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, 240 insertions, 0 deletions

diff --git a/drivers/acpi/spcr.c b/drivers/acpi/spcr.c
new file mode 100644
index 000000000..73cb933fd
--- /dev/null
+++ b/drivers/acpi/spcr.c
@@ -0,0 +1,240 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) 2012, Intel Corporation
+ * Copyright (c) 2015, Red Hat, Inc.
+ * Copyright (c) 2015, 2016 Linaro Ltd.
+ */
+
+#define pr_fmt(fmt) "ACPI: SPCR: " fmt
+
+#include <linux/acpi.h>
+#include <linux/console.h>
+#include <linux/kernel.h>
+#include <linux/serial_core.h>
+
+/*
+ * Erratum 44 for QDF2432v1 and QDF2400v1 SoCs describes the BUSY bit as
+ * occasionally getting stuck as 1. To avoid the potential for a hang, check
+ * TXFE == 0 instead of BUSY == 1. This may not be suitable for all UART
+ * implementations, so only do so if an affected platform is detected in
+ * acpi_parse_spcr().
+ */
+bool qdf2400_e44_present;
+EXPORT_SYMBOL(qdf2400_e44_present);
+
+/*
+ * Some Qualcomm Datacenter Technologies SoCs have a defective UART BUSY bit.
+ * Detect them by examining the OEM fields in the SPCR header, similar to PCI
+ * quirk detection in pci_mcfg.c.
+ */
+static bool qdf2400_erratum_44_present(struct acpi_table_header *h)
+{
+	if (memcmp(h->oem_id, "QCOM  ", ACPI_OEM_ID_SIZE))
+		return false;
+
+	if (!memcmp(h->oem_table_id, "QDF2432 ", ACPI_OEM_TABLE_ID_SIZE))
+		return true;
+
+	if (!memcmp(h->oem_table_id, "QDF2400 ", ACPI_OEM_TABLE_ID_SIZE) &&
+			h->oem_revision == 1)
+		return true;
+
+	return false;
+}
+
+/*
+ * APM X-Gene v1 and v2 UART hardware is an 16550 like device but has its
+ * register aligned to 32-bit. In addition, the BIOS also encoded the
+ * access width to be 8 bits. This function detects this errata condition.
+ */
+static bool xgene_8250_erratum_present(struct acpi_table_spcr *tb)
+{
+	bool xgene_8250 = false;
+
+	if (tb->interface_type != ACPI_DBG2_16550_COMPATIBLE)
+		return false;
+
+	if (memcmp(tb->header.oem_id, "APMC0D", ACPI_OEM_ID_SIZE) &&
+	    memcmp(tb->header.oem_id, "HPE   ", ACPI_OEM_ID_SIZE))
+		return false;
+
+	if (!memcmp(tb->header.oem_table_id, "XGENESPC",
+	    ACPI_OEM_TABLE_ID_SIZE) && tb->header.oem_revision == 0)
+		xgene_8250 = true;
+
+	if (!memcmp(tb->header.oem_table_id, "ProLiant",
+	    ACPI_OEM_TABLE_ID_SIZE) && tb->header.oem_revision == 1)
+		xgene_8250 = true;
+
+	return xgene_8250;
+}
+
+/**
+ * acpi_parse_spcr() - parse ACPI SPCR table and add preferred console
+ * @enable_earlycon: set up earlycon for the console specified by the table
+ * @enable_console: setup the console specified by the table.
+ *
+ * For the architectures with support for ACPI, CONFIG_ACPI_SPCR_TABLE may be
+ * defined to parse ACPI SPCR table.  As a result of the parsing preferred
+ * console is registered and if @enable_earlycon is true, earlycon is set up.
+ * If @enable_console is true the system console is also configured.
+ *
+ * When CONFIG_ACPI_SPCR_TABLE is defined, this function should be called
+ * from arch initialization code as soon as the DT/ACPI decision is made.
