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, 216 insertions, 0 deletions

diff --git a/drivers/clocksource/timer-pistachio.c b/drivers/clocksource/timer-pistachio.c
new file mode 100644
index 000000000..57b2197a0
--- /dev/null
+++ b/drivers/clocksource/timer-pistachio.c
@@ -0,0 +1,216 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Pistachio clocksource based on general-purpose timers
+ *
+ * Copyright (C) 2015 Imagination Technologies
+ */
+
+#define pr_fmt(fmt) "%s: " fmt, __func__
+
+#include <linux/clk.h>
+#include <linux/clocksource.h>
+#include <linux/clockchips.h>
+#include <linux/delay.h>
+#include <linux/err.h>
+#include <linux/init.h>
+#include <linux/spinlock.h>
+#include <linux/mfd/syscon.h>
+#include <linux/of.h>
+#include <linux/of_address.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+#include <linux/sched_clock.h>
+#include <linux/time.h>
+
+/* Top level reg */
+#define CR_TIMER_CTRL_CFG		0x00
+#define TIMER_ME_GLOBAL			BIT(0)
+#define CR_TIMER_REV			0x10
+
+/* Timer specific registers */
+#define TIMER_CFG			0x20
+#define TIMER_ME_LOCAL			BIT(0)
+#define TIMER_RELOAD_VALUE		0x24
+#define TIMER_CURRENT_VALUE		0x28
+#define TIMER_CURRENT_OVERFLOW_VALUE	0x2C
+#define TIMER_IRQ_STATUS		0x30
+#define TIMER_IRQ_CLEAR			0x34
+#define TIMER_IRQ_MASK			0x38
+
+#define PERIP_TIMER_CONTROL		0x90
+
+/* Timer specific configuration Values */
+#define RELOAD_VALUE			0xffffffff
+
+struct pistachio_clocksource {
+	void __iomem *base;
+	raw_spinlock_t lock;
+	struct clocksource cs;
+};
+
+static struct pistachio_clocksource pcs_gpt;
+
+#define to_pistachio_clocksource(cs)	\
+	container_of(cs, struct pistachio_clocksource, cs)
+
+static inline u32 gpt_readl(void __iomem *base, u32 offset, u32 gpt_id)
+{
+	return readl(base + 0x20 * gpt_id + offset);
+}
+
+static inline void gpt_writel(void __iomem *base, u32 value, u32 offset,
+		u32 gpt_id)
+{
+	writel(value, base + 0x20 * gpt_id + offset);
+}
+
+static u64 notrace
+pistachio_clocksource_read_cycles(struct clocksource *cs)
+{
+	struct pistachio_clocksource *pcs = to_pistachio_clocksource(cs);
+	__maybe_unused u32 overflow;
+	u32 counter;
+	unsigned long flags;
+
+	/*
+	 * The counter value is only refreshed after the overflow value is read.
+	 * And they must be read in strict order, hence raw spin lock added.
+	 */
+
+	raw_spin_lock_irqsave(&pcs->lock, flags);
+	overflow = gpt_readl(pcs->base, TIMER_CURRENT_OVERFLOW_VALUE, 0);
+	counter = gpt_readl(pcs->base, TIMER_CURRENT_VALUE, 0);
+	raw_spin_unlock_irqrestore(&pcs->lock, flags);
+
+	return (u64)~counter;
+}
+
+static u64 notrace pistachio_read_sched_clock(void)
+{
+	return pistachio_clocksource_read_cycles(&pcs_gpt.cs);
+}
+
+static void pistachio_clksrc_set_mode(struct clocksource *cs, int timeridx,
+			int enable)
+{
+	struct pistachio_clocksource *pcs = to_pistachio_clocksource(cs);
+	u32 val;
+
+	val = gpt_readl(pcs->base, TIMER_CFG, timeridx);
+	if (enable)
+		val |= TIMER_ME_LOCAL;
+	else
+		val &= ~TIMER_ME_LOCAL;
+
+	gpt_writel(pcs->base, val, TIMER_CFG, timeridx);
+}
