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, 222 insertions, 0 deletions

diff --git a/net/ethtool/pause.c b/net/ethtool/pause.c
new file mode 100644
index 000000000..ccaec8e87
--- /dev/null
+++ b/net/ethtool/pause.c
@@ -0,0 +1,222 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include "common.h"
+#include "netlink.h"
+
+struct pause_req_info {
+	struct ethnl_req_info		base;
+	enum ethtool_mac_stats_src	src;
+};
+
+#define PAUSE_REQINFO(__req_base) \
+	container_of(__req_base, struct pause_req_info, base)
+
+struct pause_reply_data {
+	struct ethnl_reply_data		base;
+	struct ethtool_pauseparam	pauseparam;
+	struct ethtool_pause_stats	pausestat;
+};
+
+#define PAUSE_REPDATA(__reply_base) \
+	container_of(__reply_base, struct pause_reply_data, base)
+
+const struct nla_policy ethnl_pause_get_policy[] = {
+	[ETHTOOL_A_PAUSE_HEADER]		=
+		NLA_POLICY_NESTED(ethnl_header_policy_stats),
+	[ETHTOOL_A_PAUSE_STATS_SRC]		=
+		NLA_POLICY_MAX(NLA_U32, ETHTOOL_MAC_STATS_SRC_PMAC),
+};
+
+static int pause_parse_request(struct ethnl_req_info *req_base,
+			       const struct genl_info *info,
+			       struct nlattr **tb,
+			       struct netlink_ext_ack *extack)
+{
+	enum ethtool_mac_stats_src src = ETHTOOL_MAC_STATS_SRC_AGGREGATE;
+	struct pause_req_info *req_info = PAUSE_REQINFO(req_base);
+
+	if (tb[ETHTOOL_A_PAUSE_STATS_SRC]) {
+		if (!(req_base->flags & ETHTOOL_FLAG_STATS)) {
+			NL_SET_ERR_MSG_MOD(extack,
+					   "ETHTOOL_FLAG_STATS must be set when requesting a source of stats");
+			return -EINVAL;
+		}
+
+		src = nla_get_u32(tb[ETHTOOL_A_PAUSE_STATS_SRC]);
+	}
+
+	req_info->src = src;
+
+	return 0;
+}
+
+static int pause_prepare_data(const struct ethnl_req_info *req_base,
+			      struct ethnl_reply_data *reply_base,
+			      const struct genl_info *info)
+{
+	const struct pause_req_info *req_info = PAUSE_REQINFO(req_base);
+	struct pause_reply_data *data = PAUSE_REPDATA(reply_base);
+	enum ethtool_mac_stats_src src = req_info->src;
+	struct net_device *dev = reply_base->dev;
+	int ret;
+
+	if (!dev->ethtool_ops->get_pauseparam)
+		return -EOPNOTSUPP;
+
+	ethtool_stats_init((u64 *)&data->pausestat,
+			   sizeof(data->pausestat) / 8);
+	data->pausestat.src = src;
+
+	ret = ethnl_ops_begin(dev);
+	if (ret < 0)
+		return ret;
+
+	if ((src == ETHTOOL_MAC_STATS_SRC_EMAC ||
+	     src == ETHTOOL_MAC_STATS_SRC_PMAC) &&
+	    !__ethtool_dev_mm_supported(dev)) {
+		NL_SET_ERR_MSG_MOD(info->extack,
+				   "Device does not support MAC merge layer");
+		ethnl_ops_complete(dev);
+		return -EOPNOTSUPP;
+	}
+
+	dev->ethtool_ops->get_pauseparam(dev, &data->pauseparam);
+	if (req_base->flags & ETHTOOL_FLAG_STATS &&
+	    dev->ethtool_ops->get_pause_stats)
+		dev->ethtool_ops->get_pause_stats(dev, &data->pausestat);
+
+	ethnl_ops_complete(dev);
+
+	return 0;
+}
+
+static int pause_reply_size(const struct ethnl_req_info *req_base,
+			    const struct ethnl_reply_data *reply_base)
+{
+	int n = nla_total_size(sizeof(u8)) +	/* _PAUSE_AUTONEG */
+		nla_total_size(sizeof(u8)) +	/* _PAUSE_RX */
+		nla_total_size(sizeof(u8));	/* _PAUSE_TX */
+
+	if (req_base->flags & ETHTOOL_FLAG_STATS)
+		n += nla_total_size(0) +	/* _PAUSE_STATS */
+		     nla_total_size(sizeof(u32)) + /* _PAUSE_STATS_SRC */
+		     nla_total_size_64bit(sizeof(u64)) * ETHTOOL_PAUSE_STAT_CNT;
+	return n;
+}
+
+static int ethtool_put_stat(struct sk_buff *skb, u64 val, u16 attrtype,
+			    u16 padtype)
