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, 304 insertions, 0 deletions

diff --git a/drivers/scsi/a2091.c b/drivers/scsi/a2091.c
new file mode 100644
index 000000000..204448bfd
--- /dev/null
+++ b/drivers/scsi/a2091.c
@@ -0,0 +1,304 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/types.h>
+#include <linux/init.h>
+#include <linux/interrupt.h>
+#include <linux/mm.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/zorro.h>
+#include <linux/module.h>
+
+#include <asm/page.h>
+#include <asm/amigaints.h>
+#include <asm/amigahw.h>
+
+#include <scsi/scsi.h>
+#include <scsi/scsi_cmnd.h>
+#include <scsi/scsi_device.h>
+#include <scsi/scsi_eh.h>
+#include <scsi/scsi_tcq.h>
+#include "wd33c93.h"
+#include "a2091.h"
+
+
+struct a2091_hostdata {
+	struct WD33C93_hostdata wh;
+	struct a2091_scsiregs *regs;
+	struct device *dev;
+};
+
+#define DMA_DIR(d)   ((d == DATA_OUT_DIR) ? DMA_TO_DEVICE : DMA_FROM_DEVICE)
+
+static irqreturn_t a2091_intr(int irq, void *data)
+{
+	struct Scsi_Host *instance = data;
+	struct a2091_hostdata *hdata = shost_priv(instance);
+	unsigned int status = hdata->regs->ISTR;
+	unsigned long flags;
+
+	if (!(status & (ISTR_INT_F | ISTR_INT_P)) || !(status & ISTR_INTS))
+		return IRQ_NONE;
+
+	spin_lock_irqsave(instance->host_lock, flags);
+	wd33c93_intr(instance);
+	spin_unlock_irqrestore(instance->host_lock, flags);
+	return IRQ_HANDLED;
+}
+
+static int dma_setup(struct scsi_cmnd *cmd, int dir_in)
+{
+	struct scsi_pointer *scsi_pointer = WD33C93_scsi_pointer(cmd);
+	unsigned long len = scsi_pointer->this_residual;
+	struct Scsi_Host *instance = cmd->device->host;
+	struct a2091_hostdata *hdata = shost_priv(instance);
+	struct WD33C93_hostdata *wh = &hdata->wh;
+	struct a2091_scsiregs *regs = hdata->regs;
+	unsigned short cntr = CNTR_PDMD | CNTR_INTEN;
+	dma_addr_t addr;
+
+	addr = dma_map_single(hdata->dev, scsi_pointer->ptr,
+			      len, DMA_DIR(dir_in));
+	if (dma_mapping_error(hdata->dev, addr)) {
+		dev_warn(hdata->dev, "cannot map SCSI data block %p\n",
+			 scsi_pointer->ptr);
+		return 1;
+	}
+	scsi_pointer->dma_handle = addr;
+
+	/* don't allow DMA if the physical address is bad */
+	if (addr & A2091_XFER_MASK) {
+		/* drop useless mapping */
+		dma_unmap_single(hdata->dev, scsi_pointer->dma_handle,
+				 scsi_pointer->this_residual,
+				 DMA_DIR(dir_in));
+		scsi_pointer->dma_handle = (dma_addr_t) NULL;
+
+		wh->dma_bounce_len = (scsi_pointer->this_residual + 511) & ~0x1ff;
+		wh->dma_bounce_buffer = kmalloc(wh->dma_bounce_len,
+						GFP_KERNEL);
+
+		/* can't allocate memory; use PIO */
+		if (!wh->dma_bounce_buffer) {
+			wh->dma_bounce_len = 0;
+			return 1;
+		}
+
+		if (!dir_in) {
+			/* copy to bounce buffer for a write */
+			memcpy(wh->dma_bounce_buffer, scsi_pointer->ptr,
+			       scsi_pointer->this_residual);
+		}
+
+		/* will flush/invalidate cache for us */
+		addr = dma_map_single(hdata->dev, wh->dma_bounce_buffer,
+				      wh->dma_bounce_len, DMA_DIR(dir_in));
+		/* can't map buffer; use PIO */
+		if (dma_mapping_error(hdata->dev, addr)) {
+			dev_warn(hdata->dev, "cannot map bounce buffer %p\n",
+				 wh->dma_bounce_buffer);
+			return 1;
+		}
+
+		/* the bounce buffer may not be in the first 16M of physmem */
+		if (addr & A2091_XFER_MASK) {
+			/* we could use chipmem... maybe later */
+			kfree(wh->dma_bounce_buffer);
+			wh->dma_bounce_buffer = NULL;
+			wh->dma_bounce_len = 0;
+			return 1;
+		}
+
+		scsi_pointer->dma_handle = addr;
+	}
+
+	/* setup dma direction */
+	if (!dir_in)
+		cntr |= CNTR_DDIR;
+
+	/* remember direction */
+	wh->dma_dir = dir_in;
+
+	regs->CNTR = cntr;
+
+	/* setup DMA *physical* address */
+	regs->ACR = addr;
+
+	/* no more cache flush here - dma_map_single() takes care */
+
+	/* start DMA */
+	regs->ST_DMA = 1;
+
+	/* return success */
+	return 0;
+}
+
+static void dma_stop(struct Scsi_Host *instance, struct scsi_cmnd *SCpnt,
+		     int status)
+{
+	struct scsi_pointer *scsi_pointer = WD33C93_scsi_pointer(SCpnt);
+	struct a2091_hostdata *hdata = shost_priv(instance);
