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, 306 insertions, 0 deletions

diff --git a/drivers/sh/intc/handle.c b/drivers/sh/intc/handle.c
new file mode 100644
index 000000000..7863a4491
--- /dev/null
+++ b/drivers/sh/intc/handle.c
@@ -0,0 +1,306 @@
+/*
+ * Shared interrupt handling code for IPR and INTC2 types of IRQs.
+ *
+ * Copyright (C) 2007, 2008 Magnus Damm
+ * Copyright (C) 2009, 2010 Paul Mundt
+ *
+ * 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.
+ */
+#include <linux/init.h>
+#include <linux/irq.h>
+#include <linux/spinlock.h>
+#include "internals.h"
+
+static unsigned long ack_handle[INTC_NR_IRQS];
+
+static intc_enum __init intc_grp_id(struct intc_desc *desc,
+				    intc_enum enum_id)
+{
+	struct intc_group *g = desc->hw.groups;
+	unsigned int i, j;
+
+	for (i = 0; g && enum_id && i < desc->hw.nr_groups; i++) {
+		g = desc->hw.groups + i;
+
+		for (j = 0; g->enum_ids[j]; j++) {
+			if (g->enum_ids[j] != enum_id)
+				continue;
+
+			return g->enum_id;
+		}
+	}
+
+	return 0;
+}
+
+static unsigned int __init _intc_mask_data(struct intc_desc *desc,
+					   struct intc_desc_int *d,
+					   intc_enum enum_id,
+					   unsigned int *reg_idx,
+					   unsigned int *fld_idx)
+{
+	struct intc_mask_reg *mr = desc->hw.mask_regs;
+	unsigned int fn, mode;
+	unsigned long reg_e, reg_d;
+
+	while (mr && enum_id && *reg_idx < desc->hw.nr_mask_regs) {
+		mr = desc->hw.mask_regs + *reg_idx;
+
+		for (; *fld_idx < ARRAY_SIZE(mr->enum_ids); (*fld_idx)++) {
+			if (mr->enum_ids[*fld_idx] != enum_id)
+				continue;
+
+			if (mr->set_reg && mr->clr_reg) {
+				fn = REG_FN_WRITE_BASE;
+				mode = MODE_DUAL_REG;
+				reg_e = mr->clr_reg;
+				reg_d = mr->set_reg;
+			} else {
+				fn = REG_FN_MODIFY_BASE;
+				if (mr->set_reg) {
+					mode = MODE_ENABLE_REG;
+					reg_e = mr->set_reg;
+					reg_d = mr->set_reg;
+				} else {
+					mode = MODE_MASK_REG;
+					reg_e = mr->clr_reg;
+					reg_d = mr->clr_reg;
+				}
+			}
+
+			fn += (mr->reg_width >> 3) - 1;
+			return _INTC_MK(fn, mode,
+					intc_get_reg(d, reg_e),
+					intc_get_reg(d, reg_d),
+					1,
+					(mr->reg_width - 1) - *fld_idx);
+		}
+
+		*fld_idx = 0;
+		(*reg_idx)++;
+	}
+
+	return 0;
+}
+
+unsigned int __init
+intc_get_mask_handle(struct intc_desc *desc, struct intc_desc_int *d,
+		     intc_enum enum_id, int do_grps)
+{
+	unsigned int i = 0;
+	unsigned int j = 0;
+	unsigned int ret;
+
+	ret = _intc_mask_data(desc, d, enum_id, &i, &j);
+	if (ret)
+		return ret;
+
+	if (do_grps)
+		return intc_get_mask_handle(desc, d, intc_grp_id(desc, enum_id), 0);
+
+	return 0;
+}
+
+static unsigned int __init _intc_prio_data(struct intc_desc *desc,
+					   struct intc_desc_int *d,
+					   intc_enum enum_id,
+					   unsigned int *reg_idx,
+					   unsigned int *fld_idx)
+{
+	struct intc_prio_reg *pr = desc->hw.prio_regs;
+	unsigned int fn, n, mode, bit;
+	unsigned long reg_e, reg_d;
+
+	while (pr && enum_id && *reg_idx < desc->hw.nr_prio_regs) {
+		pr = desc->hw.prio_regs + *reg_idx;
+
+		for (; *fld_idx < ARRAY_SIZE(pr->enum_ids); (*fld_idx)++) {
+			if (pr->enum_ids[*fld_idx] != enum_id)
+				continue;
+
+			if (pr->set_reg && pr->clr_reg) {
+				fn = REG_FN_WRITE_BASE;
+				mode = MODE_PCLR_REG;
+				reg_e = pr->set_reg;
+				reg_d = pr->clr_reg;
+			} else {
+				fn = REG_FN_MODIFY_BASE;
+				mode = MODE_PRIO_REG;
+				if (!pr->set_reg)
+					BUG();
+				reg_e = pr->set_reg;
+				reg_d = pr->set_reg;
+			}
+
+			fn += (pr->reg_width >> 3) - 1;
+			n = *fld_idx + 1;
+
+			BUG_ON(n * pr->field_width > pr->reg_width);
+
+			bit = pr->reg_width - (n * pr->field_width);
+
+			return _INTC_MK(fn, mode,
+					intc_get_reg(d, reg_e),
+					intc_get_reg(d, reg_d),
+					pr->field_width, bit);
+		}
+
