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, 489 insertions, 0 deletions

diff --git a/drivers/video/fbdev/vt8500lcdfb.c b/drivers/video/fbdev/vt8500lcdfb.c
new file mode 100644
index 000000000..85c7a99a7
--- /dev/null
+++ b/drivers/video/fbdev/vt8500lcdfb.c
@@ -0,0 +1,489 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  linux/drivers/video/vt8500lcdfb.c
+ *
+ *  Copyright (C) 2010 Alexey Charkov <alchark@gmail.com>
+ *
+ * Based on skeletonfb.c and pxafb.c
+ */
+
+#include <linux/delay.h>
+#include <linux/dma-mapping.h>
+#include <linux/errno.h>
+#include <linux/fb.h>
+#include <linux/init.h>
+#include <linux/interrupt.h>
+#include <linux/io.h>
+#include <linux/kernel.h>
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+#include <linux/wait.h>
+#include <video/of_display_timing.h>
+
+#include "vt8500lcdfb.h"
+#include "wmt_ge_rops.h"
+
+#ifdef CONFIG_OF
+#include <linux/of.h>
+#include <linux/of_fdt.h>
+#include <linux/memblock.h>
+#endif
+
+
+#define to_vt8500lcd_info(__info) container_of(__info, \
+						struct vt8500lcd_info, fb)
+
+static int vt8500lcd_set_par(struct fb_info *info)
+{
+	struct vt8500lcd_info *fbi = to_vt8500lcd_info(info);
+	int reg_bpp = 5; /* 16bpp */
+	int i;
+	unsigned long control0;
+
+	if (!fbi)
+		return -EINVAL;
+
+	if (info->var.bits_per_pixel <= 8) {
+		/* palettized */
+		info->var.red.offset    = 0;
+		info->var.red.length    = info->var.bits_per_pixel;
+		info->var.red.msb_right = 0;
+
+		info->var.green.offset  = 0;
+		info->var.green.length  = info->var.bits_per_pixel;
+		info->var.green.msb_right = 0;
+
+		info->var.blue.offset   = 0;
+		info->var.blue.length   = info->var.bits_per_pixel;
+		info->var.blue.msb_right = 0;
+
+		info->var.transp.offset = 0;
+		info->var.transp.length = 0;
+		info->var.transp.msb_right = 0;
+
+		info->fix.visual = FB_VISUAL_PSEUDOCOLOR;
+		info->fix.line_length = info->var.xres_virtual /
+						(8/info->var.bits_per_pixel);
+	} else {
+		/* non-palettized */
+		info->var.transp.offset = 0;
+		info->var.transp.length = 0;
+		info->var.transp.msb_right = 0;
+
+		if (info->var.bits_per_pixel == 16) {
+			/* RGB565 */
+			info->var.red.offset = 11;
+			info->var.red.length = 5;
+			info->var.red.msb_right = 0;
+			info->var.green.offset = 5;
+			info->var.green.length = 6;
+			info->var.green.msb_right = 0;
+			info->var.blue.offset = 0;
+			info->var.blue.length = 5;
+			info->var.blue.msb_right = 0;
+		} else {
+			/* Equal depths per channel */
+			info->var.red.offset = info->var.bits_per_pixel
+							* 2 / 3;
+			info->var.red.length = info->var.bits_per_pixel / 3;
+			info->var.red.msb_right = 0;
+			info->var.green.offset = info->var.bits_per_pixel / 3;
+			info->var.green.length = info->var.bits_per_pixel / 3;
+			info->var.green.msb_right = 0;
+			info->var.blue.offset = 0;
+			info->var.blue.length = info->var.bits_per_pixel / 3;
+			info->var.blue.msb_right = 0;
+		}
+
+		info->fix.visual = FB_VISUAL_TRUECOLOR;
+		info->fix.line_length = info->var.bits_per_pixel > 16 ?
