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, 207 insertions, 0 deletions

diff --git a/drivers/edac/ecs.c b/drivers/edac/ecs.c
new file mode 100644
index 000000000..51c451c7f
--- /dev/null
+++ b/drivers/edac/ecs.c
@@ -0,0 +1,207 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * The generic ECS driver is designed to support control of on-die error
+ * check scrub (e.g., DDR5 ECS). The common sysfs ECS interface abstracts
+ * the control of various ECS functionalities into a unified set of functions.
+ *
+ * Copyright (c) 2024-2025 HiSilicon Limited.
+ */
+
+#include <linux/edac.h>
+
+#define EDAC_ECS_FRU_NAME "ecs_fru"
+
+enum edac_ecs_attributes {
+	ECS_LOG_ENTRY_TYPE,
+	ECS_MODE,
+	ECS_RESET,
+	ECS_THRESHOLD,
+	ECS_MAX_ATTRS
+};
+
+struct edac_ecs_dev_attr {
+	struct device_attribute dev_attr;
+	int fru_id;
+};
+
+struct edac_ecs_fru_context {
+	char name[EDAC_FEAT_NAME_LEN];
+	struct edac_ecs_dev_attr dev_attr[ECS_MAX_ATTRS];
+	struct attribute *ecs_attrs[ECS_MAX_ATTRS + 1];
+	struct attribute_group group;
+};
+
+struct edac_ecs_context {
+	u16 num_media_frus;
+	struct edac_ecs_fru_context *fru_ctxs;
+};
+
+#define TO_ECS_DEV_ATTR(_dev_attr)	\
+	container_of(_dev_attr, struct edac_ecs_dev_attr, dev_attr)
+
+#define EDAC_ECS_ATTR_SHOW(attrib, cb, type, format)				\
+static ssize_t attrib##_show(struct device *ras_feat_dev,			\
+			     struct device_attribute *attr, char *buf)		\
+{										\
+	struct edac_ecs_dev_attr *dev_attr = TO_ECS_DEV_ATTR(attr);		\
+	struct edac_dev_feat_ctx *ctx = dev_get_drvdata(ras_feat_dev);		\
+	const struct edac_ecs_ops *ops = ctx->ecs.ecs_ops;			\
+	type data;								\
+	int ret;								\
+										\
+	ret = ops->cb(ras_feat_dev->parent, ctx->ecs.private,			\
+		      dev_attr->fru_id, &data);					\
+	if (ret)								\
+		return ret;							\
+										\
+	return sysfs_emit(buf, format, data);					\
+}
+
+EDAC_ECS_ATTR_SHOW(log_entry_type, get_log_entry_type, u32, "%u\n")
+EDAC_ECS_ATTR_SHOW(mode, get_mode, u32, "%u\n")
+EDAC_ECS_ATTR_SHOW(threshold, get_threshold, u32, "%u\n")
+
+#define EDAC_ECS_ATTR_STORE(attrib, cb, type, conv_func)			\
+static ssize_t attrib##_store(struct device *ras_feat_dev,			\
+			      struct device_attribute *attr,			\
+			      const char *buf, size_t len)			\
+{										\
+	struct edac_ecs_dev_attr *dev_attr = TO_ECS_DEV_ATTR(attr);		\
+	struct edac_dev_feat_ctx *ctx = dev_get_drvdata(ras_feat_dev);		\
+	const struct edac_ecs_ops *ops = ctx->ecs.ecs_ops;			\
+	type data;								\
+	int ret;								\
+										\
+	ret = conv_func(buf, 0, &data);						\
+	if (ret < 0)								\
+		return ret;							\
+										\
+	ret = ops->cb(ras_feat_dev->parent, ctx->ecs.private,			\
+		      dev_attr->fru_id, data);					\
+	if (ret)								\
+		return ret;							\
+										\
+	return len;								\
+}
+
+EDAC_ECS_ATTR_STORE(log_entry_type, set_log_entry_type, unsigned long, kstrtoul)
+EDAC_ECS_ATTR_STORE(mode, set_mode, unsigned long, kstrtoul)
+EDAC_ECS_ATTR_STORE(reset, reset, unsigned long, kstrtoul)
+EDAC_ECS_ATTR_STORE(threshold, set_threshold, unsigned long, kstrtoul)
+
+static umode_t ecs_attr_visible(struct kobject *kobj, struct attribute *a, int attr_id)
