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, 200 insertions, 0 deletions

diff --git a/drivers/mtd/maps/physmap-gemini.c b/drivers/mtd/maps/physmap-gemini.c
new file mode 100644
index 000000000..1c34b4ef7
--- /dev/null
+++ b/drivers/mtd/maps/physmap-gemini.c
@@ -0,0 +1,200 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Cortina Systems Gemini OF physmap add-on
+ * Copyright (C) 2017 Linus Walleij <linus.walleij@linaro.org>
+ *
+ * This SoC has an elaborate flash control register, so we need to
+ * detect and set it up when booting on this platform.
+ */
+#include <linux/export.h>
+#include <linux/of.h>
+#include <linux/mtd/map.h>
+#include <linux/mtd/xip.h>
+#include <linux/mfd/syscon.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+#include <linux/bitops.h>
+#include <linux/pinctrl/consumer.h>
+#include "physmap-gemini.h"
+
+/*
+ * The Flash-relevant parts of the global status register
+ * These would also be relevant for a NAND driver.
+ */
+#define GLOBAL_STATUS			0x04
+#define FLASH_TYPE_MASK			(0x3 << 24)
+#define FLASH_TYPE_NAND_2K		(0x3 << 24)
+#define FLASH_TYPE_NAND_512		(0x2 << 24)
+#define FLASH_TYPE_PARALLEL		(0x1 << 24)
+#define FLASH_TYPE_SERIAL		(0x0 << 24)
+/* if parallel */
+#define FLASH_WIDTH_16BIT		(1 << 23)	/* else 8 bit */
+/* if serial */
+#define FLASH_ATMEL			(1 << 23)	/* else STM */
+
+#define FLASH_SIZE_MASK			(0x3 << 21)
+#define NAND_256M			(0x3 << 21)	/* and more */
+#define NAND_128M			(0x2 << 21)
+#define NAND_64M			(0x1 << 21)
+#define NAND_32M			(0x0 << 21)
+#define ATMEL_16M			(0x3 << 21)	/* and more */
+#define ATMEL_8M			(0x2 << 21)
+#define ATMEL_4M_2M			(0x1 << 21)
+#define ATMEL_1M			(0x0 << 21)	/* and less */
+#define STM_32M				(1 << 22)	/* and more */
+#define STM_16M				(0 << 22)	/* and less */
+
+#define FLASH_PARALLEL_HIGH_PIN_CNT	(1 << 20)	/* else low pin cnt */
+
+struct gemini_flash {
+	struct device *dev;
+	struct pinctrl *p;
+	struct pinctrl_state *enabled_state;
+	struct pinctrl_state *disabled_state;
+};
+
+/* Static local state */
+static struct gemini_flash *gf;
+
+static void gemini_flash_enable_pins(void)
+{
+	int ret;
+
+	if (IS_ERR(gf->enabled_state))
+		return;
+	ret = pinctrl_select_state(gf->p, gf->enabled_state);
+	if (ret)
+		dev_err(gf->dev, "failed to enable pins\n");
+}
+
+static void gemini_flash_disable_pins(void)
+{
+	int ret;
+
+	if (IS_ERR(gf->disabled_state))
+		return;
+	ret = pinctrl_select_state(gf->p, gf->disabled_state);
+	if (ret)
+		dev_err(gf->dev, "failed to disable pins\n");
+}
+
+static map_word __xipram gemini_flash_map_read(struct map_info *map,
+					       unsigned long ofs)
+{
+	map_word ret;
+
+	gemini_flash_enable_pins();
+	ret = inline_map_read(map, ofs);
+	gemini_flash_disable_pins();
+
+	return ret;
+}
+
+static void __xipram gemini_flash_map_write(struct map_info *map,
+					    const map_word datum,
+					    unsigned long ofs)
+{
+	gemini_flash_enable_pins();
+	inline_map_write(map, datum, ofs);
+	gemini_flash_disable_pins();
+}
+
+static void __xipram gemini_flash_map_copy_from(struct map_info *map,
+						void *to, unsigned long from,
+						ssize_t len)
+{
+	gemini_flash_enable_pins();
+	inline_map_copy_from(map, to, from, len);
+	gemini_flash_disable_pins();
+}
+
+static void __xipram gemini_flash_map_copy_to(struct map_info *map,
+					      unsigned long to,
+					      const void *from, ssize_t len)
+{
+	gemini_flash_enable_pins();
+	inline_map_copy_to(map, to, from, len);
+	gemini_flash_disable_pins();
+}
+
+int of_flash_probe_gemini(struct platform_device *pdev,
+			  struct device_node *np,
+			  struct map_info *map)
+{
+	struct regmap *rmap;
+	struct device *dev = &pdev->dev;
+	u32 val;
+	int ret;
+
+	/* Multiplatform guard */
+	if (!of_device_is_compatible(np, "cortina,gemini-flash"))
+		return 0;
+
+	gf = devm_kzalloc(dev, sizeof(*gf), GFP_KERNEL);
+	if (!gf)
+		return -ENOMEM;
+	gf->dev = dev;
+
+	rmap = syscon_regmap_lookup_by_phandle(np, "syscon");
+	if (IS_ERR(rmap)) {
+		dev_err(dev, "no syscon\n");
+		return PTR_ERR(rmap);
+	}
+
+	ret = regmap_read(rmap, GLOBAL_STATUS, &val);
+	if (ret) {
+		dev_err(dev, "failed to read global status register\n");
+		return -ENODEV;
+	}
+	dev_dbg(dev, "global status reg: %08x\n", val);
+
+	/*
+	 * It would be contradictory if a physmap flash was NOT parallel.
+	 */
+	if ((val & FLASH_TYPE_MASK) != FLASH_TYPE_PARALLEL) {
+		dev_err(dev, "flash is not parallel\n");
+		return -ENODEV;
+	}
+
+	/*
+	 * Complain if DT data and hardware definition is different.
+	 */
+	if (val & FLASH_WIDTH_16BIT) {
+		if (map->bankwidth != 2)
+			dev_warn(dev, "flash hardware say flash is 16 bit wide but DT says it is %d bits wide\n",
+				 map->bankwidth * 8);
+	} else {
+		if (map->bankwidth != 1)
+			dev_warn(dev, "flash hardware say flash is 8 bit wide but DT says it is %d bits wide\n",
+				 map->bankwidth * 8);
+	}
+
+	gf->p = devm_pinctrl_get(dev);
+	if (IS_ERR(gf->p)) {
+		dev_err(dev, "no pinctrl handle\n");
+		ret = PTR_ERR(gf->p);
+		return ret;
+	}
+
+	gf->enabled_state = pinctrl_lookup_state(gf->p, "enabled");
+	if (IS_ERR(gf->enabled_state))
+		dev_err(dev, "no enabled pin control state\n");
+
+	gf->disabled_state = pinctrl_lookup_state(gf->p, "disabled");
+	if (IS_ERR(gf->disabled_state)) {
+		dev_err(dev, "no disabled pin control state\n");
+	} else {
+		ret = pinctrl_select_state(gf->p, gf->disabled_state);
+		if (ret)
+			dev_err(gf->dev, "failed to disable pins\n");
+	}
+
+	map->read = gemini_flash_map_read;
+	map->write = gemini_flash_map_write;
+	map->copy_from = gemini_flash_map_copy_from;
+	map->copy_to = gemini_flash_map_copy_to;
+
+	dev_info(dev, "initialized Gemini-specific physmap control\n");
+
+	return 0;
+}