[PATCH] libio: Add small optimization on fmemopen

[Paul Eggert]

On 09/21/2016 11:47 AM, Florian Weimer wrote:
> We don't know the nature of the GCC issue, so we cannot work around it 
> reliably.  The most likely explanation is that Address Sanitizer does 
> not account for a valid GCC optimization.

That's not the sense that I get from looking at Bug 66661. GCC is 
assuming it can do an aligned word load of the trailing bytes of a 
flexible array member in a properly-aligned structure. This assumption 
is something we can easily work around reliably, e.g., with the patch I 
suggested. Although the followups to Bug 66661 suggest that there may be 
further problems with overaligned structures, the code here is not using 
_Alignas so these further problems are not an issue here.