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authorLibravatar Junio C Hamano <gitster@pobox.com>2022-02-09 14:21:01 -0800
committerLibravatar Junio C Hamano <gitster@pobox.com>2022-02-09 14:21:01 -0800
commitc7a42644b0b0329cd77911203d47674608d96ee7 (patch)
tree6e8d4f787cf7400fa8905ad329539a248f22ea59
parentMerge branch 'js/sparse-vs-split-index' (diff)
parentmem-pool: don't assume uintmax_t is aligned enough for all types (diff)
downloadtgif-c7a42644b0b0329cd77911203d47674608d96ee7.tar.xz
Merge branch 'jc/mem-pool-alignment'
Update the logic to compute alignment requirement for our mem-pool. * jc/mem-pool-alignment: mem-pool: don't assume uintmax_t is aligned enough for all types
-rw-r--r--mem-pool.c26
1 files changed, 23 insertions, 3 deletions
diff --git a/mem-pool.c b/mem-pool.c
index ccdcad2e3d..599d8e895f 100644
--- a/mem-pool.c
+++ b/mem-pool.c
@@ -8,6 +8,26 @@
#define BLOCK_GROWTH_SIZE (1024 * 1024 - sizeof(struct mp_block))
/*
+ * The inner union is an approximation for C11's max_align_t, and the
+ * struct + offsetof computes _Alignof. This can all just be replaced
+ * with _Alignof(max_align_t) if/when C11 is part of the baseline.
+ * Note that _Alignof(X) need not be the same as sizeof(X); it's only
+ * required to be a (possibly trivial) factor. They are the same for
+ * most architectures, but m68k for example has only 2-byte alignment
+ * for its 4-byte and 8-byte types, so using sizeof would waste space.
+ *
+ * Add more types to the union if the current set is insufficient.
+ */
+struct git_max_alignment {
+ char unalign;
+ union {
+ uintmax_t max_align_uintmax;
+ void *max_align_pointer;
+ } aligned;
+};
+#define GIT_MAX_ALIGNMENT offsetof(struct git_max_alignment, aligned)
+
+/*
* Allocate a new mp_block and insert it after the block specified in
* `insert_after`. If `insert_after` is NULL, then insert block at the
* head of the linked list.
@@ -69,9 +89,9 @@ void *mem_pool_alloc(struct mem_pool *pool, size_t len)
struct mp_block *p = NULL;
void *r;
- /* round up to a 'uintmax_t' alignment */
- if (len & (sizeof(uintmax_t) - 1))
- len += sizeof(uintmax_t) - (len & (sizeof(uintmax_t) - 1));
+ /* round up to a 'GIT_MAX_ALIGNMENT' alignment */
+ if (len & (GIT_MAX_ALIGNMENT - 1))
+ len += GIT_MAX_ALIGNMENT - (len & (GIT_MAX_ALIGNMENT - 1));
if (pool->mp_block &&
pool->mp_block->end - pool->mp_block->next_free >= len)