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, 345 insertions, 0 deletions

diff --git a/drivers/memory/mvebu-devbus.c b/drivers/memory/mvebu-devbus.c
new file mode 100644
index 000000000..406fddcdb
--- /dev/null
+++ b/drivers/memory/mvebu-devbus.c
@@ -0,0 +1,345 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Marvell EBU SoC Device Bus Controller
+ * (memory controller for NOR/NAND/SRAM/FPGA devices)
+ *
+ * Copyright (C) 2013-2014 Marvell
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/err.h>
+#include <linux/io.h>
+#include <linux/clk.h>
+#include <linux/mbus.h>
+#include <linux/of_platform.h>
+#include <linux/of_address.h>
+#include <linux/platform_device.h>
+
+/* Register definitions */
+#define ARMADA_DEV_WIDTH_SHIFT		30
+#define ARMADA_BADR_SKEW_SHIFT		28
+#define ARMADA_RD_HOLD_SHIFT		23
+#define ARMADA_ACC_NEXT_SHIFT		17
+#define ARMADA_RD_SETUP_SHIFT		12
+#define ARMADA_ACC_FIRST_SHIFT		6
+
+#define ARMADA_SYNC_ENABLE_SHIFT	24
+#define ARMADA_WR_HIGH_SHIFT		16
+#define ARMADA_WR_LOW_SHIFT		8
+
+#define ARMADA_READ_PARAM_OFFSET	0x0
+#define ARMADA_WRITE_PARAM_OFFSET	0x4
+
+#define ORION_RESERVED			(0x2 << 30)
+#define ORION_BADR_SKEW_SHIFT		28
+#define ORION_WR_HIGH_EXT_BIT		BIT(27)
+#define ORION_WR_HIGH_EXT_MASK		0x8
+#define ORION_WR_LOW_EXT_BIT		BIT(26)
+#define ORION_WR_LOW_EXT_MASK		0x8
+#define ORION_ALE_WR_EXT_BIT		BIT(25)
+#define ORION_ALE_WR_EXT_MASK		0x8
+#define ORION_ACC_NEXT_EXT_BIT		BIT(24)
+#define ORION_ACC_NEXT_EXT_MASK		0x10
+#define ORION_ACC_FIRST_EXT_BIT		BIT(23)
+#define ORION_ACC_FIRST_EXT_MASK	0x10
+#define ORION_TURN_OFF_EXT_BIT		BIT(22)
+#define ORION_TURN_OFF_EXT_MASK		0x8
+#define ORION_DEV_WIDTH_SHIFT		20
+#define ORION_WR_HIGH_SHIFT		17
+#define ORION_WR_HIGH_MASK		0x7
+#define ORION_WR_LOW_SHIFT		14
+#define ORION_WR_LOW_MASK		0x7
+#define ORION_ALE_WR_SHIFT		11
+#define ORION_ALE_WR_MASK		0x7
+#define ORION_ACC_NEXT_SHIFT		7
+#define ORION_ACC_NEXT_MASK		0xF
+#define ORION_ACC_FIRST_SHIFT		3
+#define ORION_ACC_FIRST_MASK		0xF
+#define ORION_TURN_OFF_SHIFT		0
+#define ORION_TURN_OFF_MASK		0x7
+
+struct devbus_read_params {
+	u32 bus_width;
+	u32 badr_skew;
+	u32 turn_off;
+	u32 acc_first;
+	u32 acc_next;
+	u32 rd_setup;
+	u32 rd_hold;
+};
+
+struct devbus_write_params {
+	u32 sync_enable;
+	u32 wr_high;
+	u32 wr_low;
+	u32 ale_wr;
+};
+
+struct devbus {
+	struct device *dev;
+	void __iomem *base;
+	unsigned long tick_ps;
+};
+
+static int get_timing_param_ps(struct devbus *devbus,
+			       struct device_node *node,
+			       const char *name,
+			       u32 *ticks)
+{
+	u32 time_ps;
+	int err;
+
+	err = of_property_read_u32(node, name, &time_ps);
+	if (err < 0) {
+		dev_err(devbus->dev, "%pOF has no '%s' property\n",
+			node, name);
+		return err;
+	}
+
+	*ticks = (time_ps + devbus->tick_ps - 1) / devbus->tick_ps;
+
+	dev_dbg(devbus->dev, "%s: %u ps -> 0x%x\n",
+		name, time_ps, *ticks);
+	return 0;
+}
+
+static int devbus_get_timing_params(struct devbus *devbus,
+				    struct device_node *node,
+				    struct devbus_read_params *r,
+				    struct devbus_write_params *w)
+{
+	int err;
+
+	err = of_property_read_u32(node, "devbus,bus-width", &r->bus_width);
+	if (err < 0) {
+		dev_err(devbus->dev,
+			"%pOF has no 'devbus,bus-width' property\n",
+			node);
+		return err;
+	}
+
+	/*
+	 * The bus width is encoded into the register as 0 for 8 bits,
+	 * and 1 for 16 bits, so we do the necessary conversion here.
