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, 354 insertions, 0 deletions

diff --git a/drivers/cache/sifive_ccache.c b/drivers/cache/sifive_ccache.c
new file mode 100644
index 000000000..2acb8bdf0
--- /dev/null
+++ b/drivers/cache/sifive_ccache.c
@@ -0,0 +1,354 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * SiFive composable cache controller Driver
+ *
+ * Copyright (C) 2018-2022 SiFive, Inc.
+ *
+ */
+
+#define pr_fmt(fmt) "CCACHE: " fmt
+
+#include <linux/align.h>
+#include <linux/debugfs.h>
+#include <linux/interrupt.h>
+#include <linux/of_irq.h>
+#include <linux/of_address.h>
+#include <linux/device.h>
+#include <linux/bitfield.h>
+#include <linux/platform_device.h>
+#include <linux/property.h>
+#include <asm/cacheflush.h>
+#include <asm/cacheinfo.h>
+#include <asm/dma-noncoherent.h>
+#include <soc/sifive/sifive_ccache.h>
+
+#define SIFIVE_CCACHE_DIRECCFIX_LOW 0x100
+#define SIFIVE_CCACHE_DIRECCFIX_HIGH 0x104
+#define SIFIVE_CCACHE_DIRECCFIX_COUNT 0x108
+
+#define SIFIVE_CCACHE_DIRECCFAIL_LOW 0x120
+#define SIFIVE_CCACHE_DIRECCFAIL_HIGH 0x124
+#define SIFIVE_CCACHE_DIRECCFAIL_COUNT 0x128
+
+#define SIFIVE_CCACHE_DATECCFIX_LOW 0x140
+#define SIFIVE_CCACHE_DATECCFIX_HIGH 0x144
+#define SIFIVE_CCACHE_DATECCFIX_COUNT 0x148
+
+#define SIFIVE_CCACHE_DATECCFAIL_LOW 0x160
+#define SIFIVE_CCACHE_DATECCFAIL_HIGH 0x164
+#define SIFIVE_CCACHE_DATECCFAIL_COUNT 0x168
+
+#define SIFIVE_CCACHE_CONFIG 0x00
+#define SIFIVE_CCACHE_CONFIG_BANK_MASK GENMASK_ULL(7, 0)
+#define SIFIVE_CCACHE_CONFIG_WAYS_MASK GENMASK_ULL(15, 8)
+#define SIFIVE_CCACHE_CONFIG_SETS_MASK GENMASK_ULL(23, 16)
+#define SIFIVE_CCACHE_CONFIG_BLKS_MASK GENMASK_ULL(31, 24)
+
+#define SIFIVE_CCACHE_FLUSH64 0x200
+#define SIFIVE_CCACHE_FLUSH32 0x240
+
+#define SIFIVE_CCACHE_WAYENABLE 0x08
+#define SIFIVE_CCACHE_ECCINJECTERR 0x40
+
+#define SIFIVE_CCACHE_MAX_ECCINTR 4
+#define SIFIVE_CCACHE_LINE_SIZE 64
+
+static void __iomem *ccache_base;
+static int g_irq[SIFIVE_CCACHE_MAX_ECCINTR];
+static struct riscv_cacheinfo_ops ccache_cache_ops;
+static int level;
+
+enum {
+	DIR_CORR = 0,
+	DATA_CORR,
+	DATA_UNCORR,
+	DIR_UNCORR,
+};
+
+enum {
+	QUIRK_NONSTANDARD_CACHE_OPS	= BIT(0),
+	QUIRK_BROKEN_DATA_UNCORR	= BIT(1),
+};
+
+#ifdef CONFIG_DEBUG_FS
+static struct dentry *sifive_test;
+
+static ssize_t ccache_write(struct file *file, const char __user *data,
+			    size_t count, loff_t *ppos)
+{
+	unsigned int val;
+
+	if (kstrtouint_from_user(data, count, 0, &val))
+		return -EINVAL;
+	if ((val < 0xFF) || (val >= 0x10000 && val < 0x100FF))
+		writel(val, ccache_base + SIFIVE_CCACHE_ECCINJECTERR);
+	else
+		return -EINVAL;
+	return count;
+}
+
+static const struct file_operations ccache_fops = {
+	.owner = THIS_MODULE,
+	.open = simple_open,
+	.write = ccache_write
+};
+
+static void setup_sifive_debug(void)
+{
+	sifive_test = debugfs_create_dir("sifive_ccache_cache", NULL);
+
+	debugfs_create_file("sifive_debug_inject_error", 0200,
+			    sifive_test, NULL, &ccache_fops);
+}
+#endif
+
+static void ccache_config_read(void)
+{
+	u32 cfg;
+
+	cfg = readl(ccache_base + SIFIVE_CCACHE_CONFIG);
+	pr_info("%llu banks, %llu ways, sets/bank=%llu, bytes/block=%llu\n",
+		FIELD_GET(SIFIVE_CCACHE_CONFIG_BANK_MASK, cfg),
+		FIELD_GET(SIFIVE_CCACHE_CONFIG_WAYS_MASK, cfg),
+		BIT_ULL(FIELD_GET(SIFIVE_CCACHE_CONFIG_SETS_MASK, cfg)),
+		BIT_ULL(FIELD_GET(SIFIVE_CCACHE_CONFIG_BLKS_MASK, cfg)));
+
