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, 226 insertions, 0 deletions

diff --git a/net/ethtool/linkstate.c b/net/ethtool/linkstate.c
new file mode 100644
index 000000000..24569e929
--- /dev/null
+++ b/net/ethtool/linkstate.c
@@ -0,0 +1,226 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <linux/phy.h>
+#include <linux/phylib_stubs.h>
+
+#include "common.h"
+#include "netlink.h"
+
+struct linkstate_req_info {
+	struct ethnl_req_info		base;
+};
+
+struct linkstate_reply_data {
+	struct ethnl_reply_data			base;
+	int					link;
+	int					sqi;
+	int					sqi_max;
+	struct ethtool_link_ext_stats		link_stats;
+	bool					link_ext_state_provided;
+	struct ethtool_link_ext_state_info	ethtool_link_ext_state_info;
+};
+
+#define LINKSTATE_REPDATA(__reply_base) \
+	container_of(__reply_base, struct linkstate_reply_data, base)
+
+const struct nla_policy ethnl_linkstate_get_policy[] = {
+	[ETHTOOL_A_LINKSTATE_HEADER]		=
+		NLA_POLICY_NESTED(ethnl_header_policy_stats),
+};
+
+static int linkstate_get_sqi(struct phy_device *phydev)
+{
+	int ret;
+
+	if (!phydev)
+		return -EOPNOTSUPP;
+
+	mutex_lock(&phydev->lock);
+	if (!phydev->drv || !phydev->drv->get_sqi)
+		ret = -EOPNOTSUPP;
+	else if (!phydev->link)
+		ret = -ENETDOWN;
+	else
+		ret = phydev->drv->get_sqi(phydev);
+	mutex_unlock(&phydev->lock);
+
+	return ret;
+}
+
+static int linkstate_get_sqi_max(struct phy_device *phydev)
+{
+	int ret;
+
+	if (!phydev)
+		return -EOPNOTSUPP;
+
+	mutex_lock(&phydev->lock);
+	if (!phydev->drv || !phydev->drv->get_sqi_max)
+		ret = -EOPNOTSUPP;
+	else if (!phydev->link)
+		ret = -ENETDOWN;
+	else
+		ret = phydev->drv->get_sqi_max(phydev);
+	mutex_unlock(&phydev->lock);
+
+	return ret;
+};
+
+static bool linkstate_sqi_critical_error(int sqi)
+{
+	return sqi < 0 && sqi != -EOPNOTSUPP && sqi != -ENETDOWN;
+}
+
+static bool linkstate_sqi_valid(struct linkstate_reply_data *data)
+{
+	return data->sqi >= 0 && data->sqi_max >= 0 &&
+	       data->sqi <= data->sqi_max;
+}
+
+static int linkstate_get_link_ext_state(struct net_device *dev,
+					struct linkstate_reply_data *data)
+{
+	int err;
+
+	if (!dev->ethtool_ops->get_link_ext_state)
+		return -EOPNOTSUPP;
+
+	err = dev->ethtool_ops->get_link_ext_state(dev, &data->ethtool_link_ext_state_info);
+	if (err)
+		return err;
+
+	data->link_ext_state_provided = true;
+
+	return 0;
+}
+
+static int linkstate_prepare_data(const struct ethnl_req_info *req_base,
+				  struct ethnl_reply_data *reply_base,
+				  const struct genl_info *info)
+{
+	struct linkstate_reply_data *data = LINKSTATE_REPDATA(reply_base);
+	struct net_device *dev = reply_base->dev;
+	struct nlattr **tb = info->attrs;
+	struct phy_device *phydev;
+	int ret;
+
+	phydev = ethnl_req_get_phydev(req_base, tb, ETHTOOL_A_LINKSTATE_HEADER,
+				      info->extack);
+	if (IS_ERR(phydev))
+		return PTR_ERR(phydev);
+
+	ret = ethnl_ops_begin(dev);
+	if (ret < 0)
+		return ret;
+	data->link = __ethtool_get_link(dev);
+
+	ret = linkstate_get_sqi(phydev);
+	if (linkstate_sqi_critical_error(ret))
+		goto out;
+	data->sqi = ret;
+
