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>

4 files changed, 317 insertions, 0 deletions

diff --git a/drivers/soc/versatile/Kconfig b/drivers/soc/versatile/Kconfig
new file mode 100644
index 000000000..7bbf54a8d
--- /dev/null
+++ b/drivers/soc/versatile/Kconfig
@@ -0,0 +1,20 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# ARM Versatile SoC drivers
+#
+config SOC_INTEGRATOR_CM
+	bool "SoC bus device for the ARM Integrator platform core modules"
+	depends on ARCH_INTEGRATOR || COMPILE_TEST
+	select SOC_BUS
+	help
+	  Include support for the SoC bus on the ARM Integrator platform
+	  core modules providing some sysfs information about the ASIC
+	  variant.
+
+config SOC_REALVIEW
+	bool "SoC bus device for the ARM RealView platforms"
+	depends on ARCH_REALVIEW || COMPILE_TEST
+	select SOC_BUS
+	help
+	  Include support for the SoC bus on the ARM RealView platforms
+	  providing some sysfs information about the ASIC variant.
diff --git a/drivers/soc/versatile/Makefile b/drivers/soc/versatile/Makefile
new file mode 100644
index 000000000..1e0a37c0a
--- /dev/null
+++ b/drivers/soc/versatile/Makefile
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0-only
+obj-$(CONFIG_SOC_INTEGRATOR_CM)	+= soc-integrator.o
+obj-$(CONFIG_SOC_REALVIEW)	+= soc-realview.o
diff --git a/drivers/soc/versatile/soc-integrator.c b/drivers/soc/versatile/soc-integrator.c
new file mode 100644
index 000000000..b67a7fd4a
--- /dev/null
+++ b/drivers/soc/versatile/soc-integrator.c
@@ -0,0 +1,150 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2014 Linaro Ltd.
+ *
+ * Author: Linus Walleij <linus.walleij@linaro.org>
+ */
+#include <linux/init.h>
+#include <linux/io.h>
+#include <linux/slab.h>
+#include <linux/sys_soc.h>
+#include <linux/platform_device.h>
+#include <linux/mfd/syscon.h>
+#include <linux/regmap.h>
+#include <linux/of.h>
+
+#define INTEGRATOR_HDR_ID_OFFSET	0x00
+
+static u32 integrator_coreid;
+
+static const struct of_device_id integrator_cm_match[] = {
+	{ .compatible = "arm,core-module-integrator", },
+	{ }
+};
+
+static const char *integrator_arch_str(u32 id)
+{
+	switch ((id >> 16) & 0xff) {
+	case 0x00:
+		return "ASB little-endian";
+	case 0x01:
+		return "AHB little-endian";
+	case 0x03:
+		return "AHB-Lite system bus, bi-endian";
+	case 0x04:
+		return "AHB";
+	case 0x08:
+		return "AHB system bus, ASB processor bus";
+	default:
+		return "Unknown";
+	}
+}
+
+static const char *integrator_fpga_str(u32 id)
+{
+	switch ((id >> 12) & 0xf) {
+	case 0x01:
+		return "XC4062";
+	case 0x02:
+		return "XC4085";
+	case 0x03:
+		return "XVC600";
+	case 0x04:
+		return "EPM7256AE (Altera PLD)";
+	default:
+		return "Unknown";
+	}
+}
+
+static ssize_t
+manufacturer_show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	return sprintf(buf, "%02x\n", integrator_coreid >> 24);
+}
+
+static DEVICE_ATTR_RO(manufacturer);
+
+static ssize_t
+arch_show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	return sprintf(buf, "%s\n", integrator_arch_str(integrator_coreid));
+}
+
+static DEVICE_ATTR_RO(arch);
+
+static ssize_t
+fpga_show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	return sprintf(buf, "%s\n", integrator_fpga_str(integrator_coreid));
+}
+
+static DEVICE_ATTR_RO(fpga);
+
+static ssize_t
+build_show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	return sprintf(buf, "%02x\n", (integrator_coreid >> 4) & 0xFF);
+}
+
+static DEVICE_ATTR_RO(build);
+
+static struct attribute *integrator_attrs[] = {
+	&dev_attr_manufacturer.attr,
+	&dev_attr_arch.attr,
+	&dev_attr_fpga.attr,
+	&dev_attr_build.attr,
+	NULL
+};
+
+ATTRIBUTE_GROUPS(integrator);
+
+static int __init integrator_soc_init(void)
+{
+	struct regmap *syscon_regmap;
+	struct soc_device *soc_dev;
+	struct soc_device_attribute *soc_dev_attr;
+	struct device_node *np;
+	struct device *dev;
+	u32 val;
+	int ret;
+
+	np = of_find_matching_node(NULL, integrator_cm_match);
+	if (!np)
+		return -ENODEV;
+
+	syscon_regmap = syscon_node_to_regmap(np);
+	of_node_put(np);
+	if (IS_ERR(syscon_regmap))
+		return PTR_ERR(syscon_regmap);
+
+	ret = regmap_read(syscon_regmap, INTEGRATOR_HDR_ID_OFFSET,
+			  &val);
+	if (ret)
+		return -ENODEV;
+	integrator_coreid = val;
+
+	soc_dev_attr = kzalloc_obj(*soc_dev_attr);
+	if (!soc_dev_attr)
+		return -ENOMEM;
+
+	soc_dev_attr->soc_id = "Integrator";
+	soc_dev_attr->machine = "Integrator";
+	soc_dev_attr->family = "Versatile";
+	soc_dev_attr->custom_attr_group = integrator_groups[0];
+	soc_dev = soc_device_register(soc_dev_attr);
+	if (IS_ERR(soc_dev)) {
+		kfree(soc_dev_attr);
+		return -ENODEV;
+	}
+	dev = soc_device_to_device(soc_dev);
+
+	dev_info(dev, "Detected ARM core module:\n");
+	dev_info(dev, "    Manufacturer: %02x\n", (val >> 24));
+	dev_info(dev, "    Architecture: %s\n", integrator_arch_str(val));
+	dev_info(dev, "    FPGA: %s\n", integrator_fpga_str(val));
+	dev_info(dev, "    Build: %02x\n", (val >> 4) & 0xFF);
+	dev_info(dev, "    Rev: %c\n", ('A' + (val & 0x03)));
+
+	return 0;
+}
+device_initcall(integrator_soc_init);
diff --git a/drivers/soc/versatile/soc-realview.c b/drivers/soc/versatile/soc-realview.c
new file mode 100644
index 000000000..cf91abe07
--- /dev/null
+++ b/drivers/soc/versatile/soc-realview.c
@@ -0,0 +1,144 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2014 Linaro Ltd.
