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, 251 insertions, 0 deletions

diff --git a/net/ethtool/eeprom.c b/net/ethtool/eeprom.c
new file mode 100644
index 000000000..0b8cfeddb
--- /dev/null
+++ b/net/ethtool/eeprom.c
@@ -0,0 +1,251 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <linux/ethtool.h>
+#include <linux/sfp.h>
+
+#include "common.h"
+#include "netlink.h"
+
+struct eeprom_req_info {
+	struct ethnl_req_info	base;
+	u32			offset;
+	u32			length;
+	u8			page;
+	u8			bank;
+	u8			i2c_address;
+};
+
+struct eeprom_reply_data {
+	struct ethnl_reply_data base;
+	u32			length;
+	u8			*data;
+};
+
+#define MODULE_EEPROM_REQINFO(__req_base) \
+	container_of(__req_base, struct eeprom_req_info, base)
+
+#define MODULE_EEPROM_REPDATA(__reply_base) \
+	container_of(__reply_base, struct eeprom_reply_data, base)
+
+static int fallback_set_params(struct eeprom_req_info *request,
+			       struct ethtool_modinfo *modinfo,
+			       struct ethtool_eeprom *eeprom)
+{
+	u32 offset = request->offset;
+	u32 length = request->length;
+
+	if (request->page)
+		offset = request->page * ETH_MODULE_EEPROM_PAGE_LEN + offset;
+
+	if (modinfo->type == ETH_MODULE_SFF_8472 &&
+	    request->i2c_address == 0x51)
+		offset += ETH_MODULE_EEPROM_PAGE_LEN * 2;
+
+	if (offset >= modinfo->eeprom_len)
+		return -EINVAL;
+
+	if (length > modinfo->eeprom_len - offset)
+		return -EINVAL;
+
+	eeprom->cmd = ETHTOOL_GMODULEEEPROM;
+	eeprom->len = length;
+	eeprom->offset = offset;
+
+	return 0;
+}
+
+static int eeprom_fallback(struct eeprom_req_info *request,
+			   struct eeprom_reply_data *reply)
+{
+	struct net_device *dev = reply->base.dev;
+	struct ethtool_modinfo modinfo = {0};
+	struct ethtool_eeprom eeprom = {0};
+	u8 *data;
+	int err;
+
+	modinfo.cmd = ETHTOOL_GMODULEINFO;
+	err = ethtool_get_module_info_call(dev, &modinfo);
+	if (err < 0)
+		return err;
+
+	err = fallback_set_params(request, &modinfo, &eeprom);
+	if (err < 0)
+		return err;
+
+	data = kzalloc(eeprom.len, GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+	err = ethtool_get_module_eeprom_call(dev, &eeprom, data);
+	if (err < 0)
+		goto err_out;
+
+	reply->data = data;
+	reply->length = eeprom.len;
+
+	return 0;
+
+err_out:
+	kfree(data);
+	return err;
+}
+
+static int get_module_eeprom_by_page(struct net_device *dev,
+				     struct ethtool_module_eeprom *page_data,
+				     struct netlink_ext_ack *extack)
+{
+	const struct ethtool_ops *ops = dev->ethtool_ops;
+
+	if (dev->ethtool->module_fw_flash_in_progress) {
+		NL_SET_ERR_MSG(extack,
+			       "Module firmware flashing is in progress");
+		return -EBUSY;
+	}
+
+	if (dev->sfp_bus)
+		return sfp_get_module_eeprom_by_page(dev->sfp_bus, page_data, extack);
+
+	if (ops->get_module_eeprom_by_page)
+		return ops->get_module_eeprom_by_page(dev, page_data, extack);
+
+	return -EOPNOTSUPP;
+}
+
+static int eeprom_prepare_data(const struct ethnl_req_info *req_base,
+			       struct ethnl_reply_data *reply_base,
+			       const struct genl_info *info)
+{
+	struct eeprom_reply_data *reply = MODULE_EEPROM_REPDATA(reply_base);
+	struct eeprom_req_info *request = MODULE_EEPROM_REQINFO(req_base);
+	struct ethtool_module_eeprom page_data = {0};
+	struct net_device *dev = reply_base->dev;
+	int ret;
+
+	page_data.offset = request->offset;
+	page_data.length = request->length;
+	page_data.i2c_address = request->i2c_address;
+	page_data.page = request->page;
+	page_data.bank = request->bank;
+	page_data.data = kmalloc(page_data.length, GFP_KERNEL);
+	if (!page_data.data)
+		return -ENOMEM;
+
+	ret = ethnl_ops_begin(dev);
+	if (ret)
+		goto err_free;
+
+	ret = get_module_eeprom_by_page(dev, &page_data, info->extack);
+	if (ret < 0)
+		goto err_ops;
+
+	reply->length = ret;
+	reply->data = page_data.data;
+
+	ethnl_ops_complete(dev);
+	return 0;
+
+err_ops:
+	if (ret == -EOPNOTSUPP)
+		ret = eeprom_fallback(request, reply);
+	ethnl_ops_complete(dev);
+err_free:
+	kfree(page_data.data);
+	return ret;
+}
+
+static int eeprom_parse_request(struct ethnl_req_info *req_info,
+				const struct genl_info *info,
+				struct nlattr **tb,
+				struct netlink_ext_ack *extack)
+{
+	struct eeprom_req_info *request = MODULE_EEPROM_REQINFO(req_info);
+
+	if (GENL_REQ_ATTR_CHECK(info, ETHTOOL_A_MODULE_EEPROM_OFFSET) ||
+	    GENL_REQ_ATTR_CHECK(info, ETHTOOL_A_MODULE_EEPROM_LENGTH) ||
+	    GENL_REQ_ATTR_CHECK(info, ETHTOOL_A_MODULE_EEPROM_PAGE) ||
+	    GENL_REQ_ATTR_CHECK(info, ETHTOOL_A_MODULE_EEPROM_I2C_ADDRESS))
+		return -EINVAL;
+
+	request->i2c_address = nla_get_u8(tb[ETHTOOL_A_MODULE_EEPROM_I2C_ADDRESS]);
+	request->offset = nla_get_u32(tb[ETHTOOL_A_MODULE_EEPROM_OFFSET]);
+	request->length = nla_get_u32(tb[ETHTOOL_A_MODULE_EEPROM_LENGTH]);
+
+	/* The following set of conditions limit the API to only dump 1/2
+	 * EEPROM page without crossing low page boundary located at offset 128.