+	 */
+	if (r->bus_width == 8) {
+		r->bus_width = 0;
+	} else if (r->bus_width == 16) {
+		r->bus_width = 1;
+	} else {
+		dev_err(devbus->dev, "invalid bus width %d\n", r->bus_width);
+		return -EINVAL;
+	}
+
+	err = get_timing_param_ps(devbus, node, "devbus,badr-skew-ps",
+				  &r->badr_skew);
+	if (err < 0)
+		return err;
+
+	err = get_timing_param_ps(devbus, node, "devbus,turn-off-ps",
+				  &r->turn_off);
+	if (err < 0)
+		return err;
+
+	err = get_timing_param_ps(devbus, node, "devbus,acc-first-ps",
+				  &r->acc_first);
+	if (err < 0)
+		return err;
+
+	err = get_timing_param_ps(devbus, node, "devbus,acc-next-ps",
+				  &r->acc_next);
+	if (err < 0)
+		return err;
+
+	if (of_device_is_compatible(devbus->dev->of_node, "marvell,mvebu-devbus")) {
+		err = get_timing_param_ps(devbus, node, "devbus,rd-setup-ps",
+					  &r->rd_setup);
+		if (err < 0)
+			return err;
+
+		err = get_timing_param_ps(devbus, node, "devbus,rd-hold-ps",
+					  &r->rd_hold);
+		if (err < 0)
+			return err;
+
+		err = of_property_read_u32(node, "devbus,sync-enable",
+					   &w->sync_enable);
+		if (err < 0) {
+			dev_err(devbus->dev,
+				"%pOF has no 'devbus,sync-enable' property\n",
+				node);
+			return err;
+		}
+	}
+
+	err = get_timing_param_ps(devbus, node, "devbus,ale-wr-ps",
+				  &w->ale_wr);
+	if (err < 0)
+		return err;
+
+	err = get_timing_param_ps(devbus, node, "devbus,wr-low-ps",
+				  &w->wr_low);
+	if (err < 0)
+		return err;
+
+	err = get_timing_param_ps(devbus, node, "devbus,wr-high-ps",
+				  &w->wr_high);
+	if (err < 0)
+		return err;
+
+	return 0;
+}
+
+static void devbus_orion_set_timing_params(struct devbus *devbus,
+					  struct device_node *node,
+					  struct devbus_read_params *r,
+					  struct devbus_write_params *w)
+{
+	u32 value;
+
+	/*
+	 * The hardware designers found it would be a good idea to
+	 * split most of the values in the register into two fields:
+	 * one containing all the low-order bits, and another one
+	 * containing just the high-order bit. For all of those
+	 * fields, we have to split the value into these two parts.
+	 */
+	value =	(r->turn_off   & ORION_TURN_OFF_MASK)  << ORION_TURN_OFF_SHIFT  |
+		(r->acc_first  & ORION_ACC_FIRST_MASK) << ORION_ACC_FIRST_SHIFT |
+		(r->acc_next   & ORION_ACC_NEXT_MASK)  << ORION_ACC_NEXT_SHIFT  |
+		(w->ale_wr     & ORION_ALE_WR_MASK)    << ORION_ALE_WR_SHIFT    |
+		(w->wr_low     & ORION_WR_LOW_MASK)    << ORION_WR_LOW_SHIFT    |
+		(w->wr_high    & ORION_WR_HIGH_MASK)   << ORION_WR_HIGH_SHIFT   |
+		r->bus_width                           << ORION_DEV_WIDTH_SHIFT |
+		((r->turn_off  & ORION_TURN_OFF_EXT_MASK)  ? ORION_TURN_OFF_EXT_BIT  : 0) |
+		((r->acc_first & ORION_ACC_FIRST_EXT_MASK) ? ORION_ACC_FIRST_EXT_BIT : 0) |
+		((r->acc_next  & ORION_ACC_NEXT_EXT_MASK)  ? ORION_ACC_NEXT_EXT_BIT  : 0) |
+		((w->ale_wr    & ORION_ALE_WR_EXT_MASK)    ? ORION_ALE_WR_EXT_BIT    : 0) |
+		((w->wr_low    & ORION_WR_LOW_EXT_MASK)    ? ORION_WR_LOW_EXT_BIT    : 0) |
+		((w->wr_high   & ORION_WR_HIGH_EXT_MASK)   ? ORION_WR_HIGH_EXT_BIT   : 0) |
+		(r->badr_skew << ORION_BADR_SKEW_SHIFT) |
+		ORION_RESERVED;
+
+	writel(value, devbus->base);
+}
+
+static void devbus_armada_set_timing_params(struct devbus *devbus,
+					   struct device_node *node,
