[PATCH] x86: Use pad in pthread_unwind_buf to preserve shadow stack register

[Joseph Myers]

On Fri, 6 Apr 2018, H.J. Lu wrote:

> https://github.com/hjl-tools/glibc/commit/9bf6aefa8fb45f8df140d42ce9cf890bb24076e1
> 
> It should be binary backward compatible.  I will investigate if there is a way

Increasing the size of a public type is always dangerous, because you can 
end up with one part of a program expecting the new, larger size but 
another part only allocating the old, smaller size.

It might in some cases be compatible to the extent that existing linked 
programs and shared libraries work with new glibc, if new glibc will never 
try to write into the unallocated part of such objects allocated by an 
existing linked program or shared library.  However, any such change would 
need a careful analysis of how the type gets written to, and to what 
extent external libraries have interfaces that depend on the size of the 
type, and would need a NEWS entry explaining the change and discussing the 
compatibility issues with it.

-- 
Joseph S. Myers
joseph@codesourcery.com