+ *
+ * Author: Linus Walleij <linus.walleij@linaro.org>
+ */
+#include <linux/device.h>
+#include <linux/init.h>
+#include <linux/io.h>
+#include <linux/slab.h>
+#include <linux/sys_soc.h>
+#include <linux/platform_device.h>
+#include <linux/mfd/syscon.h>
+#include <linux/regmap.h>
+#include <linux/of.h>
+
+/* System ID in syscon */
+#define REALVIEW_SYS_ID_OFFSET 0x00
+
+static const struct of_device_id realview_soc_of_match[] = {
+	{ .compatible = "arm,realview-eb-soc",	},
+	{ .compatible = "arm,realview-pb1176-soc", },
+	{ .compatible = "arm,realview-pb11mp-soc", },
+	{ .compatible = "arm,realview-pba8-soc", },
+	{ .compatible = "arm,realview-pbx-soc", },
+	{ }
+};
+
+static u32 realview_coreid;
+
+static const char *realview_arch_str(u32 id)
+{
+	switch ((id >> 8) & 0xf) {
+	case 0x04:
+		return "AHB";
+	case 0x05:
+		return "Multi-layer AXI";
+	default:
+		return "Unknown";
+	}
+}
+
+static ssize_t
+manufacturer_show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	return sprintf(buf, "%02x\n", realview_coreid >> 24);
+}
+
+static DEVICE_ATTR_RO(manufacturer);
+
+static ssize_t
+board_show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	return sprintf(buf, "HBI-%03x\n", ((realview_coreid >> 16) & 0xfff));
+}
+
+static DEVICE_ATTR_RO(board);
+
+static ssize_t
+fpga_show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	return sprintf(buf, "%s\n", realview_arch_str(realview_coreid));
+}
+
+static DEVICE_ATTR_RO(fpga);
+
+static ssize_t
+build_show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	return sprintf(buf, "%02x\n", (realview_coreid & 0xFF));
+}
+
+static DEVICE_ATTR_RO(build);
+
+static struct attribute *realview_attrs[] = {
+	&dev_attr_manufacturer.attr,
+	&dev_attr_board.attr,
+	&dev_attr_fpga.attr,
+	&dev_attr_build.attr,
+	NULL
+};
+
+ATTRIBUTE_GROUPS(realview);
+
+static void realview_soc_socdev_release(void *data)
+{
+	struct soc_device *soc_dev = data;
+
+	soc_device_unregister(soc_dev);
+}
+
+static int realview_soc_probe(struct platform_device *pdev)
+{
+	struct regmap *syscon_regmap;
+	struct soc_device *soc_dev;
+	struct soc_device_attribute *soc_dev_attr;
+	struct device_node *np = pdev->dev.of_node;
+	int ret;
+
+	syscon_regmap = syscon_regmap_lookup_by_phandle(np, "regmap");
+	if (IS_ERR(syscon_regmap))
+		return PTR_ERR(syscon_regmap);
+
+	soc_dev_attr = devm_kzalloc(&pdev->dev, sizeof(*soc_dev_attr), GFP_KERNEL);
+	if (!soc_dev_attr)
+		return -ENOMEM;
+
+	ret = of_property_read_string(np, "compatible",
+				      &soc_dev_attr->soc_id);
+	if (ret)
+		return -EINVAL;
+
+	soc_dev_attr->machine = "RealView";
+	soc_dev_attr->family = "Versatile";
+	soc_dev_attr->custom_attr_group = realview_groups[0];
+	soc_dev = soc_device_register(soc_dev_attr);
+	if (IS_ERR(soc_dev))
+		return -ENODEV;
+
+	ret = devm_add_action_or_reset(&pdev->dev, realview_soc_socdev_release,
+				       soc_dev);
+	if (ret)
+		return ret;
+
+	ret = regmap_read(syscon_regmap, REALVIEW_SYS_ID_OFFSET,
+			  &realview_coreid);
+	if (ret)
+		return -ENODEV;
+
+	dev_info(&pdev->dev, "RealView Syscon Core ID: 0x%08x, HBI-%03x\n",
+		 realview_coreid,
+		 ((realview_coreid >> 16) & 0xfff));
+	/* FIXME: add attributes for SoC to sysfs */
+	return 0;
+}
+
+static struct platform_driver realview_soc_driver = {
+	.probe = realview_soc_probe,
+	.driver = {
+		.name = "realview-soc",
+		.of_match_table = realview_soc_of_match,
+	},
+};
+builtin_platform_driver(realview_soc_driver);