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, 253 insertions, 0 deletions

diff --git a/arch/mips/bmips/setup.c b/arch/mips/bmips/setup.c
new file mode 100644
index 000000000..2572fd49a
--- /dev/null
+++ b/arch/mips/bmips/setup.c
@@ -0,0 +1,253 @@
+/*
+ * 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>
+ * Copyright (C) 2014 Kevin Cernekee <cernekee@gmail.com>
+ */
+
+#include <linux/init.h>
+#include <linux/bitops.h>
+#include <linux/memblock.h>
+#include <linux/ioport.h>
+#include <linux/kernel.h>
+#include <linux/io.h>
+#include <linux/of.h>
+#include <linux/of_clk.h>
+#include <linux/of_fdt.h>
+#include <linux/libfdt.h>
+#include <linux/smp.h>
+#include <asm/addrspace.h>
+#include <asm/bmips.h>
+#include <asm/bootinfo.h>
+#include <asm/cpu-type.h>
+#include <asm/mipsregs.h>
+#include <asm/prom.h>
+#include <asm/smp-ops.h>
+#include <asm/time.h>
+#include <asm/traps.h>
+#include <asm/fw/cfe/cfe_api.h>
+
+#define RELO_NORMAL_VEC		BIT(18)
+
+#define REG_BCM6328_OTP		((void __iomem *)CKSEG1ADDR(0x1000062c))
+#define BCM6328_TP1_DISABLED	BIT(9)
+
+/*
+ * 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;
+
+extern bool bmips_rac_flush_disable;
+
+static const unsigned long kbase = VMLINUX_LOAD_ADDRESS & 0xfff00000;
+
+struct bmips_quirk {
+	const char		*compatible;
+	void			(*quirk_fn)(void);
+};
+
+static void kbase_setup(void)
+{
+	__raw_writel(kbase | RELO_NORMAL_VEC,
+		     BMIPS_GET_CBR() + BMIPS_RELO_VECTOR_CONTROL_1);
+	ebase = kbase;
+}
+
+static void bcm3384_viper_quirks(void)
+{
+	/*
+	 * Some experimental CM boxes are set up to let CM own the Viper TP0
+	 * and let Linux own TP1.  This requires moving the kernel
+	 * load address to a non-conflicting region (e.g. via
+	 * CONFIG_PHYSICAL_START) and supplying an alternate DTB.
+	 * If we detect this condition, we need to move the MIPS exception
+	 * vectors up to an area that we own.
+	 *
+	 * This is distinct from the OTHER special case mentioned in
+	 * smp-bmips.c (boot on TP1, but enable SMP, then TP0 becomes our
+	 * logical CPU#1).  For the Viper TP1 case, SMP is off limits.
+	 *
+	 * Also note that many BMIPS435x CPUs do not have a
+	 * BMIPS_RELO_VECTOR_CONTROL_1 register, so it isn't safe to just
+	 * write VMLINUX_LOAD_ADDRESS into that register on every SoC.
+	 */
+	board_ebase_setup = &kbase_setup;
+	bmips_smp_enabled = 0;
+}
+
+static void bcm63xx_fixup_cpu1(void)
+{
+	/*
+	 * The bootloader has set up the CPU1 reset vector at
+	 * 0xa000_0200.
+	 * This conflicts with the special interrupt vector (IV).
+	 * The bootloader has also set up CPU1 to respond to the wrong
+	 * IPI interrupt.
+	 * Here we will start up CPU1 in the background and ask it to
+	 * reconfigure itself then go back to sleep.
+	 */
+	memcpy((void *)0xa0000200, &bmips_smp_movevec, 0x20);
+	__sync();
+	set_c0_cause(C_SW0);
+	cpumask_set_cpu(1, &bmips_booted_mask);
+}
+
+static void bcm6328_quirks(void)
+{
+	/* Check CPU1 status in OTP (it is usually disabled) */
+	if (__raw_readl(REG_BCM6328_OTP) & BCM6328_TP1_DISABLED)
+		bmips_smp_enabled = 0;
+	else
+		bcm63xx_fixup_cpu1();
+}
+
+static void bcm6358_quirks(void)
+{
+	/*
+	 * BCM3368/BCM6358 need special handling for their shared TLB, so
+	 * disable SMP for now
+	 */
+	bmips_smp_enabled = 0;
+
+	/*
+	 * RAC flush causes kernel panics on BCM6358 when booting from TP1
+	 * because the bootloader is not initializing it properly.