+	 * This means user may only request dumps of length limited to 128 from
+	 * either low 128 bytes or high 128 bytes.
+	 * For pages higher than 0 only high 128 bytes are accessible.
+	 */
+	request->page = nla_get_u8(tb[ETHTOOL_A_MODULE_EEPROM_PAGE]);
+	if (request->page && request->offset < ETH_MODULE_EEPROM_PAGE_LEN) {
+		NL_SET_ERR_MSG_ATTR(extack, tb[ETHTOOL_A_MODULE_EEPROM_PAGE],
+				    "reading from lower half page is allowed for page 0 only");
+		return -EINVAL;
+	}
+
+	if (request->offset < ETH_MODULE_EEPROM_PAGE_LEN &&
+	    request->offset + request->length > ETH_MODULE_EEPROM_PAGE_LEN) {
+		NL_SET_ERR_MSG_ATTR(extack, tb[ETHTOOL_A_MODULE_EEPROM_LENGTH],
+				    "reading cross half page boundary is illegal");
+		return -EINVAL;
+	} else if (request->offset + request->length > ETH_MODULE_EEPROM_PAGE_LEN * 2) {
+		NL_SET_ERR_MSG_ATTR(extack, tb[ETHTOOL_A_MODULE_EEPROM_LENGTH],
+				    "reading cross page boundary is illegal");
+		return -EINVAL;
+	}
+
+	if (tb[ETHTOOL_A_MODULE_EEPROM_BANK])
+		request->bank = nla_get_u8(tb[ETHTOOL_A_MODULE_EEPROM_BANK]);
+
+	return 0;
+}
+
+static int eeprom_reply_size(const struct ethnl_req_info *req_base,
+			     const struct ethnl_reply_data *reply_base)
+{
+	const struct eeprom_req_info *request = MODULE_EEPROM_REQINFO(req_base);
+
+	return nla_total_size(sizeof(u8) * request->length); /* _EEPROM_DATA */
+}
+
+static int eeprom_fill_reply(struct sk_buff *skb,
+			     const struct ethnl_req_info *req_base,
+			     const struct ethnl_reply_data *reply_base)
+{
+	struct eeprom_reply_data *reply = MODULE_EEPROM_REPDATA(reply_base);
+
+	return nla_put(skb, ETHTOOL_A_MODULE_EEPROM_DATA, reply->length, reply->data);
+}
+
+static void eeprom_cleanup_data(struct ethnl_reply_data *reply_base)
+{
+	struct eeprom_reply_data *reply = MODULE_EEPROM_REPDATA(reply_base);
+
+	kfree(reply->data);
+}
+
+const struct ethnl_request_ops ethnl_module_eeprom_request_ops = {
+	.request_cmd		= ETHTOOL_MSG_MODULE_EEPROM_GET,
+	.reply_cmd		= ETHTOOL_MSG_MODULE_EEPROM_GET_REPLY,
+	.hdr_attr		= ETHTOOL_A_MODULE_EEPROM_HEADER,
+	.req_info_size		= sizeof(struct eeprom_req_info),
+	.reply_data_size	= sizeof(struct eeprom_reply_data),
+
+	.parse_request		= eeprom_parse_request,
+	.prepare_data		= eeprom_prepare_data,
+	.reply_size		= eeprom_reply_size,
+	.fill_reply		= eeprom_fill_reply,
+	.cleanup_data		= eeprom_cleanup_data,
+};
+
+const struct nla_policy ethnl_module_eeprom_get_policy[] = {
+	[ETHTOOL_A_MODULE_EEPROM_HEADER]	= NLA_POLICY_NESTED(ethnl_header_policy),
+	[ETHTOOL_A_MODULE_EEPROM_OFFSET]	=
+		NLA_POLICY_MAX(NLA_U32, ETH_MODULE_EEPROM_PAGE_LEN * 2 - 1),
+	[ETHTOOL_A_MODULE_EEPROM_LENGTH]	=
+		NLA_POLICY_RANGE(NLA_U32, 1, ETH_MODULE_EEPROM_PAGE_LEN),
+	[ETHTOOL_A_MODULE_EEPROM_PAGE]		= { .type = NLA_U8 },
+	[ETHTOOL_A_MODULE_EEPROM_BANK]		= { .type = NLA_U8 },
+	[ETHTOOL_A_MODULE_EEPROM_I2C_ADDRESS]	=
+		NLA_POLICY_RANGE(NLA_U8, 0, ETH_MODULE_MAX_I2C_ADDRESS),
+};
+