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, 77 insertions, 0 deletions

diff --git a/drivers/edac/layerscape_edac.c b/drivers/edac/layerscape_edac.c
new file mode 100644
index 000000000..a2caa7fc5
--- /dev/null
+++ b/drivers/edac/layerscape_edac.c
@@ -0,0 +1,77 @@
+/*
+ * Freescale Memory Controller kernel module
+ *
+ * Author: York Sun <york.sun@nxp.com>
+ *
+ * Copyright 2016 NXP Semiconductor
+ *
+ * Derived from mpc85xx_edac.c
+ * Author: Dave Jiang <djiang@mvista.com>
+ *
+ * 2006-2007 (c) MontaVista Software, Inc. This file is licensed under
+ * the terms of the GNU General Public License version 2. This program
+ * is licensed "as is" without any warranty of any kind, whether express
+ * or implied.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include "edac_module.h"
+#include "fsl_ddr_edac.h"
+
+static const struct of_device_id fsl_ddr_mc_err_of_match[] = {
+	{ .compatible = "fsl,qoriq-memory-controller", },
+	{ .compatible = "nxp,imx9-memory-controller", .data = (void *)TYPE_IMX9, },
+	{},
+};
+MODULE_DEVICE_TABLE(of, fsl_ddr_mc_err_of_match);
+
+static struct platform_driver fsl_ddr_mc_err_driver = {
+	.probe = fsl_mc_err_probe,
+	.remove = fsl_mc_err_remove,
+	.driver = {
+		.name = "fsl_ddr_mc_err",
+		.of_match_table = fsl_ddr_mc_err_of_match,
+	},
+};
+
+static int __init fsl_ddr_mc_init(void)
+{
+	int res;
+
+	if (ghes_get_devices())
+		return -EBUSY;
+
+	/* make sure error reporting method is sane */
+	switch (edac_op_state) {
+	case EDAC_OPSTATE_POLL:
+	case EDAC_OPSTATE_INT:
+		break;
+	default:
+		edac_op_state = EDAC_OPSTATE_INT;
+		break;
+	}
+
+	res = platform_driver_register(&fsl_ddr_mc_err_driver);
+	if (res) {
+		pr_err("MC fails to register\n");
+		return res;
+	}
+
+	return 0;
+}
+
+module_init(fsl_ddr_mc_init);
+
+static void __exit fsl_ddr_mc_exit(void)
+{
+	platform_driver_unregister(&fsl_ddr_mc_err_driver);
+}
+
+module_exit(fsl_ddr_mc_exit);
+
+MODULE_DESCRIPTION("Freescale Layerscape EDAC driver");
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("NXP Semiconductor");
+module_param(edac_op_state, int, 0444);
+MODULE_PARM_DESC(edac_op_state, "EDAC Error Reporting state: 0=Poll, 2=Interrupt");