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Fix shm_toc.c to always return buffer-aligned memory.

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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
This commit is contained in:
Heikki Linnakangas
2017-08-16 21:52:38 +03:00
parent 4395f7daf3
commit ac883ac453
2 changed files with 20 additions and 5 deletions
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src/include/c.h
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@@ -598,6 +598,7 @@ typedef NameData *Name;
#define LONGALIGN_DOWN(LEN) TYPEALIGN_DOWN(ALIGNOF_LONG, (LEN))
#define DOUBLEALIGN_DOWN(LEN) TYPEALIGN_DOWN(ALIGNOF_DOUBLE, (LEN))
#define MAXALIGN_DOWN(LEN) TYPEALIGN_DOWN(MAXIMUM_ALIGNOF, (LEN))
#define BUFFERALIGN_DOWN(LEN) TYPEALIGN_DOWN(ALIGNOF_BUFFER, (LEN))
/*
* The above macros will not work with types wider than uintptr_t, like with