+{
+	struct device *ras_feat_dev = kobj_to_dev(kobj);
+	struct edac_dev_feat_ctx *ctx = dev_get_drvdata(ras_feat_dev);
+	const struct edac_ecs_ops *ops = ctx->ecs.ecs_ops;
+
+	switch (attr_id) {
+	case ECS_LOG_ENTRY_TYPE:
+		if (ops->get_log_entry_type)  {
+			if (ops->set_log_entry_type)
+				return a->mode;
+			else
+				return 0444;
+		}
+		break;
+	case ECS_MODE:
+		if (ops->get_mode) {
+			if (ops->set_mode)
+				return a->mode;
+			else
+				return 0444;
+		}
+		break;
+	case ECS_RESET:
+		if (ops->reset)
+			return a->mode;
+		break;
+	case ECS_THRESHOLD:
+		if (ops->get_threshold) {
+			if (ops->set_threshold)
+				return a->mode;
+			else
+				return 0444;
+		}
+		break;
+	default:
+		break;
+	}
+
+	return 0;
+}
+
+#define EDAC_ECS_ATTR_RO(_name, _fru_id)       \
+	((struct edac_ecs_dev_attr) { .dev_attr = __ATTR_RO(_name), \
+				     .fru_id = _fru_id })
+
+#define EDAC_ECS_ATTR_WO(_name, _fru_id)       \
+	((struct edac_ecs_dev_attr) { .dev_attr = __ATTR_WO(_name), \
+				     .fru_id = _fru_id })
+
+#define EDAC_ECS_ATTR_RW(_name, _fru_id)       \
+	((struct edac_ecs_dev_attr) { .dev_attr = __ATTR_RW(_name), \
+				     .fru_id = _fru_id })
+
+static int ecs_create_desc(struct device *ecs_dev, const struct attribute_group **attr_groups,
+			   u16 num_media_frus)
+{
+	struct edac_ecs_context *ecs_ctx;
+	u32 fru;
+
+	ecs_ctx = devm_kzalloc(ecs_dev, sizeof(*ecs_ctx), GFP_KERNEL);
+	if (!ecs_ctx)
+		return -ENOMEM;
+
+	ecs_ctx->num_media_frus = num_media_frus;
+	ecs_ctx->fru_ctxs = devm_kcalloc(ecs_dev, num_media_frus,
+					 sizeof(*ecs_ctx->fru_ctxs),
+					 GFP_KERNEL);
+	if (!ecs_ctx->fru_ctxs)
+		return -ENOMEM;
+
+	for (fru = 0; fru < num_media_frus; fru++) {
+		struct edac_ecs_fru_context *fru_ctx = &ecs_ctx->fru_ctxs[fru];
+		struct attribute_group *group = &fru_ctx->group;
+		int i;
+
+		fru_ctx->dev_attr[ECS_LOG_ENTRY_TYPE]	= EDAC_ECS_ATTR_RW(log_entry_type, fru);
+		fru_ctx->dev_attr[ECS_MODE]		= EDAC_ECS_ATTR_RW(mode, fru);
+		fru_ctx->dev_attr[ECS_RESET]		= EDAC_ECS_ATTR_WO(reset, fru);
+		fru_ctx->dev_attr[ECS_THRESHOLD]	= EDAC_ECS_ATTR_RW(threshold, fru);
+
+		for (i = 0; i < ECS_MAX_ATTRS; i++) {
+			sysfs_attr_init(&fru_ctx->dev_attr[i].dev_attr.attr);
+			fru_ctx->ecs_attrs[i] = &fru_ctx->dev_attr[i].dev_attr.attr;
+		}
+
+		sprintf(fru_ctx->name, "%s%d", EDAC_ECS_FRU_NAME, fru);
+		group->name = fru_ctx->name;
+		group->attrs = fru_ctx->ecs_attrs;
+		group->is_visible  = ecs_attr_visible;
+
+		attr_groups[fru] = group;
+	}
+
+	return 0;
+}
+
+/**
+ * edac_ecs_get_desc - get EDAC ECS descriptors
+ * @ecs_dev: client device, supports ECS feature
+ * @attr_groups: pointer to attribute group container
+ * @num_media_frus: number of media FRUs in the device
+ *
+ * Return:
+ *  * %0	- Success.
+ *  * %-EINVAL	- Invalid parameters passed.
+ *  * %-ENOMEM	- Dynamic memory allocation failed.
+ */
+int edac_ecs_get_desc(struct device *ecs_dev,
+		      const struct attribute_group **attr_groups, u16 num_media_frus)
+{
+	if (!ecs_dev || !attr_groups || !num_media_frus)
+		return -EINVAL;
+
+	return ecs_create_desc(ecs_dev, attr_groups, num_media_frus);
+}