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, 201 insertions, 0 deletions

diff --git a/drivers/ssb/driver_extif.c b/drivers/ssb/driver_extif.c
new file mode 100644
index 000000000..bc275968f
--- /dev/null
+++ b/drivers/ssb/driver_extif.c
@@ -0,0 +1,201 @@
+/*
+ * Sonics Silicon Backplane
+ * Broadcom EXTIF core driver
+ *
+ * Copyright 2005, Broadcom Corporation
+ * Copyright 2006, 2007, Michael Buesch <m@bues.ch>
+ * Copyright 2006, 2007, Felix Fietkau <nbd@openwrt.org>
+ * Copyright 2007, Aurelien Jarno <aurelien@aurel32.net>
+ *
+ * Licensed under the GNU/GPL. See COPYING for details.
+ */
+
+#include "ssb_private.h"
+
+#include <linux/serial.h>
+#include <linux/serial_core.h>
+#include <linux/serial_reg.h>
+
+
+static inline u32 extif_read32(struct ssb_extif *extif, u16 offset)
+{
+	return ssb_read32(extif->dev, offset);
+}
+
+static inline void extif_write32(struct ssb_extif *extif, u16 offset, u32 value)
+{
+	ssb_write32(extif->dev, offset, value);
+}
+
+static inline u32 extif_write32_masked(struct ssb_extif *extif, u16 offset,
+				       u32 mask, u32 value)
+{
+	value &= mask;
+	value |= extif_read32(extif, offset) & ~mask;
+	extif_write32(extif, offset, value);
+
+	return value;
+}
+
+#ifdef CONFIG_SSB_SERIAL
+static bool serial_exists(u8 *regs)
+{
+	u8 save_mcr, msr = 0;
+
+	if (regs) {
+		save_mcr = regs[UART_MCR];
+		regs[UART_MCR] = (UART_MCR_LOOP | UART_MCR_OUT2 | UART_MCR_RTS);
+		msr = regs[UART_MSR] & (UART_MSR_DCD | UART_MSR_RI
+					| UART_MSR_CTS | UART_MSR_DSR);
+		regs[UART_MCR] = save_mcr;
+	}
+	return (msr == (UART_MSR_DCD | UART_MSR_CTS));
+}
+
+int ssb_extif_serial_init(struct ssb_extif *extif, struct ssb_serial_port *ports)
+{
+	u32 i, nr_ports = 0;
+
+	/* Disable GPIO interrupt initially */
+	extif_write32(extif, SSB_EXTIF_GPIO_INTPOL, 0);
+	extif_write32(extif, SSB_EXTIF_GPIO_INTMASK, 0);
+
+	for (i = 0; i < 2; i++) {
+		void __iomem *uart_regs;
+
+		uart_regs = ioremap(SSB_EUART, 16);
+		if (uart_regs) {
+			uart_regs += (i * 8);
+
+			if (serial_exists(uart_regs) && ports) {
+				extif_write32(extif, SSB_EXTIF_GPIO_INTMASK, 2);
+
+				nr_ports++;
+				ports[i].regs = uart_regs;
+				ports[i].irq = 2;
+				ports[i].baud_base = 13500000;
+				ports[i].reg_shift = 0;
+			}
+			iounmap(uart_regs);
+		}
+	}
+	return nr_ports;
+}
+#endif /* CONFIG_SSB_SERIAL */
+
+void ssb_extif_timing_init(struct ssb_extif *extif, unsigned long ns)
+{
+	u32 tmp;
+
+	/* Initialize extif so we can get to the LEDs and external UART */
+	extif_write32(extif, SSB_EXTIF_PROG_CFG, SSB_EXTCFG_EN);
+
+	/* Set timing for the flash */
+	tmp  = DIV_ROUND_UP(10, ns) << SSB_PROG_WCNT_3_SHIFT;
+	tmp |= DIV_ROUND_UP(40, ns) << SSB_PROG_WCNT_1_SHIFT;
+	tmp |= DIV_ROUND_UP(120, ns);
+	extif_write32(extif, SSB_EXTIF_PROG_WAITCNT, tmp);
+
