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, 178 insertions, 0 deletions

diff --git a/arch/mips/bcm63xx/setup.c b/arch/mips/bcm63xx/setup.c
new file mode 100644
index 000000000..81529084b
--- /dev/null
+++ b/arch/mips/bcm63xx/setup.c
@@ -0,0 +1,178 @@
+/*
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ *
+ * Copyright (C) 2008 Maxime Bizon <mbizon@freebox.fr>
+ */
+
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/delay.h>
+#include <linux/memblock.h>
+#include <linux/ioport.h>
+#include <linux/pm.h>
+#include <asm/bmips.h>
+#include <asm/bootinfo.h>
+#include <asm/time.h>
+#include <asm/reboot.h>
+#include <asm/cacheflush.h>
+#include <bcm63xx_board.h>
+#include <bcm63xx_cpu.h>
+#include <bcm63xx_regs.h>
+#include <bcm63xx_io.h>
+#include <bcm63xx_gpio.h>
+
+/*
+ * CBR addr doesn't change and we can cache it.
+ * For broken SoC/Bootloader CBR addr might also be provided via DT
+ * with "brcm,bmips-cbr-reg" in the "cpus" node.
+ */
+void __iomem *bmips_cbr_addr __read_mostly;
+
+void bcm63xx_machine_halt(void)
+{
+	pr_info("System halted\n");
+	while (1)
+		;
+}
+
+static void bcm6348_a1_reboot(void)
+{
+	u32 reg;
+
+	/* soft reset all blocks */
+	pr_info("soft-resetting all blocks ...\n");
+	reg = bcm_perf_readl(PERF_SOFTRESET_REG);
+	reg &= ~SOFTRESET_6348_ALL;
+	bcm_perf_writel(reg, PERF_SOFTRESET_REG);
+	mdelay(10);
+
+	reg = bcm_perf_readl(PERF_SOFTRESET_REG);
+	reg |= SOFTRESET_6348_ALL;
+	bcm_perf_writel(reg, PERF_SOFTRESET_REG);
+	mdelay(10);
+
+	/* Jump to the power on address. */
+	pr_info("jumping to reset vector.\n");
+	/* set high vectors (base at 0xbfc00000 */
+	set_c0_status(ST0_BEV | ST0_ERL);
+	/* run uncached in kseg0 */
+	change_c0_config(CONF_CM_CMASK, CONF_CM_UNCACHED);
+	__flush_cache_all();
+	/* remove all wired TLB entries */
+	write_c0_wired(0);
+	__asm__ __volatile__(
+		"jr\t%0"
+		:
+		: "r" (0xbfc00000));
+	while (1)
+		;
+}
+
+void bcm63xx_machine_reboot(void)
+{
+	u32 reg, perf_regs[2] = { 0, 0 };
+	unsigned int i;
+
+	/* mask and clear all external irq */
+	switch (bcm63xx_get_cpu_id()) {
+	case BCM3368_CPU_ID:
+		perf_regs[0] = PERF_EXTIRQ_CFG_REG_3368;
+		break;
+	case BCM6328_CPU_ID:
+		perf_regs[0] = PERF_EXTIRQ_CFG_REG_6328;
+		break;
+	case BCM6338_CPU_ID:
+		perf_regs[0] = PERF_EXTIRQ_CFG_REG_6338;
+		break;
+	case BCM6345_CPU_ID:
+		perf_regs[0] = PERF_EXTIRQ_CFG_REG_6345;
+		break;
+	case BCM6348_CPU_ID:
+		perf_regs[0] = PERF_EXTIRQ_CFG_REG_6348;
+		break;
+	case BCM6358_CPU_ID:
+		perf_regs[0] = PERF_EXTIRQ_CFG_REG_6358;
+		break;
+	case BCM6362_CPU_ID:
+		perf_regs[0] = PERF_EXTIRQ_CFG_REG_6362;
+		break;
+	}
+
+	for (i = 0; i < 2; i++) {
+		if (!perf_regs[i])
+			break;
+
+		reg = bcm_perf_readl(perf_regs[i]);
+		if (BCMCPU_IS_6348()) {
+			reg &= ~EXTIRQ_CFG_MASK_ALL_6348;
+			reg |= EXTIRQ_CFG_CLEAR_ALL_6348;
+		} else {
+			reg &= ~EXTIRQ_CFG_MASK_ALL;
+			reg |= EXTIRQ_CFG_CLEAR_ALL;
+		}
+		bcm_perf_writel(reg, perf_regs[i]);
+	}
+
+	if (BCMCPU_IS_6348() && (bcm63xx_get_cpu_rev() == 0xa1))
+		bcm6348_a1_reboot();
+
+	pr_info("triggering watchdog soft-reset...\n");
+	if (BCMCPU_IS_6328()) {
+		bcm_wdt_writel(1, WDT_SOFTRESET_REG);
+	} else {
+		reg = bcm_perf_readl(PERF_SYS_PLL_CTL_REG);
+		reg |= SYS_PLL_SOFT_RESET;
+		bcm_perf_writel(reg, PERF_SYS_PLL_CTL_REG);
+	}
+	while (1)
+		;
+}
+
+static void __bcm63xx_machine_reboot(char *p)
+{
+	bcm63xx_machine_reboot();
+}
+
+/*
+ * return system type in /proc/cpuinfo
+ */
+const char *get_system_type(void)
+{
+	static char buf[128];
+	snprintf(buf, sizeof(buf), "bcm63xx/%s (0x%04x/0x%02X)",
+		 board_get_name(),
+		 bcm63xx_get_cpu_id(), bcm63xx_get_cpu_rev());
+	return buf;
+}
+
+void __init plat_time_init(void)
+{
+	mips_hpt_frequency = bcm63xx_get_cpu_freq() / 2;
+}
+
+void __init plat_mem_setup(void)
+{
+	memblock_add(0, bcm63xx_get_memory_size());
+
+	_machine_halt = bcm63xx_machine_halt;
+	_machine_restart = __bcm63xx_machine_reboot;
+	pm_power_off = bcm63xx_machine_halt;
+
+	set_io_port_base(0);
+	ioport_resource.start = 0;
+	ioport_resource.end = ~0;
+
+	board_setup();
+}
+
+static int __init bcm63xx_register_devices(void)
+{
+	/* register gpiochip */
+	bcm63xx_gpio_init();
+
+	return board_register_devices();
+}
+
+arch_initcall(bcm63xx_register_devices);