+					info->var.xres_virtual << 2 :
+					info->var.xres_virtual << 1;
+	}
+
+	for (i = 0; i < 8; i++) {
+		if (bpp_values[i] == info->var.bits_per_pixel)
+			reg_bpp = i;
+	}
+
+	control0 = readl(fbi->regbase) & ~0xf;
+	writel(0, fbi->regbase);
+	while (readl(fbi->regbase + 0x38) & 0x10)
+		/* wait */;
+	writel((((info->var.hsync_len - 1) & 0x3f) << 26)
+		| ((info->var.left_margin & 0xff) << 18)
+		| (((info->var.xres - 1) & 0x3ff) << 8)
+		| (info->var.right_margin & 0xff), fbi->regbase + 0x4);
+	writel((((info->var.vsync_len - 1) & 0x3f) << 26)
+		| ((info->var.upper_margin & 0xff) << 18)
+		| (((info->var.yres - 1) & 0x3ff) << 8)
+		| (info->var.lower_margin & 0xff), fbi->regbase + 0x8);
+	writel((((info->var.yres - 1) & 0x400) << 2)
+		| ((info->var.xres - 1) & 0x400), fbi->regbase + 0x10);
+	writel(0x80000000, fbi->regbase + 0x20);
+	writel(control0 | (reg_bpp << 1) | 0x100, fbi->regbase);
+
+	return 0;
+}
+
+static inline u_int chan_to_field(u_int chan, struct fb_bitfield *bf)
+{
+	chan &= 0xffff;
+	chan >>= 16 - bf->length;
+	return chan << bf->offset;
+}
+
+static int vt8500lcd_setcolreg(unsigned regno, unsigned red, unsigned green,
+			   unsigned blue, unsigned transp,
+			   struct fb_info *info) {
+	struct vt8500lcd_info *fbi = to_vt8500lcd_info(info);
+	int ret = 1;
+	unsigned int val;
+	if (regno >= 256)
+		return -EINVAL;
+
+	if (info->var.grayscale)
+		red = green = blue =
+			(19595 * red + 38470 * green + 7471 * blue) >> 16;
+
+	switch (fbi->fb.fix.visual) {
+	case FB_VISUAL_TRUECOLOR:
+		if (regno < 16) {
+			u32 *pal = fbi->fb.pseudo_palette;
+
+			val  = chan_to_field(red, &fbi->fb.var.red);
+			val |= chan_to_field(green, &fbi->fb.var.green);
+			val |= chan_to_field(blue, &fbi->fb.var.blue);
+
+			pal[regno] = val;
+			ret = 0;
+		}
+		break;
+
+	case FB_VISUAL_STATIC_PSEUDOCOLOR:
+	case FB_VISUAL_PSEUDOCOLOR:
+		writew((red & 0xf800)
+		      | ((green >> 5) & 0x7e0)
+		      | ((blue >> 11) & 0x1f),
+		       fbi->palette_cpu + sizeof(u16) * regno);
+		break;
+	}
+
+	return ret;
+}
+
+static int vt8500lcd_ioctl(struct fb_info *info, unsigned int cmd,
+			 unsigned long arg)
+{
+	int ret = 0;
+	struct vt8500lcd_info *fbi = to_vt8500lcd_info(info);
+
+	if (cmd == FBIO_WAITFORVSYNC) {
+		/* Unmask End of Frame interrupt */
+		writel(0xffffffff ^ (1 << 3), fbi->regbase + 0x3c);
+		ret = wait_event_interruptible_timeout(fbi->wait,
+			readl(fbi->regbase + 0x38) & (1 << 3), HZ / 10);
+		/* Mask back to reduce unwanted interrupt traffic */
+		writel(0xffffffff, fbi->regbase + 0x3c);
+		if (ret < 0)
+			return ret;
+		if (ret == 0)
+			return -ETIMEDOUT;
+	}
+
+	return ret;
+}
+
+static int vt8500lcd_pan_display(struct fb_var_screeninfo *var,
+				struct fb_info *info)
+{
+	unsigned pixlen = info->fix.line_length / info->var.xres_virtual;
+	unsigned off = pixlen * var->xoffset
+		      + info->fix.line_length * var->yoffset;
+	struct vt8500lcd_info *fbi = to_vt8500lcd_info(info);
+
+	writel((1 << 31)
+	     | (((info->var.xres_virtual - info->var.xres) * pixlen / 4) << 20)
+	     | (off >> 2), fbi->regbase + 0x20);
+	return 0;
+}
+
+/*
+ * vt8500lcd_blank():
+ *	Blank the display by setting all palette values to zero.  Note,
+ * 	True Color modes do not really use the palette, so this will not
+ *      blank the display in all modes.
