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, 265 insertions, 0 deletions

diff --git a/arch/mips/sni/setup.c b/arch/mips/sni/setup.c
new file mode 100644
index 000000000..fc7da1228
--- /dev/null
+++ b/arch/mips/sni/setup.c
@@ -0,0 +1,265 @@
+/*
+ * Setup pointers to hardware-dependent routines.
+ *
+ * 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.
+ *
+ * Copyright (C) 1996, 97, 98, 2000, 03, 04, 06 Ralf Baechle (ralf@linux-mips.org)
+ * Copyright (C) 2006,2007 Thomas Bogendoerfer (tsbogend@alpha.franken.de)
+ */
+#include <linux/eisa.h>
+#include <linux/init.h>
+#include <linux/export.h>
+#include <linux/console.h>
+#include <linux/screen_info.h>
+#include <linux/string.h>
+
+#ifdef CONFIG_FW_ARC
+#include <asm/fw/arc/types.h>
+#include <asm/sgialib.h>
+#endif
+
+#ifdef CONFIG_FW_SNIPROM
+#include <asm/mipsprom.h>
+#endif
+
+#include <asm/bootinfo.h>
+#include <asm/cpu.h>
+#include <asm/io.h>
+#include <asm/reboot.h>
+#include <asm/sni.h>
+
+unsigned int sni_brd_type;
+EXPORT_SYMBOL(sni_brd_type);
+
+extern void sni_machine_restart(char *command);
+extern void sni_machine_power_off(void);
+
+static void __init sni_display_setup(void)
+{
+#if defined(CONFIG_VGA_CONSOLE) && defined(CONFIG_FW_ARC)
+	static struct screen_info si;
+	DISPLAY_STATUS *di;
+
+	di = ArcGetDisplayStatus(1);
+
+	if (di) {
+		si.orig_x		= di->CursorXPosition;
+		si.orig_y		= di->CursorYPosition;
+		si.orig_video_cols	= di->CursorMaxXPosition;
+		si.orig_video_lines	= di->CursorMaxYPosition;
+		si.orig_video_isVGA	= VIDEO_TYPE_VGAC;
+		si.orig_video_points	= 16;
+
+		vgacon_register_screen(&si);
+	}
+#endif
+}
+
+static void __init sni_console_setup(void)
+{
+#ifndef CONFIG_FW_ARC
+	char *ctype;
+	char *cdev;
+	char *baud;
+	int port;
+	static char options[8] __initdata;
+
+	cdev = prom_getenv("console_dev");
+	if (strncmp(cdev, "tty", 3) == 0) {
+		ctype = prom_getenv("console");
+		switch (*ctype) {
+		default:
+		case 'l':
+			port = 0;
+			baud = prom_getenv("lbaud");
+			break;
+		case 'r':
+			port = 1;
+			baud = prom_getenv("rbaud");
+			break;
+		}
+		if (baud)
+			strscpy(options, baud);
+		if (strncmp(cdev, "tty552", 6) == 0)
+			add_preferred_console("ttyS", port,
+					      baud ? options : NULL);
+		else
+			add_preferred_console("ttySC", port,
+					      baud ? options : NULL);
+	}
+#endif
+}
+
+#ifdef DEBUG
+static void __init sni_idprom_dump(void)
+{
+	int	i;
+
+	pr_debug("SNI IDProm dump:\n");
+	for (i = 0; i < 256; i++) {
+		if (i%16 == 0)
+			pr_debug("%04x ", i);
+
+		printk("%02x ", *(unsigned char *) (SNI_IDPROM_BASE + i));
+
+		if (i % 16 == 15)
+			printk("\n");
+	}
+}
+#endif
+
+void __init plat_mem_setup(void)
+{
+	int cputype;
+
+	set_io_port_base(SNI_PORT_BASE);
+//	ioport_resource.end = sni_io_resource.end;
+
+	/*
+	 * Setup (E)ISA I/O memory access stuff
+	 */
+#ifdef CONFIG_EISA
+	EISA_bus = 1;
+#endif
+
+	sni_brd_type = *(unsigned char *)SNI_IDPROM_BRDTYPE;
+	cputype = *(unsigned char *)SNI_IDPROM_CPUTYPE;
+	switch (sni_brd_type) {
+	case SNI_BRD_TOWER_OASIC:
