ia64: fix small struct return
ia64: fix small struct return

This change fixes libffi.call/struct10.c failure on ia64:
FAIL: libffi.call/struct10.c -W -Wall -Wno-psabi -O0 execution test

.Lst_small_struct handles returns for structs less than 32 bytes
(following ia64 return value ABI [1]). Subroutine does roughly the
following:

```
    mov [sp+0]  = r8
    mov [sp+8]  = r9
    mov [sp+16] = r10
    mov [sp+24] = r11
    memcpy(destination, source=sp, 12);
```

The problem: ia64 ABI guarantees that top 16 bytes of stack are
scratch space for callee function. Thus it can clobber it. [1]
says (7.1 Procedure Frames):
"""
* Scratch area. This 16-byte region is provided as scratch storage
  for procedures that are called by the current procedure. Leaf
  procedures do not need to allocate this region. A procedure may
  use the 16 bytes at the top of its own frame as scratch memory,
  but the contents of this area are not preserved by a procedure call.
"""

In our case 16 top bytes are clobbered by a PLT resolver when memcpy()
is called for the first time. As a result memcpy implementation reads
already clobbered data frop top of stack.

The fix is simple: allocate 16 bytes of scrats space prior to memcpy()
call.

[1]: https://www.intel.com/content/dam/www/public/us/en/documents/guides/itanium-software-runtime-architecture-guide.pdf

Bug: https://bugs.gentoo.org/634190
Signed-off-by: Sergei Trofimovich <110fdadc76b6bce16977f568bdb4723eaed6fb3f@gentoo.org>

plicease/libffi,plicease/libffi,plicease/libffi,plicease/libffi