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, 109 insertions, 0 deletions

diff --git a/drivers/ata/pata_netcell.c b/drivers/ata/pata_netcell.c
new file mode 100644
index 000000000..c0b2897fc
--- /dev/null
+++ b/drivers/ata/pata_netcell.c
@@ -0,0 +1,109 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *    pata_netcell.c - Netcell PATA driver
+ *
+ *	(c) 2006 Red Hat
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/pci.h>
+#include <linux/blkdev.h>
+#include <linux/delay.h>
+#include <linux/device.h>
+#include <scsi/scsi_host.h>
+#include <linux/libata.h>
+#include <linux/ata.h>
+
+#define DRV_NAME	"pata_netcell"
+#define DRV_VERSION	"0.1.7"
+
+/* No PIO or DMA methods needed for this device */
+
+static unsigned int netcell_read_id(struct ata_device *adev,
+				    struct ata_taskfile *tf, __le16 *id)
+{
+	unsigned int err_mask = ata_do_dev_read_id(adev, tf, id);
+
+	/* Firmware forgets to mark words 85-87 valid */
+	if (err_mask == 0)
+		id[ATA_ID_CSF_DEFAULT] |= cpu_to_le16(0x4000);
+	return err_mask;
+}
+
+static const struct scsi_host_template netcell_sht = {
+	ATA_BMDMA_SHT(DRV_NAME),
+};
+
+static struct ata_port_operations netcell_ops = {
+	.inherits	= &ata_bmdma_port_ops,
+	.cable_detect	= ata_cable_80wire,
+	.read_id	= netcell_read_id,
+};
+
+
+/**
+ *	netcell_init_one - Register Netcell ATA PCI device with kernel services
+ *	@pdev: PCI device to register
+ *	@ent: Entry in netcell_pci_tbl matching with @pdev
+ *
+ *	Called from kernel PCI layer.
+ *
+ *	LOCKING:
+ *	Inherited from PCI layer (may sleep).
+ *
+ *	RETURNS:
+ *	Zero on success, or -ERRNO value.
+ */
+
+static int netcell_init_one (struct pci_dev *pdev, const struct pci_device_id *ent)
+{
+	static const struct ata_port_info info = {
+		.flags		= ATA_FLAG_SLAVE_POSS,
+		/* Actually we don't really care about these as the
+		   firmware deals with it */
+		.pio_mask	= ATA_PIO4,
+		.mwdma_mask	= ATA_MWDMA2,
+		.udma_mask 	= ATA_UDMA5, /* UDMA 133 */
+		.port_ops	= &netcell_ops,
+	};
+	const struct ata_port_info *port_info[] = { &info, NULL };
+	int rc;
+
+	ata_print_version_once(&pdev->dev, DRV_VERSION);
+
+	rc = pcim_enable_device(pdev);
+	if (rc)
+		return rc;
+
+	/* Any chip specific setup/optimisation/messages here */
+	ata_pci_bmdma_clear_simplex(pdev);
+
+	/* And let the library code do the work */
+	return ata_pci_bmdma_init_one(pdev, port_info, &netcell_sht, NULL, 0);
+}
+
+static const struct pci_device_id netcell_pci_tbl[] = {
+	{ PCI_VDEVICE(NETCELL, PCI_DEVICE_ID_REVOLUTION), },
+
+	{ }	/* terminate list */
+};
+
+static struct pci_driver netcell_pci_driver = {
+	.name			= DRV_NAME,
+	.id_table		= netcell_pci_tbl,
+	.probe			= netcell_init_one,
+	.remove			= ata_pci_remove_one,
+#ifdef CONFIG_PM_SLEEP
+	.suspend		= ata_pci_device_suspend,
+	.resume			= ata_pci_device_resume,
+#endif
+};
+
+module_pci_driver(netcell_pci_driver);
+
+MODULE_AUTHOR("Alan Cox");
+MODULE_DESCRIPTION("SCSI low-level driver for Netcell PATA RAID");
+MODULE_LICENSE("GPL");
+MODULE_DEVICE_TABLE(pci, netcell_pci_tbl);
+MODULE_VERSION(DRV_VERSION);