On 08/16/2017 08:10 PM, Andres Freund wrote:
Afaict shm_create/shm_toc_allocate don't actually guarantee that the end
of the toc's memory is suitably aligned. But I didn't yet have any
coffee, so ...
Robert, I'm not quite sure what the intended behaviour of shm_toc is wrt
alignment. I see that individual chunks are BUFFERALIGNed (both during
estimation, and allocation). But I don't see how the size of the entire
toc is aligned, which seems a requirement, given we allocate from the
end.
Seems like we'd just have to add alignment of the total size to
shm_toc_estimate()?
Yeah, that's the gist of it.
The attached patch seems to fix this. I'm not too familiar with this DSM
stuff, but this seems right to me. Unless someone has a better idea
soon, I'll commit this to make the buildfarm happy.
- Heikki
diff --git a/src/backend/storage/ipc/shm_toc.c b/src/backend/storage/ipc/shm_toc.c
index 9f259441f0..121d5a1ec9 100644
--- a/src/backend/storage/ipc/shm_toc.c
+++ b/src/backend/storage/ipc/shm_toc.c
@@ -44,7 +44,7 @@ shm_toc_create(uint64 magic, void *address, Size nbytes)
Assert(nbytes > offsetof(shm_toc, toc_entry));
toc->toc_magic = magic;
SpinLockInit(&toc->toc_mutex);
- toc->toc_total_bytes = nbytes;
+ toc->toc_total_bytes = BUFFERALIGN_DOWN(nbytes);
toc->toc_allocated_bytes = 0;
toc->toc_nentry = 0;
@@ -252,7 +252,8 @@ shm_toc_lookup(shm_toc *toc, uint64 key, bool noError)
Size
shm_toc_estimate(shm_toc_estimator *e)
{
- return add_size(offsetof(shm_toc, toc_entry),
- add_size(mul_size(e->number_of_keys, sizeof(shm_toc_entry)),
- e->space_for_chunks));
+ return BUFFERALIGN(
+ add_size(offsetof(shm_toc, toc_entry),
+ add_size(mul_size(e->number_of_keys, sizeof(shm_toc_entry)),
+ e->space_for_chunks)));
}
diff --git a/src/include/c.h b/src/include/c.h
index 9066e3c578..af799dc1df 100644
--- a/src/include/c.h
+++ b/src/include/c.h
@@ -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
--
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