[PATCH] D39876: [support] allocate exact size required for mapping in Support/Windws/Path.inc

[Zachary Turner via llvm-commits]

On Thu, Nov 9, 2017 at 3:56 PM Bob Haarman via Phabricator <
reviews at reviews.llvm.org> wrote:

> inglorion created this revision.
> Herald added a subscriber: hiraditya.
>
> zturner suggested that mapped_file_region::init() on Windows seems to
> create mappings that are larger than they need to be: Offset+Size
> instead of Size. Indeed, that appears to be the case. I confirmed that
> tests pass with mappings of just Size bytes, and fail with Size-1
> bytes, suggesting that Size is indeed the correct value.
>
>
> https://reviews.llvm.org/D39876
>
> Files:
>   llvm/lib/Support/Windows/Path.inc
>
>
> Index: llvm/lib/Support/Windows/Path.inc
> ===================================================================
> --- llvm/lib/Support/Windows/Path.inc
> +++ llvm/lib/Support/Windows/Path.inc
> @@ -734,8 +734,8 @@
>
>    HANDLE FileMappingHandle =
>        ::CreateFileMappingW(FileHandle, 0, flprotect,
> -                           (Offset + Size) >> 32,
> -                           (Offset + Size) & 0xffffffff,
> +                           Size >> 32,
> +                           Size & 0xffffffff,


Oops!  Turns out this is undefined behavior when building x86 where size_t
is 32-bits, and you're shifting right by 32.  I think we can replace this
with Hi_32 and Lo_32 instead.  I'll fix it, just wanted to point it out.
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