+		switch (cputype) {
+		case SNI_CPU_M8030:
+			system_type = "RM400-330";
+			break;
+		case SNI_CPU_M8031:
+			system_type = "RM400-430";
+			break;
+		case SNI_CPU_M8037:
+			system_type = "RM400-530";
+			break;
+		case SNI_CPU_M8034:
+			system_type = "RM400-730";
+			break;
+		default:
+			system_type = "RM400-xxx";
+			break;
+		}
+		break;
+	case SNI_BRD_MINITOWER:
+		switch (cputype) {
+		case SNI_CPU_M8021:
+		case SNI_CPU_M8043:
+			system_type = "RM400-120";
+			break;
+		case SNI_CPU_M8040:
+			system_type = "RM400-220";
+			break;
+		case SNI_CPU_M8053:
+			system_type = "RM400-225";
+			break;
+		case SNI_CPU_M8050:
+			system_type = "RM400-420";
+			break;
+		default:
+			system_type = "RM400-xxx";
+			break;
+		}
+		break;
+	case SNI_BRD_PCI_TOWER:
+		system_type = "RM400-Cxx";
+		break;
+	case SNI_BRD_RM200:
+		system_type = "RM200-xxx";
+		break;
+	case SNI_BRD_PCI_MTOWER:
+		system_type = "RM300-Cxx";
+		break;
+	case SNI_BRD_PCI_DESKTOP:
+		switch (read_c0_prid() & PRID_IMP_MASK) {
+		case PRID_IMP_R4600:
+		case PRID_IMP_R4700:
+			system_type = "RM200-C20";
+			break;
+		case PRID_IMP_R5000:
+			system_type = "RM200-C40";
+			break;
+		default:
+			system_type = "RM200-Cxx";
+			break;
+		}
+		break;
+	case SNI_BRD_PCI_TOWER_CPLUS:
+		system_type = "RM400-Exx";
+		break;
+	case SNI_BRD_PCI_MTOWER_CPLUS:
+		system_type = "RM300-Exx";
+		break;
+	}
+	pr_debug("Found SNI brdtype %02x name %s\n", sni_brd_type, system_type);
+
+#ifdef DEBUG
+	sni_idprom_dump();
+#endif
+
+	switch (sni_brd_type) {
+	case SNI_BRD_10:
+	case SNI_BRD_10NEW:
+	case SNI_BRD_TOWER_OASIC:
+	case SNI_BRD_MINITOWER:
+		sni_a20r_init();
+		break;
+
+	case SNI_BRD_PCI_TOWER:
+	case SNI_BRD_PCI_TOWER_CPLUS:
+		sni_pcit_init();
+		break;
+
+	case SNI_BRD_RM200:
+		sni_rm200_init();
+		break;
+
+	case SNI_BRD_PCI_MTOWER:
+	case SNI_BRD_PCI_DESKTOP:
+	case SNI_BRD_PCI_MTOWER_CPLUS:
+		sni_pcimt_init();
+		break;
+	}
+
+	_machine_restart = sni_machine_restart;
+	pm_power_off = sni_machine_power_off;
+
+	sni_display_setup();
+	sni_console_setup();
+}
+
+#ifdef CONFIG_PCI
+
+#include <linux/pci.h>
+#include <video/vga.h>
+#include <video/cirrus.h>
+
+static void quirk_cirrus_ram_size(struct pci_dev *dev)
+{
+	u16 cmd;
+
+	/*
+	 * firmware doesn't set the ram size correct, so we
+	 * need to do it here, otherwise we get screen corruption
+	 * on older Cirrus chips
+	 */
+	pci_read_config_word(dev, PCI_COMMAND, &cmd);
+	if ((cmd & (PCI_COMMAND_IO|PCI_COMMAND_MEMORY))
+		== (PCI_COMMAND_IO|PCI_COMMAND_MEMORY)) {
+		vga_wseq(NULL, CL_SEQR6, 0x12); /* unlock all extension registers */
+		vga_wseq(NULL, CL_SEQRF, 0x18);
+	}
+}
+
+DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_CIRRUS, PCI_DEVICE_ID_CIRRUS_5434_8,
+			quirk_cirrus_ram_size);
+DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_CIRRUS, PCI_DEVICE_ID_CIRRUS_5436,
+			quirk_cirrus_ram_size);
+DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_CIRRUS, PCI_DEVICE_ID_CIRRUS_5446,
+			quirk_cirrus_ram_size);
+#endif