Re: RELASZ is set to 0 on x86_64 when developing EFI applications with gnu-efi

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Sun, Jun 8, 2014 at 7:07 PM, éæ <yanmiaobest@gmail.com> wrote:
> Forgot to cc the list.
>
> 2014-06-06 23:08 GMT+08:00 H.J. Lu <hjl.tools@gmail.com>:
>> On Fri, Jun 6, 2014 at 12:21 AM, éæ <yanmiaobest@gmail.com> wrote:
>>> Hi Experts,
>>>
>>>       I am developing EFI applications using gnu-efi library and I
>>> need to use some of the existing code base which groups initialization
>>> functions together in a special section.
>>>
>>>       The gnu-efi library uses the symbol _DYNAMIC to locate the
>>> relocation section and does fixups before calling main. Without the
>>> special section for init functions, there is only a '.rela' section
>>> pointed by _DYMAMIC and everything works fine. But after I modified
>>> the default linker script, the produced ELF image contains 2
>>> relocation sections:
>>> --------------------------------------------------------------------------------------------------------------
>>> Relocation section '.rela.dyn' at offset 0x23850 contains 1 entries:
>>>   Offset          Info           Type           Sym. Value    Sym. Name + Addend
>>> 000000027de0  000000000008 R_X86_64_RELATIVE                    000000000000b7d0
>>>
>>
>> What change you made causes rela.dyn section?
>
>
> In one of the source file, I have:
>
> void xxxInit(void)
>     {
>     ....
>     }
> static void * __func_xxxInit
> __attribute__((section(".init.
> before.shell"))) =  (void *)xxxInit;

You put a function pointer, which is in data section, in
".init.before.shell" section, which you put in text
section in linker script:

 .text :
  {
   *(.text)

    /* XXX: added for constructors */
    init_start = .;
    KEEP(*(.init.before.memory))
    einit_before_memory = .;

    KEEP(*(.init.before.fs))
    einit_before_fs = .;

    KEEP(*(.init.before.shell))
    einit_before_shell = .;
    /* XXX: added for constructors */

  }

Did you want to put the function xxxInit in .init.before.shell?

> And in linker script I added this:
>
> KEEP(*(.init.before.shell))
> einit_before_shell = .;
>
> The relocation entry is for the function pointer. If I remove the
> "__attribute__((section(...)))" part, then
> the problem disappears.
>
> Thanks,
> Miao



-- 
H.J.