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, 278 insertions, 0 deletions

diff --git a/net/sunrpc/socklib.c b/net/sunrpc/socklib.c
new file mode 100644
index 000000000..d8d8842c7
--- /dev/null
+++ b/net/sunrpc/socklib.c
@@ -0,0 +1,278 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * linux/net/sunrpc/socklib.c
+ *
+ * Common socket helper routines for RPC client and server
+ *
+ * Copyright (C) 1995, 1996 Olaf Kirch <okir@monad.swb.de>
+ */
+
+#include <linux/compiler.h>
+#include <linux/netdevice.h>
+#include <linux/gfp.h>
+#include <linux/skbuff.h>
+#include <linux/types.h>
+#include <linux/pagemap.h>
+#include <linux/udp.h>
+#include <linux/sunrpc/msg_prot.h>
+#include <linux/sunrpc/sched.h>
+#include <linux/sunrpc/xdr.h>
+#include <linux/export.h>
+
+#include "socklib.h"
+
+/*
+ * Helper structure for copying from an sk_buff.
+ */
+struct xdr_skb_reader {
+	struct sk_buff	*skb;
+	unsigned int	offset;
+	bool		need_checksum;
+	size_t		count;
+	__wsum		csum;
+};
+
+/**
+ * xdr_skb_read_bits - copy some data bits from skb to internal buffer
+ * @desc: sk_buff copy helper
+ * @to: copy destination
+ * @len: number of bytes to copy
+ *
+ * Possibly called several times to iterate over an sk_buff and copy data out of
+ * it.
+ */
+static size_t
+xdr_skb_read_bits(struct xdr_skb_reader *desc, void *to, size_t len)
+{
+	len = min(len, desc->count);
+
+	if (desc->need_checksum) {
+		__wsum csum;
+
+		csum = skb_copy_and_csum_bits(desc->skb, desc->offset, to, len);
+		desc->csum = csum_block_add(desc->csum, csum, desc->offset);
+	} else {
+		if (unlikely(skb_copy_bits(desc->skb, desc->offset, to, len)))
+			return 0;
+	}
+
+	desc->count -= len;
+	desc->offset += len;
+	return len;
+}
+
+static ssize_t
+xdr_partial_copy_from_skb(struct xdr_buf *xdr, struct xdr_skb_reader *desc)
+{
+	struct page **ppage = xdr->pages + (xdr->page_base >> PAGE_SHIFT);
+	unsigned int poff = xdr->page_base & ~PAGE_MASK;
+	unsigned int pglen = xdr->page_len;
+	ssize_t copied = 0;
+	size_t ret;
+
+	if (xdr->head[0].iov_len == 0)
+		return 0;
+
+	ret = xdr_skb_read_bits(desc, xdr->head[0].iov_base,
+				xdr->head[0].iov_len);
+	if (ret != xdr->head[0].iov_len || !desc->count)
+		return ret;
+	copied += ret;
+
+	while (pglen) {
+		unsigned int len = min(PAGE_SIZE - poff, pglen);
+		char *kaddr;
+
+		/* ACL likes to be lazy in allocating pages - ACLs
+		 * are small by default but can get huge. */
+		if ((xdr->flags & XDRBUF_SPARSE_PAGES) && *ppage == NULL) {
+			*ppage = alloc_page(GFP_NOWAIT);
+			if (unlikely(*ppage == NULL)) {
+				if (copied == 0)
+					return -ENOMEM;
+				return copied;
+			}
+		}
+
+		kaddr = kmap_atomic(*ppage);
+		ret = xdr_skb_read_bits(desc, kaddr + poff, len);
+		flush_dcache_page(*ppage);
+		kunmap_atomic(kaddr);
+
+		copied += ret;
+		if (ret != len || !desc->count)
+			return copied;
+		ppage++;
+		pglen -= len;
+		poff = 0;
+	}
+
+	if (xdr->tail[0].iov_len) {
+		copied += xdr_skb_read_bits(desc, xdr->tail[0].iov_base,
+					xdr->tail[0].iov_len);
+	}
+
+	return copied;
+}
+
+/**
+ * csum_partial_copy_to_xdr - checksum and copy data
+ * @xdr: target XDR buffer
+ * @skb: source skb
+ *
+ * We have set things up such that we perform the checksum of the UDP
+ * packet in parallel with the copies into the RPC client iovec.  -DaveM
+ */
+int csum_partial_copy_to_xdr(struct xdr_buf *xdr, struct sk_buff *skb)
+{
+	struct xdr_skb_reader desc = {
+		.skb		= skb,
+		.count		= skb->len - desc.offset,
+	};
+
+	if (skb_csum_unnecessary(skb)) {
+		if (xdr_partial_copy_from_skb(xdr, &desc) < 0)
+			return -1;
+		if (desc.count)
+			return -1;
+		return 0;
+	}
+
+	desc.need_checksum = true;