+
+static void pistachio_clksrc_enable(struct clocksource *cs, int timeridx)
+{
+	struct pistachio_clocksource *pcs = to_pistachio_clocksource(cs);
+
+	/* Disable GPT local before loading reload value */
+	pistachio_clksrc_set_mode(cs, timeridx, false);
+	gpt_writel(pcs->base, RELOAD_VALUE, TIMER_RELOAD_VALUE, timeridx);
+	pistachio_clksrc_set_mode(cs, timeridx, true);
+}
+
+static void pistachio_clksrc_disable(struct clocksource *cs, int timeridx)
+{
+	/* Disable GPT local */
+	pistachio_clksrc_set_mode(cs, timeridx, false);
+}
+
+static int pistachio_clocksource_enable(struct clocksource *cs)
+{
+	pistachio_clksrc_enable(cs, 0);
+	return 0;
+}
+
+static void pistachio_clocksource_disable(struct clocksource *cs)
+{
+	pistachio_clksrc_disable(cs, 0);
+}
+
+/* Desirable clock source for pistachio platform */
+static struct pistachio_clocksource pcs_gpt = {
+	.cs =	{
+		.name		= "gptimer",
+		.rating		= 300,
+		.enable		= pistachio_clocksource_enable,
+		.disable	= pistachio_clocksource_disable,
+		.read		= pistachio_clocksource_read_cycles,
+		.mask		= CLOCKSOURCE_MASK(32),
+		.flags		= CLOCK_SOURCE_IS_CONTINUOUS |
+				  CLOCK_SOURCE_SUSPEND_NONSTOP,
+		},
+};
+
+static int __init pistachio_clksrc_of_init(struct device_node *node)
+{
+	struct clk *sys_clk, *fast_clk;
+	struct regmap *periph_regs;
+	unsigned long rate;
+	int ret;
+
+	pcs_gpt.base = of_iomap(node, 0);
+	if (!pcs_gpt.base) {
+		pr_err("cannot iomap\n");
+		return -ENXIO;
+	}
+
+	periph_regs = syscon_regmap_lookup_by_phandle(node, "img,cr-periph");
+	if (IS_ERR(periph_regs)) {
+		pr_err("cannot get peripheral regmap (%ld)\n",
+		       PTR_ERR(periph_regs));
+		return PTR_ERR(periph_regs);
+	}
+
+	/* Switch to using the fast counter clock */
+	ret = regmap_update_bits(periph_regs, PERIP_TIMER_CONTROL,
+				 0xf, 0x0);
+	if (ret)
+		return ret;
+
+	sys_clk = of_clk_get_by_name(node, "sys");
+	if (IS_ERR(sys_clk)) {
+		pr_err("clock get failed (%ld)\n", PTR_ERR(sys_clk));
+		return PTR_ERR(sys_clk);
+	}
+
+	fast_clk = of_clk_get_by_name(node, "fast");
+	if (IS_ERR(fast_clk)) {
+		pr_err("clock get failed (%lu)\n", PTR_ERR(fast_clk));
+		return PTR_ERR(fast_clk);
+	}
+
+	ret = clk_prepare_enable(sys_clk);
+	if (ret < 0) {
+		pr_err("failed to enable clock (%d)\n", ret);
+		return ret;
+	}
+
+	ret = clk_prepare_enable(fast_clk);
+	if (ret < 0) {
+		pr_err("failed to enable clock (%d)\n", ret);
+		clk_disable_unprepare(sys_clk);
+		return ret;
+	}
+
+	rate = clk_get_rate(fast_clk);
+
+	/* Disable irq's for clocksource usage */
+	gpt_writel(pcs_gpt.base, 0, TIMER_IRQ_MASK, 0);
+	gpt_writel(pcs_gpt.base, 0, TIMER_IRQ_MASK, 1);
+	gpt_writel(pcs_gpt.base, 0, TIMER_IRQ_MASK, 2);
+	gpt_writel(pcs_gpt.base, 0, TIMER_IRQ_MASK, 3);
+
+	/* Enable timer block */
+	writel(TIMER_ME_GLOBAL, pcs_gpt.base);
+
+	raw_spin_lock_init(&pcs_gpt.lock);
+	sched_clock_register(pistachio_read_sched_clock, 32, rate);
+	return clocksource_register_hz(&pcs_gpt.cs, rate);
+}
+TIMER_OF_DECLARE(pistachio_gptimer, "img,pistachio-gptimer",
+		       pistachio_clksrc_of_init);