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, 514 insertions, 0 deletions

diff --git a/drivers/video/fbdev/hitfb.c b/drivers/video/fbdev/hitfb.c
new file mode 100644
index 000000000..97db325df
--- /dev/null
+++ b/drivers/video/fbdev/hitfb.c
@@ -0,0 +1,514 @@
+/*
+ * linux/drivers/video/hitfb.c -- Hitachi LCD frame buffer device
+ *
+ * (C) 1999 Mihai Spatar
+ * (C) 2000 YAEGASHI Takeshi
+ * (C) 2003, 2004 Paul Mundt
+ * (C) 2003, 2004, 2006 Andriy Skulysh
+ *
+ *  This file is subject to the terms and conditions of the GNU General Public
+ *  License. See the file COPYING in the main directory of this archive for
+ *  more details.
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/string.h>
+#include <linux/mm.h>
+#include <linux/delay.h>
+#include <linux/init.h>
+#include <linux/platform_device.h>
+#include <linux/fb.h>
+
+#include <asm/machvec.h>
+#include <linux/uaccess.h>
+#include <asm/io.h>
+#include <asm/hd64461.h>
+#include <cpu/dac.h>
+
+#define	WIDTH 640
+
+static struct fb_var_screeninfo hitfb_var = {
+	.activate	= FB_ACTIVATE_NOW,
+	.height		= -1,
+	.width		= -1,
+	.vmode		= FB_VMODE_NONINTERLACED,
+};
+
+static struct fb_fix_screeninfo hitfb_fix = {
+	.id		= "Hitachi HD64461",
+	.type		= FB_TYPE_PACKED_PIXELS,
+	.accel		= FB_ACCEL_NONE,
+};
+
+static volatile void __iomem *hitfb_offset_to_addr(unsigned int offset)
+{
+	return (__force volatile void __iomem *)(uintptr_t)offset;
+}
+
+static u16 hitfb_readw(unsigned int offset)
+{
+	return fb_readw(hitfb_offset_to_addr(offset));
+}
+
+static void hitfb_writew(u16 value, unsigned int offset)
+{
+	fb_writew(value, hitfb_offset_to_addr(offset));
+}
+
+static inline void hitfb_accel_wait(void)
+{
+	while (hitfb_readw(HD64461_GRCFGR) & HD64461_GRCFGR_ACCSTATUS)
+		;
+}
+
+static inline void hitfb_accel_start(int truecolor)
+{
+	if (truecolor) {
+		hitfb_writew(6, HD64461_GRCFGR);
+	} else {
+		hitfb_writew(7, HD64461_GRCFGR);
+	}
+}
+
+static inline void hitfb_accel_set_dest(int truecolor, u16 dx, u16 dy,
+					u16 width, u16 height)
+{
+	u32 saddr = WIDTH * dy + dx;
+	if (truecolor)
+		saddr <<= 1;
+
+	hitfb_writew(width-1, HD64461_BBTDWR);
+	hitfb_writew(height-1, HD64461_BBTDHR);
+
+	hitfb_writew(saddr & 0xffff, HD64461_BBTDSARL);
+	hitfb_writew(saddr >> 16, HD64461_BBTDSARH);
+
+}
+
+static inline void hitfb_accel_bitblt(int truecolor, u16 sx, u16 sy, u16 dx,
+				      u16 dy, u16 width, u16 height, u16 rop,
+				      u32 mask_addr)
+{
+	u32 saddr, daddr;
+	u32 maddr = 0;
+
+	height--;
+	width--;
+	hitfb_writew(rop, HD64461_BBTROPR);
+	if ((sy < dy) || ((sy == dy) && (sx <= dx))) {
+		saddr = WIDTH * (sy + height) + sx + width;
+		daddr = WIDTH * (dy + height) + dx + width;
+		if (mask_addr) {
+			if (truecolor)
+				maddr = ((width >> 3) + 1) * (height + 1) - 1;
+			else
+				maddr =
+				    (((width >> 4) + 1) * (height + 1) - 1) * 2;
+
+			hitfb_writew((1 << 5) | 1, HD64461_BBTMDR);
+		} else
+			hitfb_writew(1, HD64461_BBTMDR);
+	} else {
+		saddr = WIDTH * sy + sx;
+		daddr = WIDTH * dy + dx;
+		if (mask_addr) {
+			hitfb_writew((1 << 5), HD64461_BBTMDR);
+		} else {
