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, 100 insertions, 0 deletions

diff --git a/arch/m68k/sun3/sun3ints.c b/arch/m68k/sun3/sun3ints.c
new file mode 100644
index 000000000..32eaf55f8
--- /dev/null
+++ b/arch/m68k/sun3/sun3ints.c
@@ -0,0 +1,100 @@
+ /*
+ * linux/arch/m68k/sun3/sun3ints.c -- Sun-3(x) Linux interrupt handling code
+ *
+ * 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/types.h>
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/kernel_stat.h>
+#include <linux/interrupt.h>
+#include <asm/intersil.h>
+#include <asm/oplib.h>
+#include <asm/sun3ints.h>
+#include <asm/irq_regs.h>
+#include <linux/seq_file.h>
+
+#include "sun3.h"
+
+void sun3_disable_interrupts(void)
+{
+	sun3_disable_irq(0);
+}
+
+void sun3_enable_interrupts(void)
+{
+	sun3_enable_irq(0);
+}
+
+static unsigned char led_pattern[8] = {
+	(u8)~(0x80), (u8)~(0x01),
+	(u8)~(0x40), (u8)~(0x02),
+	(u8)~(0x20), (u8)~(0x04),
+	(u8)~(0x10), (u8)~(0x08)
+};
+
+volatile unsigned char* sun3_intreg;
+
+void sun3_enable_irq(unsigned int irq)
+{
+	*sun3_intreg |=  (1 << irq);
+}
+
+void sun3_disable_irq(unsigned int irq)
+{
+	*sun3_intreg &= ~(1 << irq);
+}
+
+static irqreturn_t sun3_int7(int irq, void *dev_id)
+{
+	unsigned int cnt;
+
+	cnt = kstat_irqs_cpu(irq, 0);
+	if (!(cnt % 2000))
+		sun3_leds(led_pattern[cnt % 16000 / 2000]);
+	return IRQ_HANDLED;
+}
+
+static irqreturn_t sun3_int5(int irq, void *dev_id)
+{
+	unsigned long flags;
+	unsigned int cnt;
+
+	local_irq_save(flags);
+#ifdef CONFIG_SUN3
+	intersil_clear();
+#endif
+	sun3_disable_irq(5);
+	sun3_enable_irq(5);
+#ifdef CONFIG_SUN3
+	intersil_clear();
+#endif
+	legacy_timer_tick(1);
+	cnt = kstat_irqs_cpu(irq, 0);
+	if (!(cnt % 20))
+		sun3_leds(led_pattern[cnt % 160 / 20]);
+	local_irq_restore(flags);
+	return IRQ_HANDLED;
+}
+
+static irqreturn_t sun3_vec255(int irq, void *dev_id)
+{
+	return IRQ_HANDLED;
+}
+
+void __init sun3_init_IRQ(void)
+{
+	*sun3_intreg = 1;
+
+	m68k_setup_user_interrupt(VEC_USER, 128);
+
+	if (request_irq(IRQ_AUTO_5, sun3_int5, 0, "clock", NULL))
+		pr_err("Couldn't register %s interrupt\n", "int5");
+	if (request_irq(IRQ_AUTO_7, sun3_int7, 0, "nmi", NULL))
+		pr_err("Couldn't register %s interrupt\n", "int7");
+	if (request_irq(IRQ_USER+127, sun3_vec255, 0, "vec255", NULL))
+		pr_err("Couldn't register %s interrupt\n", "vec255");
+}