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 <aol...@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
