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, 322 insertions, 0 deletions

diff --git a/drivers/video/fbdev/goldfishfb.c b/drivers/video/fbdev/goldfishfb.c
new file mode 100644
index 000000000..e5d79886e
--- /dev/null
+++ b/drivers/video/fbdev/goldfishfb.c
@@ -0,0 +1,322 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2007 Google, Inc.
+ * Copyright (C) 2012 Intel, Inc.
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/dma-mapping.h>
+#include <linux/errno.h>
+#include <linux/string.h>
+#include <linux/slab.h>
+#include <linux/delay.h>
+#include <linux/mm.h>
+#include <linux/fb.h>
+#include <linux/init.h>
+#include <linux/interrupt.h>
+#include <linux/ioport.h>
+#include <linux/platform_device.h>
+#include <linux/acpi.h>
+
+enum {
+	FB_GET_WIDTH        = 0x00,
+	FB_GET_HEIGHT       = 0x04,
+	FB_INT_STATUS       = 0x08,
+	FB_INT_ENABLE       = 0x0c,
+	FB_SET_BASE         = 0x10,
+	FB_SET_ROTATION     = 0x14,
+	FB_SET_BLANK        = 0x18,
+	FB_GET_PHYS_WIDTH   = 0x1c,
+	FB_GET_PHYS_HEIGHT  = 0x20,
+
+	FB_INT_VSYNC             = 1U << 0,
+	FB_INT_BASE_UPDATE_DONE  = 1U << 1
+};
+
+struct goldfish_fb {
+	void __iomem *reg_base;
+	int irq;
+	spinlock_t lock;
+	wait_queue_head_t wait;
+	int base_update_count;
+	int rotation;
+	struct fb_info fb;
+	u32 cmap[16];
+};
+
+static irqreturn_t goldfish_fb_interrupt(int irq, void *dev_id)
+{
+	unsigned long irq_flags;
+	struct goldfish_fb *fb = dev_id;
+	u32 status;
+
+	spin_lock_irqsave(&fb->lock, irq_flags);
+	status = readl(fb->reg_base + FB_INT_STATUS);
+	if (status & FB_INT_BASE_UPDATE_DONE) {
+		fb->base_update_count++;
+		wake_up(&fb->wait);
+	}
+	spin_unlock_irqrestore(&fb->lock, irq_flags);
+	return status ? IRQ_HANDLED : IRQ_NONE;
+}
+
+static inline u32 convert_bitfield(int val, struct fb_bitfield *bf)
+{
+	unsigned int mask = (1 << bf->length) - 1;
+
+	return (val >> (16 - bf->length) & mask) << bf->offset;
+}
+
+static int
+goldfish_fb_setcolreg(unsigned int regno, unsigned int red, unsigned int green,
+		 unsigned int blue, unsigned int transp, struct fb_info *info)
+{
+	struct goldfish_fb *fb = container_of(info, struct goldfish_fb, fb);
+
+	if (regno < 16) {
+		fb->cmap[regno] = convert_bitfield(transp, &fb->fb.var.transp) |
+				  convert_bitfield(blue, &fb->fb.var.blue) |
+				  convert_bitfield(green, &fb->fb.var.green) |
+				  convert_bitfield(red, &fb->fb.var.red);
+		return 0;
+	} else {
+		return 1;
+	}
+}
+
+static int goldfish_fb_check_var(struct fb_var_screeninfo *var,
+							struct fb_info *info)
+{
+	if ((var->rotate & 1) != (info->var.rotate & 1)) {
+		if ((var->xres != info->var.yres) ||
+				(var->yres != info->var.xres) ||
+				(var->xres_virtual != info->var.yres) ||
+				(var->yres_virtual > info->var.xres * 2) ||
+				(var->yres_virtual < info->var.xres)) {
+			return -EINVAL;
+		}
+	} else {
+		if ((var->xres != info->var.xres) ||
+		   (var->yres != info->var.yres) ||
+		   (var->xres_virtual != info->var.xres) ||
