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, 193 insertions, 0 deletions

diff --git a/drivers/cdx/cdx_msi.c b/drivers/cdx/cdx_msi.c
new file mode 100644
index 000000000..c8d832b0b
--- /dev/null
+++ b/drivers/cdx/cdx_msi.c
@@ -0,0 +1,193 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * AMD CDX bus driver MSI support
+ *
+ * Copyright (C) 2022-2023, Advanced Micro Devices, Inc.
+ */
+
+#include <linux/of.h>
+#include <linux/of_device.h>
+#include <linux/of_address.h>
+#include <linux/of_irq.h>
+#include <linux/irq.h>
+#include <linux/irqdomain.h>
+#include <linux/msi.h>
+#include <linux/cdx/cdx_bus.h>
+
+#include "cdx.h"
+
+static void cdx_msi_write_msg(struct irq_data *irq_data, struct msi_msg *msg)
+{
+	struct msi_desc *msi_desc = irq_data_get_msi_desc(irq_data);
+	struct cdx_device *cdx_dev = to_cdx_device(msi_desc->dev);
+
+	/* We would not operate on msg here rather we wait for irq_bus_sync_unlock()
+	 * to be called from preemptible task context.
+	 */
+	msi_desc->msg = *msg;
+	cdx_dev->msi_write_pending = true;
+}
+
+static void cdx_msi_write_irq_lock(struct irq_data *irq_data)
+{
+	struct msi_desc *msi_desc = irq_data_get_msi_desc(irq_data);
+	struct cdx_device *cdx_dev = to_cdx_device(msi_desc->dev);
+
+	mutex_lock(&cdx_dev->irqchip_lock);
+}
+
+static void cdx_msi_write_irq_unlock(struct irq_data *irq_data)
+{
+	struct msi_desc *msi_desc = irq_data_get_msi_desc(irq_data);
+	struct cdx_device *cdx_dev = to_cdx_device(msi_desc->dev);
+	struct cdx_controller *cdx = cdx_dev->cdx;
+	struct cdx_device_config dev_config;
+
+	if (!cdx_dev->msi_write_pending) {
+		mutex_unlock(&cdx_dev->irqchip_lock);
+		return;
+	}
+
+	cdx_dev->msi_write_pending = false;
+	mutex_unlock(&cdx_dev->irqchip_lock);
+
+	dev_config.msi.msi_index = msi_desc->msi_index;
+	dev_config.msi.data = msi_desc->msg.data;
+	dev_config.msi.addr = ((u64)(msi_desc->msg.address_hi) << 32) | msi_desc->msg.address_lo;
+
+	/*
+	 * dev_configure() is a controller callback which can interact with
+	 * Firmware or other entities, and can sleep, so invoke this function
+	 * outside of the mutex held region.
+	 */
+	dev_config.type = CDX_DEV_MSI_CONF;
+	if (cdx->ops->dev_configure)
+		cdx->ops->dev_configure(cdx, cdx_dev->bus_num, cdx_dev->dev_num, &dev_config);
+}
+
+int cdx_enable_msi(struct cdx_device *cdx_dev)
+{
+	struct cdx_controller *cdx = cdx_dev->cdx;
+	struct cdx_device_config dev_config;
+
+	dev_config.type = CDX_DEV_MSI_ENABLE;
+	dev_config.msi_enable = true;
+	if (cdx->ops->dev_configure) {
+		return cdx->ops->dev_configure(cdx, cdx_dev->bus_num, cdx_dev->dev_num,
+					       &dev_config);
+	}
+
+	return -EOPNOTSUPP;
+}
+EXPORT_SYMBOL_GPL(cdx_enable_msi);
+
+void cdx_disable_msi(struct cdx_device *cdx_dev)
+{
+	struct cdx_controller *cdx = cdx_dev->cdx;
+	struct cdx_device_config dev_config;
+
+	dev_config.type = CDX_DEV_MSI_ENABLE;
+	dev_config.msi_enable = false;
+	if (cdx->ops->dev_configure)
+		cdx->ops->dev_configure(cdx, cdx_dev->bus_num, cdx_dev->dev_num, &dev_config);
+}
