ret;
+}
+
+ssize_t trace_report(int fd, struct trace_event *tevent, bool __repipe)
+{
+	char buf[BUFSIZ];
+	char test[] = { 23, 8, 68 };
+	char *version;
+	int show_version = 0;
+	int show_funcs = 0;
+	int show_printk = 0;
+	ssize_t size = -1;
+	int file_bigendian;
+	int host_bigendian;
+	int file_long_size;
+	int file_page_size;
+	struct tep_handle *pevent = NULL;
+	int err;
+
+	repipe = __repipe;
+	input_fd = fd;
+
+	if (do_read(buf, 3) < 0)
+		return -1;
+	if (memcmp(buf, test, 3) != 0) {
+		pr_debug("no trace data in the file");
+		return -1;
+	}
+
+	if (do_read(buf, 7) < 0)
+		return -1;
+	if (memcmp(buf, "tracing", 7) != 0) {
+		pr_debug("not a trace file (missing 'tracing' tag)");
+		return -1;
+	}
+
+	version = read_string();
+	if (version == NULL)
+		return -1;
+	if (show_version)
+		printf("version = %s\n", version);
+
+	if (do_read(buf, 1) < 0) {
+		free(version);
+		return -1;
+	}
+	file_bigendian = buf[0];
+	host_bigendian = host_is_bigendian() ? 1 : 0;
+
+	if (trace_event__init(tevent)) {
+		pr_debug("trace_event__init failed");
+		goto out;
+	}
+
+	pevent = tevent->pevent;
+
+	tep_set_flag(pevent, TEP_NSEC_OUTPUT);
+	tep_set_file_bigendian(pevent, file_bigendian);
+	tep_set_local_bigendian(pevent, host_bigendian);
+
+	if (do_read(buf, 1) < 0)
+		goto out;
+	file_long_size = buf[0];
+
+	file_page_size = read4(pevent);
+	if (!file_page_size)
+		goto out;
+
+	tep_set_long_size(pevent, file_long_size);
+	tep_set_page_size(pevent, file_page_size);
+
+	err = read_header_files(pevent);
+	if (err)
+		goto out;
+	err = read_ftrace_files(pevent);
+	if (err)
+		goto out;
+	err = read_event_files(pevent);
+	if (err)
+		goto out;
+	err = read_proc_kallsyms(pevent);
+	if (err)
+		goto out;
+	err = read_ftrace_printk(pevent);
+	if (err)
+		goto out;
+	if (atof(version) >= 0.6) {
+		err = read_saved_cmdline(pevent);
+		if (err)
+			goto out;
+	}
+
+	size = trace_data_size;
+	repipe = false;
+
+	if (show_funcs) {
+		tep_print_funcs(pevent);
+	} else if (show_printk) {
+		tep_print_printk(pevent);
+	}
+
+	pevent = NULL;
+
+out:
+	if (pevent)
+		trace_event__cleanup(tevent);
+	free(version);
+	return size;
+}