Re: [PATCH 2/5] LoongArch: Use explicit relocs for GOT access when -mexplicit-relocs=auto and LTO during a final link with linker plugin

[Xi Ruoyao <xry111@xry111.site>]

On Sat, 2023-10-21 at 15:32 +0800, chenglulu wrote:
> > +  /* If we are performing LTO for a final link, and we have the linker
> > +     plugin so we know the resolution of the symbols, then all GOT
> > +     references are binding to external symbols or preemptable symbols.
> > +     So the linker cannot relax them.  */
> > +  return (in_lto_p
> > +	  && !flag_incremental_link
> 
> I don’t quite understand this condition "!flag_incremental_link". Can 
> you explain it? Others LGTM.
> 
> Thanks.

If we have two (or several) .o files containing LTO bytecode, GCC
supports "LTO incremental linking" with:

gcc a.o b.o -o ab.o -O2 -flto -flinker-output=nolto-rel

The resulted ab.o will include data and code in a.o and b.o, but it
contains machine code instead of LTO bytecode.  Now if ab.o refers to an
external symbol c, the linker may relax "la.global c" to "la.local c"
(if ab.o is linked together with another file c.o which contains the
definition of c) or not.  As we cannot exclude the possibility of a
relaxation on la.global for incremental linking, just emit la.global and
let the linker to do the correct thing.

-- 
Xi Ruoyao <xry111@xry111.site>
School of Aerospace Science and Technology, Xidian University