Power 64 ELFv2 w.r.t toc(cmodel=medium) on windows.

[Umesh Kalappa]

Cced maintainer like David Edelsohn and Segher Boessenkool .

Any suggestions/comments for the below query ?
Thank you
~Umesh
On Thu, Oct 25, 2018 at 9:23 PM Umesh Kalappa <umesh.kalappa0@gmail.com> wrote:
>
> Hi All,
>
> For the below code (test.c)
>
> int foo()
> {
>   printf("Hello World");
> }
>
> On linux :
> ccpc -mcpu=e6500 -mno-altivec -mabi=no-altivec -D_WRS_HARDWARE_FP
> -mabi=elfv2 -mcmodel=med -mhard-float -S test.c
>
> linux asm :
> the constant string fetched like
>
>  addis 3,2,.LC0@toc@ha
>  addi 3,3,.LC0@toc@l
>
> where offset  signed 32 bit used  relatively to  toc base  on linux as
> expected  for the  medium code model .
> and the relocation entry will be generated by gas  :
> R_PPC64_TOC16_HA   and  R_PPC64_TOC16_LO
>
> For Windows :
>
> same command  and windows asm looks like
>
> la 3,.LC0@toc(2)
>
> where offset used  signed 16  bit used  relatively to  toc base  why it so ?.
> and the relocation entry will be :
> R_PPC64_TOC16  (signed 16 bit offset )
>
> why this difference and when we greping the .md file and  we found
> patterns (rs6000.md ) like
>
> ;; Largetoc support
> (define_insn "*largetoc_high"
>   [(set (match_operand:DI 0 "gpc_reg_operand" "=b*r")
>         (high:DI
>           (unspec [(match_operand:DI 1 "" "")
>                    (match_operand:DI 2 "gpc_reg_operand" "b")]
>                   UNSPEC_TOCREL)))]
>    "TARGET_ELF && TARGET_CMODEL != CMODEL_SMALL"
>    "addis %0,%2,%1@toc@ha")
>
> (define_insn "*largetoc_high_aix<mode>"
>   [(set (match_operand:P 0 "gpc_reg_operand" "=b*r")
>         (high:P
>           (unspec [(match_operand:P 1 "" "")
>                    (match_operand:P 2 "gpc_reg_operand" "b")]
>                   UNSPEC_TOCREL)))]
>    "TARGET_XCOFF && TARGET_CMODEL != CMODEL_SMALL"
>    "addis %0,%1@u(%2)")
>
> the above patterns  answered the difference b/w windows and linux .
>
> Questions to the expert  is that using the medium code model ,how we
> can get the same linux semantics  on windows (without source code
> changes) ?
>
> or above distinguish patterns  for  a reason and which we are missing here  ?
>
> Thank you and awaiting for any comments
> ~Umesh