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

[Umesh Kalappa <umesh dot kalappa0 at gmail dot com>]

Thank you David for the information.
>>Are you asking about semantics or syntax?  Which source code do you
not want to change?
My bad was not clear in the first go and the questions was why on PE
format the relocation is R_PPC64_TOC16 is generated for global access
and on ELF why its R_PPC64_TOC16_HA and R_PPC64_TOC16_LO  is generated
for same  global access ? why this difference ?

then irrespective of object  file formats ,the RELOCATION should be
same for the given target,right ?

for more info
we are using bintuills (2.29) and we run the assembler like
$as.exe -v -a64 -me6500 -many -mbig -o test.o test.s

lets compiler(gcc)  emit the syntax as PE format ,but we need
assembler emit relocations like ELF for mcmodel=medium /large .,is
that possible .

or like you suggested change the compiler to emit the ELF syntax for
global access ?

Thank you again
~Umesh


On Fri, Oct 26, 2018 at 6:57 PM David Edelsohn <dje.gcc@gmail.com> wrote:
>
> On Thu, Oct 25, 2018 at 11:53 AM 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  ?
>
> Linux uses the ELF file format and assembler syntax.  AIX uses the AIX
> file format and assembler syntax.
>
> Windows uses PE file format and syntax, which is not supported in the
> rs6000 or powerpcspe ports.
>
> Are you asking about semantics or syntax?  Which source code do you
> not want to change?  If you want to target PE assembler, GCC needs to
> be taught about that syntax, or at least it needs to generate the ELF
> syntax for Windows PE.
>
> Thanks, David