#2917: alloca and allocaArray do not respect alignment
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Reporter: guest | Owner:
Type: bug | Status: new
Priority: high | Milestone: 6.10.2
Component: Compiler (FFI) | Version: 6.10.1
Severity: normal | Resolution:
Keywords: | Difficulty: Unknown
Testcase: | Os: Unknown/Multiple
Architecture: x86 |
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Comment (by igloo):
I'm a little nervous about rushing this in, particularly as it changes
(adds to) some APIs, and I'm not sure exactly what the behaviour should
be.
You say
{{{
mallocAlignment :: Int
mallocAlignment = 16
allocaAlignment :: Int
allocaAlignment = 8
}}}
but my manpage says
{{{
GNU libc malloc() always returns 8-byte aligned memory addresses
}}}
Where did 16 come from? It also seems strange to me that `allocaAlignment`
should be different to `mallocAlignment`.
According to my OS X manpages, OS X doesn't have `posix_memalign` or
`memalign`, although it does have `valloc` ("The allocated memory is
aligned on a page boundary."). However, for all the allocation functions
on OS X, "The allocated memory is aligned such that it can be used for any
data type, including AltiVec- and SSE-related types.". So if we're told
the alignment is 32, and we get memory 16-byte aligned, should we fail?
It's not clear to me.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2917#comment:7>
GHC <http://www.haskell.org/ghc/>
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