+			hitfb_writew(0, HD64461_BBTMDR);
+		}
+	}
+	if (truecolor) {
+		saddr <<= 1;
+		daddr <<= 1;
+	}
+	hitfb_writew(width, HD64461_BBTDWR);
+	hitfb_writew(height, HD64461_BBTDHR);
+	hitfb_writew(saddr & 0xffff, HD64461_BBTSSARL);
+	hitfb_writew(saddr >> 16, HD64461_BBTSSARH);
+	hitfb_writew(daddr & 0xffff, HD64461_BBTDSARL);
+	hitfb_writew(daddr >> 16, HD64461_BBTDSARH);
+	if (mask_addr) {
+		maddr += mask_addr;
+		hitfb_writew(maddr & 0xffff, HD64461_BBTMARL);
+		hitfb_writew(maddr >> 16, HD64461_BBTMARH);
+	}
+	hitfb_accel_start(truecolor);
+}
+
+static void hitfb_fillrect(struct fb_info *p, const struct fb_fillrect *rect)
+{
+	if (rect->rop != ROP_COPY)
+		cfb_fillrect(p, rect);
+	else {
+		hitfb_accel_wait();
+		hitfb_writew(0x00f0, HD64461_BBTROPR);
+		hitfb_writew(16, HD64461_BBTMDR);
+
+		if (p->var.bits_per_pixel == 16) {
+			hitfb_writew(((u32 *) (p->pseudo_palette))[rect->color],
+				  HD64461_GRSCR);
+			hitfb_accel_set_dest(1, rect->dx, rect->dy, rect->width,
+					     rect->height);
+			hitfb_accel_start(1);
+		} else {
+			hitfb_writew(rect->color, HD64461_GRSCR);
+			hitfb_accel_set_dest(0, rect->dx, rect->dy, rect->width,
+					     rect->height);
+			hitfb_accel_start(0);
+		}
+	}
+}
+
+static void hitfb_copyarea(struct fb_info *p, const struct fb_copyarea *area)
+{
+	hitfb_accel_wait();
+	hitfb_accel_bitblt(p->var.bits_per_pixel == 16, area->sx, area->sy,
+			   area->dx, area->dy, area->width, area->height,
+			   0x00cc, 0);
+}
+
+static int hitfb_pan_display(struct fb_var_screeninfo *var,
+			     struct fb_info *info)
+{
+	int xoffset = var->xoffset;
+	int yoffset = var->yoffset;
+
+	if (xoffset != 0)
+		return -EINVAL;
+
+	hitfb_writew((yoffset*info->fix.line_length)>>10, HD64461_LCDCBAR);
+
+	return 0;
+}
+
+static int hitfb_blank(int blank_mode, struct fb_info *info)
+{
+	unsigned short v;
+
+	if (blank_mode) {
+		v = hitfb_readw(HD64461_LDR1);
+		v &= ~HD64461_LDR1_DON;
+		hitfb_writew(v, HD64461_LDR1);
+
+		v = hitfb_readw(HD64461_LCDCCR);
+		v |= HD64461_LCDCCR_MOFF;
+		hitfb_writew(v, HD64461_LCDCCR);
+
+		v = hitfb_readw(HD64461_STBCR);
+		v |= HD64461_STBCR_SLCDST;
+		hitfb_writew(v, HD64461_STBCR);
+	} else {
+		v = hitfb_readw(HD64461_STBCR);
+		v &= ~HD64461_STBCR_SLCDST;
+		hitfb_writew(v, HD64461_STBCR);
+
+		v = hitfb_readw(HD64461_LCDCCR);
+		v &= ~(HD64461_LCDCCR_MOFF | HD64461_LCDCCR_STREQ);
+		hitfb_writew(v, HD64461_LCDCCR);
+
+		do {
+		    v = hitfb_readw(HD64461_LCDCCR);
+		} while(v&HD64461_LCDCCR_STBACK);
+
+		v = hitfb_readw(HD64461_LDR1);
+		v |= HD64461_LDR1_DON;
+		hitfb_writew(v, HD64461_LDR1);
+	}
+	return 0;
+}
+
+static int hitfb_setcolreg(unsigned regno, unsigned red, unsigned green,
+			   unsigned blue, unsigned transp, struct fb_info *info)
+{
+	if (regno >= 256)
+		return 1;
+
+	switch (info->var.bits_per_pixel) {
+	case 8:
+		hitfb_writew(regno << 8, HD64461_CPTWAR);
+		hitfb_writew(red >> 10, HD64461_CPTWDR);
+		hitfb_writew(green >> 10, HD64461_CPTWDR);
+		hitfb_writew(blue >> 10, HD64461_CPTWDR);
+		break;
+	case 16:
+		if (regno >= 16)
+			return 1;
+		((u32 *) (info->pseudo_palette))[regno] =
