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, 250 insertions, 0 deletions

diff --git a/drivers/video/fbdev/sunxvr2500.c b/drivers/video/fbdev/sunxvr2500.c
new file mode 100644
index 000000000..b7587ff4d
--- /dev/null
+++ b/drivers/video/fbdev/sunxvr2500.c
@@ -0,0 +1,250 @@
+/* sunxvr2500.c: Sun 3DLABS XVR-2500 et al. fb driver for sparc64 systems
+ *
+ * License: GPL
+ *
+ * Copyright (C) 2007 David S. Miller (davem@davemloft.net)
+ */
+
+#include <linux/aperture.h>
+#include <linux/kernel.h>
+#include <linux/fb.h>
+#include <linux/pci.h>
+#include <linux/init.h>
+#include <linux/of.h>
+
+#include <asm/io.h>
+
+struct s3d_info {
+	struct fb_info		*info;
+	struct pci_dev		*pdev;
+
+	char __iomem		*fb_base;
+	unsigned long		fb_base_phys;
+
+	struct device_node	*of_node;
+
+	unsigned int		width;
+	unsigned int		height;
+	unsigned int		depth;
+	unsigned int		fb_size;
+
+	u32			pseudo_palette[16];
+};
+
+static int s3d_get_props(struct s3d_info *sp)
+{
+	sp->width = of_getintprop_default(sp->of_node, "width", 0);
+	sp->height = of_getintprop_default(sp->of_node, "height", 0);
+	sp->depth = of_getintprop_default(sp->of_node, "depth", 8);
+
+	if (!sp->width || !sp->height) {
+		pci_err(sp->pdev, "Critical properties missing\n");
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static int s3d_setcolreg(unsigned regno,
+			 unsigned red, unsigned green, unsigned blue,
+			 unsigned transp, struct fb_info *info)
+{
+	u32 value;
+
+	if (regno < 16) {
+		red >>= 8;
+		green >>= 8;
+		blue >>= 8;
+
+		value = (blue << 24) | (green << 16) | (red << 8);
+		((u32 *)info->pseudo_palette)[regno] = value;
+	}
+
+	return 0;
+}
+
+static const struct fb_ops s3d_ops = {
+	.owner			= THIS_MODULE,
+	FB_DEFAULT_IOMEM_OPS,
+	.fb_setcolreg		= s3d_setcolreg,
+};
+
+static int s3d_set_fbinfo(struct s3d_info *sp)
+{
+	struct fb_info *info = sp->info;
+	struct fb_var_screeninfo *var = &info->var;
+
+	info->fbops = &s3d_ops;
+	info->screen_base = sp->fb_base;
+	info->screen_size = sp->fb_size;
+
+	info->pseudo_palette = sp->pseudo_palette;
+
+	/* Fill fix common fields */
+	strscpy(info->fix.id, "s3d", sizeof(info->fix.id));
+        info->fix.smem_start = sp->fb_base_phys;
+        info->fix.smem_len = sp->fb_size;
+        info->fix.type = FB_TYPE_PACKED_PIXELS;
+	if (sp->depth == 32 || sp->depth == 24)
+		info->fix.visual = FB_VISUAL_TRUECOLOR;
+	else
+		info->fix.visual = FB_VISUAL_PSEUDOCOLOR;
+
+	var->xres = sp->width;
+	var->yres = sp->height;
+	var->xres_virtual = var->xres;
+	var->yres_virtual = var->yres;
+	var->bits_per_pixel = sp->depth;
+
+	var->red.offset = 8;
+	var->red.length = 8;
+	var->green.offset = 16;
+	var->green.length = 8;
+	var->blue.offset = 24;
+	var->blue.length = 8;
+	var->transp.offset = 0;
+	var->transp.length = 0;
+
+	if (fb_alloc_cmap(&info->cmap, 256, 0)) {
+		pci_err(sp->pdev, "Cannot allocate color map\n");
+		return -ENOMEM;
+	}
+
+        return 0;
+}
+
