Re: Setting up crt0 and libs for arm-unknown-coff

[Richard Earnshaw <rearnsha at arm dot com>]

> I am trying to build a cross-gcc/newlib environment for an 
> arm-unknown-coff target on a linux host.
> 
> I am following the Cross-GCC FAQ using GCC 2.95.2, binutils 
> 2.9.1, and newlib 1.8.2.  First, I run the one-tree-1.6.sh
> script.  Then I edit newlib-1.8.2/newlib/configure.host and
> comment out both ARM_RDP_MONITOR and ARM_RDI_MONITOR since
> I am not using those tools.  Next, I run the build script:
> build-cross.sh arm-unknown-coff.  Finally, I su-root and
> install.
> 
> The target is an ARM4 architecture StrongARM core inside an 
> Intel/LevelOne IXP1200 network processor.
> 
> I am at the point where I can compile and run a program
> which prints "Hello, World" over the serial line using the
> UART.  I now want to get the libraries setup so that I 
> can use "printf".
> 
> I know I need to create a new (or modify an old) crt0.S file. 
> I also know I need to hook my UART routines into read() and 
> write().
> 
> Here are some observations which may or may not help isolate 
> the remaining things I need to do:
> 
> 1. The first few lines of output from the build-cross.sh
>    script are troubling:
>       ./build-cross.sh: started Mon May  8 15:38:54 EDT 2000
>       ./build-cross.sh: configure for arm-unknown-coff.
>       Configuring for a i686-pc-linux-gnu host.
>       *** This configuration is not supported in the following
>       subdirectories:
>            target-libgloss
>           (Any other directories should still work fine.)
>       Created "Makefile" in /home/CrossGCC/b-arm-unknown-coff
> 
>    Is this a problem?  Do I need to modify the configuration
>    files so that libgloss can be made?
> 

This shouldn't be a problem.  I don't think you need anything from 
libgloss.


> 
> 2. When I compile an empty main() program, I get a couple of
>    errors:
>       $ cat main.c
>       int main(void) { return 0; }
>       $ arm-unknown-coff-gcc -I. -mcpu=strongarm110 -mapcs-32
>         -mno-sched-prolog -fvolatile -fno-builtin -Wall
>         -Wstrict-prototypes -O2 -c main.c -o main.o
>       $ arm-unknown-coff-ld -o main.coff main.o -X -N
>         -Ttext 00001000 -lc
>       arm-unknown-coff-ld: warning: cannot find entry symbol
>       _start; defaulting to 00001000
>       main.o(.text+0xc):fake: undefined reference to `__gccmain'
> 
>    Where should __gccmain be resolved?  In crt0.o or a library?
>    What type of object is it?  (Or, is there a way to prevent
>    it from being generated if that is more appropriate?)
> 

It's normally better to use gcc to do your linking (at least until you 
really need to control the linker in a much finer manner).  In this case, 
you need to add gcc's runtime support library (libgcc); but gcc will add 
that automatically.

Try:
   arm-unknown-coff-gcc -o main.coff main.o

adding -v to the above will force gcc to show you the command line that it 
passes to the linker.

> 
> 3. When I compile the traditional "Hello, World" program, I get
>    the above errors plus a slew of undefined references:
>       $ cat hw.c
>       #include <stdio.h>
>       int main(void) { printf("Hello, World\n"); return 0; }
> 
>       $ arm-unknown-coff-gcc -I. -mcpu=strongarm110 -mapcs-32
>         -mno-sched-prolog -fvolatile -fno-builtin -Wall
>         -Wstrict-prototypes -O2 -c hw.c -o hw.o
>       $ arm-unknown-coff-ld -o hw2.coff hw2.o -X -N
>         -Ttext 00001000 -lc
>       arm-unknown-coff-ld: warning: cannot find entry symbol
>       _start; defaulting to 00001000
>       /usr/xcc/arm/arm-unknown-coff/lib/libc.a(vfprintf.o):
>       In function `vfprintf_r': /home/CrossGCC/b-arm-unknown-coff/
>       arm-unknown-coff/newlib/libc/stdio/../../../../../src/newlib/
>       libc/stdio/vfprintf.c:565: undefined reference to `__ltdf2'
>       /home/CrossGCC/b-arm-unknown-coff/arm-unknown-coff/newlib/
>       libc/stdio/../../../../../src/newlib/libc/stdio/vfprintf.c:721:
>       undefined reference to `__umodsi3'
>       /home/CrossGCC/b-arm-unknown-coff/arm-unknown-coff/newlib/
>       libc/stdio/../../../../../src/newlib/libc/stdio/vfprintf.c:722:
>       undefined reference to `__udivsi3'
>       [...remainder deleted...]
> 
>    This looks like it is related the common difficulty addressed in
>    the CrossGCC FAQ: http://www.objsw.com/CrossGCC/FAQ-5.html#ss5.4
>    While I can stub out system library calls, I'll still need to
>    provide real versions of __ltdf2, __umodsi3, __udivsi3, ...
>    I assume these routines are either in newlib (which may have been
>    built incorrectly), or in libgloss (which didn't get built).

Same answer as above.

R.



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