+		    ((red & 0xf800)) |
+		    ((green & 0xfc00) >> 5) | ((blue & 0xf800) >> 11);
+		break;
+	}
+	return 0;
+}
+
+static int hitfb_sync(struct fb_info *info)
+{
+	hitfb_accel_wait();
+
+	return 0;
+}
+
+static int hitfb_check_var(struct fb_var_screeninfo *var, struct fb_info *info)
+{
+	int maxy;
+
+	var->xres = info->var.xres;
+	var->xres_virtual = info->var.xres;
+	var->yres = info->var.yres;
+
+	if ((var->bits_per_pixel != 8) && (var->bits_per_pixel != 16))
+		var->bits_per_pixel = info->var.bits_per_pixel;
+
+	if (var->yres_virtual < var->yres)
+		var->yres_virtual = var->yres;
+
+	maxy = info->fix.smem_len / var->xres;
+
+	if (var->bits_per_pixel == 16)
+		maxy /= 2;
+
+	if (var->yres_virtual > maxy)
+		var->yres_virtual = maxy;
+
+	var->xoffset = 0;
+	var->yoffset = 0;
+
+	switch (var->bits_per_pixel) {
+	case 8:
+		var->red.offset = 0;
+		var->red.length = 8;
+		var->green.offset = 0;
+		var->green.length = 8;
+		var->blue.offset = 0;
+		var->blue.length = 8;
+		var->transp.offset = 0;
+		var->transp.length = 0;
+		break;
+	case 16:		/* RGB 565 */
+		var->red.offset = 11;
+		var->red.length = 5;
+		var->green.offset = 5;
+		var->green.length = 6;
+		var->blue.offset = 0;
+		var->blue.length = 5;
+		var->transp.offset = 0;
+		var->transp.length = 0;
+		break;
+	}
+
+	return 0;
+}
+
+static int hitfb_set_par(struct fb_info *info)
+{
+	unsigned short ldr3;
+
+	switch (info->var.bits_per_pixel) {
+	case 8:
+		info->fix.line_length = info->var.xres;
+		info->fix.visual = FB_VISUAL_PSEUDOCOLOR;
+		info->fix.ypanstep = 16;
+		break;
+	case 16:
+		info->fix.line_length = info->var.xres*2;
+		info->fix.visual = FB_VISUAL_TRUECOLOR;
+		info->fix.ypanstep = 8;
+		break;
+	}
+
+	hitfb_writew(info->fix.line_length, HD64461_LCDCLOR);
+	ldr3 = hitfb_readw(HD64461_LDR3);
+	ldr3 &= ~15;
+	ldr3 |= (info->var.bits_per_pixel == 8) ? 4 : 8;
+	hitfb_writew(ldr3, HD64461_LDR3);
+	return 0;
+}
+
+static const struct fb_ops hitfb_ops = {
+	.owner		= THIS_MODULE,
+	__FB_DEFAULT_IOMEM_OPS_RDWR,
+	.fb_check_var	= hitfb_check_var,
+	.fb_set_par	= hitfb_set_par,
+	.fb_setcolreg	= hitfb_setcolreg,
+	.fb_blank	= hitfb_blank,
+	.fb_sync	= hitfb_sync,
+	.fb_pan_display = hitfb_pan_display,
+	.fb_fillrect	= hitfb_fillrect,
+	.fb_copyarea	= hitfb_copyarea,
+	.fb_imageblit	= cfb_imageblit,
+	__FB_DEFAULT_IOMEM_OPS_MMAP,
+};
+
+static int hitfb_probe(struct platform_device *dev)
+{
+	unsigned short lcdclor, ldr3, ldvndr;
+	struct fb_info *info;
+	int ret;
+
+	if (fb_get_options("hitfb", NULL))
+		return -ENODEV;
+
+	hitfb_fix.mmio_start = HD64461_IO_OFFSET(0x1000);
+	hitfb_fix.mmio_len = 0x1000;
+	hitfb_fix.smem_start = HD64461_IO_OFFSET(0x02000000);
+	hitfb_fix.smem_len = 512 * 1024;
+
+	lcdclor = hitfb_readw(HD64461_LCDCLOR);
+	ldvndr = hitfb_readw(HD64461_LDVNDR);
+	ldr3 = hitfb_readw(HD64461_LDR3);
+
+	switch (ldr3 & 15) {
+	default:
+	case 4:
+		hitfb_var.bits_per_pixel = 8;
+		hitfb_var.xres = lcdclor;
+		break;
+	case 8:
+		hitfb_var.bits_per_pixel = 16;
+		hitfb_var.xres = lcdclor / 2;
+		break;
+	}
+	hitfb_fix.line_length = lcdclor;
+	hitfb_fix.visual = (hitfb_var.bits_per_pixel == 8) ?
