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, 421 insertions, 0 deletions

diff --git a/drivers/misc/dw-xdata-pcie.c b/drivers/misc/dw-xdata-pcie.c
new file mode 100644
index 000000000..a604c0e9c
--- /dev/null
+++ b/drivers/misc/dw-xdata-pcie.c
@@ -0,0 +1,421 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2020 Synopsys, Inc. and/or its affiliates.
+ * Synopsys DesignWare xData driver
+ *
+ * Author: Gustavo Pimentel <gustavo.pimentel@synopsys.com>
+ */
+
+#include <linux/miscdevice.h>
+#include <linux/bitfield.h>
+#include <linux/pci-epf.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/device.h>
+#include <linux/bitops.h>
+#include <linux/mutex.h>
+#include <linux/delay.h>
+#include <linux/pci.h>
+#include <linux/string_choices.h>
+
+#define DW_XDATA_DRIVER_NAME		"dw-xdata-pcie"
+
+#define DW_XDATA_EP_MEM_OFFSET		0x8000000
+
+static DEFINE_IDA(xdata_ida);
+
+#define STATUS_DONE			BIT(0)
+
+#define CONTROL_DOORBELL		BIT(0)
+#define CONTROL_IS_WRITE		BIT(1)
+#define CONTROL_LENGTH(a)		FIELD_PREP(GENMASK(13, 2), a)
+#define CONTROL_PATTERN_INC		BIT(16)
+#define CONTROL_NO_ADDR_INC		BIT(18)
+
+#define XPERF_CONTROL_ENABLE		BIT(5)
+
+#define BURST_REPEAT			BIT(31)
+#define BURST_VALUE			0x1001
+
+#define PATTERN_VALUE			0x0
+
+struct dw_xdata_regs {
+	u32 addr_lsb;					/* 0x000 */
+	u32 addr_msb;					/* 0x004 */
+	u32 burst_cnt;					/* 0x008 */
+	u32 control;					/* 0x00c */
+	u32 pattern;					/* 0x010 */
+	u32 status;					/* 0x014 */
+	u32 RAM_addr;					/* 0x018 */
+	u32 RAM_port;					/* 0x01c */
+	u32 _reserved0[14];				/* 0x020..0x054 */
+	u32 perf_control;				/* 0x058 */
+	u32 _reserved1[41];				/* 0x05c..0x0fc */
+	u32 wr_cnt_lsb;					/* 0x100 */
+	u32 wr_cnt_msb;					/* 0x104 */
+	u32 rd_cnt_lsb;					/* 0x108 */
+	u32 rd_cnt_msb;					/* 0x10c */
+} __packed;
+
+struct dw_xdata_region {
+	phys_addr_t paddr;				/* physical address */
+	void __iomem *vaddr;				/* virtual address */
+};
+
+struct dw_xdata {
+	struct dw_xdata_region rg_region;		/* registers */
+	size_t max_wr_len;				/* max wr xfer len */
+	size_t max_rd_len;				/* max rd xfer len */
+	struct mutex mutex;
+	struct pci_dev *pdev;
+	struct miscdevice misc_dev;
+};
+
+static inline struct dw_xdata_regs __iomem *__dw_regs(struct dw_xdata *dw)
+{
+	return dw->rg_region.vaddr;
+}
+
+static void dw_xdata_stop(struct dw_xdata *dw)
+{
+	u32 burst;
+
+	mutex_lock(&dw->mutex);
+
+	burst = readl(&(__dw_regs(dw)->burst_cnt));
+
+	if (burst & BURST_REPEAT) {
+		burst &= ~(u32)BURST_REPEAT;
+		writel(burst, &(__dw_regs(dw)->burst_cnt));
+	}
+
+	mutex_unlock(&dw->mutex);
+}
+
+static void dw_xdata_start(struct dw_xdata *dw, bool write)
+{
+	struct device *dev = &dw->pdev->dev;
+	u32 control, status;
+
+	/* Stop first if xfer in progress */
+	dw_xdata_stop(dw);
+
+	mutex_lock(&dw->mutex);
+
+	/* Clear status register */
+	writel(0x0, &(__dw_regs(dw)->status));
+
+	/* Burst count register set for continuous until stopped */
+	writel(BURST_REPEAT | BURST_VALUE, &(__dw_regs(dw)->burst_cnt));
+
+	/* Pattern register */
+	writel(PATTERN_VALUE, &(__dw_regs(dw)->pattern));
+
+	/* Control register */
+	control = CONTROL_DOORBELL | CONTROL_PATTERN_INC | CONTROL_NO_ADDR_INC;
+	if (write) {
+		control |= CONTROL_IS_WRITE;
+		control |= CONTROL_LENGTH(dw->max_wr_len);
+	} else {
+		control |= CONTROL_LENGTH(dw->max_rd_len);
+	}
+	writel(control, &(__dw_regs(dw)->control));
+
+	/*
+	 * The xData HW block needs about 100 ms to initiate the traffic
+	 * generation according this HW block datasheet.
