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, 265 insertions, 0 deletions

diff --git a/drivers/firmware/dmi-id.c b/drivers/firmware/dmi-id.c
new file mode 100644
index 000000000..477a37e2e
--- /dev/null
+++ b/drivers/firmware/dmi-id.c
@@ -0,0 +1,265 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Export SMBIOS/DMI info via sysfs to userspace
+ *
+ * Copyright 2007, Lennart Poettering
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/dmi.h>
+#include <linux/device.h>
+#include <linux/slab.h>
+
+struct dmi_device_attribute{
+	struct device_attribute dev_attr;
+	int field;
+};
+#define to_dmi_dev_attr(_dev_attr) \
+	container_of(_dev_attr, struct dmi_device_attribute, dev_attr)
+
+static ssize_t sys_dmi_field_show(struct device *dev,
+				  struct device_attribute *attr,
+				  char *page)
+{
+	int field = to_dmi_dev_attr(attr)->field;
+	ssize_t len;
+	len = scnprintf(page, PAGE_SIZE, "%s\n", dmi_get_system_info(field));
+	page[len-1] = '\n';
+	return len;
+}
+
+#define DMI_ATTR(_name, _mode, _show, _field)			\
+	{ .dev_attr = __ATTR(_name, _mode, _show, NULL),	\
+	  .field = _field }
+
+#define DEFINE_DMI_ATTR_WITH_SHOW(_name, _mode, _field)		\
+static struct dmi_device_attribute sys_dmi_##_name##_attr =	\
+	DMI_ATTR(_name, _mode, sys_dmi_field_show, _field);
+
+DEFINE_DMI_ATTR_WITH_SHOW(bios_vendor,		0444, DMI_BIOS_VENDOR);
+DEFINE_DMI_ATTR_WITH_SHOW(bios_version,		0444, DMI_BIOS_VERSION);
+DEFINE_DMI_ATTR_WITH_SHOW(bios_date,		0444, DMI_BIOS_DATE);
+DEFINE_DMI_ATTR_WITH_SHOW(sys_vendor,		0444, DMI_SYS_VENDOR);
+DEFINE_DMI_ATTR_WITH_SHOW(bios_release,		0444, DMI_BIOS_RELEASE);
+DEFINE_DMI_ATTR_WITH_SHOW(ec_firmware_release,	0444, DMI_EC_FIRMWARE_RELEASE);
+DEFINE_DMI_ATTR_WITH_SHOW(product_name,		0444, DMI_PRODUCT_NAME);
+DEFINE_DMI_ATTR_WITH_SHOW(product_version,	0444, DMI_PRODUCT_VERSION);
+DEFINE_DMI_ATTR_WITH_SHOW(product_serial,	0400, DMI_PRODUCT_SERIAL);
+DEFINE_DMI_ATTR_WITH_SHOW(product_uuid,		0400, DMI_PRODUCT_UUID);
+DEFINE_DMI_ATTR_WITH_SHOW(product_sku,		0444, DMI_PRODUCT_SKU);
+DEFINE_DMI_ATTR_WITH_SHOW(product_family,	0444, DMI_PRODUCT_FAMILY);
+DEFINE_DMI_ATTR_WITH_SHOW(board_vendor,		0444, DMI_BOARD_VENDOR);
+DEFINE_DMI_ATTR_WITH_SHOW(board_name,		0444, DMI_BOARD_NAME);
+DEFINE_DMI_ATTR_WITH_SHOW(board_version,	0444, DMI_BOARD_VERSION);
+DEFINE_DMI_ATTR_WITH_SHOW(board_serial,		0400, DMI_BOARD_SERIAL);
+DEFINE_DMI_ATTR_WITH_SHOW(board_asset_tag,	0444, DMI_BOARD_ASSET_TAG);
+DEFINE_DMI_ATTR_WITH_SHOW(chassis_vendor,	0444, DMI_CHASSIS_VENDOR);
+DEFINE_DMI_ATTR_WITH_SHOW(chassis_type,		0444, DMI_CHASSIS_TYPE);
+DEFINE_DMI_ATTR_WITH_SHOW(chassis_version,	0444, DMI_CHASSIS_VERSION);
+DEFINE_DMI_ATTR_WITH_SHOW(chassis_serial,	0400, DMI_CHASSIS_SERIAL);
+DEFINE_DMI_ATTR_WITH_SHOW(chassis_asset_tag,	0444, DMI_CHASSIS_ASSET_TAG);
+
+static void ascii_filter(char *d, const char *s)
+{
+	/* Filter out characters we don't want to see in the modalias string */
+	for (; *s; s++)
+		if (*s > ' ' && *s < 127 && *s != ':')
+			*(d++) = *s;
+
+	*d = 0;
+}
+
+static ssize_t get_modalias(char *buffer, size_t buffer_size)
+{
+	/*
+	 * Note new fields need to be added at the end to keep compatibility
+	 * with udev's hwdb which does matches on "`cat dmi/id/modalias`*".
