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, 207 insertions, 0 deletions

diff --git a/include/media/v4l2-rect.h b/include/media/v4l2-rect.h
new file mode 100644
index 000000000..bd587d0c0
--- /dev/null
+++ b/include/media/v4l2-rect.h
@@ -0,0 +1,207 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * v4l2-rect.h - v4l2_rect helper functions
+ *
+ * Copyright 2014 Cisco Systems, Inc. and/or its affiliates. All rights reserved.
+ */
+
+#ifndef _V4L2_RECT_H_
+#define _V4L2_RECT_H_
+
+#include <linux/videodev2.h>
+
+/**
+ * v4l2_rect_set_size_to() - copy the width/height values.
+ * @r: rect whose width and height fields will be set
+ * @size: rect containing the width and height fields you need.
+ */
+static inline void v4l2_rect_set_size_to(struct v4l2_rect *r,
+					 const struct v4l2_rect *size)
+{
+	r->width = size->width;
+	r->height = size->height;
+}
+
+/**
+ * v4l2_rect_set_min_size() - width and height of r should be >= min_size.
+ * @r: rect whose width and height will be modified
+ * @min_size: rect containing the minimal width and height
+ */
+static inline void v4l2_rect_set_min_size(struct v4l2_rect *r,
+					  const struct v4l2_rect *min_size)
+{
+	if (r->width < min_size->width)
+		r->width = min_size->width;
+	if (r->height < min_size->height)
+		r->height = min_size->height;
+}
+
+/**
+ * v4l2_rect_set_max_size() - width and height of r should be <= max_size
+ * @r: rect whose width and height will be modified
+ * @max_size: rect containing the maximum width and height
+ */
+static inline void v4l2_rect_set_max_size(struct v4l2_rect *r,
+					  const struct v4l2_rect *max_size)
+{
+	if (r->width > max_size->width)
+		r->width = max_size->width;
+	if (r->height > max_size->height)
+		r->height = max_size->height;
+}
+
+/**
+ * v4l2_rect_map_inside()- r should be inside boundary.
+ * @r: rect that will be modified
+ * @boundary: rect containing the boundary for @r
+ */
+static inline void v4l2_rect_map_inside(struct v4l2_rect *r,
+					const struct v4l2_rect *boundary)
+{
+	v4l2_rect_set_max_size(r, boundary);
+	if (r->left < boundary->left)
+		r->left = boundary->left;
+	if (r->top < boundary->top)
+		r->top = boundary->top;
+	if (r->left + r->width > boundary->left + boundary->width)
+		r->left = boundary->left + boundary->width - r->width;
+	if (r->top + r->height > boundary->top + boundary->height)
+		r->top = boundary->top + boundary->height - r->height;
+}
+
+/**
+ * v4l2_rect_same_size() - return true if r1 has the same size as r2
+ * @r1: rectangle.
+ * @r2: rectangle.
+ *
+ * Return true if both rectangles have the same size.
+ */
+static inline bool v4l2_rect_same_size(const struct v4l2_rect *r1,
+				       const struct v4l2_rect *r2)
+{
+	return r1->width == r2->width && r1->height == r2->height;
+}
+
+/**
+ * v4l2_rect_same_position() - return true if r1 has the same position as r2
+ * @r1: rectangle.
+ * @r2: rectangle.
+ *
+ * Return true if both rectangles have the same position
+ */
+static inline bool v4l2_rect_same_position(const struct v4l2_rect *r1,
+					   const struct v4l2_rect *r2)
+{
+	return r1->top == r2->top && r1->left == r2->left;
+}
+
+/**
+ * v4l2_rect_equal() - return true if r1 equals r2
+ * @r1: rectangle.
+ * @r2: rectangle.
+ *
+ * Return true if both rectangles have the same size and position.
+ */
+static inline bool v4l2_rect_equal(const struct v4l2_rect *r1,
+				   const struct v4l2_rect *r2)
+{
+	return v4l2_rect_same_size(r1, r2) && v4l2_rect_same_position(r1, r2);
+}
+
+/**
+ * v4l2_rect_intersect() - calculate the intersection of two rects.
+ * @r: intersection of @r1 and @r2.
+ * @r1: rectangle.
+ * @r2: rectangle.
+ */
+static inline void v4l2_rect_intersect(struct v4l2_rect *r,
+				       const struct v4l2_rect *r1,
+				       const struct v4l2_rect *r2)
+{
+	int right, bottom;
+
+	r->top = max(r1->top, r2->top);
+	r->left = max(r1->left, r2->left);
+	bottom = min(r1->top + r1->height, r2->top + r2->height);
+	right = min(r1->left + r1->width, r2->left + r2->width);
+	r->height = max(0, bottom - r->top);
+	r->width = max(0, right - r->left);
+}
+
+/**
+ * v4l2_rect_scale() - scale rect r by to/from
+ * @r: rect to be scaled.
+ * @from: from rectangle.
+ * @to: to rectangle.
+ *
+ * This scales rectangle @r horizontally by @to->width / @from->width and
+ * vertically by @to->height / @from->height.
+ *
+ * Typically @r is a rectangle inside @from and you want the rectangle as
+ * it would appear after scaling @from to @to. So the resulting @r will
+ * be the scaled rectangle inside @to.
+ */
+static inline void v4l2_rect_scale(struct v4l2_rect *r,
+				   const struct v4l2_rect *from,
+				   const struct v4l2_rect *to)
+{
+	if (from->width == 0 || from->height == 0) {
+		r->left = r->top = r->width = r->height = 0;
+		return;
+	}
+	r->left = (((r->left - from->left) * to->width) / from->width) & ~1;
+	r->width = ((r->width * to->width) / from->width) & ~1;
+	r->top = ((r->top - from->top) * to->height) / from->height;
+	r->height = (r->height * to->height) / from->height;
+}
+
+/**
+ * v4l2_rect_overlap() - do r1 and r2 overlap?
+ * @r1: rectangle.
+ * @r2: rectangle.
+ *
+ * Returns true if @r1 and @r2 overlap.
+ */
+static inline bool v4l2_rect_overlap(const struct v4l2_rect *r1,
+				     const struct v4l2_rect *r2)
+{
+	/*
+	 * IF the left side of r1 is to the right of the right side of r2 OR
+	 *    the left side of r2 is to the right of the right side of r1 THEN
+	 * they do not overlap.
+	 */
+	if (r1->left >= r2->left + r2->width ||
+	    r2->left >= r1->left + r1->width)
+		return false;
+	/*
+	 * IF the top side of r1 is below the bottom of r2 OR
+	 *    the top side of r2 is below the bottom of r1 THEN
+	 * they do not overlap.
+	 */
+	if (r1->top >= r2->top + r2->height ||
+	    r2->top >= r1->top + r1->height)
+		return false;
+	return true;
+}
+
+/**
+ * v4l2_rect_enclosed() - is r1 enclosed in r2?
+ * @r1: rectangle.
+ * @r2: rectangle.
+ *
+ * Returns true if @r1 is enclosed in @r2.
+ */
+static inline bool v4l2_rect_enclosed(struct v4l2_rect *r1,
+				      struct v4l2_rect *r2)
+{
+	if (r1->left < r2->left || r1->top < r2->top)
+		return false;
+	if (r1->left + r1->width > r2->left + r2->width)
+		return false;
+	if (r1->top + r1->height > r2->top + r2->height)
+		return false;
+
+	return true;
+}
+
+#endif