+	 */
+	bmips_rac_flush_disable = !!(read_c0_brcm_cmt_local() & (1 << 31)) ||
+				  !!bmips_cbr_addr;
+}
+
+static void bcm6368_quirks(void)
+{
+	bcm63xx_fixup_cpu1();
+}
+
+static const struct bmips_quirk bmips_quirk_list[] = {
+	{ "brcm,bcm3368",		&bcm6358_quirks			},
+	{ "brcm,bcm3384-viper",		&bcm3384_viper_quirks		},
+	{ "brcm,bcm33843-viper",	&bcm3384_viper_quirks		},
+	{ "brcm,bcm6328",		&bcm6328_quirks			},
+	{ "brcm,bcm6358",		&bcm6358_quirks			},
+	{ "brcm,bcm6362",		&bcm6368_quirks			},
+	{ "brcm,bcm6368",		&bcm6368_quirks			},
+	{ "brcm,bcm63168",		&bcm6368_quirks			},
+	{ "brcm,bcm63268",		&bcm6368_quirks			},
+	{ },
+};
+
+static void __init bmips_init_cfe(void)
+{
+	cfe_seal = fw_arg3;
+
+	if (cfe_seal != CFE_EPTSEAL)
+		return;
+
+	cfe_init(fw_arg0, fw_arg2);
+}
+
+void __init prom_init(void)
+{
+	/* Cache CBR addr before CPU/DMA setup */
+	bmips_cbr_addr = BMIPS_GET_CBR();
+	bmips_init_cfe();
+	bmips_cpu_setup();
+	register_bmips_smp_ops();
+}
+
+const char *get_system_type(void)
+{
+	return "Generic BMIPS kernel";
+}
+
+void __init plat_time_init(void)
+{
+	struct device_node *np;
+	u32 freq;
+
+	np = of_find_node_by_name(NULL, "cpus");
+	if (!np)
+		panic("missing 'cpus' DT node");
+	if (of_property_read_u32(np, "mips-hpt-frequency", &freq) < 0)
+		panic("missing 'mips-hpt-frequency' property");
+	of_node_put(np);
+
+	mips_hpt_frequency = freq;
+}
+
+void __init plat_mem_setup(void)
+{
+	void *dtb;
+	const struct bmips_quirk *q;
+
+	set_io_port_base(0);
+	ioport_resource.start = 0;
+	ioport_resource.end = ~0;
+
+	/*
+	 * intended to somewhat resemble ARM; see
+	 * Documentation/arch/arm/booting.rst
+	 */
+	if (fw_arg0 == 0 && fw_arg1 == 0xffffffff)
+		dtb = phys_to_virt(fw_arg2);
+	else
+		dtb = get_fdt();
+
+	if (!dtb)
+		cfe_die("no dtb found");
+
+	__dt_setup_arch(dtb);
+
+	for (q = bmips_quirk_list; q->quirk_fn; q++) {
+		if (of_flat_dt_is_compatible(of_get_flat_dt_root(),
+					     q->compatible)) {
+			q->quirk_fn();
+		}
+	}
+}
+
+void __init device_tree_init(void)
+{
+	struct device_node *np;
+	u32 addr;
+
+	unflatten_and_copy_device_tree();
+
+	/* Disable SMP boot unless both CPUs are listed in DT and !disabled */
+	np = of_find_node_by_name(NULL, "cpus");
+	if (!np)
+		return;
+
+	if (of_get_available_child_count(np) <= 1)
+		bmips_smp_enabled = 0;
+
+	/* Check if DT provide a CBR address */
+	if (of_property_read_u32(np, "brcm,bmips-cbr-reg", &addr))
+		goto exit;
+
+	/* Make sure CBR address is outside DRAM window */
+	if (addr >= (u32)memblock_start_of_DRAM() &&
+	    addr < (u32)memblock_end_of_DRAM()) {
+		WARN(1, "DT CBR %x inside DRAM window. Ignoring DT CBR.\n",
+		     addr);
+		goto exit;
+	}
+
+	bmips_cbr_addr = (void __iomem *)addr;
+	/* Since CBR is provided by DT, enable RAC flush */
+	bmips_rac_flush_disable = false;
+
+exit:
+	of_node_put(np);
+}
+
+static int __init plat_dev_init(void)
+{
+	of_clk_init(NULL);
+	return 0;
+}
+
+arch_initcall(plat_dev_init);