+	 */
+	static const struct mafield {
+		const char *prefix;
+		int field;
+	} fields[] = {
+		{ "bvn", DMI_BIOS_VENDOR },
+		{ "bvr", DMI_BIOS_VERSION },
+		{ "bd",  DMI_BIOS_DATE },
+		{ "br",  DMI_BIOS_RELEASE },
+		{ "efr", DMI_EC_FIRMWARE_RELEASE },
+		{ "svn", DMI_SYS_VENDOR },
+		{ "pn",  DMI_PRODUCT_NAME },
+		{ "pvr", DMI_PRODUCT_VERSION },
+		{ "rvn", DMI_BOARD_VENDOR },
+		{ "rn",  DMI_BOARD_NAME },
+		{ "rvr", DMI_BOARD_VERSION },
+		{ "cvn", DMI_CHASSIS_VENDOR },
+		{ "ct",  DMI_CHASSIS_TYPE },
+		{ "cvr", DMI_CHASSIS_VERSION },
+		{ "sku", DMI_PRODUCT_SKU },
+		{ "pfa", DMI_PRODUCT_FAMILY },
+		{ NULL,  DMI_NONE }
+	};
+
+	ssize_t l, left;
+	char *p;
+	const struct mafield *f;
+
+	strcpy(buffer, "dmi");
+	p = buffer + 3; left = buffer_size - 4;
+
+	for (f = fields; f->prefix && left > 0; f++) {
+		const char *c;
+		char *t;
+
+		c = dmi_get_system_info(f->field);
+		if (!c)
+			continue;
+
+		t = kmalloc(strlen(c) + 1, GFP_KERNEL);
+		if (!t)
+			break;
+		ascii_filter(t, c);
+		l = scnprintf(p, left, ":%s%s", f->prefix, t);
+		kfree(t);
+
+		p += l;
+		left -= l;
+	}
+
+	p[0] = ':';
+	p[1] = 0;
+
+	return p - buffer + 1;
+}
+
+static ssize_t sys_dmi_modalias_show(struct device *dev,
+				     struct device_attribute *attr, char *page)
+{
+	ssize_t r;
+	r = get_modalias(page, PAGE_SIZE-1);
+	page[r] = '\n';
+	page[r+1] = 0;
+	return r+1;
+}
+
+static struct device_attribute sys_dmi_modalias_attr =
+	__ATTR(modalias, 0444, sys_dmi_modalias_show, NULL);
+
+static struct attribute *sys_dmi_attributes[DMI_STRING_MAX+2];
+
+static struct attribute_group sys_dmi_attribute_group = {
+	.attrs = sys_dmi_attributes,
+};
+
+static const struct attribute_group* sys_dmi_attribute_groups[] = {
+	&sys_dmi_attribute_group,
+	NULL
+};
+
+static int dmi_dev_uevent(const struct device *dev, struct kobj_uevent_env *env)
+{
+	ssize_t len;
+
+	if (add_uevent_var(env, "MODALIAS="))
+		return -ENOMEM;
+	len = get_modalias(&env->buf[env->buflen - 1],
+			   sizeof(env->buf) - env->buflen);
+	if (len >= (sizeof(env->buf) - env->buflen))
+		return -ENOMEM;
+	env->buflen += len;
+	return 0;
+}
+
+static void dmi_dev_release(struct device *dev)
+{
+	kfree(dev);
+}
+
+static struct class dmi_class = {
+	.name = "dmi",
+	.dev_release = dmi_dev_release,
+	.dev_uevent = dmi_dev_uevent,
+};
+
+static struct device *dmi_dev;
+
