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, 407 insertions, 0 deletions

diff --git a/drivers/video/fbdev/wm8505fb.c b/drivers/video/fbdev/wm8505fb.c
new file mode 100644
index 000000000..5caf74ca9
--- /dev/null
+++ b/drivers/video/fbdev/wm8505fb.c
@@ -0,0 +1,407 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  WonderMedia WM8505 Frame Buffer device driver
+ *
+ *  Copyright (C) 2010 Ed Spiridonov <edo.rus@gmail.com>
+ *    Based on vt8500lcdfb.c
+ */
+
+#include <linux/delay.h>
+#include <linux/dma-mapping.h>
+#include <linux/fb.h>
+#include <linux/errno.h>
+#include <linux/err.h>
+#include <linux/init.h>
+#include <linux/interrupt.h>
+#include <linux/io.h>
+#include <linux/kernel.h>
+#include <linux/memblock.h>
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_fdt.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 "wm8505fb_regs.h"
+#include "wmt_ge_rops.h"
+
+#define DRIVER_NAME "wm8505-fb"
+
+#define to_wm8505fb_info(__info) container_of(__info, \
+						struct wm8505fb_info, fb)
+struct wm8505fb_info {
+	struct fb_info		fb;
+	void __iomem		*regbase;
+	unsigned int		contrast;
+};
+
+
+static int wm8505fb_init_hw(struct fb_info *info)
+{
+	struct wm8505fb_info *fbi = to_wm8505fb_info(info);
+
+	int i;
+
+	/* I know the purpose only of few registers, so clear unknown */
+	for (i = 0; i < 0x200; i += 4)
+		writel(0, fbi->regbase + i);
+
+	/* Set frame buffer address */
+	writel(fbi->fb.fix.smem_start, fbi->regbase + WMT_GOVR_FBADDR);
+	writel(fbi->fb.fix.smem_start, fbi->regbase + WMT_GOVR_FBADDR1);
+
+	/*
+	 * Set in-memory picture format to RGB
+	 * 0x31C sets the correct color mode (RGB565) for WM8650
+	 * Bit 8+9 (0x300) are ignored on WM8505 as reserved
+	 */
+	writel(0x31c,		       fbi->regbase + WMT_GOVR_COLORSPACE);
+	writel(1,		       fbi->regbase + WMT_GOVR_COLORSPACE1);
+
+	/* Virtual buffer size */
+	writel(info->var.xres,	       fbi->regbase + WMT_GOVR_XRES);
+	writel(info->var.xres_virtual, fbi->regbase + WMT_GOVR_XRES_VIRTUAL);
+
+	/* black magic ;) */
+	writel(0xf,		       fbi->regbase + WMT_GOVR_FHI);
+	writel(4,		       fbi->regbase + WMT_GOVR_DVO_SET);
+	writel(1,		       fbi->regbase + WMT_GOVR_MIF_ENABLE);
+	writel(1,		       fbi->regbase + WMT_GOVR_REG_UPDATE);
+
+	return 0;
+}
+
+static int wm8505fb_set_timing(struct fb_info *info)
+{
+	struct wm8505fb_info *fbi = to_wm8505fb_info(info);
+
+	int h_start = info->var.left_margin;
+	int h_end = h_start + info->var.xres;
+	int h_all = h_end + info->var.right_margin;
+	int h_sync = info->var.hsync_len;
+
+	int v_start = info->var.upper_margin;
+	int v_end = v_start + info->var.yres;
+	int v_all = v_end + info->var.lower_margin;
+	int v_sync = info->var.vsync_len;
+
+	writel(0, fbi->regbase + WMT_GOVR_TG);
+
+	writel(h_start, fbi->regbase + WMT_GOVR_TIMING_H_START);
+	writel(h_end,   fbi->regbase + WMT_GOVR_TIMING_H_END);
+	writel(h_all,   fbi->regbase + WMT_GOVR_TIMING_H_ALL);
+	writel(h_sync,  fbi->regbase + WMT_GOVR_TIMING_H_SYNC);
+
+	writel(v_start, fbi->regbase + WMT_GOVR_TIMING_V_START);
+	writel(v_end,   fbi->regbase + WMT_GOVR_TIMING_V_END);
+	writel(v_all,   fbi->regbase + WMT_GOVR_TIMING_V_ALL);
+	writel(v_sync,  fbi->regbase + WMT_GOVR_TIMING_V_SYNC);
+
+	writel(1, fbi->regbase + WMT_GOVR_TG);
+
