[MIPS] fix CRT_CALL_STATIC_FUNCTION macro

[Maciej W. Rozycki]

On Thu, 22 Jan 2015, Matthew Fortune wrote:

> > This is a follow-up to a change [1] in glibc. It fixes the issue [2]
> > when jal can not reach a target in different region.

 Is it not a problem that can be solved with rearranging the order of
sections in output?

> > It has been tested with DejaGnu for mips32/o32, mips64/n32 and
> > mips64/n64.

 You forgot a ChangeLog entry, the lack of which made me chase the bits 
you intend to change. :(

> > Let me know what you think.

 You need to use DLA rather than LA for n64.  This should have been caught 
in testing as a combination of the GAS warning and -Werror should have 
caused the compilation to bail out.  But perhaps this isn't covered for 
some reason.

> Otherwise for PIC the issue is dealt with by the assembler with the
> JAL <sym> being expanded to a load from the got and indirect call through
> t9. Previously t9 would not have been set up for the callee if the code
> was built non-pic (as it would just use a JAL). That would have made
> the setup of gp somewhat pointless in the CRT_CALL_STATIC_FUNCTION
> code. I am therefore a little confused by the existing code that sets
> up GP but then it seemingly is not used unless built for PIC.

 Bear in mind MIPS used to be PIC for everything except bare iron, so you 
had to set up $gp even in executables.  Support for non-PIC abicalls is a 
relatively recent addition, so it looks to me nobody bothered to optimise 
these chunks as only executed once each and not really critical for 
performance.

 This code dates back to:

2003-01-15  Alexandre Oliva  <aoliva@redhat.com>

	* config/mips/mips.h (CRT_CALL_STATIC_FUNCTION): Define so as
	to set $gp before the call.

and as I have suspected it was made with multi-GOT support in mind or 
otherwise $gp could have been set up the usual way.  See the original 
submission here:

http://gcc.gnu.org/ml/gcc-patches/2003-01/msg00919.html

All this predates non-PIC abicalls by over 5 years and has only changed a 
little since the original addition.

  Maciej