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c-rbtree: fix alignment assertion on m64k

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We want to assert that our alignment-guarantees do not exceed the
guarantees of the system-linker or system-allocator on the target
platform. Hence, we check against max_align_t. This is a lower bound,
but not the exact check we actually want. And as it turns out, on m64k
it is too low. Add a static check against 4-byte alignment for m64k as
a workaround.

Reported-by: Michael Biebl
Signed-off-by: David Rheinsberg <david.rheinsberg@gmail.com>

https://github.com/c-util/c-rbtree/issues/9
eb778d3969
This commit is contained in:
David Rheinsberg 2022-05-18 11:31:45 +02:00 • committed by Thomas Haller
parent 9bc7278da3
commit 78831d127f
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1 changed files with 17 additions and 4 deletions
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21
src/c-rbtree/src/c-rbtree.c
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@ -35,12 +35,25 @@
* CRBNode is 4-byte aligned, so the lower 2 bits are actually unused. We also
* sometimes store a pointer to the root-node, so make sure this one is also 4
* byte aligned.
* Note that there are actually some architectures where `max_align_t` is 4, so
* we do not have much wiggle-room to extend this flag-set.
*
* Additionally, we want to avoid an alignment that is bigger than the
* alignment guaranteed by the system allocator or supported by the system
* linker. As there is no standard way to check this, we simply verify against
* `alignof(max_align_t)`, as this alignment must be supported by the
* toolchain.
*
* m64k is special here, as it only has a 2-byte max-alignment, but still
* guarantees a >=4-byte alignment on allocations. So hard-code the maximum for
* it.
*/
static_assert(alignof(CRBNode) <= alignof(max_align_t), "Invalid RBNode alignment");
#ifdef __m68k__
# define C_RBTREE_MAX_ALIGN (C_MAX(4, alignof(max_align_t)))
#else
# define C_RBTREE_MAX_ALIGN (alignof(max_align_t))
#endif
static_assert(alignof(CRBNode) <= C_RBTREE_MAX_ALIGN, "Invalid RBNode alignment");
static_assert(alignof(CRBNode) >= 4, "Invalid CRBNode alignment");
static_assert(alignof(CRBTree) <= alignof(max_align_t), "Invalid RBTree alignment");
static_assert(alignof(CRBTree) <= C_RBTREE_MAX_ALIGN, "Invalid RBTree alignment");
static_assert(alignof(CRBTree) >= 4, "Invalid CRBTree alignment");
/**