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>

3 files changed, 199 insertions, 0 deletions

diff --git a/net/ife/Kconfig b/net/ife/Kconfig
new file mode 100644
index 000000000..de36a5b91
--- /dev/null
+++ b/net/ife/Kconfig
@@ -0,0 +1,16 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# IFE subsystem configuration
+#
+
+menuconfig NET_IFE
+	tristate "Inter-FE based on IETF ForCES InterFE LFB"
+	default n
+	help
+	  Say Y here to add support of IFE encapsulation protocol
+	  For details refer to netdev01 paper:
+	  "Distributing Linux Traffic Control Classifier-Action Subsystem"
+	   Authors: Jamal Hadi Salim and Damascene M. Joachimpillai
+
+	  To compile this support as a module, choose M here: the module will
+	  be called ife.
diff --git a/net/ife/Makefile b/net/ife/Makefile
new file mode 100644
index 000000000..1258fcb07
--- /dev/null
+++ b/net/ife/Makefile
@@ -0,0 +1,6 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# Makefile for the IFE encapsulation protocol
+#
+
+obj-$(CONFIG_NET_IFE) += ife.o
diff --git a/net/ife/ife.c b/net/ife/ife.c
new file mode 100644
index 000000000..7a75947a3
--- /dev/null
+++ b/net/ife/ife.c
@@ -0,0 +1,177 @@
+/*
+ * net/ife/ife.c - Inter-FE protocol based on ForCES WG InterFE LFB
+ * Copyright (c) 2015 Jamal Hadi Salim <jhs@mojatatu.com>
+ * Copyright (c) 2017 Yotam Gigi <yotamg@mellanox.com>
+ *
+ * Refer to: draft-ietf-forces-interfelfb-03 and netdev01 paper:
+ * "Distributing Linux Traffic Control Classifier-Action Subsystem"
+ * Authors: Jamal Hadi Salim and Damascene M. Joachimpillai
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation.
+ */
+
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/string.h>
+#include <linux/errno.h>
+#include <linux/skbuff.h>
+#include <linux/rtnetlink.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <net/net_namespace.h>
+#include <net/netlink.h>
+#include <net/pkt_sched.h>
+#include <linux/etherdevice.h>
+#include <net/ife.h>
+
+struct ifeheadr {
+	__be16 metalen;
+	u8 tlv_data[];
+};
+
+void *ife_encode(struct sk_buff *skb, u16 metalen)
+{
+	/* OUTERHDR:TOTMETALEN:{TLVHDR:Metadatum:TLVHDR..}:ORIGDATA
+	 * where ORIGDATA = original ethernet header ...
+	 */
+	int hdrm = metalen + IFE_METAHDRLEN;
+	int total_push = hdrm + skb->dev->hard_header_len;
+	struct ifeheadr *ifehdr;
+	struct ethhdr *iethh;	/* inner ether header */
+	int skboff = 0;
+	int err;
+
+	err = skb_cow_head(skb, total_push);
+	if (unlikely(err))
+		return NULL;
+
+	iethh = (struct ethhdr *) skb->data;
+
+	__skb_push(skb, total_push);
+	memcpy(skb->data, iethh, skb->dev->hard_header_len);
+	skb_reset_mac_header(skb);
+	skboff += skb->dev->hard_header_len;
+
+	/* total metadata length */
+	ifehdr = (struct ifeheadr *) (skb->data + skboff);
+	metalen += IFE_METAHDRLEN;
+	ifehdr->metalen = htons(metalen);
+
+	return ifehdr->tlv_data;
+}