+	 */
+	usleep_range(100, 150);
+
+	status = readl(&(__dw_regs(dw)->status));
+
+	mutex_unlock(&dw->mutex);
+
+	if (!(status & STATUS_DONE))
+		dev_dbg(dev, "xData: started %s direction\n",
+			str_write_read(write));
+}
+
+static void dw_xdata_perf_meas(struct dw_xdata *dw, u64 *data, bool write)
+{
+	if (write) {
+		*data = readl(&(__dw_regs(dw)->wr_cnt_msb));
+		*data <<= 32;
+		*data |= readl(&(__dw_regs(dw)->wr_cnt_lsb));
+	} else {
+		*data = readl(&(__dw_regs(dw)->rd_cnt_msb));
+		*data <<= 32;
+		*data |= readl(&(__dw_regs(dw)->rd_cnt_lsb));
+	}
+}
+
+static u64 dw_xdata_perf_diff(u64 *m1, u64 *m2, u64 time)
+{
+	u64 rate = (*m1 - *m2);
+
+	rate *= (1000 * 1000 * 1000);
+	rate >>= 20;
+	rate = DIV_ROUND_CLOSEST_ULL(rate, time);
+
+	return rate;
+}
+
+static void dw_xdata_perf(struct dw_xdata *dw, u64 *rate, bool write)
+{
+	struct device *dev = &dw->pdev->dev;
+	u64 data[2], time[2], diff;
+
+	mutex_lock(&dw->mutex);
+
+	/* First acquisition of current count frames */
+	writel(0x0, &(__dw_regs(dw)->perf_control));
+	dw_xdata_perf_meas(dw, &data[0], write);
+	time[0] = jiffies;
+	writel((u32)XPERF_CONTROL_ENABLE, &(__dw_regs(dw)->perf_control));
+
+	/*
+	 * Wait 100ms between the 1st count frame acquisition and the 2nd
+	 * count frame acquisition, in order to calculate the speed later
+	 */
+	mdelay(100);
+
+	/* Second acquisition of current count frames */
+	writel(0x0, &(__dw_regs(dw)->perf_control));
+	dw_xdata_perf_meas(dw, &data[1], write);
+	time[1] = jiffies;
+	writel((u32)XPERF_CONTROL_ENABLE, &(__dw_regs(dw)->perf_control));
+
+	/*
+	 * Speed calculation
+	 *
+	 * rate = (2nd count frames - 1st count frames) / (time elapsed)
+	 */
+	diff = jiffies_to_nsecs(time[1] - time[0]);
+	*rate = dw_xdata_perf_diff(&data[1], &data[0], diff);
+
+	mutex_unlock(&dw->mutex);
+
+	dev_dbg(dev, "xData: time=%llu us, %s=%llu MB/s\n",
+		diff, str_write_read(write), *rate);
+}
+
+static struct dw_xdata *misc_dev_to_dw(struct miscdevice *misc_dev)
+{
+	return container_of(misc_dev, struct dw_xdata, misc_dev);
+}
+
+static ssize_t write_show(struct device *dev, struct device_attribute *attr,
+			  char *buf)
+{
+	struct miscdevice *misc_dev = dev_get_drvdata(dev);
+	struct dw_xdata *dw = misc_dev_to_dw(misc_dev);
+	u64 rate;
+
+	dw_xdata_perf(dw, &rate, true);
+
+	return sysfs_emit(buf, "%llu\n", rate);
+}
+