+	struct WD33C93_hostdata *wh = &hdata->wh;
+	struct a2091_scsiregs *regs = hdata->regs;
+
+	/* disable SCSI interrupts */
+	unsigned short cntr = CNTR_PDMD;
+
+	if (!wh->dma_dir)
+		cntr |= CNTR_DDIR;
+
+	/* disable SCSI interrupts */
+	regs->CNTR = cntr;
+
+	/* flush if we were reading */
+	if (wh->dma_dir) {
+		regs->FLUSH = 1;
+		while (!(regs->ISTR & ISTR_FE_FLG))
+			;
+	}
+
+	/* clear a possible interrupt */
+	regs->CINT = 1;
+
+	/* stop DMA */
+	regs->SP_DMA = 1;
+
+	/* restore the CONTROL bits (minus the direction flag) */
+	regs->CNTR = CNTR_PDMD | CNTR_INTEN;
+
+	dma_unmap_single(hdata->dev, scsi_pointer->dma_handle,
+			 scsi_pointer->this_residual,
+			 DMA_DIR(wh->dma_dir));
+
+	/* copy from a bounce buffer, if necessary */
+	if (status && wh->dma_bounce_buffer) {
+		if (wh->dma_dir)
+			memcpy(scsi_pointer->ptr, wh->dma_bounce_buffer,
+			       scsi_pointer->this_residual);
+		kfree(wh->dma_bounce_buffer);
+		wh->dma_bounce_buffer = NULL;
+		wh->dma_bounce_len = 0;
+	}
+}
+
+static const struct scsi_host_template a2091_scsi_template = {
+	.module			= THIS_MODULE,
+	.name			= "Commodore A2091/A590 SCSI",
+	.show_info		= wd33c93_show_info,
+	.write_info		= wd33c93_write_info,
+	.proc_name		= "A2901",
+	.queuecommand		= wd33c93_queuecommand,
+	.eh_abort_handler	= wd33c93_abort,
+	.eh_host_reset_handler	= wd33c93_host_reset,
+	.can_queue		= CAN_QUEUE,
+	.this_id		= 7,
+	.sg_tablesize		= SG_ALL,
+	.cmd_per_lun		= CMD_PER_LUN,
+	.dma_boundary		= PAGE_SIZE - 1,
+	.cmd_size		= sizeof(struct scsi_pointer),
+};
+
+static int a2091_probe(struct zorro_dev *z, const struct zorro_device_id *ent)
+{
+	struct Scsi_Host *instance;
+	int error;
+	struct a2091_scsiregs *regs;
+	wd33c93_regs wdregs;
+	struct a2091_hostdata *hdata;
+
+	if (dma_set_mask_and_coherent(&z->dev, DMA_BIT_MASK(24))) {
+		dev_warn(&z->dev, "cannot use 24 bit DMA\n");
+		return -ENODEV;
+	}
+
+	if (!request_mem_region(z->resource.start, 256, "wd33c93"))
+		return -EBUSY;
+
+	instance = scsi_host_alloc(&a2091_scsi_template,
+				   sizeof(struct a2091_hostdata));
+	if (!instance) {
+		error = -ENOMEM;
+		goto fail_alloc;
+	}
+
+	instance->irq = IRQ_AMIGA_PORTS;
+	instance->unique_id = z->slotaddr;
+
+	regs = ZTWO_VADDR(z->resource.start);
+	regs->DAWR = DAWR_A2091;
+
+	wdregs.SASR = &regs->SASR;
+	wdregs.SCMD = &regs->SCMD;
+
+	hdata = shost_priv(instance);
+	hdata->dev = &z->dev;
+	hdata->wh.no_sync = 0xff;
+	hdata->wh.fast = 0;
+	hdata->wh.dma_mode = CTRL_DMA;
+	hdata->regs = regs;
+
+	wd33c93_init(instance, wdregs, dma_setup, dma_stop, WD33C93_FS_8_10);
+	error = request_irq(IRQ_AMIGA_PORTS, a2091_intr, IRQF_SHARED,
+			    "A2091 SCSI", instance);
+	if (error)
+		goto fail_irq;
+
+	regs->CNTR = CNTR_PDMD | CNTR_INTEN;
+
+	error = scsi_add_host(instance, NULL);
+	if (error)
+		goto fail_host;
+
+	zorro_set_drvdata(z, instance);
+
+	scsi_scan_host(instance);
+	return 0;
+
+fail_host:
+	free_irq(IRQ_AMIGA_PORTS, instance);
+fail_irq:
+	scsi_host_put(instance);
+fail_alloc:
+	release_mem_region(z->resource.start, 256);
+	return error;
+}
+
+static void a2091_remove(struct zorro_dev *z)
+{
+	struct Scsi_Host *instance = zorro_get_drvdata(z);
+	struct a2091_hostdata *hdata = shost_priv(instance);
+
+	hdata->regs->CNTR = 0;
+	scsi_remove_host(instance);
+	free_irq(IRQ_AMIGA_PORTS, instance);
+	scsi_host_put(instance);
+	release_mem_region(z->resource.start, 256);
+}
+
+static struct zorro_device_id a2091_zorro_tbl[] = {
+	{ ZORRO_PROD_CBM_A590_A2091_1 },
+	{ ZORRO_PROD_CBM_A590_A2091_2 },
+	{ 0 }
+};
+MODULE_DEVICE_TABLE(zorro, a2091_zorro_tbl);
+
+static struct zorro_driver a2091_driver = {
+	.name		= "a2091",
+	.id_table	= a2091_zorro_tbl,
+	.probe		= a2091_probe,
+	.remove		= a2091_remove,
+};
+
+static int __init a2091_init(void)
+{
+	return zorro_register_driver(&a2091_driver);
+}
+module_init(a2091_init);
+
+static void __exit a2091_exit(void)
+{
+	zorro_unregister_driver(&a2091_driver);
+}
+module_exit(a2091_exit);
+
+MODULE_DESCRIPTION("Commodore A2091/A590 SCSI");
+MODULE_LICENSE("GPL");