+static int s3d_pci_register(struct pci_dev *pdev,
+			    const struct pci_device_id *ent)
+{
+	struct fb_info *info;
+	struct s3d_info *sp;
+	int err;
+
+	err = aperture_remove_conflicting_pci_devices(pdev, "s3dfb");
+	if (err)
+		return err;
+
+	err = pci_enable_device(pdev);
+	if (err < 0) {
+		pci_err(pdev, "Cannot enable PCI device\n");
+		goto err_out;
+	}
+
+	info = framebuffer_alloc(sizeof(struct s3d_info), &pdev->dev);
+	if (!info) {
+		err = -ENOMEM;
+		goto err_disable;
+	}
+
+	sp = info->par;
+	sp->info = info;
+	sp->pdev = pdev;
+	sp->of_node = pci_device_to_OF_node(pdev);
+	if (!sp->of_node) {
+		pci_err(pdev, "Cannot find OF node\n");
+		err = -ENODEV;
+		goto err_release_fb;
+	}
+
+	sp->fb_base_phys = pci_resource_start (pdev, 1);
+
+	err = pci_request_region(pdev, 1, "s3d framebuffer");
+	if (err < 0) {
+		pci_err(pdev, "Cannot request region 1\n");
+		goto err_release_fb;
+	}
+
+	err = s3d_get_props(sp);
+	if (err)
+		goto err_release_pci;
+
+	/* XXX 'linebytes' is often wrong, it is equal to the width
+	 * XXX with depth of 32 on my XVR-2500 which is clearly not
+	 * XXX right.  So we don't try to use it.
+	 */
+	switch (sp->depth) {
+	case 8:
+		info->fix.line_length = sp->width;
+		break;
+	case 16:
+		info->fix.line_length = sp->width * 2;
+		break;
+	case 24:
+		info->fix.line_length = sp->width * 3;
+		break;
+	case 32:
+		info->fix.line_length = sp->width * 4;
+		break;
+	}
+	sp->fb_size = info->fix.line_length * sp->height;
+
+	sp->fb_base = ioremap(sp->fb_base_phys, sp->fb_size);
+	if (!sp->fb_base) {
+		err = -ENOMEM;
+		goto err_release_pci;
+	}
+
+	err = s3d_set_fbinfo(sp);
+	if (err)
+		goto err_unmap_fb;
+
+	pci_set_drvdata(pdev, info);
+
+	pci_info(pdev, "Found device\n");
+
+	err = register_framebuffer(info);
+	if (err < 0) {
+		pci_err(pdev, "Could not register framebuffer\n");
+		goto err_unmap_fb;
+	}
+
+	return 0;
+
+err_unmap_fb:
+	iounmap(sp->fb_base);
+
+err_release_pci:
+	pci_release_region(pdev, 1);
+
+err_release_fb:
+        framebuffer_release(info);
+
+err_disable:
+	pci_disable_device(pdev);
+
+err_out:
+	return err;
+}
+
+static const struct pci_device_id s3d_pci_table[] = {
+	{	PCI_DEVICE(PCI_VENDOR_ID_3DLABS, 0x002c),	},
+	{	PCI_DEVICE(PCI_VENDOR_ID_3DLABS, 0x002d),	},
+	{	PCI_DEVICE(PCI_VENDOR_ID_3DLABS, 0x002e),	},
+	{	PCI_DEVICE(PCI_VENDOR_ID_3DLABS, 0x002f),	},
+	{	PCI_DEVICE(PCI_VENDOR_ID_3DLABS, 0x0030),	},
+	{	PCI_DEVICE(PCI_VENDOR_ID_3DLABS, 0x0031),	},
+	{	PCI_DEVICE(PCI_VENDOR_ID_3DLABS, 0x0032),	},
+	{	PCI_DEVICE(PCI_VENDOR_ID_3DLABS, 0x0033),	},
+	{ 0, }
+};
+
+static struct pci_driver s3d_driver = {
+	.driver = {
+		.suppress_bind_attrs = true,
+	},
+	.name		= "s3d",
+	.id_table	= s3d_pci_table,
+	.probe		= s3d_pci_register,
+};
+
+static int __init s3d_init(void)
+{
+	if (fb_modesetting_disabled("s3d"))
+		return -ENODEV;
+
+	if (fb_get_options("s3d", NULL))
+		return -ENODEV;
+
+	return pci_register_driver(&s3d_driver);
+}
+device_initcall(s3d_init);