+{
+	if (val == ETHTOOL_STAT_NOT_SET)
+		return 0;
+	if (nla_put_u64_64bit(skb, attrtype, val, padtype))
+		return -EMSGSIZE;
+
+	return 0;
+}
+
+static int pause_put_stats(struct sk_buff *skb,
+			   const struct ethtool_pause_stats *pause_stats)
+{
+	const u16 pad = ETHTOOL_A_PAUSE_STAT_PAD;
+	struct nlattr *nest;
+
+	if (nla_put_u32(skb, ETHTOOL_A_PAUSE_STATS_SRC, pause_stats->src))
+		return -EMSGSIZE;
+
+	nest = nla_nest_start(skb, ETHTOOL_A_PAUSE_STATS);
+	if (!nest)
+		return -EMSGSIZE;
+
+	if (ethtool_put_stat(skb, pause_stats->tx_pause_frames,
+			     ETHTOOL_A_PAUSE_STAT_TX_FRAMES, pad) ||
+	    ethtool_put_stat(skb, pause_stats->rx_pause_frames,
+			     ETHTOOL_A_PAUSE_STAT_RX_FRAMES, pad) ||
+	    ethtool_put_stat(skb, pause_stats->tx_pause_storm_events,
+			     ETHTOOL_A_PAUSE_STAT_TX_PAUSE_STORM_EVENTS, pad))
+		goto err_cancel;
+
+	nla_nest_end(skb, nest);
+	return 0;
+
+err_cancel:
+	nla_nest_cancel(skb, nest);
+	return -EMSGSIZE;
+}
+
+static int pause_fill_reply(struct sk_buff *skb,
+			    const struct ethnl_req_info *req_base,
+			    const struct ethnl_reply_data *reply_base)
+{
+	const struct pause_reply_data *data = PAUSE_REPDATA(reply_base);
+	const struct ethtool_pauseparam *pauseparam = &data->pauseparam;
+
+	if (nla_put_u8(skb, ETHTOOL_A_PAUSE_AUTONEG, !!pauseparam->autoneg) ||
+	    nla_put_u8(skb, ETHTOOL_A_PAUSE_RX, !!pauseparam->rx_pause) ||
+	    nla_put_u8(skb, ETHTOOL_A_PAUSE_TX, !!pauseparam->tx_pause))
+		return -EMSGSIZE;
+
+	if (req_base->flags & ETHTOOL_FLAG_STATS &&
+	    pause_put_stats(skb, &data->pausestat))
+		return -EMSGSIZE;
+
+	return 0;
+}
+
+/* PAUSE_SET */
+
+const struct nla_policy ethnl_pause_set_policy[] = {
+	[ETHTOOL_A_PAUSE_HEADER]		=
+		NLA_POLICY_NESTED(ethnl_header_policy),
+	[ETHTOOL_A_PAUSE_AUTONEG]		= { .type = NLA_U8 },
+	[ETHTOOL_A_PAUSE_RX]			= { .type = NLA_U8 },
+	[ETHTOOL_A_PAUSE_TX]			= { .type = NLA_U8 },
+	[ETHTOOL_A_PAUSE_STATS_SRC]		= { .type = NLA_REJECT },
+};
+
+static int
+ethnl_set_pause_validate(struct ethnl_req_info *req_info,
+			 struct genl_info *info)
+{
+	const struct ethtool_ops *ops = req_info->dev->ethtool_ops;
+
+	return ops->get_pauseparam && ops->set_pauseparam ? 1 : -EOPNOTSUPP;
+}
+
+static int
+ethnl_set_pause(struct ethnl_req_info *req_info, struct genl_info *info)
+{
+	struct net_device *dev = req_info->dev;
+	struct ethtool_pauseparam params = {};
+	struct nlattr **tb = info->attrs;
+	bool mod = false;
+	int ret;
+
+	dev->ethtool_ops->get_pauseparam(dev, &params);
+
+	ethnl_update_bool32(&params.autoneg, tb[ETHTOOL_A_PAUSE_AUTONEG], &mod);
+	ethnl_update_bool32(&params.rx_pause, tb[ETHTOOL_A_PAUSE_RX], &mod);
+	ethnl_update_bool32(&params.tx_pause, tb[ETHTOOL_A_PAUSE_TX], &mod);
+	if (!mod)
+		return 0;
+
+	ret = dev->ethtool_ops->set_pauseparam(dev, &params);
+	return ret < 0 ? ret : 1;
+}
+
+const struct ethnl_request_ops ethnl_pause_request_ops = {
+	.request_cmd		= ETHTOOL_MSG_PAUSE_GET,
+	.reply_cmd		= ETHTOOL_MSG_PAUSE_GET_REPLY,
+	.hdr_attr		= ETHTOOL_A_PAUSE_HEADER,
+	.req_info_size		= sizeof(struct pause_req_info),
+	.reply_data_size	= sizeof(struct pause_reply_data),
+
+	.parse_request		= pause_parse_request,
+	.prepare_data		= pause_prepare_data,
+	.reply_size		= pause_reply_size,
+	.fill_reply		= pause_fill_reply,
+
+	.set_validate		= ethnl_set_pause_validate,
+	.set			= ethnl_set_pause,
+	.set_ntf_cmd		= ETHTOOL_MSG_PAUSE_NTF,
+};