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, 262 insertions, 0 deletions

diff --git a/drivers/base/topology.c b/drivers/base/topology.c
new file mode 100644
index 000000000..c890e2a5b
--- /dev/null
+++ b/drivers/base/topology.c
@@ -0,0 +1,262 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * driver/base/topology.c - Populate sysfs with cpu topology information
+ *
+ * Written by: Zhang Yanmin, Intel Corporation
+ *
+ * Copyright (C) 2006, Intel Corp.
+ *
+ * All rights reserved.
+ */
+#include <linux/mm.h>
+#include <linux/cpu.h>
+#include <linux/module.h>
+#include <linux/hardirq.h>
+#include <linux/topology.h>
+
+#define define_id_show_func(name, fmt)					\
+static ssize_t name##_show(struct device *dev,				\
+			   struct device_attribute *attr, char *buf)	\
+{									\
+	return sysfs_emit(buf, fmt "\n", topology_##name(dev->id));	\
+}
+
+#define define_siblings_read_func(name, mask)					\
+static ssize_t name##_read(struct file *file, struct kobject *kobj,		\
+			   const struct bin_attribute *attr, char *buf,		\
+			   loff_t off, size_t count)				\
+{										\
+	struct device *dev = kobj_to_dev(kobj);                                 \
+	cpumask_var_t mask;							\
+	ssize_t n;								\
+										\
+	if (!alloc_cpumask_var(&mask, GFP_KERNEL))				\
+		return -ENOMEM;							\
+										\
+	cpumask_copy(mask, topology_##mask(dev->id));				\
+	n = cpumap_print_bitmask_to_buf(buf, mask, off, count);			\
+	free_cpumask_var(mask);							\
+										\
+	return n;								\
+}										\
+										\
+static ssize_t name##_list_read(struct file *file, struct kobject *kobj,	\
+				const struct bin_attribute *attr, char *buf,	\
+				loff_t off, size_t count)			\
+{										\
+	struct device *dev = kobj_to_dev(kobj);					\
+	cpumask_var_t mask;							\
+	ssize_t n;								\
+										\
+	if (!alloc_cpumask_var(&mask, GFP_KERNEL))				\
+		return -ENOMEM;							\
+										\
+	cpumask_copy(mask, topology_##mask(dev->id));				\
+	n = cpumap_print_list_to_buf(buf, mask, off, count);			\
+	free_cpumask_var(mask);							\
+										\
+	return n;								\
+}
+
+define_id_show_func(physical_package_id, "%d");
+static DEVICE_ATTR_RO(physical_package_id);
+
+#ifdef TOPOLOGY_DIE_SYSFS
+define_id_show_func(die_id, "%d");
+static DEVICE_ATTR_RO(die_id);
+#endif
+
+#ifdef TOPOLOGY_CLUSTER_SYSFS
+define_id_show_func(cluster_id, "%d");
+static DEVICE_ATTR_RO(cluster_id);
+#endif
+
+define_id_show_func(core_id, "%d");
+static DEVICE_ATTR_RO(core_id);
+
+define_id_show_func(ppin, "0x%llx");
+static DEVICE_ATTR_ADMIN_RO(ppin);
+
+define_siblings_read_func(thread_siblings, sibling_cpumask);
+static const BIN_ATTR_RO(thread_siblings, CPUMAP_FILE_MAX_BYTES);
+static const BIN_ATTR_RO(thread_siblings_list, CPULIST_FILE_MAX_BYTES);
+
+define_siblings_read_func(core_cpus, sibling_cpumask);
+static const BIN_ATTR_RO(core_cpus, CPUMAP_FILE_MAX_BYTES);
+static const BIN_ATTR_RO(core_cpus_list, CPULIST_FILE_MAX_BYTES);
+
+define_siblings_read_func(core_siblings, core_cpumask);
+static const BIN_ATTR_RO(core_siblings, CPUMAP_FILE_MAX_BYTES);
+static const BIN_ATTR_RO(core_siblings_list, CPULIST_FILE_MAX_BYTES);
+
+#ifdef TOPOLOGY_CLUSTER_SYSFS
+define_siblings_read_func(cluster_cpus, cluster_cpumask);
+static const BIN_ATTR_RO(cluster_cpus, CPUMAP_FILE_MAX_BYTES);
+static const BIN_ATTR_RO(cluster_cpus_list, CPULIST_FILE_MAX_BYTES);
+#endif
+
+#ifdef TOPOLOGY_DIE_SYSFS
+define_siblings_read_func(die_cpus, die_cpumask);
+static const BIN_ATTR_RO(die_cpus, CPUMAP_FILE_MAX_BYTES);
+static const BIN_ATTR_RO(die_cpus_list, CPULIST_FILE_MAX_BYTES);
+#endif
+
+define_siblings_read_func(package_cpus, core_cpumask);
+static const BIN_ATTR_RO(package_cpus, CPUMAP_FILE_MAX_BYTES);
+static const BIN_ATTR_RO(package_cpus_list, CPULIST_FILE_MAX_BYTES);
+
+#ifdef TOPOLOGY_BOOK_SYSFS
+define_id_show_func(book_id, "%d");