+ */
+static int vt8500lcd_blank(int blank, struct fb_info *info)
+{
+	int i;
+
+	switch (blank) {
+	case FB_BLANK_POWERDOWN:
+	case FB_BLANK_VSYNC_SUSPEND:
+	case FB_BLANK_HSYNC_SUSPEND:
+	case FB_BLANK_NORMAL:
+		if (info->fix.visual == FB_VISUAL_PSEUDOCOLOR ||
+		    info->fix.visual == FB_VISUAL_STATIC_PSEUDOCOLOR)
+			for (i = 0; i < 256; i++)
+				vt8500lcd_setcolreg(i, 0, 0, 0, 0, info);
+		fallthrough;
+	case FB_BLANK_UNBLANK:
+		if (info->fix.visual == FB_VISUAL_PSEUDOCOLOR ||
+		    info->fix.visual == FB_VISUAL_STATIC_PSEUDOCOLOR)
+			fb_set_cmap(&info->cmap, info);
+	}
+	return 0;
+}
+
+static const struct fb_ops vt8500lcd_ops = {
+	.owner		= THIS_MODULE,
+	__FB_DEFAULT_DMAMEM_OPS_RDWR,
+	.fb_set_par	= vt8500lcd_set_par,
+	.fb_setcolreg	= vt8500lcd_setcolreg,
+	.fb_fillrect	= wmt_ge_fillrect,
+	.fb_copyarea	= wmt_ge_copyarea,
+	.fb_imageblit	= sys_imageblit,
+	.fb_sync	= wmt_ge_sync,
+	.fb_ioctl	= vt8500lcd_ioctl,
+	.fb_pan_display	= vt8500lcd_pan_display,
+	.fb_blank	= vt8500lcd_blank,
+	// .fb_mmap needs DMA mmap
+};
+
+static irqreturn_t vt8500lcd_handle_irq(int irq, void *dev_id)
+{
+	struct vt8500lcd_info *fbi = dev_id;
+
+	if (readl(fbi->regbase + 0x38) & (1 << 3))
+		wake_up_interruptible(&fbi->wait);
+
+	writel(0xffffffff, fbi->regbase + 0x38);
+	return IRQ_HANDLED;
+}
+
+static int vt8500lcd_probe(struct platform_device *pdev)
+{
+	struct vt8500lcd_info *fbi;
+	struct resource *res;
+	struct display_timings *disp_timing;
+	void *addr;
+	int irq, ret;
+
+	struct fb_videomode	of_mode;
+	u32			bpp;
+	dma_addr_t fb_mem_phys;
+	unsigned long fb_mem_len;
+	void *fb_mem_virt;
+
+	ret = -ENOMEM;
+	fbi = NULL;
+
+	fbi = devm_kzalloc(&pdev->dev, sizeof(struct vt8500lcd_info)
+			+ sizeof(u32) * 16, GFP_KERNEL);
+	if (!fbi)
+		return -ENOMEM;
+
+	strcpy(fbi->fb.fix.id, "VT8500 LCD");
+
+	fbi->fb.fix.type	= FB_TYPE_PACKED_PIXELS;
+	fbi->fb.fix.xpanstep	= 0;
+	fbi->fb.fix.ypanstep	= 1;
+	fbi->fb.fix.ywrapstep	= 0;
+	fbi->fb.fix.accel	= FB_ACCEL_NONE;
+
+	fbi->fb.var.nonstd	= 0;
+	fbi->fb.var.activate	= FB_ACTIVATE_NOW;
+	fbi->fb.var.height	= -1;
+	fbi->fb.var.width	= -1;
+	fbi->fb.var.vmode	= FB_VMODE_NONINTERLACED;
+
+	fbi->fb.fbops		= &vt8500lcd_ops;
+	fbi->fb.flags		= FBINFO_HWACCEL_COPYAREA
+				| FBINFO_HWACCEL_FILLRECT
+				| FBINFO_HWACCEL_YPAN
+				| FBINFO_VIRTFB