+EXPORT_SYMBOL_GPL(cdx_disable_msi);
+
+static struct irq_chip cdx_msi_irq_chip = {
+	.name			= "CDX-MSI",
+	.irq_mask		= irq_chip_mask_parent,
+	.irq_unmask		= irq_chip_unmask_parent,
+	.irq_eoi		= irq_chip_eoi_parent,
+	.irq_set_affinity	= msi_domain_set_affinity,
+	.irq_write_msi_msg	= cdx_msi_write_msg,
+	.irq_bus_lock		= cdx_msi_write_irq_lock,
+	.irq_bus_sync_unlock	= cdx_msi_write_irq_unlock
+};
+
+/* Convert an msi_desc to a unique identifier within the domain. */
+static irq_hw_number_t cdx_domain_calc_hwirq(struct cdx_device *dev,
+					     struct msi_desc *desc)
+{
+	return ((irq_hw_number_t)dev->msi_dev_id << 10) | desc->msi_index;
+}
+
+static void cdx_msi_set_desc(msi_alloc_info_t *arg, struct msi_desc *desc)
+{
+	arg->desc = desc;
+	arg->hwirq = cdx_domain_calc_hwirq(to_cdx_device(desc->dev), desc);
+}
+
+static int cdx_msi_prepare(struct irq_domain *msi_domain,
+			   struct device *dev,
+			   int nvec, msi_alloc_info_t *info)
+{
+	struct of_phandle_args msi_spec = {};
+	struct cdx_device *cdx_dev = to_cdx_device(dev);
+	struct device *parent = cdx_dev->cdx->dev;
+	struct msi_domain_info *msi_info;
+	int ret;
+
+	/* Retrieve device ID from requestor ID using parent device */
+	ret = of_map_msi_id(parent->of_node, cdx_dev->msi_dev_id, NULL, &msi_spec);
+	if (ret) {
+		dev_err(dev, "of_map_msi_id failed for MSI: %d\n", ret);
+		return ret;
+	}
+	of_node_put(msi_spec.np);
+
+#ifdef GENERIC_MSI_DOMAIN_OPS
+	/* Set the device Id to be passed to the GIC-ITS */
+	info->scratchpad[0].ul = msi_spec.args[0];
+#endif
+
+	msi_info = msi_get_domain_info(msi_domain->parent);
+
+	return msi_info->ops->msi_prepare(msi_domain->parent, dev, nvec, info);
+}
+
+static struct msi_domain_ops cdx_msi_ops = {
+	.msi_prepare	= cdx_msi_prepare,
+	.set_desc	= cdx_msi_set_desc
+};
+
+static struct msi_domain_info cdx_msi_domain_info = {
+	.ops	= &cdx_msi_ops,
+	.chip	= &cdx_msi_irq_chip,
+	.flags	= MSI_FLAG_USE_DEF_DOM_OPS | MSI_FLAG_USE_DEF_CHIP_OPS |
+		  MSI_FLAG_ALLOC_SIMPLE_MSI_DESCS | MSI_FLAG_FREE_MSI_DESCS
+};
+
+struct irq_domain *cdx_msi_domain_init(struct device *dev)
+{
+	struct device_node *np = dev->of_node;
+	struct fwnode_handle *fwnode_handle;
+	struct irq_domain *cdx_msi_domain;
+	struct device_node *parent_node;
+	struct irq_domain *parent;
+
+	fwnode_handle = of_fwnode_handle(np);
+
+	parent_node = of_parse_phandle(np, "msi-map", 1);
+	if (!parent_node) {
+		dev_err(dev, "msi-map not present on cdx controller\n");
+		return NULL;
+	}
+
+	parent = irq_find_matching_fwnode(of_fwnode_handle(parent_node), DOMAIN_BUS_NEXUS);
+	of_node_put(parent_node);
+	if (!parent || !msi_get_domain_info(parent)) {
+		dev_err(dev, "unable to locate ITS domain\n");
+		return NULL;
+	}
+
+	cdx_msi_domain = msi_create_irq_domain(fwnode_handle, &cdx_msi_domain_info, parent);
+	if (!cdx_msi_domain) {
+		dev_err(dev, "unable to create CDX-MSI domain\n");
+		return NULL;
+	}
+
+	dev_dbg(dev, "CDX-MSI domain created\n");
+
+	return cdx_msi_domain;
+}
+EXPORT_SYMBOL_NS_GPL(cdx_msi_domain_init, "CDX_BUS_CONTROLLER");