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, 195 insertions, 0 deletions

diff --git a/net/ethtool/privflags.c b/net/ethtool/privflags.c
new file mode 100644
index 000000000..46a4d2a43
--- /dev/null
+++ b/net/ethtool/privflags.c
@@ -0,0 +1,195 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include "bitset.h"
+#include "common.h"
+#include "netlink.h"
+
+struct privflags_req_info {
+	struct ethnl_req_info		base;
+};
+
+struct privflags_reply_data {
+	struct ethnl_reply_data		base;
+	const char			(*priv_flag_names)[ETH_GSTRING_LEN];
+	unsigned int			n_priv_flags;
+	u32				priv_flags;
+};
+
+#define PRIVFLAGS_REPDATA(__reply_base) \
+	container_of(__reply_base, struct privflags_reply_data, base)
+
+const struct nla_policy ethnl_privflags_get_policy[] = {
+	[ETHTOOL_A_PRIVFLAGS_HEADER]		=
+		NLA_POLICY_NESTED(ethnl_header_policy),
+};
+
+static int ethnl_get_priv_flags_info(struct net_device *dev,
+				     unsigned int *count,
+				     const char (**names)[ETH_GSTRING_LEN])
+{
+	const struct ethtool_ops *ops = dev->ethtool_ops;
+	int nflags;
+
+	nflags = ops->get_sset_count(dev, ETH_SS_PRIV_FLAGS);
+	if (nflags < 0)
+		return nflags;
+
+	if (names) {
+		*names = kcalloc(nflags, ETH_GSTRING_LEN, GFP_KERNEL);
+		if (!*names)
+			return -ENOMEM;
+		ops->get_strings(dev, ETH_SS_PRIV_FLAGS, (u8 *)*names);
+	}
+
+	/* We can pass more than 32 private flags to userspace via netlink but
+	 * we cannot get more with ethtool_ops::get_priv_flags(). Note that we
+	 * must not adjust nflags before allocating the space for flag names
+	 * as the buffer must be large enough for all flags.
+	 */
+	if (WARN_ONCE(nflags > 32,
+		      "device %s reports more than 32 private flags (%d)\n",
+		      netdev_name(dev), nflags))
+		nflags = 32;
+	*count = nflags;
+
+	return 0;
+}
+
+static int privflags_prepare_data(const struct ethnl_req_info *req_base,
+				  struct ethnl_reply_data *reply_base,
+				  const struct genl_info *info)
+{
+	struct privflags_reply_data *data = PRIVFLAGS_REPDATA(reply_base);
+	struct net_device *dev = reply_base->dev;
+	const char (*names)[ETH_GSTRING_LEN];
+	const struct ethtool_ops *ops;
+	unsigned int nflags;
+	int ret;
+
+	ops = dev->ethtool_ops;
+	if (!ops->get_priv_flags || !ops->get_sset_count || !ops->get_strings)
+		return -EOPNOTSUPP;
+	ret = ethnl_ops_begin(dev);
+	if (ret < 0)
+		return ret;
+
+	ret = ethnl_get_priv_flags_info(dev, &nflags, &names);
+	if (ret < 0)
+		goto out_ops;
+	data->priv_flags = ops->get_priv_flags(dev);
+	data->priv_flag_names = names;
+	data->n_priv_flags = nflags;
+
+out_ops:
+	ethnl_ops_complete(dev);
+	return ret;
+}
+
+static int privflags_reply_size(const struct ethnl_req_info *req_base,
+				const struct ethnl_reply_data *reply_base)
+{
+	const struct privflags_reply_data *data = PRIVFLAGS_REPDATA(reply_base);
+	bool compact = req_base->flags & ETHTOOL_FLAG_COMPACT_BITSETS;
+	const u32 all_flags = ~(u32)0 >> (32 - data->n_priv_flags);
