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>

3 files changed, 170 insertions, 0 deletions

diff --git a/drivers/soc/fujitsu/Kconfig b/drivers/soc/fujitsu/Kconfig
new file mode 100644
index 000000000..987731e80
--- /dev/null
+++ b/drivers/soc/fujitsu/Kconfig
@@ -0,0 +1,16 @@
+# SPDX-License-Identifier: GPL-2.0-only
+menu "fujitsu SoC drivers"
+
+config A64FX_DIAG
+	bool "A64FX diag driver"
+	depends on ARM64
+	depends on ACPI
+	help
+	  Say Y here if you want to enable diag interrupt on Fujitsu A64FX.
+	  This driver enables BMC's diagnostic requests and enables
+	  A64FX-specific interrupts. This allows administrators to obtain
+	  kernel dumps via diagnostic requests using ipmitool, etc.
+
+	  If unsure, say N.
+
+endmenu
diff --git a/drivers/soc/fujitsu/Makefile b/drivers/soc/fujitsu/Makefile
new file mode 100644
index 000000000..945bc1c14
--- /dev/null
+++ b/drivers/soc/fujitsu/Makefile
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0
+
+obj-$(CONFIG_A64FX_DIAG)	+= a64fx-diag.o
diff --git a/drivers/soc/fujitsu/a64fx-diag.c b/drivers/soc/fujitsu/a64fx-diag.c
new file mode 100644
index 000000000..76cb0b6a2
--- /dev/null
+++ b/drivers/soc/fujitsu/a64fx-diag.c
@@ -0,0 +1,151 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * A64FX diag driver.
+ * Copyright (c) 2022 Fujitsu Ltd.
+ */
+
+#include <linux/acpi.h>
+#include <linux/interrupt.h>
+#include <linux/irq.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+
+#define A64FX_DIAG_IRQ 1
+#define BMC_DIAG_INTERRUPT_ENABLE 0x40
+#define BMC_DIAG_INTERRUPT_STATUS 0x44
+#define BMC_DIAG_INTERRUPT_MASK BIT(31)
+
+struct a64fx_diag_priv {
+	void __iomem *mmsc_reg_base;
+	int irq;
+	bool has_nmi;
+};
+
+static irqreturn_t a64fx_diag_handler_nmi(int irq, void *dev_id)
+{
+	nmi_panic(NULL, "a64fx_diag: interrupt received\n");
+
+	return IRQ_HANDLED;
+}
+
+static irqreturn_t a64fx_diag_handler_irq(int irq, void *dev_id)
+{
+	panic("a64fx_diag: interrupt received\n");
+
+	return IRQ_HANDLED;
+}
+
+static void a64fx_diag_interrupt_clear(struct a64fx_diag_priv *priv)
+{
+	void __iomem *diag_status_reg_addr;
+	u32 mmsc;
+
+	diag_status_reg_addr = priv->mmsc_reg_base + BMC_DIAG_INTERRUPT_STATUS;
+	mmsc = readl(diag_status_reg_addr);
+	if (mmsc & BMC_DIAG_INTERRUPT_MASK)
+		writel(BMC_DIAG_INTERRUPT_MASK, diag_status_reg_addr);
+}
+
+static void a64fx_diag_interrupt_enable(struct a64fx_diag_priv *priv)
+{
+	void __iomem *diag_enable_reg_addr;
+	u32 mmsc;
+
+	diag_enable_reg_addr = priv->mmsc_reg_base + BMC_DIAG_INTERRUPT_ENABLE;
+	mmsc = readl(diag_enable_reg_addr);
+	if (!(mmsc & BMC_DIAG_INTERRUPT_MASK)) {
+		mmsc |= BMC_DIAG_INTERRUPT_MASK;
+		writel(mmsc, diag_enable_reg_addr);
+	}
+}
+
+static void a64fx_diag_interrupt_disable(struct a64fx_diag_priv *priv)
+{
+	void __iomem *diag_enable_reg_addr;
+	u32 mmsc;
+
+	diag_enable_reg_addr = priv->mmsc_reg_base + BMC_DIAG_INTERRUPT_ENABLE;
+	mmsc = readl(diag_enable_reg_addr);
+	if (mmsc & BMC_DIAG_INTERRUPT_MASK) {
+		mmsc &= ~BMC_DIAG_INTERRUPT_MASK;
+		writel(mmsc, diag_enable_reg_addr);
+	}
+}
+
+static int a64fx_diag_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct a64fx_diag_priv *priv;
+	unsigned long irq_flags;
+	int ret;
+
+	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
+	if (priv == NULL)
+		return -ENOMEM;
+
+	priv->mmsc_reg_base = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(priv->mmsc_reg_base))
+		return PTR_ERR(priv->mmsc_reg_base);
+
+	priv->irq = platform_get_irq(pdev, A64FX_DIAG_IRQ);
+	if (priv->irq < 0)
+		return priv->irq;
+
+	platform_set_drvdata(pdev, priv);
+
+	irq_flags = IRQF_PERCPU | IRQF_NOBALANCING | IRQF_NO_AUTOEN |
+		   IRQF_NO_THREAD;
+	ret = request_nmi(priv->irq, &a64fx_diag_handler_nmi, irq_flags,
+			"a64fx_diag_nmi", NULL);
+	if (ret) {
+		ret = request_irq(priv->irq, &a64fx_diag_handler_irq,
+				irq_flags, "a64fx_diag_irq", NULL);
+		if (ret) {
+			dev_err(dev, "cannot register IRQ %d\n", ret);
+			return ret;
+		}
+		enable_irq(priv->irq);
+	} else {
+		enable_nmi(priv->irq);
+		priv->has_nmi = true;
+	}
+
+	a64fx_diag_interrupt_clear(priv);
+	a64fx_diag_interrupt_enable(priv);
+
+	return 0;
+}
+
+static void a64fx_diag_remove(struct platform_device *pdev)
+{
+	struct a64fx_diag_priv *priv = platform_get_drvdata(pdev);
+
+	a64fx_diag_interrupt_disable(priv);
+	a64fx_diag_interrupt_clear(priv);
+
+	if (priv->has_nmi)
+		free_nmi(priv->irq, NULL);
+	else
+		free_irq(priv->irq, NULL);
+}
+
+static const struct acpi_device_id a64fx_diag_acpi_match[] = {
+	{ "FUJI2007", 0 },
+	{ },
+};
+MODULE_DEVICE_TABLE(acpi, a64fx_diag_acpi_match);
+
+
+static struct platform_driver a64fx_diag_driver = {
+	.driver = {
+		.name = "a64fx_diag_driver",
+		.acpi_match_table = ACPI_PTR(a64fx_diag_acpi_match),
+	},
+	.probe = a64fx_diag_probe,
+	.remove = a64fx_diag_remove,
+};
+
+module_platform_driver(a64fx_diag_driver);
+
+MODULE_AUTHOR("Hitomi Hasegawa <hasegawa-hitomi@fujitsu.com>");
+MODULE_DESCRIPTION("A64FX diag driver");