+static DEVICE_ATTR_RO(book_id);
+define_siblings_read_func(book_siblings, book_cpumask);
+static const BIN_ATTR_RO(book_siblings, CPUMAP_FILE_MAX_BYTES);
+static const BIN_ATTR_RO(book_siblings_list, CPULIST_FILE_MAX_BYTES);
+#endif
+
+#ifdef TOPOLOGY_DRAWER_SYSFS
+define_id_show_func(drawer_id, "%d");
+static DEVICE_ATTR_RO(drawer_id);
+define_siblings_read_func(drawer_siblings, drawer_cpumask);
+static const BIN_ATTR_RO(drawer_siblings, CPUMAP_FILE_MAX_BYTES);
+static const BIN_ATTR_RO(drawer_siblings_list, CPULIST_FILE_MAX_BYTES);
+#endif
+
+static const struct bin_attribute *const bin_attrs[] = {
+	&bin_attr_core_cpus,
+	&bin_attr_core_cpus_list,
+	&bin_attr_thread_siblings,
+	&bin_attr_thread_siblings_list,
+	&bin_attr_core_siblings,
+	&bin_attr_core_siblings_list,
+#ifdef TOPOLOGY_CLUSTER_SYSFS
+	&bin_attr_cluster_cpus,
+	&bin_attr_cluster_cpus_list,
+#endif
+#ifdef TOPOLOGY_DIE_SYSFS
+	&bin_attr_die_cpus,
+	&bin_attr_die_cpus_list,
+#endif
+	&bin_attr_package_cpus,
+	&bin_attr_package_cpus_list,
+#ifdef TOPOLOGY_BOOK_SYSFS
+	&bin_attr_book_siblings,
+	&bin_attr_book_siblings_list,
+#endif
+#ifdef TOPOLOGY_DRAWER_SYSFS
+	&bin_attr_drawer_siblings,
+	&bin_attr_drawer_siblings_list,
+#endif
+	NULL
+};
+
+static struct attribute *default_attrs[] = {
+	&dev_attr_physical_package_id.attr,
+#ifdef TOPOLOGY_DIE_SYSFS
+	&dev_attr_die_id.attr,
+#endif
+#ifdef TOPOLOGY_CLUSTER_SYSFS
+	&dev_attr_cluster_id.attr,
+#endif
+	&dev_attr_core_id.attr,
+#ifdef TOPOLOGY_BOOK_SYSFS
+	&dev_attr_book_id.attr,
+#endif
+#ifdef TOPOLOGY_DRAWER_SYSFS
+	&dev_attr_drawer_id.attr,
+#endif
+	&dev_attr_ppin.attr,
+	NULL
+};
+
+static umode_t topology_is_visible(struct kobject *kobj,
+				   struct attribute *attr, int unused)
+{
+	if (attr == &dev_attr_ppin.attr && !topology_ppin(kobj_to_dev(kobj)->id))
+		return 0;
+
+	return attr->mode;
+}
+
+static const struct attribute_group topology_attr_group = {
+	.attrs = default_attrs,
+	.bin_attrs = bin_attrs,
+	.is_visible = topology_is_visible,
+	.name = "topology"
+};
+
+/* Add/Remove cpu_topology interface for CPU device */
+static int topology_add_dev(unsigned int cpu)
+{
+	struct device *dev = get_cpu_device(cpu);
+
+	return sysfs_create_group(&dev->kobj, &topology_attr_group);
+}
+
+static int topology_remove_dev(unsigned int cpu)
+{
+	struct device *dev = get_cpu_device(cpu);
+
+	sysfs_remove_group(&dev->kobj, &topology_attr_group);
+	return 0;
+}
+
+static int __init topology_sysfs_init(void)
+{
+	return cpuhp_setup_state(CPUHP_TOPOLOGY_PREPARE,
+				 "base/topology:prepare", topology_add_dev,
+				 topology_remove_dev);
+}
+
+device_initcall(topology_sysfs_init);
+
+DEFINE_PER_CPU(unsigned long, cpu_scale) = SCHED_CAPACITY_SCALE;
+EXPORT_PER_CPU_SYMBOL_GPL(cpu_scale);
+
+void topology_set_cpu_scale(unsigned int cpu, unsigned long capacity)
+{
+	per_cpu(cpu_scale, cpu) = capacity;
+}
+
+static ssize_t cpu_capacity_show(struct device *dev,
+				 struct device_attribute *attr,
+				 char *buf)
+{
+	struct cpu *cpu = container_of(dev, struct cpu, dev);
+
+	return sysfs_emit(buf, "%lu\n", topology_get_cpu_scale(cpu->dev.id));
+}
+
+static DEVICE_ATTR_RO(cpu_capacity);
+
+static int cpu_capacity_sysctl_add(unsigned int cpu)
+{
+	struct device *cpu_dev = get_cpu_device(cpu);
+
+	if (!cpu_dev)
+		return -ENOENT;
+
+	device_create_file(cpu_dev, &dev_attr_cpu_capacity);
+
+	return 0;
+}
+
+static int cpu_capacity_sysctl_remove(unsigned int cpu)
+{
+	struct device *cpu_dev = get_cpu_device(cpu);
+
+	if (!cpu_dev)
+		return -ENOENT;
+
+	device_remove_file(cpu_dev, &dev_attr_cpu_capacity);
+
+	return 0;
+}
+
+static int register_cpu_capacity_sysctl(void)
+{
+	cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "topology/cpu-capacity",
+			  cpu_capacity_sysctl_add, cpu_capacity_sysctl_remove);
+
+	return 0;
+}
+subsys_initcall(register_cpu_capacity_sysctl);