+/* Initialization */
+
+#define ADD_DMI_ATTR(_name, _field) \
+	if (dmi_get_system_info(_field)) \
+		sys_dmi_attributes[i++] = &sys_dmi_##_name##_attr.dev_attr.attr;
+
+/* In a separate function to keep gcc 3.2 happy - do NOT merge this in
+   dmi_id_init! */
+static void __init dmi_id_init_attr_table(void)
+{
+	int i;
+
+	/* Not necessarily all DMI fields are available on all
+	 * systems, hence let's built an attribute table of just
+	 * what's available */
+	i = 0;
+	ADD_DMI_ATTR(bios_vendor,       DMI_BIOS_VENDOR);
+	ADD_DMI_ATTR(bios_version,      DMI_BIOS_VERSION);
+	ADD_DMI_ATTR(bios_date,         DMI_BIOS_DATE);
+	ADD_DMI_ATTR(bios_release,      DMI_BIOS_RELEASE);
+	ADD_DMI_ATTR(ec_firmware_release, DMI_EC_FIRMWARE_RELEASE);
+	ADD_DMI_ATTR(sys_vendor,        DMI_SYS_VENDOR);
+	ADD_DMI_ATTR(product_name,      DMI_PRODUCT_NAME);
+	ADD_DMI_ATTR(product_version,   DMI_PRODUCT_VERSION);
+	ADD_DMI_ATTR(product_serial,    DMI_PRODUCT_SERIAL);
+	ADD_DMI_ATTR(product_uuid,      DMI_PRODUCT_UUID);
+	ADD_DMI_ATTR(product_family,    DMI_PRODUCT_FAMILY);
+	ADD_DMI_ATTR(product_sku,       DMI_PRODUCT_SKU);
+	ADD_DMI_ATTR(board_vendor,      DMI_BOARD_VENDOR);
+	ADD_DMI_ATTR(board_name,        DMI_BOARD_NAME);
+	ADD_DMI_ATTR(board_version,     DMI_BOARD_VERSION);
+	ADD_DMI_ATTR(board_serial,      DMI_BOARD_SERIAL);
+	ADD_DMI_ATTR(board_asset_tag,   DMI_BOARD_ASSET_TAG);
+	ADD_DMI_ATTR(chassis_vendor,    DMI_CHASSIS_VENDOR);
+	ADD_DMI_ATTR(chassis_type,      DMI_CHASSIS_TYPE);
+	ADD_DMI_ATTR(chassis_version,   DMI_CHASSIS_VERSION);
+	ADD_DMI_ATTR(chassis_serial,    DMI_CHASSIS_SERIAL);
+	ADD_DMI_ATTR(chassis_asset_tag, DMI_CHASSIS_ASSET_TAG);
+	sys_dmi_attributes[i++] = &sys_dmi_modalias_attr.attr;
+}
+
+static int __init dmi_id_init(void)
+{
+	int ret;
+
+	if (!dmi_available)
+		return -ENODEV;
+
+	dmi_id_init_attr_table();
+
+	ret = class_register(&dmi_class);
+	if (ret)
+		return ret;
+
+	dmi_dev = kzalloc_obj(*dmi_dev);
+	if (!dmi_dev) {
+		ret = -ENOMEM;
+		goto fail_class_unregister;
+	}
+
+	dmi_dev->class = &dmi_class;
+	dev_set_name(dmi_dev, "id");
+	dmi_dev->groups = sys_dmi_attribute_groups;
+
+	ret = device_register(dmi_dev);
+	if (ret)
+		goto fail_put_dmi_dev;
+
+	return 0;
+
+fail_put_dmi_dev:
+	put_device(dmi_dev);
+
+fail_class_unregister:
+	class_unregister(&dmi_class);
+
+	return ret;
+}
+
+arch_initcall(dmi_id_init);