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>

4 files changed, 117 insertions, 0 deletions

diff --git a/arch/mips/power/Makefile b/arch/mips/power/Makefile
new file mode 100644
index 000000000..14b7d9ee6
--- /dev/null
+++ b/arch/mips/power/Makefile
@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
+obj-$(CONFIG_HIBERNATION) += cpu.o hibernate.o hibernate_asm.o
diff --git a/arch/mips/power/cpu.c b/arch/mips/power/cpu.c
new file mode 100644
index 000000000..d8ef7778e
--- /dev/null
+++ b/arch/mips/power/cpu.c
@@ -0,0 +1,43 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Suspend support specific for mips.
+ *
+ * Copyright (C) 2009 Lemote Inc.
+ * Author: Hu Hongbing <huhb@lemote.com>
+ *	   Wu Zhangjin <wuzhangjin@gmail.com>
+ */
+#include <linux/suspend.h>
+#include <asm/sections.h>
+#include <asm/fpu.h>
+#include <asm/dsp.h>
+
+static u32 saved_status;
+struct pt_regs saved_regs;
+
+void save_processor_state(void)
+{
+	saved_status = read_c0_status();
+
+	if (is_fpu_owner())
+		save_fp(current);
+
+	save_dsp(current);
+}
+
+void restore_processor_state(void)
+{
+	write_c0_status(saved_status);
+
+	if (is_fpu_owner())
+		restore_fp(current);
+
+	restore_dsp(current);
+}
+
+int pfn_is_nosave(unsigned long pfn)
+{
+	unsigned long nosave_begin_pfn = PFN_DOWN(__pa(&__nosave_begin));
+	unsigned long nosave_end_pfn = PFN_UP(__pa(&__nosave_end));
+
+	return	(pfn >= nosave_begin_pfn) && (pfn < nosave_end_pfn);
+}
diff --git a/arch/mips/power/hibernate.c b/arch/mips/power/hibernate.c
new file mode 100644
index 000000000..192879e76
--- /dev/null
+++ b/arch/mips/power/hibernate.c
@@ -0,0 +1,12 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/suspend.h>
+#include <asm/tlbflush.h>
+
+extern int restore_image(void);
+
+int swsusp_arch_resume(void)
+{
+	/* Avoid TLB mismatch during and after kernel resume */
+	local_flush_tlb_all();
+	return restore_image();
+}
diff --git a/arch/mips/power/hibernate_asm.S b/arch/mips/power/hibernate_asm.S
new file mode 100644
index 000000000..e62538734
--- /dev/null
+++ b/arch/mips/power/hibernate_asm.S
@@ -0,0 +1,60 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Hibernation support specific for mips - temporary page tables
+ *
+ * Copyright (C) 2009 Lemote Inc.
+ * Author: Hu Hongbing <huhb@lemote.com>
+ *	   Wu Zhangjin <wuzhangjin@gmail.com>
+ */
+#include <asm/asm-offsets.h>
+#include <asm/regdef.h>
+#include <asm/asm.h>
+
+.text
+LEAF(swsusp_arch_suspend)
+	PTR_LA t0, saved_regs
+	PTR_S ra, PT_R31(t0)
+	PTR_S sp, PT_R29(t0)
+	PTR_S fp, PT_R30(t0)
+	PTR_S gp, PT_R28(t0)
+	PTR_S s0, PT_R16(t0)
+	PTR_S s1, PT_R17(t0)
+	PTR_S s2, PT_R18(t0)
+	PTR_S s3, PT_R19(t0)
+	PTR_S s4, PT_R20(t0)
+	PTR_S s5, PT_R21(t0)
+	PTR_S s6, PT_R22(t0)
+	PTR_S s7, PT_R23(t0)
+	j swsusp_save
+END(swsusp_arch_suspend)
+
+LEAF(restore_image)
+	PTR_L t0, restore_pblist
+0:
+	PTR_L t1, PBE_ADDRESS(t0)   /* source */
+	PTR_L t2, PBE_ORIG_ADDRESS(t0) /* destination */
+	PTR_ADDU t3, t1, _PAGE_SIZE
+1:
+	REG_L t8, (t1)
+	REG_S t8, (t2)
+	PTR_ADDIU t1, t1, SZREG
+	PTR_ADDIU t2, t2, SZREG
+	bne t1, t3, 1b
+	PTR_L t0, PBE_NEXT(t0)
+	bnez t0, 0b
+	PTR_LA t0, saved_regs
+	PTR_L ra, PT_R31(t0)
+	PTR_L sp, PT_R29(t0)
+	PTR_L fp, PT_R30(t0)
+	PTR_L gp, PT_R28(t0)
+	PTR_L s0, PT_R16(t0)
+	PTR_L s1, PT_R17(t0)
+	PTR_L s2, PT_R18(t0)
+	PTR_L s3, PT_R19(t0)
+	PTR_L s4, PT_R20(t0)
+	PTR_L s5, PT_R21(t0)
+	PTR_L s6, PT_R22(t0)
+	PTR_L s7, PT_R23(t0)
+	PTR_LI v0, 0x0
+	jr ra
+END(restore_image)