Re: Problem in using powerpc-eabi cross linker...

[Michael Eager <eager at eagercon dot com>]

Jeffi Edward.J wrote:
> Again the doubt is on powerpc-eabi cross toolchain with newlib.
>
> Although I built the tool chain, I'm facing problem in using the cross built
> tools.
>
> I wrote a simple hello world test program and compiled.
> The following errors are issued from linker:
>
> powerpc-eabi-ld: warning: cannot find entry symbol _start; defaulting to
> 01800074
> libgcc.a(eabi.o): In function `__eabi':
> eabi.S:232: undefined reference to `__init'
> libgcc.a(eabi.o):(.got2+0x8): undefined reference to `__SDATA_START__'
> libgcc.a(eabi.o):(.got2+0xc): undefined reference to `__SBSS_END__'
> libgcc.a(eabi.o):(.got2+0x14): undefined  reference to `__SDATA2_START__'
> ...
> ...
> libgcc.a(eabi.o):(.got2+0x50): undefined reference to `__EXCEPT_END__'
> collect2: ld returned 1 exit status
>
> If I add -msim or -mads, it is compiled and linked succesfully.

Powerpc-eabi-gcc requires that you specify or supply a library
(essentially, the board support package, BSP) which provides the
low-level support routines.  When you specify -mads or -msim,
the correct library name is automatically passed to the linker.

> I'm not able to understand what '-mads' is for. Could any one please beief
> this?

From info gcc, but not really helpful:

-mads'
     On embedded PowerPC systems, assume that the startup module is
     called `crt0.o' and the standard C libraries are `libads.a' and
     `libc.a'.

This really means that the target board is a Motorola ADS board.

> Moreover, when I invoked the compiler and linker separately, linker issues
> error.
>
> powerpc-eabi-gcc -c test.c -> test.o is generated.
>
> I tried the following variant options for linker.
>
> powerpc-eabi-ld test.o
> powerpc-eabi-ld /path_to_startup/crt0.o test.o -lc
>
> All resulted in error as above.

Yes, you need to supply the target board library to the linker.

> what are all the extra options I should supply to linker? Or is it the
> problem in building of my tool chain?
> Can't the linker automatically look for standard libraries like libc.a,
> libm.c and the startup module crt0.o?

The linker does look for libc.a and libm.a.  But it can't know what
target board you want to execute on unless you tell it, so it doesn't
know which crt0.o to use.

> I used --target=powerpc-eabi to build my tool chain. Should I use specific
> target like powerpc-eabisim (for 
> simulator)?

Only if you want to run on the simulator.

> My target is an embedded PowerPC processor with non-linux OS running in
> big-endian mode.

If it is one of the boards supported by powerpc-eabi (look in "info gcc")
then you can specify the board name as "-m<name>".  If not, then you
need to create a BSP for that board which includes crt0.c, etc.  You
will likely need to create a linker script as well which describes
where various sections are loaded.


--
Michael Eager	 eager@eagercon.com
1960 Park Blvd., Palo Alto, CA 94306  650-325-8077