ld scripting help

ld scripting help

[Davis, Clayton]

I am trying to link a file in a specific way and need help understanding how to write the linker script.
I know that the order of the sections needs to be.

SECTIONS
}
.text
.syscall
.fixaddr
.fixtype
.intercall
.interfunc
.rodata
.secinfo
.data
.bss
}

And I know that the application needs to start at 0x00000000.

I tried 

OUTPUT_FORMAT("elf32-littlearm", "elf32-bigarm","elf32-littlearm")
OUTPUT_ARCH(arm)
ENTRY(_start)
SEARCH_DIR("/scratch/paul/release/install/i686-mingw32/arm-none-elf/arm-none-elf/lib");
SECTIONS
{
            .text 0x00000000 : {*(.test)}
            current = .;
            .syscall current :{*(.syscall)}
            current = .;
            .fixaddr current :{*(.fixaddr)}
            current = .;
            .fixtype current :{*(.fixtype)}
            current = .;
            .intercall current :{*(.intercall)}
            current = .;
            .rodata current :{*(.rodata)}
            current = .;
            .secinfo current :{*(.secinfo)}
            current = .;
            .data current :{*(.data)}
            current = .;
            .bss current :{*(.bss)}



}
Just to see if it would work

I'm new to linker scripts so I would appreciate any help you could give me. I am using ld 2.15.94 on windows 2000.

Additionally I am getting a "_start not found" error. I have tried to include crt0.o directly from the lib directory and using the script I just showed, but is complains about

 In function _sbrk within file Libg.a 
            End <- undefined reference

In function start within file crt0.S
            _int
            __bss_start__
            __bss_end__
            _fini

Thank you for your time.

Re: ld scripting help

[Nick Clifton]

Hi Clayton,

> I know that the order of the sections needs to be.
> 
> SECTIONS
> }

I assume that you meant "{" here ... :)

> .text
> .syscall
> .fixaddr
> .fixtype
> .intercall
> .interfunc
> .rodata
> .secinfo
> .data
> .bss
> }
> 
> And I know that the application needs to start at 0x00000000.

The start address can be specified on the linker command line via the --entry 
command line option.  A linker script can provide a default start address which 
is used when the linker command line option is not provided.  This is done via 
the ENTRY() directive in the script which names a symbol whose value is the 
start address.  (You mention encountering problems with the _start symbol being 
undefined.  This is because it was used in the ENTRY() command in your linker 
script, but you had not provided a definition of the _start symbol).


> I tried 

> SECTIONS
> {
>             .text 0x00000000 : {*(.test)}
>             current = .;
>             .syscall current :{*(.syscall)}

Using "current" like this should not be necessary.  By default the linker will 
place each named output section after the end of the previously named output 
section.  ie you can do this:

            .text 0x0 : { *(.test) }
            .syscall  : { *(.syscall} }

etc.  By the way did you really mean "*(.test)" as being the input sections 
that should be placed into the .text output section, or did you mean "*(.text)" ?

> Just to see if it would work

The implication being that it did not work.  Can you say how it failed ?

By the way if you use the "-Map <file>" linker command line switch you can have 
the linker create a map file (called <file>) which will show you exactly how 
the linker has laid out the executable that it creates.

> I'm new to linker scripts so I would appreciate any help you could give me.

Try reading the linker manual.  It has a large section on linker scripts 
including examples of how the directives work.

Also try running "ld --verbose" to see the default, built-in linker script. 
You can load this output into a text editor, trim away the unnecessary comments 
at the start and end and then use the resulting file as your own linker script. 
      In this way you could tweak the order of the output sections to get the 
ordering that you want.

> I am using ld 2.15.94 on windows 2000.

Version 2.18 of the linker (and other binutils) is now out, so it would be a 
very good idea to upgrade to them if you can.

> Additionally I am getting a "_start not found" error. I have tried to include crt0.o directly from the lib directory and using the script I just showed, but is complains about
> 
>  In function _sbrk within file Libg.a 
>             End <- undefined reference

The answer to this problem has already been given to you on the gnu-arm mailing 
list...

Cheers
   Nick