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, 307 insertions, 0 deletions

diff --git a/drivers/acpi/acpica/utbuffer.c b/drivers/acpi/acpica/utbuffer.c
new file mode 100644
index 000000000..4193ceb93
--- /dev/null
+++ b/drivers/acpi/acpica/utbuffer.c
@@ -0,0 +1,307 @@
+// SPDX-License-Identifier: BSD-3-Clause OR GPL-2.0
+/******************************************************************************
+ *
+ * Module Name: utbuffer - Buffer dump routines
+ *
+ * Copyright (C) 2000 - 2026, Intel Corp.
+ *
+ *****************************************************************************/
+
+#include <acpi/acpi.h>
+#include "accommon.h"
+
+#define _COMPONENT          ACPI_UTILITIES
+ACPI_MODULE_NAME("utbuffer")
+
+/*******************************************************************************
+ *
+ * FUNCTION:    acpi_ut_dump_buffer
+ *
+ * PARAMETERS:  buffer              - Buffer to dump
+ *              count               - Amount to dump, in bytes
+ *              display             - BYTE, WORD, DWORD, or QWORD display:
+ *                                      DB_BYTE_DISPLAY
+ *                                      DB_WORD_DISPLAY
+ *                                      DB_DWORD_DISPLAY
+ *                                      DB_QWORD_DISPLAY
+ *              base_offset         - Beginning buffer offset (display only)
+ *
+ * RETURN:      None
+ *
+ * DESCRIPTION: Generic dump buffer in both hex and ascii.
+ *
+ ******************************************************************************/
+void acpi_ut_dump_buffer(u8 *buffer, u32 count, u32 display, u32 base_offset)
+{
+	u32 i = 0;
+	u32 j;
+	u32 temp32;
+	u8 buf_char;
+	u32 display_data_only = display & DB_DISPLAY_DATA_ONLY;
+
+	display &= ~DB_DISPLAY_DATA_ONLY;
+	if (!buffer) {
+		acpi_os_printf("Null Buffer Pointer in DumpBuffer!\n");
+		return;
+	}
+
+	if ((count < 4) || (count & 0x01)) {
+		display = DB_BYTE_DISPLAY;
+	}
+
+	/* Nasty little dump buffer routine! */
+
+	while (i < count) {
+
+		/* Print current offset */
+
+		if (!display_data_only) {
+			acpi_os_printf("%8.4X: ", (base_offset + i));
+		}
+
+		/* Print 16 hex chars */
+
+		for (j = 0; j < 16;) {
+			if (i + j >= count) {
+
+				/* Dump fill spaces */
+
+				acpi_os_printf("%*s", ((display * 2) + 1), " ");
+				j += display;
+				continue;
+			}
+
+			switch (display) {
+			case DB_BYTE_DISPLAY:
+			default:	/* Default is BYTE display */
+
+				acpi_os_printf("%02X ",
+					       buffer[(acpi_size)i + j]);
+				break;
+
+			case DB_WORD_DISPLAY:
+
+				ACPI_MOVE_16_TO_32(&temp32,
+						   &buffer[(acpi_size)i + j]);
+				acpi_os_printf("%04X ", temp32);
+				break;
+
+			case DB_DWORD_DISPLAY:
+
+				ACPI_MOVE_32_TO_32(&temp32,
+						   &buffer[(acpi_size)i + j]);
+				acpi_os_printf("%08X ", temp32);
+				break;
+
+			case DB_QWORD_DISPLAY:
+
+				ACPI_MOVE_32_TO_32(&temp32,
+						   &buffer[(acpi_size)i + j]);
+				acpi_os_printf("%08X", temp32);
+
+				ACPI_MOVE_32_TO_32(&temp32,
+						   &buffer[(acpi_size)i + j +
+							   4]);
+				acpi_os_printf("%08X ", temp32);
+				break;
+			}
+
+			j += display;
+		}
+
+		/*
+		 * Print the ASCII equivalent characters but watch out for the bad
+		 * unprintable ones (printable chars are 0x20 through 0x7E)
+		 */
+		if (!display_data_only) {
+			acpi_os_printf(" ");
+			for (j = 0; j < 16; j++) {
+				if (i + j >= count) {
+					acpi_os_printf("\n");
+					return;
+				}
+
+				/*
+				 * Add comment characters so rest of line is ignored when
+				 * compiled
+				 */
+				if (j == 0) {
+					acpi_os_printf("// ");
+				}
+
+				buf_char = buffer[(acpi_size)i + j];
+				if (isprint(buf_char)) {
+					acpi_os_printf("%c", buf_char);
+				} else {
+					acpi_os_printf(".");
+				}
+			}
+
+			/* Done with that line. */
+
+			acpi_os_printf("\n");
+		}
+		i += 16;
+	}
+
+	return;
+}
+
+/*******************************************************************************
+ *
+ * FUNCTION:    acpi_ut_debug_dump_buffer
+ *
+ * PARAMETERS:  buffer              - Buffer to dump
+ *              count               - Amount to dump, in bytes
+ *              display             - BYTE, WORD, DWORD, or QWORD display:
+ *                                      DB_BYTE_DISPLAY
+ *                                      DB_WORD_DISPLAY
+ *                                      DB_DWORD_DISPLAY
+ *                                      DB_QWORD_DISPLAY
+ *              component_ID        - Caller's component ID
+ *
+ * RETURN:      None
+ *
+ * DESCRIPTION: Generic dump buffer in both hex and ascii.