+static ssize_t write_store(struct device *dev, struct device_attribute *attr,
+			   const char *buf, size_t size)
+{
+	struct miscdevice *misc_dev = dev_get_drvdata(dev);
+	struct dw_xdata *dw = misc_dev_to_dw(misc_dev);
+	bool enabled;
+	int ret;
+
+	ret = kstrtobool(buf, &enabled);
+	if (ret < 0)
+		return ret;
+
+	if (enabled) {
+		dev_dbg(dev, "xData: requested write transfer\n");
+		dw_xdata_start(dw, true);
+	} else {
+		dev_dbg(dev, "xData: requested stop transfer\n");
+		dw_xdata_stop(dw);
+	}
+
+	return size;
+}
+
+static DEVICE_ATTR_RW(write);
+
+static ssize_t read_show(struct device *dev, struct device_attribute *attr,
+			 char *buf)
+{
+	struct miscdevice *misc_dev = dev_get_drvdata(dev);
+	struct dw_xdata *dw = misc_dev_to_dw(misc_dev);
+	u64 rate;
+
+	dw_xdata_perf(dw, &rate, false);
+
+	return sysfs_emit(buf, "%llu\n", rate);
+}
+
+static ssize_t read_store(struct device *dev, struct device_attribute *attr,
+			  const char *buf, size_t size)
+{
+	struct miscdevice *misc_dev = dev_get_drvdata(dev);
+	struct dw_xdata *dw = misc_dev_to_dw(misc_dev);
+	bool enabled;
+	int ret;
+
+	ret = kstrtobool(buf, &enabled);
+	if (ret < 0)
+		return ret;
+
+	if (enabled) {
+		dev_dbg(dev, "xData: requested read transfer\n");
+		dw_xdata_start(dw, false);
+	} else {
+		dev_dbg(dev, "xData: requested stop transfer\n");
+		dw_xdata_stop(dw);
+	}
+
+	return size;
+}
+
+static DEVICE_ATTR_RW(read);
+
+static struct attribute *xdata_attrs[] = {
+	&dev_attr_write.attr,
+	&dev_attr_read.attr,
+	NULL,
+};
+
+ATTRIBUTE_GROUPS(xdata);
+
+static int dw_xdata_pcie_probe(struct pci_dev *pdev,
+			       const struct pci_device_id *pid)
+{
+	struct device *dev = &pdev->dev;
+	struct dw_xdata *dw;
+	char name[24];
+	u64 addr;
+	int err;
+	int id;
+
+	/* Enable PCI device */
+	err = pcim_enable_device(pdev);
+	if (err) {
+		dev_err(dev, "enabling device failed\n");
+		return err;
+	}
+
+	/* Mapping PCI BAR regions */
+	err = pcim_iomap_regions(pdev, BIT(BAR_0), pci_name(pdev));
+	if (err) {
+		dev_err(dev, "xData BAR I/O remapping failed\n");
+		return err;
+	}
+
+	pci_set_master(pdev);
+
+	/* Allocate memory */
+	dw = devm_kzalloc(dev, sizeof(*dw), GFP_KERNEL);
+	if (!dw)
+		return -ENOMEM;
+
+	/* Data structure initialization */
+	mutex_init(&dw->mutex);
+
+	dw->rg_region.vaddr = pcim_iomap_table(pdev)[BAR_0];
+	if (!dw->rg_region.vaddr)