+					   struct devbus_read_params *r,
+					   struct devbus_write_params *w)
+{
+	u32 value;
+
+	/* Set read timings */
+	value = r->bus_width << ARMADA_DEV_WIDTH_SHIFT |
+		r->badr_skew << ARMADA_BADR_SKEW_SHIFT |
+		r->rd_hold   << ARMADA_RD_HOLD_SHIFT   |
+		r->acc_next  << ARMADA_ACC_NEXT_SHIFT  |
+		r->rd_setup  << ARMADA_RD_SETUP_SHIFT  |
+		r->acc_first << ARMADA_ACC_FIRST_SHIFT |
+		r->turn_off;
+
+	dev_dbg(devbus->dev, "read parameters register 0x%p = 0x%x\n",
+		devbus->base + ARMADA_READ_PARAM_OFFSET,
+		value);
+
+	writel(value, devbus->base + ARMADA_READ_PARAM_OFFSET);
+
+	/* Set write timings */
+	value = w->sync_enable  << ARMADA_SYNC_ENABLE_SHIFT |
+		w->wr_low       << ARMADA_WR_LOW_SHIFT      |
+		w->wr_high      << ARMADA_WR_HIGH_SHIFT     |
+		w->ale_wr;
+
+	dev_dbg(devbus->dev, "write parameters register: 0x%p = 0x%x\n",
+		devbus->base + ARMADA_WRITE_PARAM_OFFSET,
+		value);
+
+	writel(value, devbus->base + ARMADA_WRITE_PARAM_OFFSET);
+}
+
+static int mvebu_devbus_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct device_node *node = pdev->dev.of_node;
+	struct devbus_read_params r;
+	struct devbus_write_params w;
+	struct devbus *devbus;
+	struct clk *clk;
+	unsigned long rate;
+	int err;
+
+	devbus = devm_kzalloc(&pdev->dev, sizeof(struct devbus), GFP_KERNEL);
+	if (!devbus)
+		return -ENOMEM;
+
+	devbus->dev = dev;
+	devbus->base = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(devbus->base))
+		return PTR_ERR(devbus->base);
+
+	clk = devm_clk_get_enabled(&pdev->dev, NULL);
+	if (IS_ERR(clk))
+		return PTR_ERR(clk);
+
+	/*
+	 * Obtain clock period in picoseconds,
+	 * we need this in order to convert timing
+	 * parameters from cycles to picoseconds.
+	 */
+	rate = clk_get_rate(clk) / 1000;
+	devbus->tick_ps = 1000000000 / rate;
+
+	dev_dbg(devbus->dev, "Setting timing parameter, tick is %lu ps\n",
+		devbus->tick_ps);
+
+	if (!of_property_read_bool(node, "devbus,keep-config")) {
+		/* Read the Device Tree node */
+		err = devbus_get_timing_params(devbus, node, &r, &w);
+		if (err < 0)
+			return err;
+
+		/* Set the new timing parameters */
+		if (of_device_is_compatible(node, "marvell,orion-devbus"))
+			devbus_orion_set_timing_params(devbus, node, &r, &w);
+		else
+			devbus_armada_set_timing_params(devbus, node, &r, &w);
+	}
+
+	/*
+	 * We need to create a child device explicitly from here to
+	 * guarantee that the child will be probed after the timing
+	 * parameters for the bus are written.
+	 */
+	err = of_platform_populate(node, NULL, NULL, dev);
+	if (err < 0)
+		return err;
+
+	return 0;
+}
+
+static const struct of_device_id mvebu_devbus_of_match[] = {
+	{ .compatible = "marvell,mvebu-devbus" },
+	{ .compatible = "marvell,orion-devbus" },
+	{},
+};
+MODULE_DEVICE_TABLE(of, mvebu_devbus_of_match);
+
+static struct platform_driver mvebu_devbus_driver = {
+	.probe		= mvebu_devbus_probe,
+	.driver		= {
+		.name	= "mvebu-devbus",
+		.of_match_table = mvebu_devbus_of_match,
+	},
+};
+
+static int __init mvebu_devbus_init(void)
+{
+	return platform_driver_register(&mvebu_devbus_driver);
+}
+module_init(mvebu_devbus_init);
+
+MODULE_AUTHOR("Ezequiel Garcia <ezequiel.garcia@free-electrons.com>");
+MODULE_DESCRIPTION("Marvell EBU SoC Device Bus controller");