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, 182 insertions, 0 deletions

diff --git a/samples/hidraw/hid-example.c b/samples/hidraw/hid-example.c
new file mode 100644
index 000000000..0f73ace3c
--- /dev/null
+++ b/samples/hidraw/hid-example.c
@@ -0,0 +1,182 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Hidraw Userspace Example
+ *
+ * Copyright (c) 2010 Alan Ott <alan@signal11.us>
+ * Copyright (c) 2010 Signal 11 Software
+ *
+ * The code may be used by anyone for any purpose,
+ * and can serve as a starting point for developing
+ * applications using hidraw.
+ */
+
+/* Linux */
+#include <linux/types.h>
+#include <linux/input.h>
+#include <linux/hidraw.h>
+
+/*
+ * Ugly hack to work around failing compilation on systems that don't
+ * yet populate new version of hidraw.h to userspace.
+ */
+#ifndef HIDIOCSFEATURE
+#warning Please have your distro update the userspace kernel headers
+#define HIDIOCSFEATURE(len)    _IOC(_IOC_WRITE|_IOC_READ, 'H', 0x06, len)
+#define HIDIOCGFEATURE(len)    _IOC(_IOC_WRITE|_IOC_READ, 'H', 0x07, len)
+#endif
+
+/* Unix */
+#include <sys/ioctl.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+/* C */
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include <errno.h>
+
+const char *bus_str(int bus);
+
+int main(int argc, char **argv)
+{
+	int fd;
+	int i, res, desc_size = 0;
+	char buf[256];
+	struct hidraw_report_descriptor rpt_desc;
+	struct hidraw_devinfo info;
+	char *device = "/dev/hidraw0";
+
+	if (argc > 1)
+		device = argv[1];
+
+	/* Open the Device with non-blocking reads. In real life,
+	   don't use a hard coded path; use libudev instead. */
+	fd = open(device, O_RDWR|O_NONBLOCK);
+
+	if (fd < 0) {
+		perror("Unable to open device");
+		return 1;
+	}
+
+	memset(&rpt_desc, 0x0, sizeof(rpt_desc));
+	memset(&info, 0x0, sizeof(info));
+	memset(buf, 0x0, sizeof(buf));
+
+	/* Get Report Descriptor Size */
+	res = ioctl(fd, HIDIOCGRDESCSIZE, &desc_size);
+	if (res < 0)
+		perror("HIDIOCGRDESCSIZE");
+	else
+		printf("Report Descriptor Size: %d\n", desc_size);
+
+	/* Get Report Descriptor */
+	rpt_desc.size = desc_size;
+	res = ioctl(fd, HIDIOCGRDESC, &rpt_desc);
+	if (res < 0) {
+		perror("HIDIOCGRDESC");
+	} else {
+		printf("Report Descriptor:\n");
+		for (i = 0; i < rpt_desc.size; i++)
+			printf("%hhx ", rpt_desc.value[i]);
+		puts("\n");
+	}
+
+	/* Get Raw Name */
+	res = ioctl(fd, HIDIOCGRAWNAME(256), buf);
+	if (res < 0)
+		perror("HIDIOCGRAWNAME");
+	else
+		printf("Raw Name: %s\n", buf);
+
+	/* Get Physical Location */
+	res = ioctl(fd, HIDIOCGRAWPHYS(256), buf);
+	if (res < 0)
+		perror("HIDIOCGRAWPHYS");
+	else
+		printf("Raw Phys: %s\n", buf);
+
+	/* Get Raw Info */
+	res = ioctl(fd, HIDIOCGRAWINFO, &info);
+	if (res < 0) {
+		perror("HIDIOCGRAWINFO");
+	} else {
+		printf("Raw Info:\n");
+		printf("\tbustype: %d (%s)\n",
+			info.bustype, bus_str(info.bustype));
+		printf("\tvendor: 0x%04hx\n", info.vendor);
+		printf("\tproduct: 0x%04hx\n", info.product);
+	}
+
+	/* Set Feature */
+	buf[0] = 0x9; /* Report Number */
+	buf[1] = 0xff;
+	buf[2] = 0xff;
+	buf[3] = 0xff;
+	res = ioctl(fd, HIDIOCSFEATURE(4), buf);
+	if (res < 0)
+		perror("HIDIOCSFEATURE");
+	else
+		printf("ioctl HIDIOCSFEATURE returned: %d\n", res);
+
+	/* Get Feature */
+	buf[0] = 0x9; /* Report Number */
+	res = ioctl(fd, HIDIOCGFEATURE(256), buf);
+	if (res < 0) {
+		perror("HIDIOCGFEATURE");
+	} else {
+		printf("ioctl HIDIOCGFEATURE returned: %d\n", res);
+		printf("Report data:\n\t");
+		for (i = 0; i < res; i++)
+			printf("%hhx ", buf[i]);
+		puts("\n");
+	}
+
+	/* Send a Report to the Device */
+	buf[0] = 0x1; /* Report Number */
+	buf[1] = 0x77;
+	res = write(fd, buf, 2);
+	if (res < 0) {
+		printf("Error: %d\n", errno);
+		perror("write");
+	} else {
+		printf("write() wrote %d bytes\n", res);
+	}
+
+	/* Get a report from the device */
+	res = read(fd, buf, 16);
+	if (res < 0) {
+		perror("read");
+	} else {
+		printf("read() read %d bytes:\n\t", res);
+		for (i = 0; i < res; i++)
+			printf("%hhx ", buf[i]);
+		puts("\n");
+	}
+	close(fd);
+	return 0;
+}
+
+const char *
+bus_str(int bus)
+{
+	switch (bus) {
+	case BUS_USB:
+		return "USB";
+		break;
+	case BUS_HIL:
+		return "HIL";
+		break;
+	case BUS_BLUETOOTH:
+		return "Bluetooth";
+		break;
+	case BUS_VIRTUAL:
+		return "Virtual";
+		break;
+	default:
+		return "Other";
+		break;
+	}
+}