+				| FBINFO_PARTIAL_PAN_OK;
+	fbi->fb.node		= -1;
+
+	addr = fbi;
+	addr = addr + sizeof(struct vt8500lcd_info);
+	fbi->fb.pseudo_palette	= addr;
+
+	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+	if (res == NULL) {
+		dev_err(&pdev->dev, "no I/O memory resource defined\n");
+		return -ENODEV;
+	}
+
+	res = request_mem_region(res->start, resource_size(res), "vt8500lcd");
+	if (res == NULL) {
+		dev_err(&pdev->dev, "failed to request I/O memory\n");
+		return -EBUSY;
+	}
+
+	fbi->regbase = ioremap(res->start, resource_size(res));
+	if (fbi->regbase == NULL) {
+		dev_err(&pdev->dev, "failed to map I/O memory\n");
+		ret = -EBUSY;
+		goto failed_free_res;
+	}
+
+	disp_timing = of_get_display_timings(pdev->dev.of_node);
+	if (!disp_timing) {
+		ret = -EINVAL;
+		goto failed_free_io;
+	}
+
+	ret = of_get_fb_videomode(pdev->dev.of_node, &of_mode,
+							OF_USE_NATIVE_MODE);
+	if (ret)
+		goto failed_free_io;
+
+	ret = of_property_read_u32(pdev->dev.of_node, "bits-per-pixel", &bpp);
+	if (ret)
+		goto failed_free_io;
+
+	/* try allocating the framebuffer */
+	fb_mem_len = of_mode.xres * of_mode.yres * 2 * (bpp / 8);
+	fb_mem_virt = dma_alloc_coherent(&pdev->dev, fb_mem_len, &fb_mem_phys,
+				GFP_KERNEL);
+	if (!fb_mem_virt) {
+		pr_err("%s: Failed to allocate framebuffer\n", __func__);
+		ret = -ENOMEM;
+		goto failed_free_io;
+	}
+
+	fbi->fb.fix.smem_start	= fb_mem_phys;
+	fbi->fb.fix.smem_len	= fb_mem_len;
+	fbi->fb.screen_buffer	= fb_mem_virt;
+
+	fbi->palette_size	= PAGE_ALIGN(512);
+	fbi->palette_cpu	= dma_alloc_coherent(&pdev->dev,
+						     fbi->palette_size,
+						     &fbi->palette_phys,
+						     GFP_KERNEL);
+	if (fbi->palette_cpu == NULL) {
+		dev_err(&pdev->dev, "Failed to allocate palette buffer\n");
+		ret = -ENOMEM;
+		goto failed_free_mem_virt;
+	}
+
+	irq = platform_get_irq(pdev, 0);
+	if (irq < 0) {
+		ret = -ENODEV;
+		goto failed_free_palette;
+	}
+
+	ret = request_irq(irq, vt8500lcd_handle_irq, 0, "LCD", fbi);
+	if (ret) {
+		dev_err(&pdev->dev, "request_irq failed: %d\n", ret);
+		ret = -EBUSY;
+		goto failed_free_palette;
+	}
+
+	init_waitqueue_head(&fbi->wait);
+
+	if (fb_alloc_cmap(&fbi->fb.cmap, 256, 0) < 0) {
+		dev_err(&pdev->dev, "Failed to allocate color map\n");
+		ret = -ENOMEM;
+		goto failed_free_irq;
+	}
+
+	fb_videomode_to_var(&fbi->fb.var, &of_mode);
+