+EXPORT_SYMBOL_GPL(ife_encode);
+
+void *ife_decode(struct sk_buff *skb, u16 *metalen)
+{
+	struct ifeheadr *ifehdr;
+	int total_pull;
+	u16 ifehdrln;
+
+	if (!pskb_may_pull(skb, skb->dev->hard_header_len + IFE_METAHDRLEN))
+		return NULL;
+
+	ifehdr = (struct ifeheadr *) (skb->data + skb->dev->hard_header_len);
+	ifehdrln = ntohs(ifehdr->metalen);
+	total_pull = skb->dev->hard_header_len + ifehdrln;
+
+	if (unlikely(ifehdrln < 2))
+		return NULL;
+
+	if (unlikely(!pskb_may_pull(skb, total_pull + ETH_HLEN)))
+		return NULL;
+
+	ifehdr = (struct ifeheadr *)(skb->data + skb->dev->hard_header_len);
+	skb_set_mac_header(skb, total_pull);
+	__skb_pull(skb, total_pull);
+	*metalen = ifehdrln - IFE_METAHDRLEN;
+
+	return &ifehdr->tlv_data;
+}
+EXPORT_SYMBOL_GPL(ife_decode);
+
+struct meta_tlvhdr {
+	__be16 type;
+	__be16 len;
+};
+
+static bool __ife_tlv_meta_valid(const unsigned char *skbdata,
+				 const unsigned char *ifehdr_end)
+{
+	const struct meta_tlvhdr *tlv;
+	u16 tlvlen;
+
+	if (unlikely(skbdata + sizeof(*tlv) > ifehdr_end))
+		return false;
+
+	tlv = (const struct meta_tlvhdr *)skbdata;
+	tlvlen = ntohs(tlv->len);
+
+	/* tlv length field is inc header, check on minimum */
+	if (tlvlen < NLA_HDRLEN)
+		return false;
+
+	/* overflow by NLA_ALIGN check */
+	if (NLA_ALIGN(tlvlen) < tlvlen)
+		return false;
+
+	if (unlikely(skbdata + NLA_ALIGN(tlvlen) > ifehdr_end))
+		return false;
+
+	return true;
+}
+
+/* Caller takes care of presenting data in network order
+ */
+void *ife_tlv_meta_decode(void *skbdata, const void *ifehdr_end, u16 *attrtype,
+			  u16 *dlen, u16 *totlen)
+{
+	struct meta_tlvhdr *tlv;
+
+	if (!__ife_tlv_meta_valid(skbdata, ifehdr_end))
+		return NULL;
+
+	tlv = (struct meta_tlvhdr *)skbdata;
+	*dlen = ntohs(tlv->len) - NLA_HDRLEN;
+	*attrtype = ntohs(tlv->type);
+
+	if (totlen)
+		*totlen = nla_total_size(*dlen);
+
+	return skbdata + sizeof(struct meta_tlvhdr);
+}
+EXPORT_SYMBOL_GPL(ife_tlv_meta_decode);
+
+void *ife_tlv_meta_next(void *skbdata)
+{
+	struct meta_tlvhdr *tlv = (struct meta_tlvhdr *) skbdata;
+	u16 tlvlen = ntohs(tlv->len);
+
+	tlvlen = NLA_ALIGN(tlvlen);
+
+	return skbdata + tlvlen;
+}
+EXPORT_SYMBOL_GPL(ife_tlv_meta_next);
+
+/* Caller takes care of presenting data in network order
+ */
+int ife_tlv_meta_encode(void *skbdata, u16 attrtype, u16 dlen, const void *dval)
+{
+	__be32 *tlv = (__be32 *) (skbdata);
+	u16 totlen = nla_total_size(dlen);	/*alignment + hdr */
+	char *dptr = (char *) tlv + NLA_HDRLEN;
+	u32 htlv = attrtype << 16 | (dlen + NLA_HDRLEN);
+
+	*tlv = htonl(htlv);
+	memset(dptr, 0, totlen - NLA_HDRLEN);
+	memcpy(dptr, dval, dlen);
+
+	return totlen;
+}
+EXPORT_SYMBOL_GPL(ife_tlv_meta_encode);
+
+MODULE_AUTHOR("Jamal Hadi Salim <jhs@mojatatu.com>");
+MODULE_AUTHOR("Yotam Gigi <yotam.gi@gmail.com>");
+MODULE_DESCRIPTION("Inter-FE LFB action");
+MODULE_LICENSE("GPL");