+ *
+ ******************************************************************************/
+
+void
+acpi_ut_debug_dump_buffer(u8 *buffer, u32 count, u32 display, u32 component_id)
+{
+
+	/* Only dump the buffer if tracing is enabled */
+
+	if (!((ACPI_LV_TABLES & acpi_dbg_level) &&
+	      (component_id & acpi_dbg_layer))) {
+		return;
+	}
+
+	acpi_ut_dump_buffer(buffer, count, display, 0);
+}
+
+#ifdef ACPI_APPLICATION
+/*******************************************************************************
+ *
+ * FUNCTION:    acpi_ut_dump_buffer_to_file
+ *
+ * PARAMETERS:  file                - File descriptor
+ *              buffer              - Buffer to dump
+ *              count               - Amount to dump, in bytes
+ *              display             - BYTE, WORD, DWORD, or QWORD display:
+ *                                      DB_BYTE_DISPLAY
+ *                                      DB_WORD_DISPLAY
+ *                                      DB_DWORD_DISPLAY
+ *                                      DB_QWORD_DISPLAY
+ *              base_offset         - Beginning buffer offset (display only)
+ *
+ * RETURN:      None
+ *
+ * DESCRIPTION: Generic dump buffer in both hex and ascii to a file.
+ *
+ ******************************************************************************/
+
+void
+acpi_ut_dump_buffer_to_file(ACPI_FILE file,
+			    u8 *buffer, u32 count, u32 display, u32 base_offset)
+{
+	u32 i = 0;
+	u32 j;
+	u32 temp32;
+	u8 buf_char;
+
+	if (!buffer) {
+		fprintf(file, "Null Buffer Pointer in DumpBuffer!\n");
+		return;
+	}
+
+	if ((count < 4) || (count & 0x01)) {
+		display = DB_BYTE_DISPLAY;
+	}
+
+	/* Nasty little dump buffer routine! */
+
+	while (i < count) {
+
+		/* Print current offset */
+
+		fprintf(file, "%8.4X: ", (base_offset + i));
+
+		/* Print 16 hex chars */
+
+		for (j = 0; j < 16;) {
+			if (i + j >= count) {
+
+				/* Dump fill spaces */
+
+				fprintf(file, "%*s", ((display * 2) + 1), " ");
+				j += display;
+				continue;
+			}
+
+			switch (display) {
+			case DB_BYTE_DISPLAY:
+			default:	/* Default is BYTE display */
+
+				fprintf(file, "%02X ",
+					buffer[(acpi_size)i + j]);
+				break;
+
+			case DB_WORD_DISPLAY:
+
+				ACPI_MOVE_16_TO_32(&temp32,
+						   &buffer[(acpi_size)i + j]);
+				fprintf(file, "%04X ", temp32);
+				break;
+
+			case DB_DWORD_DISPLAY:
+
+				ACPI_MOVE_32_TO_32(&temp32,
+						   &buffer[(acpi_size)i + j]);
+				fprintf(file, "%08X ", temp32);
+				break;
+
+			case DB_QWORD_DISPLAY:
+
+				ACPI_MOVE_32_TO_32(&temp32,
+						   &buffer[(acpi_size)i + j]);
+				fprintf(file, "%08X", temp32);
+
+				ACPI_MOVE_32_TO_32(&temp32,
+						   &buffer[(acpi_size)i + j +
+							   4]);
+				fprintf(file, "%08X ", temp32);
+				break;
+			}
+
+			j += display;
+		}
+
+		/*
+		 * Print the ASCII equivalent characters but watch out for the bad
+		 * unprintable ones (printable chars are 0x20 through 0x7E)
+		 */
+		fprintf(file, " ");
+		for (j = 0; j < 16; j++) {
+			if (i + j >= count) {
+				fprintf(file, "\n");
+				return;
+			}
+
+			buf_char = buffer[(acpi_size)i + j];
+			if (isprint(buf_char)) {
+				fprintf(file, "%c", buf_char);
+			} else {
+				fprintf(file, ".");
+			}
+		}
+
+		/* Done with that line. */
+
+		fprintf(file, "\n");
+		i += 16;
+	}
+
+	return;
+}
+#endif