+	/* Set programmable interface timing for external uart */
+	tmp  = DIV_ROUND_UP(10, ns) << SSB_PROG_WCNT_3_SHIFT;
+	tmp |= DIV_ROUND_UP(20, ns) << SSB_PROG_WCNT_2_SHIFT;
+	tmp |= DIV_ROUND_UP(100, ns) << SSB_PROG_WCNT_1_SHIFT;
+	tmp |= DIV_ROUND_UP(120, ns);
+	extif_write32(extif, SSB_EXTIF_PROG_WAITCNT, tmp);
+}
+
+void ssb_extif_get_clockcontrol(struct ssb_extif *extif,
+				u32 *pll_type, u32 *n, u32 *m)
+{
+	*pll_type = SSB_PLLTYPE_1;
+	*n = extif_read32(extif, SSB_EXTIF_CLOCK_N);
+	*m = extif_read32(extif, SSB_EXTIF_CLOCK_SB);
+}
+
+u32 ssb_extif_watchdog_timer_set_wdt(struct bcm47xx_wdt *wdt, u32 ticks)
+{
+	struct ssb_extif *extif = bcm47xx_wdt_get_drvdata(wdt);
+
+	return ssb_extif_watchdog_timer_set(extif, ticks);
+}
+
+u32 ssb_extif_watchdog_timer_set_ms(struct bcm47xx_wdt *wdt, u32 ms)
+{
+	struct ssb_extif *extif = bcm47xx_wdt_get_drvdata(wdt);
+	u32 ticks = (SSB_EXTIF_WATCHDOG_CLK / 1000) * ms;
+
+	ticks = ssb_extif_watchdog_timer_set(extif, ticks);
+
+	return (ticks * 1000) / SSB_EXTIF_WATCHDOG_CLK;
+}
+
+u32 ssb_extif_watchdog_timer_set(struct ssb_extif *extif, u32 ticks)
+{
+	if (ticks > SSB_EXTIF_WATCHDOG_MAX_TIMER)
+		ticks = SSB_EXTIF_WATCHDOG_MAX_TIMER;
+	extif_write32(extif, SSB_EXTIF_WATCHDOG, ticks);
+
+	return ticks;
+}
+
+void ssb_extif_init(struct ssb_extif *extif)
+{
+	if (!extif->dev)
+		return; /* We don't have a Extif core */
+	spin_lock_init(&extif->gpio_lock);
+}
+
+u32 ssb_extif_gpio_in(struct ssb_extif *extif, u32 mask)
+{
+	return extif_read32(extif, SSB_EXTIF_GPIO_IN) & mask;
+}
+
+u32 ssb_extif_gpio_out(struct ssb_extif *extif, u32 mask, u32 value)
+{
+	unsigned long flags;
+	u32 res = 0;
+
+	spin_lock_irqsave(&extif->gpio_lock, flags);
+	res = extif_write32_masked(extif, SSB_EXTIF_GPIO_OUT(0),
+				   mask, value);
+	spin_unlock_irqrestore(&extif->gpio_lock, flags);
+
+	return res;
+}
+
+u32 ssb_extif_gpio_outen(struct ssb_extif *extif, u32 mask, u32 value)
+{
+	unsigned long flags;
+	u32 res = 0;
+
+	spin_lock_irqsave(&extif->gpio_lock, flags);
+	res = extif_write32_masked(extif, SSB_EXTIF_GPIO_OUTEN(0),
+				   mask, value);
+	spin_unlock_irqrestore(&extif->gpio_lock, flags);
+
+	return res;
+}
+
+u32 ssb_extif_gpio_polarity(struct ssb_extif *extif, u32 mask, u32 value)
+{
+	unsigned long flags;
+	u32 res = 0;
+
+	spin_lock_irqsave(&extif->gpio_lock, flags);
+	res = extif_write32_masked(extif, SSB_EXTIF_GPIO_INTPOL, mask, value);
+	spin_unlock_irqrestore(&extif->gpio_lock, flags);
+
+	return res;
+}
+
+u32 ssb_extif_gpio_intmask(struct ssb_extif *extif, u32 mask, u32 value)
+{
+	unsigned long flags;
+	u32 res = 0;
+
+	spin_lock_irqsave(&extif->gpio_lock, flags);
+	res = extif_write32_masked(extif, SSB_EXTIF_GPIO_INTMASK, mask, value);
+	spin_unlock_irqrestore(&extif->gpio_lock, flags);
+
+	return res;
+}