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, 142 insertions, 0 deletions

diff --git a/drivers/interconnect/mediatek/mt8183.c b/drivers/interconnect/mediatek/mt8183.c
new file mode 100644
index 000000000..ed607a8b8
--- /dev/null
+++ b/drivers/interconnect/mediatek/mt8183.c
@@ -0,0 +1,142 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2021 MediaTek Inc.
+ * Copyright (c) 2024 Collabora Ltd.
+ *                    AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
+ */
+
+#include <linux/device.h>
+#include <linux/interconnect.h>
+#include <linux/interconnect-provider.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <dt-bindings/interconnect/mediatek,mt8183.h>
+
+#include "icc-emi.h"
+
+static struct mtk_icc_node ddr_emi = {
+	.name = "ddr-emi",
+	.id = SLAVE_DDR_EMI,
+	.ep = 1,
+};
+
+static struct mtk_icc_node mcusys = {
+	.name = "mcusys",
+	.id = MASTER_MCUSYS,
+	.ep = 0,
+	.num_links = 1,
+	.links = { SLAVE_DDR_EMI }
+};
+
+static struct mtk_icc_node gpu = {
+	.name = "gpu",
+	.id = MASTER_MFG,
+	.ep = 0,
+	.num_links = 1,
+	.links = { SLAVE_DDR_EMI }
+};
+
+static struct mtk_icc_node mmsys = {
+	.name = "mmsys",
+	.id = MASTER_MMSYS,
+	.ep = 0,
+	.num_links = 1,
+	.links = { SLAVE_DDR_EMI }
+};
+
+static struct mtk_icc_node mm_vpu = {
+	.name = "mm-vpu",
+	.id = MASTER_MM_VPU,
+	.ep = 0,
+	.num_links = 1,
+	.links = { MASTER_MMSYS }
+};
+
+static struct mtk_icc_node mm_disp = {
+	.name = "mm-disp",
+	.id = MASTER_MM_DISP,
+	.ep = 0,
+	.num_links = 1,
+	.links = { MASTER_MMSYS }
+};
+
+static struct mtk_icc_node mm_vdec = {
+	.name = "mm-vdec",
+	.id = MASTER_MM_VDEC,
+	.ep = 0,
+	.num_links = 1,
+	.links = { MASTER_MMSYS }
+};
+
+static struct mtk_icc_node mm_venc = {
+	.name = "mm-venc",
+	.id = MASTER_MM_VENC,
+	.ep = 0,
+	.num_links = 1,
+	.links = { MASTER_MMSYS }
+};
+
+static struct mtk_icc_node mm_cam = {
+	.name = "mm-cam",
+	.id = MASTER_MM_CAM,
+	.ep = 0,
+	.num_links = 1,
+	.links = { MASTER_MMSYS }
+};
+
+static struct mtk_icc_node mm_img = {
+	.name = "mm-img",
+	.id = MASTER_MM_IMG,
+	.ep = 0,
+	.num_links = 1,
+	.links = { MASTER_MMSYS }
+};
+
+static struct mtk_icc_node mm_mdp = {
+	.name = "mm-mdp",
+	.id = MASTER_MM_MDP,
+	.ep = 0,
+	.num_links = 1,
+	.links = { MASTER_MMSYS }
+};
+
+static struct mtk_icc_node *mt8183_emi_icc_nodes[] = {
+	[SLAVE_DDR_EMI] = &ddr_emi,
+	[MASTER_MCUSYS] = &mcusys,
+	[MASTER_MFG] = &gpu,
+	[MASTER_MMSYS] = &mmsys,
+	[MASTER_MM_VPU] = &mm_vpu,
+	[MASTER_MM_DISP] = &mm_disp,
+	[MASTER_MM_VDEC] = &mm_vdec,
+	[MASTER_MM_VENC] = &mm_venc,
+	[MASTER_MM_CAM] = &mm_cam,
+	[MASTER_MM_IMG] = &mm_img,
+	[MASTER_MM_MDP] = &mm_mdp
+};
+
+static const struct mtk_icc_desc mt8183_emi_icc = {
+	.nodes = mt8183_emi_icc_nodes,
+	.num_nodes = ARRAY_SIZE(mt8183_emi_icc_nodes),
+};
+
+static const struct of_device_id mtk_mt8183_emi_icc_of_match[] = {
+	{ .compatible = "mediatek,mt8183-emi", .data = &mt8183_emi_icc },
+	{ /* sentinel */ },
+};
+MODULE_DEVICE_TABLE(of, mtk_mt8183_emi_icc_of_match);
+
+static struct platform_driver mtk_emi_icc_mt8183_driver = {
+	.driver = {
+		.name = "emi-icc-mt8183",
+		.of_match_table = mtk_mt8183_emi_icc_of_match,
+		.sync_state = icc_sync_state,
+	},
+	.probe = mtk_emi_icc_probe,
+	.remove = mtk_emi_icc_remove,
+
+};
+module_platform_driver(mtk_emi_icc_mt8183_driver);
+
+MODULE_AUTHOR("AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>");
+MODULE_DESCRIPTION("MediaTek MT8183 EMI ICC driver");
+MODULE_LICENSE("GPL");