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, 194 insertions, 0 deletions

diff --git a/net/ethtool/phy.c b/net/ethtool/phy.c
new file mode 100644
index 000000000..018b0412b
--- /dev/null
+++ b/net/ethtool/phy.c
@@ -0,0 +1,194 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright 2023 Bootlin
+ *
+ */
+#include <linux/phy.h>
+#include <linux/phy_link_topology.h>
+#include <linux/sfp.h>
+#include <net/netdev_lock.h>
+
+#include "common.h"
+#include "netlink.h"
+
+struct phy_req_info {
+	struct ethnl_req_info base;
+};
+
+struct phy_reply_data {
+	struct ethnl_reply_data	base;
+	u32 phyindex;
+	char *drvname;
+	char *name;
+	unsigned int upstream_type;
+	char *upstream_sfp_name;
+	unsigned int upstream_index;
+	char *downstream_sfp_name;
+};
+
+#define PHY_REPDATA(__reply_base) \
+	container_of(__reply_base, struct phy_reply_data, base)
+
+const struct nla_policy ethnl_phy_get_policy[ETHTOOL_A_PHY_HEADER + 1] = {
+	[ETHTOOL_A_PHY_HEADER] = NLA_POLICY_NESTED(ethnl_header_policy),
+};
+
+static int phy_reply_size(const struct ethnl_req_info *req_info,
+			  const struct ethnl_reply_data *reply_data)
+{
+	struct phy_reply_data *rep_data = PHY_REPDATA(reply_data);
+	size_t size = 0;
+
+	/* ETHTOOL_A_PHY_INDEX */
+	size += nla_total_size(sizeof(u32));
+
+	/* ETHTOOL_A_DRVNAME */
+	if (rep_data->drvname)
+		size += nla_total_size(strlen(rep_data->drvname) + 1);
+
+	/* ETHTOOL_A_NAME */
+	size += nla_total_size(strlen(rep_data->name) + 1);
+
+	/* ETHTOOL_A_PHY_UPSTREAM_TYPE */
+	size += nla_total_size(sizeof(u32));
+
+	/* ETHTOOL_A_PHY_UPSTREAM_SFP_NAME */
+	if (rep_data->upstream_sfp_name)
+		size += nla_total_size(strlen(rep_data->upstream_sfp_name) + 1);
+
+	/* ETHTOOL_A_PHY_UPSTREAM_INDEX */
+	if (rep_data->upstream_index)
+		size += nla_total_size(sizeof(u32));
+
+	/* ETHTOOL_A_PHY_DOWNSTREAM_SFP_NAME */
+	if (rep_data->downstream_sfp_name)
+		size += nla_total_size(strlen(rep_data->downstream_sfp_name) + 1);
+
+	return size;
+}
+
+static int phy_prepare_data(const struct ethnl_req_info *req_info,
+			    struct ethnl_reply_data *reply_data,
+			    const struct genl_info *info)
+{
+	struct phy_link_topology *topo = reply_data->dev->link_topo;
+	struct phy_reply_data *rep_data = PHY_REPDATA(reply_data);
+	struct nlattr **tb = info->attrs;
+	struct phy_device_node *pdn;
+	struct phy_device *phydev;
+	int ret;
+
+	phydev = ethnl_req_get_phydev(req_info, tb, ETHTOOL_A_PHY_HEADER,
+				      info->extack);
+	if (IS_ERR_OR_NULL(phydev))
+		return -EOPNOTSUPP;
+
+	pdn = xa_load(&topo->phys, phydev->phyindex);
+	if (!pdn)
+		return -EOPNOTSUPP;
+
+	rep_data->phyindex = phydev->phyindex;
+
+	rep_data->name = kstrdup(dev_name(&phydev->mdio.dev), GFP_KERNEL);
+	if (!rep_data->name)
+		return -ENOMEM;