+		   (var->yres_virtual > info->var.yres * 2) ||
+		   (var->yres_virtual < info->var.yres)) {
+			return -EINVAL;
+		}
+	}
+	if ((var->xoffset != info->var.xoffset) ||
+			(var->bits_per_pixel != info->var.bits_per_pixel) ||
+			(var->grayscale != info->var.grayscale)) {
+		return -EINVAL;
+	}
+	return 0;
+}
+
+static int goldfish_fb_set_par(struct fb_info *info)
+{
+	struct goldfish_fb *fb = container_of(info, struct goldfish_fb, fb);
+
+	if (fb->rotation != fb->fb.var.rotate) {
+		info->fix.line_length = info->var.xres * 2;
+		fb->rotation = fb->fb.var.rotate;
+		writel(fb->rotation, fb->reg_base + FB_SET_ROTATION);
+	}
+	return 0;
+}
+
+
+static int goldfish_fb_pan_display(struct fb_var_screeninfo *var,
+							struct fb_info *info)
+{
+	unsigned long irq_flags;
+	int base_update_count;
+	struct goldfish_fb *fb = container_of(info, struct goldfish_fb, fb);
+
+	spin_lock_irqsave(&fb->lock, irq_flags);
+	base_update_count = fb->base_update_count;
+	writel(fb->fb.fix.smem_start + fb->fb.var.xres * 2 * var->yoffset,
+						fb->reg_base + FB_SET_BASE);
+	spin_unlock_irqrestore(&fb->lock, irq_flags);
+	if (!wait_event_timeout(fb->wait,
+				fb->base_update_count != base_update_count,
+				HZ / 15)) {
+		pr_err("%s: timeout waiting for base update\n", __func__);
+		return -ETIMEDOUT;
+	}
+	return 0;
+}
+
+static int goldfish_fb_blank(int blank, struct fb_info *info)
+{
+	struct goldfish_fb *fb = container_of(info, struct goldfish_fb, fb);
+
+	switch (blank) {
+	case FB_BLANK_NORMAL:
+		writel(1, fb->reg_base + FB_SET_BLANK);
+		break;
+	case FB_BLANK_UNBLANK:
+		writel(0, fb->reg_base + FB_SET_BLANK);
+		break;
+	}
+	return 0;
+}
+
+static const struct fb_ops goldfish_fb_ops = {
+	.owner          = THIS_MODULE,
+	FB_DEFAULT_IOMEM_OPS,
+	.fb_check_var   = goldfish_fb_check_var,
+	.fb_set_par     = goldfish_fb_set_par,
+	.fb_setcolreg   = goldfish_fb_setcolreg,
+	.fb_pan_display = goldfish_fb_pan_display,
+	.fb_blank	= goldfish_fb_blank,
+};
+
+
+static int goldfish_fb_probe(struct platform_device *pdev)
+{
+	int ret;
+	struct goldfish_fb *fb;
+	size_t framesize;
+	u32 width, height;
+	dma_addr_t fbpaddr;
+
+	fb = kzalloc_obj(*fb);
+	if (fb == NULL) {
+		ret = -ENOMEM;
+		goto err_fb_alloc_failed;
+	}
+	spin_lock_init(&fb->lock);
+	init_waitqueue_head(&fb->wait);
+	platform_set_drvdata(pdev, fb);
+
+	fb->reg_base = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(fb->reg_base)) {
+		ret = PTR_ERR(fb->reg_base);
+		goto err_no_io_base;
+	}
+
+	fb->irq = platform_get_irq(pdev, 0);
+	if (fb->irq < 0) {
+		ret = fb->irq;
+		goto err_no_irq;
+	}
+
+	width = readl(fb->reg_base + FB_GET_WIDTH);
+	height = readl(fb->reg_base + FB_GET_HEIGHT);
+
+	fb->fb.fbops		= &goldfish_fb_ops;
+	fb->fb.pseudo_palette	= fb->cmap;
+	fb->fb.fix.type		= FB_TYPE_PACKED_PIXELS;
+	fb->fb.fix.visual = FB_VISUAL_TRUECOLOR;
+	fb->fb.fix.line_length = width * 2;
+	fb->fb.fix.accel	= FB_ACCEL_NONE;
+	fb->fb.fix.ypanstep = 1;
+
+	fb->fb.var.xres		= width;