+	cfg = readl(ccache_base + SIFIVE_CCACHE_WAYENABLE);
+	pr_info("Index of the largest way enabled: %u\n", cfg);
+}
+
+static const struct of_device_id sifive_ccache_ids[] = {
+	{ .compatible = "eswin,eic7700-l3-cache",
+	  .data = (void *)(QUIRK_NONSTANDARD_CACHE_OPS) },
+	{ .compatible = "sifive,fu540-c000-ccache" },
+	{ .compatible = "sifive,fu740-c000-ccache" },
+	{ .compatible = "starfive,jh7100-ccache",
+	  .data = (void *)(QUIRK_NONSTANDARD_CACHE_OPS | QUIRK_BROKEN_DATA_UNCORR) },
+	{ .compatible = "starfive,jh7110-ccache",
+	  .data = (void *)(QUIRK_NONSTANDARD_CACHE_OPS) },
+	{ .compatible = "sifive,ccache0" },
+	{ /* end of table */ }
+};
+
+static ATOMIC_NOTIFIER_HEAD(ccache_err_chain);
+
+int register_sifive_ccache_error_notifier(struct notifier_block *nb)
+{
+	return atomic_notifier_chain_register(&ccache_err_chain, nb);
+}
+EXPORT_SYMBOL_GPL(register_sifive_ccache_error_notifier);
+
+int unregister_sifive_ccache_error_notifier(struct notifier_block *nb)
+{
+	return atomic_notifier_chain_unregister(&ccache_err_chain, nb);
+}
+EXPORT_SYMBOL_GPL(unregister_sifive_ccache_error_notifier);
+
+#ifdef CONFIG_RISCV_NONSTANDARD_CACHE_OPS
+static void ccache_flush_range(phys_addr_t start, size_t len)
+{
+	phys_addr_t end = start + len;
+	phys_addr_t line;
+
+	if (!len)
+		return;
+
+	mb(); /* complete earlier memory accesses before the cache flush */
+	for (line = ALIGN_DOWN(start, SIFIVE_CCACHE_LINE_SIZE); line < end;
+			line += SIFIVE_CCACHE_LINE_SIZE) {
+#ifdef CONFIG_32BIT
+		writel_relaxed(line >> 4, ccache_base + SIFIVE_CCACHE_FLUSH32);
+#else
+		writeq_relaxed(line, ccache_base + SIFIVE_CCACHE_FLUSH64);
+#endif
+	}
+	mb(); /* issue later memory accesses after the cache flush */
+}
+
+static const struct riscv_nonstd_cache_ops ccache_mgmt_ops __initconst = {
+	.wback = &ccache_flush_range,
+	.inv = &ccache_flush_range,
+	.wback_inv = &ccache_flush_range,
+};
+#endif /* CONFIG_RISCV_NONSTANDARD_CACHE_OPS */
+
+static int ccache_largest_wayenabled(void)
+{
+	return readl(ccache_base + SIFIVE_CCACHE_WAYENABLE) & 0xFF;
+}
+
+static ssize_t number_of_ways_enabled_show(struct device *dev,
+					   struct device_attribute *attr,
+					   char *buf)
+{
+	return sprintf(buf, "%u\n", ccache_largest_wayenabled());
+}
+
+static DEVICE_ATTR_RO(number_of_ways_enabled);
+
+static struct attribute *priv_attrs[] = {
+	&dev_attr_number_of_ways_enabled.attr,
+	NULL,
+};
+
+static const struct attribute_group priv_attr_group = {
+	.attrs = priv_attrs,
+};
+
+static const struct attribute_group *ccache_get_priv_group(struct cacheinfo
+							   *this_leaf)
+{
+	/* We want to use private group for composable cache only */
+	if (this_leaf->level == level)
+		return &priv_attr_group;
+	else
+		return NULL;
+}
+
+static irqreturn_t ccache_int_handler(int irq, void *device)
+{
+	unsigned int add_h, add_l;
+
+	if (irq == g_irq[DIR_CORR]) {
+		add_h = readl(ccache_base + SIFIVE_CCACHE_DIRECCFIX_HIGH);
+		add_l = readl(ccache_base + SIFIVE_CCACHE_DIRECCFIX_LOW);
+		pr_err("DirError @ 0x%08X.%08X\n", add_h, add_l);
+		/* Reading this register clears the DirError interrupt sig */
+		readl(ccache_base + SIFIVE_CCACHE_DIRECCFIX_COUNT);
+		atomic_notifier_call_chain(&ccache_err_chain,
+					   SIFIVE_CCACHE_ERR_TYPE_CE,
+					   "DirECCFix");
+	}
+	if (irq == g_irq[DIR_UNCORR]) {
+		add_h = readl(ccache_base + SIFIVE_CCACHE_DIRECCFAIL_HIGH);
+		add_l = readl(ccache_base + SIFIVE_CCACHE_DIRECCFAIL_LOW);
