arm-elf-gcc problem

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Hi group,

I'm a newbie regarding the GNU ARM stuff.
After many trials with intensive studying of the manuals for the gnu
linker and assembler I have no more idea to solve the following problem:

I want to compile and link a very simple main.c with startup code and
linker script (see below my sample files, its for ARM7TDMI). The linker,
invoked by arm-elf-gcc, can't find the entry point symbol, which is
referenced in my linker script and defined in the startup code as
.global. The linker complains with:

arm-elf-gcc  -nostartfiles -Wl,
-Wl,--script=my_linker_script -Wl,-cref  cstartup.o main.o -o
warning: cannot find entry symbol __main; defaulting to 04000000

This is confusing because '__main' is defined as '.global' in the
startup file. Did I miss something in the makefile? Hope anybody can
give me hint.

Thanks in advance

The startup code fragment:

   .include "../at91lib_gnu/periph/arm7tdmi/"
   .include ""
    code entry point
/* Define "__main" to ensure that C runtime system is not linked */
            .global   __main
/* Exception vectors (before Remap) */


            B       InitReset       /* reset */
            B       undefvec        /* Undefined Instruction */
            B       swivec          /* Software Interrupt */
            B       pabtvec         /* Prefetch Abort */
            B       dabtvec         /* Data Abort */
            B       rsvdvec         /* reserved */
            B       irqvec          /* reserved */
            B       fiqvec          /* reserved */

/* EBI Initialization Data */

     .word   EBI_CSR_0
     .word   EBI_CSR_1
     .word   EBI_CSR_2
     .word   EBI_CSR_3
     .word   EBI_CSR_4
     .word   EBI_CSR_5
     .word   EBI_CSR_6
     .word   EBI_CSR_7
     .word   0x00000001  /* REMAP command */
     .word   0x00000006  /* memory regions, standard read */

     .word   EBI_BASE    /* EBI Base Address */

  The reset handler before Remap
  From here, the code is executed from SRAM address
  Exporting labels used in other files


   Load System EBI Base address and CSR0 Init Value

      ldr     r0, PtEBIBase
      ldr     r1, InitTableEBI

/*- Speed up code execution by disabling wait state on Chip Select 0*/

      str     r1, [r0]
      bl      __low_level_init

  ...and so on...

pretty simple main.c:
int main(void)
     int a,b;
     volatile int my_var;


     return 0;

my linker script:


    int_ram : org = 0x00000000, len = 8K    /* internal RAM */
    ram     : org = 0x04000000, len = 1024K  /* RAM at CS1 */

   .startup :

       } > int_ram

    .text :
       } > ram

    .data :
       } > ram

     .bss :
          *(.bss) *(COMMON);
       } > ram

my makefile:

CC = arm-elf-gcc
AS = arm-elf-as

INC += -I ../at91lib_gnu

ASM.FILES += cstartup.S

ASM.FLAGS += -mthumb-interwork
ASM.FLAGS += -mcpu=arm7tdmi
ASM.FLAGS += -gstabs

C.FILES = main.c

C.FLAGS += -c
C.FLAGS += -g
C.FLAGS += -mcpu=arm7tdmi
C.FLAGS += -mthumb-interwork

L.FLAGS += -nostartfiles
L.FLAGS += -Wl,
L.FLAGS += -Wl,--script=my_linker_script
L.FLAGS += -Wl,-cref

OBJ += $(patsubst %.S,%.o,$(ASM.FILES))
OBJ += $(patsubst %.c,%.o,$(C.FILES))

%.o : %.S  makefile
         $(AS) $(INC) $(ASM.FLAGS) $< -o $@

%.o : %.c  makefile
         $(CC) $(INC) $(C.FLAGS) $< -o $@

all: $(OBJ)

exec: $(OBJ)    
         $(CC) $(L.FLAGS) $(OBJ) -o main.elf

         rm *.o
         rm *.elf
         rm *.map


Re: arm-elf-gcc problem
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 Where did you get this script file?

 For these kind of issues, I'd recommend you to join the GNUARM
mailing list: /


 pbleyer2004    /"Reliable software must kill people reliably."
We've slightly trimmed the long signature. Click to see the full one.
Re: arm-elf-gcc problem
Thanks for the reply, Pablo.

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Something wrong with that? Maybe my linker script is the reason that ld
couldn't find the global symbols?
This is my first try to write an own GNU linker script but I'm not sure
whether I catched all the syntax in the right way. I oriented towards
example scripts. I worked before with the ADS tools and, IMHO, the
scatter file syntax of the ADS stuff is more descriptive than the GNU
syntax. However, GNU is for free :-).

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Thanks for that hint. Did this a few minutes ago...


Re: arm-elf-gcc problem
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 Yes. Please read the SECTIONS command topic in the linker manual, . If you are going to link for ELF you
should be aware about how section names map for ELF objects. Also if
you put the object name in a section without specifying the
subsection, all the subsections will be inserted there. This is
usually a mistake.

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 I guess most linker script syntaxes from all the providers are
homeomorphisms between themselves, it just takes a while to know the
permutations right ;^)


Re: arm-elf-gcc problem
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Yes, got it before. I found some other examples and made some successful
steps already. However, I should take this manual at home this weekend
to read it once again slowly. But, I've less hope to get the time for
that this weekend because of my five-months-old daughter :-)))

Thanks again for the tips

Re: arm-elf-gcc problem
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You could start by looking at the object file headers with objdump
to see which sections are present in the compiled modules.

AFAIK, your script is missing many crucial ELF sections.

Are you targeting to have an ELF run-file or is the ultimate target
a binary memory image to run stand-alone? Please note that an ELF
file needs a pretty complicated loader to get it in.

Tauno Voipio
tauno voipio @ iki fi

Re: arm-elf-gcc problem

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My first step is to try to make it run in the insight gdb simulator. The
next step should be the download with our BDI2000 debugger to an
evaluation board with an AT91M55800. This should be done with a run-file
I think.

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I did some projects with the ADS tools before (with my own makefiles,
linker scripts etc. under cygwin). My programs ran successful from
external flash on the board I mentioned above. But, it seems a little
bit tough to port these former projects to the GNU environment. But I
realize that the essential point is to understand the syntax of the GNU
linker scripts in detail.


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