+		*fld_idx = 0;
+		(*reg_idx)++;
+	}
+
+	return 0;
+}
+
+unsigned int __init
+intc_get_prio_handle(struct intc_desc *desc, struct intc_desc_int *d,
+		     intc_enum enum_id, int do_grps)
+{
+	unsigned int i = 0;
+	unsigned int j = 0;
+	unsigned int ret;
+
+	ret = _intc_prio_data(desc, d, enum_id, &i, &j);
+	if (ret)
+		return ret;
+
+	if (do_grps)
+		return intc_get_prio_handle(desc, d, intc_grp_id(desc, enum_id), 0);
+
+	return 0;
+}
+
+static unsigned int intc_ack_data(struct intc_desc *desc,
+				  struct intc_desc_int *d, intc_enum enum_id)
+{
+	struct intc_mask_reg *mr = desc->hw.ack_regs;
+	unsigned int i, j, fn, mode;
+	unsigned long reg_e, reg_d;
+
+	for (i = 0; mr && enum_id && i < desc->hw.nr_ack_regs; i++) {
+		mr = desc->hw.ack_regs + i;
+
+		for (j = 0; j < ARRAY_SIZE(mr->enum_ids); j++) {
+			if (mr->enum_ids[j] != enum_id)
+				continue;
+
+			fn = REG_FN_MODIFY_BASE;
+			mode = MODE_ENABLE_REG;
+			reg_e = mr->set_reg;
+			reg_d = mr->set_reg;
+
+			fn += (mr->reg_width >> 3) - 1;
+			return _INTC_MK(fn, mode,
+					intc_get_reg(d, reg_e),
+					intc_get_reg(d, reg_d),
+					1,
+					(mr->reg_width - 1) - j);
+		}
+	}
+
+	return 0;
+}
+
+static void intc_enable_disable(struct intc_desc_int *d,
+				unsigned long handle, int do_enable)
+{
+	unsigned long addr;
+	unsigned int cpu;
+	unsigned long (*fn)(unsigned long, unsigned long,
+		   unsigned long (*)(unsigned long, unsigned long,
+				     unsigned long),
+		   unsigned int);
+
+	if (do_enable) {
+		for (cpu = 0; cpu < SMP_NR(d, _INTC_ADDR_E(handle)); cpu++) {
+			addr = INTC_REG(d, _INTC_ADDR_E(handle), cpu);
+			fn = intc_enable_noprio_fns[_INTC_MODE(handle)];
+			fn(addr, handle, intc_reg_fns[_INTC_FN(handle)], 0);
+		}
+	} else {
+		for (cpu = 0; cpu < SMP_NR(d, _INTC_ADDR_D(handle)); cpu++) {
+			addr = INTC_REG(d, _INTC_ADDR_D(handle), cpu);
+			fn = intc_disable_fns[_INTC_MODE(handle)];
+			fn(addr, handle, intc_reg_fns[_INTC_FN(handle)], 0);
+		}
+	}
+}
+
+void __init intc_enable_disable_enum(struct intc_desc *desc,
+				     struct intc_desc_int *d,
+				     intc_enum enum_id, int enable)
+{
+	unsigned int i, j, data;
+
+	/* go through and enable/disable all mask bits */
+	i = j = 0;
+	do {
+		data = _intc_mask_data(desc, d, enum_id, &i, &j);
+		if (data)
+			intc_enable_disable(d, data, enable);
+		j++;
+	} while (data);
+
+	/* go through and enable/disable all priority fields */
+	i = j = 0;
+	do {
+		data = _intc_prio_data(desc, d, enum_id, &i, &j);
+		if (data)
+			intc_enable_disable(d, data, enable);
+
+		j++;
+	} while (data);
+}
+
+unsigned int __init
+intc_get_sense_handle(struct intc_desc *desc, struct intc_desc_int *d,
+		      intc_enum enum_id)
+{
+	struct intc_sense_reg *sr = desc->hw.sense_regs;
+	unsigned int i, j, fn, bit;
+
+	for (i = 0; sr && enum_id && i < desc->hw.nr_sense_regs; i++) {
+		sr = desc->hw.sense_regs + i;
+
+		for (j = 0; j < ARRAY_SIZE(sr->enum_ids); j++) {
+			if (sr->enum_ids[j] != enum_id)
+				continue;
+
+			fn = REG_FN_MODIFY_BASE;
+			fn += (sr->reg_width >> 3) - 1;
+
+			BUG_ON((j + 1) * sr->field_width > sr->reg_width);
+
+			bit = sr->reg_width - ((j + 1) * sr->field_width);
+
+			return _INTC_MK(fn, 0, intc_get_reg(d, sr->reg),
+					0, sr->field_width, bit);
+		}
+	}
+
+	return 0;
+}
+
+
+void intc_set_ack_handle(unsigned int irq, struct intc_desc *desc,
+			 struct intc_desc_int *d, intc_enum id)
+{
+	unsigned long flags;
+
+	/*
+	 * Nothing to do for this IRQ.
+	 */
+	if (!desc->hw.ack_regs)
+		return;
+
+	raw_spin_lock_irqsave(&intc_big_lock, flags);
+	ack_handle[irq] = intc_ack_data(desc, d, id);
+	raw_spin_unlock_irqrestore(&intc_big_lock, flags);
+}
+
+unsigned long intc_get_ack_handle(unsigned int irq)
+{
+	return ack_handle[irq];
+}