[U-Boot-Users] .GOT2, PLT and fixups ?

[Charles J Gillan]

I have been examining the sections in the LD script as used by
U-Boot for the TQM8xx system.

I am puzzled by a few things and wonder if anyone could explain 
these. I know that similar, but not identical questions, have turned 
up on the list before - but I still can’t figure out exactly what's 
going on. I have also checked the GNU GCC forums and the EABI documents
without success. It seems possibly that internals of the compiler/linker are
not documented in great detail for PPC ???

I have three questions - all relating to building U-Boot for the TQM8xx:

   1. Are .GOT and .GOT1 always going to be empty when compiling
      with -fPIC?

            The SYS V ABI/EABI mentions the existence of a GOT but I can't
            find any mention of the .GOT1 or .GOT2 sections anywhere that I 
            have searched.

            I checked the assembler output for simple C code that I wrote,

            and whenever -fPIC is used this always seems to always 
            generate .GOT2 sections for global data, never .GOT and 
            never .GOT1

            Also, I noted that in u-boot.map the .GOT1 section (which the LD

            script places in the "text" section of the executable) is empty;

            the .GOT section, which the LD script places in the "reloc" 
            section, just before the .GOT2) is also empty.


   2.  How are calls to the position independent C code actually handled?

            The .PLT section (which LD script places before the text
            section) is also empty in the u-boot.map output.

            However on looking at the assembler generated by compiling 
            tqm8xx.c, I see that function calls (e.g. to upm_config) are
            handled using the 

                           upm_config at plt 

            syntax. 

            The GOT2 table appears to be the only mechanism for relocation
            available, so I assume that the function pointers are in fact

            mapped into the GOT2 somehow ? 


   3. Why does ".fixup" appear twice in the LD script, once in the 
      "text" section and once in the "reloc" section.

      Again, I note that the fixup section appears to be empty.

Thanks in advance for any information you can provide.

Regards,

Charles.

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Dr Charles J Gillan
The Institute of Electronics, Communications and Information Technology
(ECIT),               
Queen's University Belfast,
Titanic Quarter
Queen’s Road, Queen’s Island, 
Belfast, BT3 9DT
Northern Ireland, UK
 
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