+		/* Reading this register clears the DirFail interrupt sig */
+		readl(ccache_base + SIFIVE_CCACHE_DIRECCFAIL_COUNT);
+		atomic_notifier_call_chain(&ccache_err_chain,
+					   SIFIVE_CCACHE_ERR_TYPE_UE,
+					   "DirECCFail");
+		panic("CCACHE: DirFail @ 0x%08X.%08X\n", add_h, add_l);
+	}
+	if (irq == g_irq[DATA_CORR]) {
+		add_h = readl(ccache_base + SIFIVE_CCACHE_DATECCFIX_HIGH);
+		add_l = readl(ccache_base + SIFIVE_CCACHE_DATECCFIX_LOW);
+		pr_err("DataError @ 0x%08X.%08X\n", add_h, add_l);
+		/* Reading this register clears the DataError interrupt sig */
+		readl(ccache_base + SIFIVE_CCACHE_DATECCFIX_COUNT);
+		atomic_notifier_call_chain(&ccache_err_chain,
+					   SIFIVE_CCACHE_ERR_TYPE_CE,
+					   "DatECCFix");
+	}
+	if (irq == g_irq[DATA_UNCORR]) {
+		add_h = readl(ccache_base + SIFIVE_CCACHE_DATECCFAIL_HIGH);
+		add_l = readl(ccache_base + SIFIVE_CCACHE_DATECCFAIL_LOW);
+		pr_err("DataFail @ 0x%08X.%08X\n", add_h, add_l);
+		/* Reading this register clears the DataFail interrupt sig */
+		readl(ccache_base + SIFIVE_CCACHE_DATECCFAIL_COUNT);
+		atomic_notifier_call_chain(&ccache_err_chain,
+					   SIFIVE_CCACHE_ERR_TYPE_UE,
+					   "DatECCFail");
+	}
+
+	return IRQ_HANDLED;
+}
+
+static int sifive_ccache_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	unsigned long quirks;
+	int intr_num, rc;
+
+	quirks = (unsigned long)device_get_match_data(dev);
+
+	intr_num = platform_irq_count(pdev);
+	if (!intr_num)
+		return dev_err_probe(dev, -ENODEV, "No interrupts property\n");
+
+	for (int i = 0; i < intr_num; i++) {
+		if (i == DATA_UNCORR && (quirks & QUIRK_BROKEN_DATA_UNCORR))
+			continue;
+
+		g_irq[i] = platform_get_irq(pdev, i);
+		if (g_irq[i] < 0)
+			return g_irq[i];
+
+		rc = devm_request_irq(dev, g_irq[i], ccache_int_handler, 0, "ccache_ecc", NULL);
+		if (rc)
+			return dev_err_probe(dev, rc, "Could not request IRQ %d\n", g_irq[i]);
+	}
+
+	return 0;
+}
+
+static struct platform_driver sifive_ccache_driver = {
+	.probe	= sifive_ccache_probe,
+	.driver	= {
+		.name		= "sifive_ccache",
+		.of_match_table	= sifive_ccache_ids,
+	},
+};
+
+static int __init sifive_ccache_init(void)
+{
+	struct device_node *np;
+	struct resource res;
+	const struct of_device_id *match;
+	unsigned long quirks __maybe_unused;
+	int rc;
+
+	np = of_find_matching_node_and_match(NULL, sifive_ccache_ids, &match);
+	if (!np)
+		return -ENODEV;
+
+	quirks = (uintptr_t)match->data;
+
+	if (of_address_to_resource(np, 0, &res)) {
+		rc = -ENODEV;
+		goto err_node_put;
+	}
+
+	ccache_base = ioremap(res.start, resource_size(&res));
+	if (!ccache_base) {
+		rc = -ENOMEM;
+		goto err_node_put;
+	}
+
+	if (of_property_read_u32(np, "cache-level", &level)) {
+		rc = -ENOENT;
+		goto err_unmap;
+	}
+
+#ifdef CONFIG_RISCV_NONSTANDARD_CACHE_OPS
+	if (quirks & QUIRK_NONSTANDARD_CACHE_OPS) {
+		riscv_cbom_block_size = SIFIVE_CCACHE_LINE_SIZE;
+		riscv_noncoherent_supported();
+		riscv_noncoherent_register_cache_ops(&ccache_mgmt_ops);
+	}
+#endif
+
+	ccache_config_read();
+
+	ccache_cache_ops.get_priv_group = ccache_get_priv_group;
+	riscv_set_cacheinfo_ops(&ccache_cache_ops);
+
+#ifdef CONFIG_DEBUG_FS
+	setup_sifive_debug();
+#endif
+
+	rc = platform_driver_register(&sifive_ccache_driver);
+	if (rc)
+		goto err_unmap;
+
+	of_node_put(np);
+
+	return 0;
+
+err_unmap:
+	iounmap(ccache_base);
+err_node_put:
+	of_node_put(np);
+	return rc;
+}
+
+arch_initcall(sifive_ccache_init);