+	fb->fb.var.yres		= height;
+	fb->fb.var.xres_virtual	= width;
+	fb->fb.var.yres_virtual	= height * 2;
+	fb->fb.var.bits_per_pixel = 16;
+	fb->fb.var.activate	= FB_ACTIVATE_NOW;
+	fb->fb.var.height	= readl(fb->reg_base + FB_GET_PHYS_HEIGHT);
+	fb->fb.var.width	= readl(fb->reg_base + FB_GET_PHYS_WIDTH);
+	fb->fb.var.pixclock	= 0;
+
+	fb->fb.var.red.offset = 11;
+	fb->fb.var.red.length = 5;
+	fb->fb.var.green.offset = 5;
+	fb->fb.var.green.length = 6;
+	fb->fb.var.blue.offset = 0;
+	fb->fb.var.blue.length = 5;
+
+	framesize = width * height * 2 * 2;
+	fb->fb.screen_base = (char __force __iomem *)dma_alloc_coherent(
+						&pdev->dev, framesize,
+						&fbpaddr, GFP_KERNEL);
+	pr_debug("allocating frame buffer %d * %d, got %p\n",
+					width, height, fb->fb.screen_base);
+	if (fb->fb.screen_base == NULL) {
+		ret = -ENOMEM;
+		goto err_alloc_screen_base_failed;
+	}
+	fb->fb.fix.smem_start = fbpaddr;
+	fb->fb.fix.smem_len = framesize;
+
+	ret = fb_set_var(&fb->fb, &fb->fb.var);
+	if (ret)
+		goto err_fb_set_var_failed;
+
+	ret = request_irq(fb->irq, goldfish_fb_interrupt, IRQF_SHARED,
+							pdev->name, fb);
+	if (ret)
+		goto err_request_irq_failed;
+
+	writel(FB_INT_BASE_UPDATE_DONE, fb->reg_base + FB_INT_ENABLE);
+	ret = goldfish_fb_pan_display(&fb->fb.var, &fb->fb); /* updates base */
+	if (ret)
+		goto err_pan_display_failed;
+
+	ret = register_framebuffer(&fb->fb);
+	if (ret)
+		goto err_register_framebuffer_failed;
+	return 0;
+
+err_register_framebuffer_failed:
+err_pan_display_failed:
+	free_irq(fb->irq, fb);
+err_request_irq_failed:
+err_fb_set_var_failed:
+	dma_free_coherent(&pdev->dev, framesize,
+				(void *)fb->fb.screen_base,
+				fb->fb.fix.smem_start);
+err_alloc_screen_base_failed:
+err_no_irq:
+err_no_io_base:
+	kfree(fb);
+err_fb_alloc_failed:
+	return ret;
+}
+
+static void goldfish_fb_remove(struct platform_device *pdev)
+{
+	size_t framesize;
+	struct goldfish_fb *fb = platform_get_drvdata(pdev);
+
+	framesize = fb->fb.var.xres_virtual * fb->fb.var.yres_virtual * 2;
+	unregister_framebuffer(&fb->fb);
+	free_irq(fb->irq, fb);
+
+	dma_free_coherent(&pdev->dev, framesize, (void *)fb->fb.screen_base,
+						fb->fb.fix.smem_start);
+	kfree(fb);
+}
+
+static const struct of_device_id goldfish_fb_of_match[] = {
+	{ .compatible = "google,goldfish-fb", },
+	{},
+};
+MODULE_DEVICE_TABLE(of, goldfish_fb_of_match);
+
+#ifdef CONFIG_ACPI
+static const struct acpi_device_id goldfish_fb_acpi_match[] = {
+	{ "GFSH0004", 0 },
+	{ },
+};
+MODULE_DEVICE_TABLE(acpi, goldfish_fb_acpi_match);
+#endif
+
+static struct platform_driver goldfish_fb_driver = {
+	.probe		= goldfish_fb_probe,
+	.remove		= goldfish_fb_remove,
+	.driver = {
+		.name = "goldfish_fb",
+		.of_match_table = goldfish_fb_of_match,
+		.acpi_match_table = ACPI_PTR(goldfish_fb_acpi_match),
+	}
+};
+
+module_platform_driver(goldfish_fb_driver);
+
+MODULE_DESCRIPTION("Goldfish Virtual Platform Framebuffer driver");
+MODULE_LICENSE("GPL v2");