+
+	return ethnl_bitset32_size(&data->priv_flags, &all_flags,
+				   data->n_priv_flags,
+				   data->priv_flag_names, compact);
+}
+
+static int privflags_fill_reply(struct sk_buff *skb,
+				const struct ethnl_req_info *req_base,
+				const struct ethnl_reply_data *reply_base)
+{
+	const struct privflags_reply_data *data = PRIVFLAGS_REPDATA(reply_base);
+	bool compact = req_base->flags & ETHTOOL_FLAG_COMPACT_BITSETS;
+	const u32 all_flags = ~(u32)0 >> (32 - data->n_priv_flags);
+
+	return ethnl_put_bitset32(skb, ETHTOOL_A_PRIVFLAGS_FLAGS,
+				  &data->priv_flags, &all_flags,
+				  data->n_priv_flags, data->priv_flag_names,
+				  compact);
+}
+
+static void privflags_cleanup_data(struct ethnl_reply_data *reply_data)
+{
+	struct privflags_reply_data *data = PRIVFLAGS_REPDATA(reply_data);
+
+	kfree(data->priv_flag_names);
+}
+
+/* PRIVFLAGS_SET */
+
+const struct nla_policy ethnl_privflags_set_policy[] = {
+	[ETHTOOL_A_PRIVFLAGS_HEADER]		=
+		NLA_POLICY_NESTED(ethnl_header_policy),
+	[ETHTOOL_A_PRIVFLAGS_FLAGS]		= { .type = NLA_NESTED },
+};
+
+static int
+ethnl_set_privflags_validate(struct ethnl_req_info *req_info,
+			     struct genl_info *info)
+{
+	const struct ethtool_ops *ops = req_info->dev->ethtool_ops;
+
+	if (!info->attrs[ETHTOOL_A_PRIVFLAGS_FLAGS])
+		return -EINVAL;
+
+	if (!ops->get_priv_flags || !ops->set_priv_flags ||
+	    !ops->get_sset_count || !ops->get_strings)
+		return -EOPNOTSUPP;
+	return 1;
+}
+
+static int
+ethnl_set_privflags(struct ethnl_req_info *req_info, struct genl_info *info)
+{
+	const char (*names)[ETH_GSTRING_LEN] = NULL;
+	struct net_device *dev = req_info->dev;
+	struct nlattr **tb = info->attrs;
+	unsigned int nflags;
+	bool mod = false;
+	bool compact;
+	u32 flags;
+	int ret;
+
+	ret = ethnl_bitset_is_compact(tb[ETHTOOL_A_PRIVFLAGS_FLAGS], &compact);
+	if (ret < 0)
+		return ret;
+
+	ret = ethnl_get_priv_flags_info(dev, &nflags, compact ? NULL : &names);
+	if (ret < 0)
+		return ret;
+	flags = dev->ethtool_ops->get_priv_flags(dev);
+
+	ret = ethnl_update_bitset32(&flags, nflags,
+				    tb[ETHTOOL_A_PRIVFLAGS_FLAGS], names,
+				    info->extack, &mod);
+	if (ret < 0 || !mod)
+		goto out_free;
+	ret = dev->ethtool_ops->set_priv_flags(dev, flags);
+	if (ret < 0)
+		goto out_free;
+	ret = 1;
+
+out_free:
+	kfree(names);
+	return ret;
+}
+
+const struct ethnl_request_ops ethnl_privflags_request_ops = {
+	.request_cmd		= ETHTOOL_MSG_PRIVFLAGS_GET,
+	.reply_cmd		= ETHTOOL_MSG_PRIVFLAGS_GET_REPLY,
+	.hdr_attr		= ETHTOOL_A_PRIVFLAGS_HEADER,
+	.req_info_size		= sizeof(struct privflags_req_info),
+	.reply_data_size	= sizeof(struct privflags_reply_data),
+
+	.prepare_data		= privflags_prepare_data,
+	.reply_size		= privflags_reply_size,
+	.fill_reply		= privflags_fill_reply,
+	.cleanup_data		= privflags_cleanup_data,
+
+	.set_validate		= ethnl_set_privflags_validate,
+	.set			= ethnl_set_privflags,
+	.set_ntf_cmd		= ETHTOOL_MSG_PRIVFLAGS_NTF,
+};