+	return 0;
+}
+
+
+static int wm8505fb_set_par(struct fb_info *info)
+{
+	struct wm8505fb_info *fbi = to_wm8505fb_info(info);
+
+	if (!fbi)
+		return -EINVAL;
+
+	if (info->var.bits_per_pixel == 32) {
+		info->var.red.offset = 16;
+		info->var.red.length = 8;
+		info->var.red.msb_right = 0;
+		info->var.green.offset = 8;
+		info->var.green.length = 8;
+		info->var.green.msb_right = 0;
+		info->var.blue.offset = 0;
+		info->var.blue.length = 8;
+		info->var.blue.msb_right = 0;
+		info->fix.visual = FB_VISUAL_TRUECOLOR;
+		info->fix.line_length = info->var.xres_virtual << 2;
+	} else if (info->var.bits_per_pixel == 16) {
+		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;
+		info->fix.visual = FB_VISUAL_TRUECOLOR;
+		info->fix.line_length = info->var.xres_virtual << 1;
+	}
+
+	wm8505fb_set_timing(info);
+
+	writel(fbi->contrast<<16 | fbi->contrast<<8 | fbi->contrast,
+		fbi->regbase + WMT_GOVR_CONTRAST);
+
+	return 0;
+}
+
+static ssize_t contrast_show(struct device *dev,
+			     struct device_attribute *attr, char *buf)
+{
+	struct fb_info *info = dev_get_drvdata(dev);
+	struct wm8505fb_info *fbi = to_wm8505fb_info(info);
+
+	return sprintf(buf, "%u\n", fbi->contrast);
+}
+
+static ssize_t contrast_store(struct device *dev,
+			      struct device_attribute *attr,
+			      const char *buf, size_t count)
+{
+	struct fb_info *info = dev_get_drvdata(dev);
+	struct wm8505fb_info *fbi = to_wm8505fb_info(info);
+	unsigned long tmp;
+
+	if (kstrtoul(buf, 10, &tmp) || (tmp > 0xff))
+		return -EINVAL;
+	fbi->contrast = tmp;
+
+	wm8505fb_set_par(info);
+
+	return count;
+}
+
+static DEVICE_ATTR_RW(contrast);
+
+static struct attribute *wm8505fb_attrs[] = {
+	&dev_attr_contrast.attr,
+	NULL,
+};
+ATTRIBUTE_GROUPS(wm8505fb);
+
+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 wm8505fb_setcolreg(unsigned regno, unsigned red, unsigned green,
+			   unsigned blue, unsigned transp,
+			   struct fb_info *info) {
+	struct wm8505fb_info *fbi = to_wm8505fb_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 = info->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;
+	}
+
+	return ret;
+}
+
+static int wm8505fb_pan_display(struct fb_var_screeninfo *var,
+				struct fb_info *info)
+{
+	struct wm8505fb_info *fbi = to_wm8505fb_info(info);
+
+	writel(var->xoffset, fbi->regbase + WMT_GOVR_XPAN);
+	writel(var->yoffset, fbi->regbase + WMT_GOVR_YPAN);
+	return 0;
+}
+
+static int wm8505fb_blank(int blank, struct fb_info *info)
+{
+	struct wm8505fb_info *fbi = to_wm8505fb_info(info);
+
+	switch (blank) {
+	case FB_BLANK_UNBLANK:
+		wm8505fb_set_timing(info);
+		break;
+	default:
+		writel(0,  fbi->regbase + WMT_GOVR_TIMING_V_SYNC);
+		break;
+	}
+
+	return 0;
+}
+
+static const struct fb_ops wm8505fb_ops = {
+	.owner		= THIS_MODULE,
+	__FB_DEFAULT_DMAMEM_OPS_RDWR,
+	.fb_set_par	= wm8505fb_set_par,
+	.fb_setcolreg	= wm8505fb_setcolreg,
+	.fb_fillrect	= wmt_ge_fillrect,
+	.fb_copyarea	= wmt_ge_copyarea,
+	.fb_imageblit	= sys_imageblit,
+	.fb_sync	= wmt_ge_sync,
+	.fb_pan_display	= wm8505fb_pan_display,
+	.fb_blank	= wm8505fb_blank,
+	__FB_DEFAULT_IOMEM_OPS_MMAP,
+};
+
+static int wm8505fb_probe(struct platform_device *pdev)
+{
+	struct wm8505fb_info	*fbi;
+	struct display_timings *disp_timing;
+	void			*addr;
+	int ret;
+