+ */
+int __init acpi_parse_spcr(bool enable_earlycon, bool enable_console)
+{
+	static char opts[64];
+	struct acpi_table_spcr *table;
+	acpi_status status;
+	char *uart;
+	char *iotype;
+	int baud_rate;
+	int err;
+
+	if (acpi_disabled)
+		return -ENODEV;
+
+	status = acpi_get_table(ACPI_SIG_SPCR, 0, (struct acpi_table_header **)&table);
+	if (ACPI_FAILURE(status))
+		return -ENOENT;
+
+	if (table->header.revision < 2)
+		pr_info("SPCR table version %d\n", table->header.revision);
+
+	if (table->serial_port.space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY) {
+		u32 bit_width = table->serial_port.access_width;
+
+		if (bit_width > ACPI_ACCESS_BIT_MAX) {
+			pr_err(FW_BUG "Unacceptable wide SPCR Access Width. Defaulting to byte size\n");
+			bit_width = ACPI_ACCESS_BIT_DEFAULT;
+		}
+		switch (ACPI_ACCESS_BIT_WIDTH((bit_width))) {
+		default:
+			pr_err(FW_BUG "Unexpected SPCR Access Width. Defaulting to byte size\n");
+			fallthrough;
+		case 8:
+			iotype = "mmio";
+			break;
+		case 16:
+			iotype = "mmio16";
+			break;
+		case 32:
+			iotype = "mmio32";
+			break;
+		}
+	} else
+		iotype = "io";
+
+	switch (table->interface_type) {
+	case ACPI_DBG2_ARM_SBSA_32BIT:
+		iotype = "mmio32";
+		fallthrough;
+	case ACPI_DBG2_ARM_PL011:
+	case ACPI_DBG2_ARM_SBSA_GENERIC:
+	case ACPI_DBG2_BCM2835:
+		uart = "pl011";
+		break;
+	case ACPI_DBG2_16550_COMPATIBLE:
+	case ACPI_DBG2_16550_SUBSET:
+	case ACPI_DBG2_16550_WITH_GAS:
+	case ACPI_DBG2_16550_NVIDIA:
+		uart = "uart";
+		break;
+	case ACPI_DBG2_RISCV_SBI_CON:
+		uart = "sbi";
+		break;
+	default:
+		err = -ENOENT;
+		goto done;
+	}
+
+	/*
+	 * SPCR 1.09 defines Precise Baud Rate Filed contains a specific
+	 * non-zero baud rate which overrides the value of the Configured
+	 * Baud Rate field. If this field is zero or not present, Configured
+	 * Baud Rate is used.
+	 */
+	if (table->header.revision >= 4 && table->precise_baudrate)
+		baud_rate = table->precise_baudrate;
+	else switch (table->baud_rate) {
+	case 0:
+		/*
+		 * SPCR 1.04 defines 0 as a preconfigured state of UART.
+		 * Assume firmware or bootloader configures console correctly.
+		 */
+		baud_rate = 0;
+		break;
+	case 3:
+		baud_rate = 9600;
+		break;
+	case 4:
+		baud_rate = 19200;
+		break;
+	case 6:
+		baud_rate = 57600;
+		break;
+	case 7:
+		baud_rate = 115200;
+		break;
+	default:
+		err = -ENOENT;
+		goto done;
+	}
+
+	/*
+	 * If the E44 erratum is required, then we need to tell the pl011
+	 * driver to implement the work-around.
+	 *
+	 * The global variable is used by the probe function when it
+	 * creates the UARTs, whether or not they're used as a console.
+	 *
+	 * If the user specifies "traditional" earlycon, the qdf2400_e44
+	 * console name matches the EARLYCON_DECLARE() statement, and
+	 * SPCR is not used.  Parameter "earlycon" is false.
+	 *
+	 * If the user specifies "SPCR" earlycon, then we need to update
+	 * the console name so that it also says "qdf2400_e44".  Parameter
+	 * "earlycon" is true.
+	 *
+	 * For consistency, if we change the console name, then we do it
+	 * for everyone, not just earlycon.
+	 */
+	if (qdf2400_erratum_44_present(&table->header)) {
+		qdf2400_e44_present = true;
+		if (enable_earlycon)
+			uart = "qdf2400_e44";
+	}
+
+	if (xgene_8250_erratum_present(table)) {
+		iotype = "mmio32";
+
+		/*
+		 * For xgene v1 and v2 we don't know the clock rate of the
+		 * UART so don't attempt to change to the baud rate state
+		 * in the table because driver cannot calculate the dividers
+		 */
+		baud_rate = 0;
+	}
+
+	if (!baud_rate) {
+		snprintf(opts, sizeof(opts), "%s,%s,0x%llx", uart, iotype,
+			 table->serial_port.address);
+	} else {
+		snprintf(opts, sizeof(opts), "%s,%s,0x%llx,%d", uart, iotype,
+			 table->serial_port.address, baud_rate);
+	}
+
+	pr_info("console: %s\n", opts);
+
+	if (enable_earlycon)
+		setup_earlycon(opts);
+
+	if (enable_console)
+		err = add_preferred_console(uart, 0, opts + strlen(uart) + 1);
+	else
+		err = 0;
+done:
+	acpi_put_table((struct acpi_table_header *)table);
+	return err;
+}