[PATCH 0/9] PowerPC64 ELFv2 ABI support.

[Matt Thomas]

On Oct 29, 2013, at 7:19 PM, Alan Modra <amodra@gmail.com> wrote:

> This patch series makes the changes necessary in binutils to support
> the updated PowerPC64 ABI, which we're calling ELFv2.  Two major
> changes from the previous ABI are
> 
> - No function descriptors.

It would be nice if there was a similar ppc32 ABI which would make
sharing code between ppc32 and ppc64 easier.

> The global entry
>  point is the address stored in function pointers, and it is a
>  requirement that calls to the global entry point have that address
>  in r12.  

This sounds similar to ABICALLS on mips (where the function pointer
is stored in $25 (t9) upon call entry).  That value is used to derive
the $gp value by adding a constant (done by the linker) to the value
in $25.  One nice thing about the existing PPC64 ABI is that the toc 
pointer is independent of the PC and thus you can the text and 
non-text parts of a shareable library in independent parts of the 
address space.  One shared segment can have  all the read-only text 
segments and each process can have a private segment with the 
read-write segments.  If you switch to add value to r12 to get the 
toc, you can't share segments anymore.  

Unlike ABICALLS, I assume a plt is still used instead of fetching
the address of each function from the GOT and doing an indirect call.