+	fbi->fb.var.xres_virtual	= of_mode.xres;
+	fbi->fb.var.yres_virtual	= of_mode.yres * 2;
+	fbi->fb.var.bits_per_pixel	= bpp;
+
+	ret = vt8500lcd_set_par(&fbi->fb);
+	if (ret) {
+		dev_err(&pdev->dev, "Failed to set parameters\n");
+		goto failed_free_cmap;
+	}
+
+	writel(fbi->fb.fix.smem_start >> 22, fbi->regbase + 0x1c);
+	writel((fbi->palette_phys & 0xfffffe00) | 1, fbi->regbase + 0x18);
+
+	platform_set_drvdata(pdev, fbi);
+
+	ret = register_framebuffer(&fbi->fb);
+	if (ret < 0) {
+		dev_err(&pdev->dev,
+			"Failed to register framebuffer device: %d\n", ret);
+		goto failed_free_cmap;
+	}
+
+	/*
+	 * Ok, now enable the LCD controller
+	 */
+	writel(readl(fbi->regbase) | 1, fbi->regbase);
+
+	return 0;
+
+failed_free_cmap:
+	if (fbi->fb.cmap.len)
+		fb_dealloc_cmap(&fbi->fb.cmap);
+failed_free_irq:
+	free_irq(irq, fbi);
+failed_free_palette:
+	dma_free_coherent(&pdev->dev, fbi->palette_size,
+			  fbi->palette_cpu, fbi->palette_phys);
+failed_free_mem_virt:
+	dma_free_coherent(&pdev->dev, fbi->fb.fix.smem_len,
+			  fbi->fb.screen_buffer, fbi->fb.fix.smem_start);
+failed_free_io:
+	iounmap(fbi->regbase);
+failed_free_res:
+	release_mem_region(res->start, resource_size(res));
+	return ret;
+}
+
+static void vt8500lcd_remove(struct platform_device *pdev)
+{
+	struct vt8500lcd_info *fbi = platform_get_drvdata(pdev);
+	struct resource *res;
+	int irq;
+
+	unregister_framebuffer(&fbi->fb);
+
+	writel(0, fbi->regbase);
+
+	if (fbi->fb.cmap.len)
+		fb_dealloc_cmap(&fbi->fb.cmap);
+
+	irq = platform_get_irq(pdev, 0);
+	free_irq(irq, fbi);
+
+	dma_free_coherent(&pdev->dev, fbi->palette_size,
+			  fbi->palette_cpu, fbi->palette_phys);
+
+	iounmap(fbi->regbase);
+
+	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+	release_mem_region(res->start, resource_size(res));
+}
+
+static const struct of_device_id via_dt_ids[] = {
+	{ .compatible = "via,vt8500-fb", },
+	{}
+};
+
+static struct platform_driver vt8500lcd_driver = {
+	.probe		= vt8500lcd_probe,
+	.remove		= vt8500lcd_remove,
+	.driver		= {
+		.name	= "vt8500-lcd",
+		.of_match_table = of_match_ptr(via_dt_ids),
+	},
+};
+
+module_platform_driver(vt8500lcd_driver);
+
+MODULE_AUTHOR("Alexey Charkov <alchark@gmail.com>");
+MODULE_DESCRIPTION("LCD controller driver for VIA VT8500");
+MODULE_LICENSE("GPL v2");
+MODULE_DEVICE_TABLE(of, via_dt_ids);