mirror of
https://gitlab.gnome.org/GNOME/gtk.git
synced 2024-11-09 18:30:08 +00:00
214f5a6f98
When we allocate a graphene_point_t on the stack, there's no guarantee that it will be aligned at an 8-byte boundary, which is an assumption made by gsk_pathop_encode() (which wants to use the lowest 3 bits to encode the operation). In the places where it matters, force the points on the stack and embedded in structs to be nicely aligned. By using a distinct type for this (a union with a suitable size and alignment), we ensure that the compiler will warn or error whenever we can't prove that a particular point is, in fact, suitably aligned. We can go from a `GskAlignedPoint *` to a `graphene_point_t *` (which is always valid, because the `GskAlignedPoint` is aligned) via &aligned_points[0].pt, but we cannot go back the other way (which is not always valid, because the `graphene_point_t` is not necessarily aligned nicely) without a cast. In practice, it seems that a graphene_point_t on x86_64 *is* usually placed at an 8-byte boundary, but this is not the case on 32-bit architectures or on s390x. In many cases we can avoid needing an explicit reference to the more complicated type by making use of a transparent union. There's already at least one transparent union in GSK's public API, so it's presumably portable enough to match GTK's requirements. Increasing the alignment of GskAlignedPoint also requires adjusting how a GskStandardContour is allocated and initialized. This data structure allocates extra memory to hold an array of GskAlignedPoint outside the bounds of the struct itself, and that array now needs to be aligned suitably. Previously the array started with at next byte after the flexible array of gskpathop, but the alignment of a gskpathop is only 4 bytes on 32-bit architectures, so depending on the number of gskpathop in the trailing flexible array, that pointer might be an unsuitable location to allocate a GskAlignedPoint. Resolves: https://gitlab.gnome.org/GNOME/gtk/-/issues/6395 Signed-off-by: Simon McVittie <smcv@debian.org> |
||
|---|---|---|
| .. | ||
| a11y | ||
| css | ||
| gdk | ||
| gsk | ||
| gtk | ||
| headless | ||
| introspection | ||
| reftests | ||
| tools | ||
| meson.build | ||
| testutils.c | ||
| testutils.h | ||