+	struct fb_videomode	mode;
+	u32			bpp;
+	dma_addr_t fb_mem_phys;
+	unsigned long fb_mem_len;
+	void *fb_mem_virt;
+
+	fbi = devm_kzalloc(&pdev->dev, sizeof(struct wm8505fb_info) +
+			sizeof(u32) * 16, GFP_KERNEL);
+	if (!fbi)
+		return -ENOMEM;
+
+	strcpy(fbi->fb.fix.id, DRIVER_NAME);
+
+	fbi->fb.fix.type	= FB_TYPE_PACKED_PIXELS;
+	fbi->fb.fix.xpanstep	= 1;
+	fbi->fb.fix.ypanstep	= 1;
+	fbi->fb.fix.ywrapstep	= 0;
+	fbi->fb.fix.accel	= FB_ACCEL_NONE;
+
+	fbi->fb.fbops		= &wm8505fb_ops;
+	fbi->fb.flags		= FBINFO_HWACCEL_COPYAREA
+				| FBINFO_HWACCEL_FILLRECT
+				| FBINFO_HWACCEL_XPAN
+				| FBINFO_HWACCEL_YPAN
+				| FBINFO_VIRTFB
+				| FBINFO_PARTIAL_PAN_OK;
+	fbi->fb.node		= -1;
+
+	addr = fbi;
+	addr = addr + sizeof(struct wm8505fb_info);
+	fbi->fb.pseudo_palette	= addr;
+
+	fbi->regbase = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(fbi->regbase))
+		return PTR_ERR(fbi->regbase);
+
+	disp_timing = of_get_display_timings(pdev->dev.of_node);
+	if (!disp_timing)
+		return -EINVAL;
+
+	ret = of_get_fb_videomode(pdev->dev.of_node, &mode, OF_USE_NATIVE_MODE);
+	if (ret)
+		return ret;
+
+	ret = of_property_read_u32(pdev->dev.of_node, "bits-per-pixel", &bpp);
+	if (ret)
+		return ret;
+
+	fb_videomode_to_var(&fbi->fb.var, &mode);
+
+	fbi->fb.var.nonstd		= 0;
+	fbi->fb.var.activate		= FB_ACTIVATE_NOW;
+
+	fbi->fb.var.height		= -1;
+	fbi->fb.var.width		= -1;
+
+	/* try allocating the framebuffer */
+	fb_mem_len = mode.xres * mode.yres * 2 * (bpp / 8);
+	fb_mem_virt = dmam_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__);
+		return -ENOMEM;
+	}
+
+	fbi->fb.var.xres_virtual	= mode.xres;
+	fbi->fb.var.yres_virtual	= mode.yres * 2;
+	fbi->fb.var.bits_per_pixel	= bpp;
+
+	fbi->fb.fix.smem_start		= fb_mem_phys;
+	fbi->fb.fix.smem_len		= fb_mem_len;
+	fbi->fb.screen_buffer		= fb_mem_virt;
+	fbi->fb.screen_size		= fb_mem_len;
+
+	fbi->contrast = 0x10;
+	ret = wm8505fb_set_par(&fbi->fb);
+	if (ret) {
+		dev_err(&pdev->dev, "Failed to set parameters\n");
+		return ret;
+	}
+
+	if (fb_alloc_cmap(&fbi->fb.cmap, 256, 0) < 0) {
+		dev_err(&pdev->dev, "Failed to allocate color map\n");
+		return -ENOMEM;
+	}
+
+	wm8505fb_init_hw(&fbi->fb);
+
+	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);
+		if (fbi->fb.cmap.len)
+			fb_dealloc_cmap(&fbi->fb.cmap);
+		return ret;
+	}
+
+	fb_info(&fbi->fb, "%s frame buffer at 0x%lx-0x%lx\n",
+		fbi->fb.fix.id, fbi->fb.fix.smem_start,
+		fbi->fb.fix.smem_start + fbi->fb.fix.smem_len - 1);
+
+	return 0;
+}
+
+static void wm8505fb_remove(struct platform_device *pdev)
+{
+	struct wm8505fb_info *fbi = platform_get_drvdata(pdev);
+
+	unregister_framebuffer(&fbi->fb);
+
+	writel(0, fbi->regbase);
+
+	if (fbi->fb.cmap.len)
+		fb_dealloc_cmap(&fbi->fb.cmap);
+}
+
+static const struct of_device_id wmt_dt_ids[] = {
+	{ .compatible = "wm,wm8505-fb", },
+	{}
+};
+
+static struct platform_driver wm8505fb_driver = {
+	.probe		= wm8505fb_probe,
+	.remove		= wm8505fb_remove,
+	.driver		= {
+		.name	= DRIVER_NAME,
+		.of_match_table = wmt_dt_ids,
+		.dev_groups	= wm8505fb_groups,
+	},
+};
+
+module_platform_driver(wm8505fb_driver);
+
+MODULE_AUTHOR("Ed Spiridonov <edo.rus@gmail.com>");
+MODULE_DESCRIPTION("Framebuffer driver for WMT WM8505");
+MODULE_DEVICE_TABLE(of, wmt_dt_ids);