+
+	if (phydev->drv) {
+		rep_data->drvname = kstrdup(phydev->drv->name, GFP_KERNEL);
+		if (!rep_data->drvname) {
+			ret = -ENOMEM;
+			goto err_free_name;
+		}
+	}
+
+	rep_data->upstream_type = pdn->upstream_type;
+
+	if (pdn->upstream_type == PHY_UPSTREAM_PHY) {
+		struct phy_device *upstream = pdn->upstream.phydev;
+		rep_data->upstream_index = upstream->phyindex;
+	}
+
+	if (pdn->parent_sfp_bus) {
+		rep_data->upstream_sfp_name = kstrdup(sfp_get_name(pdn->parent_sfp_bus),
+						      GFP_KERNEL);
+		if (!rep_data->upstream_sfp_name) {
+			ret = -ENOMEM;
+			goto err_free_drvname;
+		}
+	}
+
+	if (phydev->sfp_bus) {
+		rep_data->downstream_sfp_name = kstrdup(sfp_get_name(phydev->sfp_bus),
+							GFP_KERNEL);
+		if (!rep_data->downstream_sfp_name) {
+			ret = -ENOMEM;
+			goto err_free_upstream_sfp;
+		}
+	}
+
+	return 0;
+
+err_free_upstream_sfp:
+	kfree(rep_data->upstream_sfp_name);
+err_free_drvname:
+	kfree(rep_data->drvname);
+err_free_name:
+	kfree(rep_data->name);
+	return ret;
+}
+
+static int phy_fill_reply(struct sk_buff *skb,
+			  const struct ethnl_req_info *req_info,
+			  const struct ethnl_reply_data *reply_data)
+{
+	struct phy_reply_data *rep_data = PHY_REPDATA(reply_data);
+
+	if (nla_put_u32(skb, ETHTOOL_A_PHY_INDEX, rep_data->phyindex) ||
+	    nla_put_string(skb, ETHTOOL_A_PHY_NAME, rep_data->name) ||
+	    nla_put_u32(skb, ETHTOOL_A_PHY_UPSTREAM_TYPE, rep_data->upstream_type))
+		return -EMSGSIZE;
+
+	if (rep_data->drvname &&
+	    nla_put_string(skb, ETHTOOL_A_PHY_DRVNAME, rep_data->drvname))
+		return -EMSGSIZE;
+
+	if (rep_data->upstream_index &&
+	    nla_put_u32(skb, ETHTOOL_A_PHY_UPSTREAM_INDEX,
+			rep_data->upstream_index))
+		return -EMSGSIZE;
+
+	if (rep_data->upstream_sfp_name &&
+	    nla_put_string(skb, ETHTOOL_A_PHY_UPSTREAM_SFP_NAME,
+			   rep_data->upstream_sfp_name))
+		return -EMSGSIZE;
+
+	if (rep_data->downstream_sfp_name &&
+	    nla_put_string(skb, ETHTOOL_A_PHY_DOWNSTREAM_SFP_NAME,
+			   rep_data->downstream_sfp_name))
+		return -EMSGSIZE;
+
+	return 0;
+}
+
+static void phy_cleanup_data(struct ethnl_reply_data *reply_data)
+{
+	struct phy_reply_data *rep_data = PHY_REPDATA(reply_data);
+
+	kfree(rep_data->drvname);
+	kfree(rep_data->name);
+	kfree(rep_data->upstream_sfp_name);
+	kfree(rep_data->downstream_sfp_name);
+}
+
+const struct ethnl_request_ops ethnl_phy_request_ops = {
+	.request_cmd		= ETHTOOL_MSG_PHY_GET,
+	.reply_cmd		= ETHTOOL_MSG_PHY_GET_REPLY,
+	.hdr_attr		= ETHTOOL_A_PHY_HEADER,
+	.req_info_size		= sizeof(struct phy_req_info),
+	.reply_data_size	= sizeof(struct phy_reply_data),
+
+	.prepare_data		= phy_prepare_data,
+	.reply_size		= phy_reply_size,
+	.fill_reply		= phy_fill_reply,
+	.cleanup_data		= phy_cleanup_data,
+};