Re: [PATCH v2 2/7] BaseTools-GenFw:Add new x86_64 Elf relocation types for PIC/PIE code

["Shi, Steven" <steven.shi@intel.com>]

> 
> CoffAddFixup() must be used for absolute symbol references only. These
> instructions contain relative symbol references, which are
> recalculated in WriteSections64().
> 
> The only absolute symbol reference is the GOT entry for 'n', and your
> code (in WriteRelocations64()) calculates the address of the GOT entry
> (which is always in .text BTW) and adds a fixup for it, i.e.,
> 
> +              CoffAddFixup(
> +                (UINT32)(UINTN)((UINT64)
> mCoffSectionsOffset[RelShdr->sh_info] + GoTPcRelPtrOffset),
> +                EFI_IMAGE_REL_BASED_DIR64);
> 
> This code adds a fixup to the PE/COFF .reloc section for the GOT entry
> containing the address of 'n', and the instructions perform a IP
> relative load of the contents of the GOT entry to retrieve the address
> of 'n'.
> 
> By adding two fixups, the PE/COFF loader will apply the load offset
> twice, resulting in an incorrect value.
> 
OK, I get your point now. Yes, the current patch could generate multiple fixups for the same GOT relocation entry. How about we introduce a simple IsDuplicatedCoffFixup() to check whether a converting fixup offset is duplicated before we use CoffAddFixup() to really add it? If it is new, we add it, otherwise just skip it.