e500 port: getcontext / setcontext / swapcontext

[Joseph S. Myers]

On Wed, 18 Sep 2013, Steven Munroe wrote:

> Joseph I must really question the wisdom of merging the e500 into the
> same source with the "classical" PPC32 code. 
> 
> The unified GPR/FPR set of the e500 impacts the ABI in many different
> ways from the classic PPC32 soft-float or hard-float that I fear this
> will be a constant source of misunderstanding and error in the future.
> 
> I am much more comfortable keeping the e500 specific codes in different
> source files and different parts of the tree.

The design is detailed at 
<https://sourceware.org/ml/libc-alpha/2013-09/msg00485.html>.  The 
function-calling ABI is identical to soft-float (the only case in which 
register high parts are used in argument passing / return is for 
e500-specific vector types).  With this port version, the other aspects of 
the glibc ABI also match soft-float, so soft-float binaries can run with 
glibc built for e500; this avoids an unnecessary proliferation of ABI 
variants (requiring their own ABI test baselines etc.).  The present 
getcontext / setcontext / swapcontext patch follows the same approach as 
the support in those functions for other optional features, with a macro 
__CONTEXT_ENABLE_E500 conditioning the e500-specific code, and in fact the 
substance of the e500 implementation is in a separate file context-e500.h 
in this case because that was the natural way to avoid code duplication in 
the swapcontext sources.

-- 
Joseph S. Myers
joseph@codesourcery.com