Fix shm_toc.c to always return buffer-aligned memory.
Previously, if you passed a non-aligned size to shm_toc_create(), the
memory returned by shm_toc_allocate() would be similarly non-aligned.
This was exposed by commit 3cda10f41b
, which allocated structs containing
a pg_atomic_uint64 field with shm_toc_allocate(). On systems with
MAXIMUM_ALIGNOF = 4, such structs still need to be 8-bytes aligned, but
the memory returned by shm_toc_allocate() was only 4-bytes aligned.
It's quite bogus that we abuse BUFFERALIGN to align the structs for
pg_atomic_uint64. It doesn't really have anything to do with buffers. But
that's a separate issue.
This ought to fix the buildfarm failures on 32-bit x86 systems.
Discussion: https://www.postgresql.org/message-id/7e0a73a5-0df9-1859-b8ae-9acf122dc38d@iki.fi
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4395f7daf3
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@ -44,7 +44,12 @@ shm_toc_create(uint64 magic, void *address, Size nbytes)
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Assert(nbytes > offsetof(shm_toc, toc_entry));
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toc->toc_magic = magic;
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SpinLockInit(&toc->toc_mutex);
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toc->toc_total_bytes = nbytes;
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/*
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* The alignment code in shm_toc_allocate() assumes that the starting
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* value is buffer-aligned.
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*/
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toc->toc_total_bytes = BUFFERALIGN_DOWN(nbytes);
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toc->toc_allocated_bytes = 0;
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toc->toc_nentry = 0;
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@ -88,7 +93,12 @@ shm_toc_allocate(shm_toc *toc, Size nbytes)
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Size nentry;
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Size toc_bytes;
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/* Make sure request is well-aligned. */
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/*
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* Make sure request is well-aligned. XXX: MAXALIGN is not enough,
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* because atomic ops might need a wider alignment. We don't have a
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* proper definition for the minimum to make atomic ops safe, but
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* BUFFERALIGN ought to be enough.
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*/
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nbytes = BUFFERALIGN(nbytes);
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SpinLockAcquire(&toc->toc_mutex);
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@ -252,7 +262,11 @@ shm_toc_lookup(shm_toc *toc, uint64 key, bool noError)
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Size
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shm_toc_estimate(shm_toc_estimator *e)
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{
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return add_size(offsetof(shm_toc, toc_entry),
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add_size(mul_size(e->number_of_keys, sizeof(shm_toc_entry)),
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e->space_for_chunks));
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Size sz;
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sz = offsetof(shm_toc, toc_entry);
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sz += add_size(sz, mul_size(e->number_of_keys, sizeof(shm_toc_entry)));
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sz += add_size(sz, e->space_for_chunks);
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return BUFFERALIGN(sz);
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}
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@ -598,6 +598,7 @@ typedef NameData *Name;
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#define LONGALIGN_DOWN(LEN) TYPEALIGN_DOWN(ALIGNOF_LONG, (LEN))
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#define DOUBLEALIGN_DOWN(LEN) TYPEALIGN_DOWN(ALIGNOF_DOUBLE, (LEN))
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#define MAXALIGN_DOWN(LEN) TYPEALIGN_DOWN(MAXIMUM_ALIGNOF, (LEN))
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#define BUFFERALIGN_DOWN(LEN) TYPEALIGN_DOWN(ALIGNOF_BUFFER, (LEN))
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/*
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* The above macros will not work with types wider than uintptr_t, like with
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