Why -mxgot on MIPS and not -fpic/-fPIC?

[Maciej W. Rozycki]

On Mon, 3 Oct 2016, Florian Weimer wrote:

> >> Or group multiple related variables in a struct.  There are likely
> >> quite a few ways GHC could generate code leading to improved
> >> relocations because the DSOs it builds do not have a stable ABI
> >> anyway.  But I bet it's not on the GHC developers' radar screen today
> >> because other platforms have less stringent limits (but would benefit
> >> from the RSS reduction as well).
> >
> >  I take it they don't support multi-GOT then, right?
> 
> GHC is used in a mode which generates C code, which is then compiled
> using GCC.  (This is why Debian could apply the -mxgot workaround so
> quicky.)

 Hmm, thanks for sharing a Debian bug report reference -- so it's the 
Glasgow Haskell Compiler you've been referring to rather than the Green 
Hills Compiler I understood thoughout our discussion so far.  That changes 
things a bit, I wasn't considering you had a generated C source and rather 
I understood you had an interlinking problem as the Green Hills Compiler 
certainly makes MIPS object code.

> >> You'll see that in Fedora eventually.  My question was prompted by a
> >> Debian build failure without -mxgot.
> >
> >  So what did fail to build then?  That's ultimately what the question I 
> > asked boils down to.
> 
> This is the Debian bug report about the build failure:
> 
>   <https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=832824>

 Thanks; if Debian developers want the linker to be updated such that 
`-mxgot' works reliably with `-mno-xgot' code, then please file an 
enhancement request with <https://sourceware.org/bugzilla/>; of course any 
patch proposal will vastly speed up the handling of such a request.  
Ultimately we may have to support mixing multi-GOT and XGOT, though 
obviously only the primary GOT will have to have special handling for 
XGOT; any R_MIPS_GOT_HI16/R_MIPS_GOT_LO16 relocation pairs resolving 
outside XGOT will calculate like R_MIPS_GOT16, i.e. the high part will be 
zero.

 HTH,

  Maciej