+	ret = linkstate_get_sqi_max(phydev);
+	if (linkstate_sqi_critical_error(ret))
+		goto out;
+	data->sqi_max = ret;
+
+	if (dev->flags & IFF_UP) {
+		ret = linkstate_get_link_ext_state(dev, data);
+		if (ret < 0 && ret != -EOPNOTSUPP && ret != -ENODATA)
+			goto out;
+	}
+
+	ethtool_stats_init((u64 *)&data->link_stats,
+			   sizeof(data->link_stats) / 8);
+
+	if (req_base->flags & ETHTOOL_FLAG_STATS) {
+		if (phydev)
+			phy_ethtool_get_link_ext_stats(phydev,
+						       &data->link_stats);
+
+		if (dev->ethtool_ops->get_link_ext_stats)
+			dev->ethtool_ops->get_link_ext_stats(dev,
+							     &data->link_stats);
+	}
+
+	ret = 0;
+out:
+	ethnl_ops_complete(dev);
+	return ret;
+}
+
+static int linkstate_reply_size(const struct ethnl_req_info *req_base,
+				const struct ethnl_reply_data *reply_base)
+{
+	struct linkstate_reply_data *data = LINKSTATE_REPDATA(reply_base);
+	int len;
+
+	len = nla_total_size(sizeof(u8)) /* LINKSTATE_LINK */
+		+ 0;
+
+	if (linkstate_sqi_valid(data)) {
+		len += nla_total_size(sizeof(u32)); /* LINKSTATE_SQI */
+		len += nla_total_size(sizeof(u32)); /* LINKSTATE_SQI_MAX */
+	}
+
+	if (data->link_ext_state_provided)
+		len += nla_total_size(sizeof(u8)); /* LINKSTATE_EXT_STATE */
+
+	if (data->ethtool_link_ext_state_info.__link_ext_substate)
+		len += nla_total_size(sizeof(u8)); /* LINKSTATE_EXT_SUBSTATE */
+
+	if (data->link_stats.link_down_events != ETHTOOL_STAT_NOT_SET)
+		len += nla_total_size(sizeof(u32));
+
+	return len;
+}
+
+static int linkstate_fill_reply(struct sk_buff *skb,
+				const struct ethnl_req_info *req_base,
+				const struct ethnl_reply_data *reply_base)
+{
+	struct linkstate_reply_data *data = LINKSTATE_REPDATA(reply_base);
+
+	if (data->link >= 0 &&
+	    nla_put_u8(skb, ETHTOOL_A_LINKSTATE_LINK, !!data->link))
+		return -EMSGSIZE;
+
+	if (linkstate_sqi_valid(data)) {
+		if (nla_put_u32(skb, ETHTOOL_A_LINKSTATE_SQI, data->sqi))
+			return -EMSGSIZE;
+
+		if (nla_put_u32(skb, ETHTOOL_A_LINKSTATE_SQI_MAX,
+				data->sqi_max))
+			return -EMSGSIZE;
+	}
+
+	if (data->link_ext_state_provided) {
+		if (nla_put_u8(skb, ETHTOOL_A_LINKSTATE_EXT_STATE,
+			       data->ethtool_link_ext_state_info.link_ext_state))
+			return -EMSGSIZE;
+
+		if (data->ethtool_link_ext_state_info.__link_ext_substate &&
+		    nla_put_u8(skb, ETHTOOL_A_LINKSTATE_EXT_SUBSTATE,
+			       data->ethtool_link_ext_state_info.__link_ext_substate))
+			return -EMSGSIZE;
+	}
+
+	if (data->link_stats.link_down_events != ETHTOOL_STAT_NOT_SET)
+		if (nla_put_u32(skb, ETHTOOL_A_LINKSTATE_EXT_DOWN_CNT,
+				data->link_stats.link_down_events))
+			return -EMSGSIZE;
+
+	return 0;
+}
+
+const struct ethnl_request_ops ethnl_linkstate_request_ops = {
+	.request_cmd		= ETHTOOL_MSG_LINKSTATE_GET,
+	.reply_cmd		= ETHTOOL_MSG_LINKSTATE_GET_REPLY,
+	.hdr_attr		= ETHTOOL_A_LINKSTATE_HEADER,
+	.req_info_size		= sizeof(struct linkstate_req_info),
+	.reply_data_size	= sizeof(struct linkstate_reply_data),
+
+	.prepare_data		= linkstate_prepare_data,
+	.reply_size		= linkstate_reply_size,
+	.fill_reply		= linkstate_fill_reply,
+};