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, 123 insertions, 0 deletions

diff --git a/drivers/misc/ibmasm/lowlevel.h b/drivers/misc/ibmasm/lowlevel.h
new file mode 100644
index 000000000..25f1ed07c
--- /dev/null
+++ b/drivers/misc/ibmasm/lowlevel.h
@@ -0,0 +1,123 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * IBM ASM Service Processor Device Driver
+ *
+ * Copyright (C) IBM Corporation, 2004
+ *
+ * Author: Max Asböck <amax@us.ibm.com>
+ */
+
+/* Condor service processor specific hardware definitions */
+
+#ifndef __IBMASM_CONDOR_H__
+#define __IBMASM_CONDOR_H__
+
+#include <asm/io.h>
+
+#define VENDORID_IBM	0x1014
+#define DEVICEID_RSA	0x010F
+
+#define GET_MFA_ADDR(x)  (x & 0xFFFFFF00)
+
+#define MAILBOX_FULL(x)  (x & 0x00000001)
+
+#define NO_MFAS_AVAILABLE     0xFFFFFFFF
+
+
+#define INBOUND_QUEUE_PORT   0x40  /* contains address of next free MFA */
+#define OUTBOUND_QUEUE_PORT  0x44  /* contains address of posted MFA    */
+
+#define SP_INTR_MASK	0x00000008
+#define UART_INTR_MASK	0x00000010
+
+#define INTR_STATUS_REGISTER   0x13A0
+#define INTR_CONTROL_REGISTER  0x13A4
+
+#define SCOUT_COM_A_BASE         0x0000
+#define SCOUT_COM_B_BASE         0x0100
+#define SCOUT_COM_C_BASE         0x0200
+#define SCOUT_COM_D_BASE         0x0300
+
+static inline int sp_interrupt_pending(void __iomem *base_address)
+{
+	return SP_INTR_MASK & readl(base_address + INTR_STATUS_REGISTER);
+}
+
+static inline int uart_interrupt_pending(void __iomem *base_address)
+{
+	return UART_INTR_MASK & readl(base_address + INTR_STATUS_REGISTER);
+}
+
+static inline void ibmasm_enable_interrupts(void __iomem *base_address, int mask)
+{
+	void __iomem *ctrl_reg = base_address + INTR_CONTROL_REGISTER;
+	writel( readl(ctrl_reg) & ~mask, ctrl_reg);
+}
+
+static inline void ibmasm_disable_interrupts(void __iomem *base_address, int mask)
+{
+	void __iomem *ctrl_reg = base_address + INTR_CONTROL_REGISTER;
+	writel( readl(ctrl_reg) | mask, ctrl_reg);
+}
+
+static inline void enable_sp_interrupts(void __iomem *base_address)
+{
+	ibmasm_enable_interrupts(base_address, SP_INTR_MASK);
+}
+
+static inline void disable_sp_interrupts(void __iomem *base_address)
+{
+	ibmasm_disable_interrupts(base_address, SP_INTR_MASK);
+}
+
+static inline void enable_uart_interrupts(void __iomem *base_address)
+{
+	ibmasm_enable_interrupts(base_address, UART_INTR_MASK);
+}
+
+static inline void disable_uart_interrupts(void __iomem *base_address)
+{
+	ibmasm_disable_interrupts(base_address, UART_INTR_MASK);
+}
+
+#define valid_mfa(mfa)	( (mfa) != NO_MFAS_AVAILABLE )
+
+static inline u32 get_mfa_outbound(void __iomem *base_address)
+{
+	int retry;
+	u32 mfa;
+
+	for (retry=0; retry<=10; retry++) {
+		mfa = readl(base_address + OUTBOUND_QUEUE_PORT);
+		if (valid_mfa(mfa))
+			break;
+	}
+	return mfa;
+}
+
+static inline void set_mfa_outbound(void __iomem *base_address, u32 mfa)
+{
+	writel(mfa, base_address + OUTBOUND_QUEUE_PORT);
+}
+
+static inline u32 get_mfa_inbound(void __iomem *base_address)
+{
+	u32 mfa = readl(base_address + INBOUND_QUEUE_PORT);
+
+	if (MAILBOX_FULL(mfa))
+		return 0;
+
+	return mfa;
+}
+
+static inline void set_mfa_inbound(void __iomem *base_address, u32 mfa)
+{
+	writel(mfa, base_address + INBOUND_QUEUE_PORT);
+}
+
+static inline struct i2o_message *get_i2o_message(void __iomem *base_address, u32 mfa)
+{
+	return (struct i2o_message *)(GET_MFA_ADDR(mfa) + base_address);
+}
+
+#endif /* __IBMASM_CONDOR_H__ */