+	desc.csum = csum_partial(skb->data, desc.offset, skb->csum);
+	if (xdr_partial_copy_from_skb(xdr, &desc) < 0)
+		return -1;
+	if (desc.offset != skb->len) {
+		__wsum csum2;
+		csum2 = skb_checksum(skb, desc.offset, skb->len - desc.offset, 0);
+		desc.csum = csum_block_add(desc.csum, csum2, desc.offset);
+	}
+	if (desc.count)
+		return -1;
+	if (csum_fold(desc.csum))
+		return -1;
+	if (unlikely(skb->ip_summed == CHECKSUM_COMPLETE) &&
+	    !skb->csum_complete_sw)
+		netdev_rx_csum_fault(skb->dev, skb);
+	return 0;
+}
+
+static inline int xprt_sendmsg(struct socket *sock, struct msghdr *msg,
+			       size_t seek)
+{
+	if (seek)
+		iov_iter_advance(&msg->msg_iter, seek);
+	return sock_sendmsg(sock, msg);
+}
+
+static int xprt_send_kvec(struct socket *sock, struct msghdr *msg,
+			  struct kvec *vec, size_t seek)
+{
+	iov_iter_kvec(&msg->msg_iter, ITER_SOURCE, vec, 1, vec->iov_len);
+	return xprt_sendmsg(sock, msg, seek);
+}
+
+static int xprt_send_pagedata(struct socket *sock, struct msghdr *msg,
+			      struct xdr_buf *xdr, size_t base)
+{
+	iov_iter_bvec(&msg->msg_iter, ITER_SOURCE, xdr->bvec, xdr_buf_pagecount(xdr),
+		      xdr->page_len + xdr->page_base);
+	return xprt_sendmsg(sock, msg, base + xdr->page_base);
+}
+
+/* Common case:
+ *  - stream transport
+ *  - sending from byte 0 of the message
+ *  - the message is wholly contained in @xdr's head iovec
+ */
+static int xprt_send_rm_and_kvec(struct socket *sock, struct msghdr *msg,
+				 rpc_fraghdr marker, struct kvec *vec,
+				 size_t base)
+{
+	struct kvec iov[2] = {
+		[0] = {
+			.iov_base	= &marker,
+			.iov_len	= sizeof(marker)
+		},
+		[1] = *vec,
+	};
+	size_t len = iov[0].iov_len + iov[1].iov_len;
+
+	iov_iter_kvec(&msg->msg_iter, ITER_SOURCE, iov, 2, len);
+	return xprt_sendmsg(sock, msg, base);
+}
+
+/**
+ * xprt_sock_sendmsg - write an xdr_buf directly to a socket
+ * @sock: open socket to send on
+ * @msg: socket message metadata
+ * @xdr: xdr_buf containing this request
+ * @base: starting position in the buffer
+ * @marker: stream record marker field
+ * @sent_p: return the total number of bytes successfully queued for sending
+ *
+ * Return values:
+ *   On success, returns zero and fills in @sent_p.
+ *   %-ENOTSOCK if  @sock is not a struct socket.
+ */
+int xprt_sock_sendmsg(struct socket *sock, struct msghdr *msg,
+		      struct xdr_buf *xdr, unsigned int base,
+		      rpc_fraghdr marker, unsigned int *sent_p)
+{
+	unsigned int rmsize = marker ? sizeof(marker) : 0;
+	unsigned int remainder = rmsize + xdr->len - base;
+	unsigned int want;
+	int err = 0;
+
+	*sent_p = 0;
+
+	if (unlikely(!sock))
+		return -ENOTSOCK;
+
+	msg->msg_flags |= MSG_MORE;
+	want = xdr->head[0].iov_len + rmsize;
+	if (base < want) {
+		unsigned int len = want - base;
+
+		remainder -= len;
+		if (remainder == 0)
+			msg->msg_flags &= ~MSG_MORE;
+		if (rmsize)
+			err = xprt_send_rm_and_kvec(sock, msg, marker,
+						    &xdr->head[0], base);
+		else
+			err = xprt_send_kvec(sock, msg, &xdr->head[0], base);
+		if (remainder == 0 || err != len)
+			goto out;
+		*sent_p += err;
+		base = 0;
+	} else {
+		base -= want;
+	}
+
+	if (base < xdr->page_len) {
+		unsigned int len = xdr->page_len - base;
+
+		remainder -= len;
+		if (remainder == 0)
+			msg->msg_flags &= ~MSG_MORE;
+		err = xprt_send_pagedata(sock, msg, xdr, base);
+		if (remainder == 0 || err != len)
+			goto out;
+		*sent_p += err;
+		base = 0;
+	} else {
+		base -= xdr->page_len;
+	}
+
+	if (base >= xdr->tail[0].iov_len)
+		return 0;
+	msg->msg_flags &= ~MSG_MORE;
+	err = xprt_send_kvec(sock, msg, &xdr->tail[0], base);
+out:
+	if (err > 0) {
+		*sent_p += err;
+		err = 0;
+	}
+	return err;
+}