+		return -ENOMEM;
+
+	dw->rg_region.paddr = pdev->resource[BAR_0].start;
+
+	dw->max_wr_len = pcie_get_mps(pdev);
+	dw->max_wr_len >>= 2;
+
+	dw->max_rd_len = pcie_get_readrq(pdev);
+	dw->max_rd_len >>= 2;
+
+	dw->pdev = pdev;
+
+	id = ida_alloc(&xdata_ida, GFP_KERNEL);
+	if (id < 0) {
+		dev_err(dev, "xData: unable to get id\n");
+		return id;
+	}
+
+	snprintf(name, sizeof(name), DW_XDATA_DRIVER_NAME ".%d", id);
+	dw->misc_dev.name = kstrdup(name, GFP_KERNEL);
+	if (!dw->misc_dev.name) {
+		err = -ENOMEM;
+		goto err_ida_remove;
+	}
+
+	dw->misc_dev.minor = MISC_DYNAMIC_MINOR;
+	dw->misc_dev.parent = dev;
+	dw->misc_dev.groups = xdata_groups;
+
+	writel(0x0, &(__dw_regs(dw)->RAM_addr));
+	writel(0x0, &(__dw_regs(dw)->RAM_port));
+
+	addr = dw->rg_region.paddr + DW_XDATA_EP_MEM_OFFSET;
+	writel(lower_32_bits(addr), &(__dw_regs(dw)->addr_lsb));
+	writel(upper_32_bits(addr), &(__dw_regs(dw)->addr_msb));
+	dev_dbg(dev, "xData: target address = 0x%.16llx\n", addr);
+
+	dev_dbg(dev, "xData: wr_len = %zu, rd_len = %zu\n",
+		dw->max_wr_len * 4, dw->max_rd_len * 4);
+
+	/* Saving data structure reference */
+	pci_set_drvdata(pdev, dw);
+
+	/* Register misc device */
+	err = misc_register(&dw->misc_dev);
+	if (err) {
+		dev_err(dev, "xData: failed to register device\n");
+		goto err_kfree_name;
+	}
+
+	return 0;
+
+err_kfree_name:
+	kfree(dw->misc_dev.name);
+
+err_ida_remove:
+	ida_free(&xdata_ida, id);
+
+	return err;
+}
+
+static void dw_xdata_pcie_remove(struct pci_dev *pdev)
+{
+	struct dw_xdata *dw = pci_get_drvdata(pdev);
+	int id;
+
+	if (sscanf(dw->misc_dev.name, DW_XDATA_DRIVER_NAME ".%d", &id) != 1)
+		return;
+
+	if (id < 0)
+		return;
+
+	dw_xdata_stop(dw);
+	misc_deregister(&dw->misc_dev);
+	kfree(dw->misc_dev.name);
+	ida_free(&xdata_ida, id);
+}
+
+static const struct pci_device_id dw_xdata_pcie_id_table[] = {
+	{ PCI_DEVICE_DATA(SYNOPSYS, EDDA, NULL) },
+	{ }
+};
+MODULE_DEVICE_TABLE(pci, dw_xdata_pcie_id_table);
+
+static struct pci_driver dw_xdata_pcie_driver = {
+	.name		= DW_XDATA_DRIVER_NAME,
+	.id_table	= dw_xdata_pcie_id_table,
+	.probe		= dw_xdata_pcie_probe,
+	.remove		= dw_xdata_pcie_remove,
+};
+
+module_pci_driver(dw_xdata_pcie_driver);
+
+MODULE_LICENSE("GPL v2");
+MODULE_DESCRIPTION("Synopsys DesignWare xData PCIe driver");
+MODULE_AUTHOR("Gustavo Pimentel <gustavo.pimentel@synopsys.com>");
+