+	    FB_VISUAL_PSEUDOCOLOR : FB_VISUAL_TRUECOLOR;
+	hitfb_var.yres = ldvndr + 1;
+	hitfb_var.xres_virtual = hitfb_var.xres;
+	hitfb_var.yres_virtual = hitfb_fix.smem_len / lcdclor;
+	switch (hitfb_var.bits_per_pixel) {
+	case 8:
+		hitfb_var.red.offset = 0;
+		hitfb_var.red.length = 8;
+		hitfb_var.green.offset = 0;
+		hitfb_var.green.length = 8;
+		hitfb_var.blue.offset = 0;
+		hitfb_var.blue.length = 8;
+		hitfb_var.transp.offset = 0;
+		hitfb_var.transp.length = 0;
+		break;
+	case 16:		/* RGB 565 */
+		hitfb_var.red.offset = 11;
+		hitfb_var.red.length = 5;
+		hitfb_var.green.offset = 5;
+		hitfb_var.green.length = 6;
+		hitfb_var.blue.offset = 0;
+		hitfb_var.blue.length = 5;
+		hitfb_var.transp.offset = 0;
+		hitfb_var.transp.length = 0;
+		break;
+	}
+
+	info = framebuffer_alloc(sizeof(u32) * 16, &dev->dev);
+	if (unlikely(!info))
+		return -ENOMEM;
+
+	info->fbops = &hitfb_ops;
+	info->var = hitfb_var;
+	info->fix = hitfb_fix;
+	info->pseudo_palette = info->par;
+	info->flags = FBINFO_HWACCEL_YPAN |
+		FBINFO_HWACCEL_FILLRECT | FBINFO_HWACCEL_COPYAREA;
+
+	info->screen_base = (char __iomem *)(uintptr_t)hitfb_fix.smem_start;
+
+	ret = fb_alloc_cmap(&info->cmap, 256, 0);
+	if (unlikely(ret < 0))
+		goto err_fb;
+
+	ret = register_framebuffer(info);
+	if (unlikely(ret < 0))
+		goto err;
+
+	platform_set_drvdata(dev, info);
+
+	fb_info(info, "%s frame buffer device\n", info->fix.id);
+
+	return 0;
+
+err:
+	fb_dealloc_cmap(&info->cmap);
+err_fb:
+	framebuffer_release(info);
+	return ret;
+}
+
+static void hitfb_remove(struct platform_device *dev)
+{
+	struct fb_info *info = platform_get_drvdata(dev);
+
+	unregister_framebuffer(info);
+	fb_dealloc_cmap(&info->cmap);
+	framebuffer_release(info);
+}
+
+static int hitfb_suspend(struct device *dev)
+{
+	u16 v;
+
+	hitfb_blank(1, NULL);
+	v = hitfb_readw(HD64461_STBCR);
+	v |= HD64461_STBCR_SLCKE_IST;
+	hitfb_writew(v, HD64461_STBCR);
+
+	return 0;
+}
+
+static int hitfb_resume(struct device *dev)
+{
+	u16 v;
+
+	v = hitfb_readw(HD64461_STBCR);
+	v &= ~HD64461_STBCR_SLCKE_OST;
+	msleep(100);
+	v = hitfb_readw(HD64461_STBCR);
+	v &= ~HD64461_STBCR_SLCKE_IST;
+	hitfb_writew(v, HD64461_STBCR);
+	hitfb_blank(0, NULL);
+
+	return 0;
+}
+
+static const struct dev_pm_ops hitfb_dev_pm_ops = {
+	.suspend	= hitfb_suspend,
+	.resume		= hitfb_resume,
+};
+
+static struct platform_driver hitfb_driver = {
+	.probe		= hitfb_probe,
+	.remove		= hitfb_remove,
+	.driver		= {
+		.name	= "hitfb",
+		.pm	= &hitfb_dev_pm_ops,
+	},
+};
+
+static struct platform_device hitfb_device = {
+	.name	= "hitfb",
+	.id	= -1,
+};
+
+static int __init hitfb_init(void)
+{
+	int ret;
+
+	ret = platform_driver_register(&hitfb_driver);
+	if (!ret) {
+		ret = platform_device_register(&hitfb_device);
+		if (ret)
+			platform_driver_unregister(&hitfb_driver);
+	}
+	return ret;
+}
+
+
+static void __exit hitfb_exit(void)
+{
+	platform_device_unregister(&hitfb_device);
+	platform_driver_unregister(&hitfb_driver);
+}
+
+module_init(hitfb_init);
+module_exit(hitfb_exit);
+
+MODULE_LICENSE("GPL");