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, 103 insertions, 0 deletions

diff --git a/drivers/bus/fsl-mc/obj-api.c b/drivers/bus/fsl-mc/obj-api.c
new file mode 100644
index 000000000..06c1dd84e
--- /dev/null
+++ b/drivers/bus/fsl-mc/obj-api.c
@@ -0,0 +1,103 @@
+// SPDX-License-Identifier: (GPL-2.0+ OR BSD-3-Clause)
+/*
+ * Copyright 2021 NXP
+ *
+ */
+#include <linux/kernel.h>
+#include <linux/fsl/mc.h>
+
+#include "fsl-mc-private.h"
+
+static int fsl_mc_get_open_cmd_id(const char *type)
+{
+	static const struct {
+		int cmd_id;
+		const char *type;
+	} dev_ids[] = {
+		{ DPRTC_CMDID_OPEN, "dprtc" },
+		{ DPRC_CMDID_OPEN, "dprc" },
+		{ DPNI_CMDID_OPEN, "dpni" },
+		{ DPIO_CMDID_OPEN, "dpio" },
+		{ DPSW_CMDID_OPEN, "dpsw" },
+		{ DPBP_CMDID_OPEN, "dpbp" },
+		{ DPCON_CMDID_OPEN, "dpcon" },
+		{ DPMCP_CMDID_OPEN, "dpmcp" },
+		{ DPMAC_CMDID_OPEN, "dpmac" },
+		{ DPSECI_CMDID_OPEN, "dpseci" },
+		{ DPDMUX_CMDID_OPEN, "dpdmux" },
+		{ DPDCEI_CMDID_OPEN, "dpdcei" },
+		{ DPAIOP_CMDID_OPEN, "dpaiop" },
+		{ DPCI_CMDID_OPEN, "dpci" },
+		{ DPDMAI_CMDID_OPEN, "dpdmai" },
+		{ DPDBG_CMDID_OPEN, "dpdbg" },
+		{ 0, NULL }
+	};
+	int i;
+
+	for (i = 0; dev_ids[i].type; i++)
+		if (!strcmp(dev_ids[i].type, type))
+			return dev_ids[i].cmd_id;
+
+	return -1;
+}
+
+int fsl_mc_obj_open(struct fsl_mc_io *mc_io,
+		    u32 cmd_flags,
+		    int obj_id,
+		    char *obj_type,
+		    u16 *token)
+{
+	struct fsl_mc_command cmd = { 0 };
+	struct fsl_mc_obj_cmd_open *cmd_params;
+	int err = 0;
+	int cmd_id = fsl_mc_get_open_cmd_id(obj_type);
+
+	if (cmd_id == -1)
+		return -ENODEV;
+
+	/* prepare command */
+	cmd.header = mc_encode_cmd_header(cmd_id, cmd_flags, 0);
+	cmd_params = (struct fsl_mc_obj_cmd_open *)cmd.params;
+	cmd_params->obj_id = cpu_to_le32(obj_id);
+
+	/* send command to mc*/
+	err = mc_send_command(mc_io, &cmd);
+	if (err)
+		return err;
+
+	/* retrieve response parameters */
+	*token = mc_cmd_hdr_read_token(&cmd);
+
+	return err;
+}
+EXPORT_SYMBOL_GPL(fsl_mc_obj_open);
+
+int fsl_mc_obj_close(struct fsl_mc_io *mc_io,
+		     u32 cmd_flags,
+		     u16 token)
+{
+	struct fsl_mc_command cmd = { 0 };
+
+	/* prepare command */
+	cmd.header = mc_encode_cmd_header(OBJ_CMDID_CLOSE, cmd_flags,
+					  token);
+
+	/* send command to mc*/
+	return mc_send_command(mc_io, &cmd);
+}
+EXPORT_SYMBOL_GPL(fsl_mc_obj_close);
+
+int fsl_mc_obj_reset(struct fsl_mc_io *mc_io,
+		     u32 cmd_flags,
+		     u16 token)
+{
+	struct fsl_mc_command cmd = { 0 };
+
+	/* prepare command */
+	cmd.header = mc_encode_cmd_header(OBJ_CMDID_RESET, cmd_flags,
+					  token);
+
+	/* send command to mc*/
+	return mc_send_command(mc_io, &cmd);
+}
+EXPORT_SYMBOL_GPL(fsl_mc_obj_reset);