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, 180 insertions, 0 deletions

diff --git a/net/sunrpc/sysctl.c b/net/sunrpc/sysctl.c
new file mode 100644
index 000000000..bdb587a72
--- /dev/null
+++ b/net/sunrpc/sysctl.c
@@ -0,0 +1,180 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * linux/net/sunrpc/sysctl.c
+ *
+ * Sysctl interface to sunrpc module.
+ *
+ * I would prefer to register the sunrpc table below sys/net, but that's
+ * impossible at the moment.
+ */
+
+#include <linux/types.h>
+#include <linux/linkage.h>
+#include <linux/ctype.h>
+#include <linux/fs.h>
+#include <linux/sysctl.h>
+#include <linux/module.h>
+
+#include <linux/uaccess.h>
+#include <linux/sunrpc/types.h>
+#include <linux/sunrpc/sched.h>
+#include <linux/sunrpc/stats.h>
+#include <linux/sunrpc/svc_xprt.h>
+
+#include "netns.h"
+
+/*
+ * Declare the debug flags here
+ */
+unsigned int	rpc_debug;
+EXPORT_SYMBOL_GPL(rpc_debug);
+
+unsigned int	nfs_debug;
+EXPORT_SYMBOL_GPL(nfs_debug);
+
+unsigned int	nfsd_debug;
+EXPORT_SYMBOL_GPL(nfsd_debug);
+
+unsigned int	nlm_debug;
+EXPORT_SYMBOL_GPL(nlm_debug);
+
+#if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
+
+static int proc_do_xprt(const struct ctl_table *table, int write,
+			void *buffer, size_t *lenp, loff_t *ppos)
+{
+	char tmpbuf[256];
+	ssize_t len;
+
+	if (write || *ppos) {
+		*lenp = 0;
+		return 0;
+	}
+	len = svc_print_xprts(tmpbuf, sizeof(tmpbuf));
+	len = memory_read_from_buffer(buffer, *lenp, ppos, tmpbuf, len);
+
+	if (len < 0) {
+		*lenp = 0;
+		return -EINVAL;
+	}
+	*lenp = len;
+	return 0;
+}
+
+static int
+proc_dodebug(const struct ctl_table *table, int write, void *buffer, size_t *lenp,
+	     loff_t *ppos)
+{
+	char		tmpbuf[20], *s = NULL;
+	char *p;
+	unsigned int	value;
+	size_t		left, len;
+
+	if ((*ppos && !write) || !*lenp) {
+		*lenp = 0;
+		return 0;
+	}
+
+	left = *lenp;
+
+	if (write) {
+		p = buffer;
+		while (left && isspace(*p)) {
+			left--;
+			p++;
+		}
+		if (!left)
+			goto done;
+
+		if (left > sizeof(tmpbuf) - 1)
+			return -EINVAL;
+		memcpy(tmpbuf, p, left);
+		tmpbuf[left] = '\0';
+
+		value = simple_strtol(tmpbuf, &s, 0);
+		if (s) {
+			left -= (s - tmpbuf);
+			if (left && !isspace(*s))
+				return -EINVAL;
+			while (left && isspace(*s)) {
+				left--;
+				s++;
+			}
+		} else
+			left = 0;
+		*(unsigned int *) table->data = value;
+		/* Display the RPC tasks on writing to rpc_debug */
+		if (strcmp(table->procname, "rpc_debug") == 0)
+			rpc_show_tasks(&init_net);
+	} else {
+		len = sprintf(tmpbuf, "0x%04x", *(unsigned int *) table->data);
+		if (len > left)
+			len = left;
+		memcpy(buffer, tmpbuf, len);
+		if ((left -= len) > 0) {
+			*((char *)buffer + len) = '\n';
+			left--;
+		}
+	}
+
+done:
+	*lenp -= left;
+	*ppos += *lenp;
+	return 0;
+}
+
+static struct ctl_table_header *sunrpc_table_header;
+
+static struct ctl_table debug_table[] = {
+	{
+		.procname	= "rpc_debug",
+		.data		= &rpc_debug,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dodebug
+	},
+	{
+		.procname	= "nfs_debug",
+		.data		= &nfs_debug,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dodebug
+	},
+	{
+		.procname	= "nfsd_debug",
+		.data		= &nfsd_debug,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dodebug
+	},
+	{
+		.procname	= "nlm_debug",
+		.data		= &nlm_debug,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dodebug
+	},
+	{
+		.procname	= "transports",
+		.maxlen		= 256,
+		.mode		= 0444,
+		.proc_handler	= proc_do_xprt,
+	},
+};
+
+void
+rpc_register_sysctl(void)
+{
+	if (!sunrpc_table_header)
+		sunrpc_table_header = register_sysctl("sunrpc", debug_table);
+}
+
+void
+rpc_unregister_sysctl(void)
+{
+	if (sunrpc_table_header) {
+		unregister_sysctl_table(sunrpc_table_header);
+		sunrpc_table_header = NULL;
+	}
+}
+#endif