Re: problem with initializing ppc-eabi r13 (sdata)

["Kulpinski, Jay" <Jay dot Kulpinski at gd-ais dot com>]

You want to use the address of _SDA_BASE_, not the contents.  In C,
it would look like this:

    int main(int argc, char **argv) {
        extern void _SDA_BASE_;
        printf("_SDA_BASE_ = 0x%08x\n", (int) &_SDA_BASE_);
        exit(0);
    }

In your _start, you can try this to set r13 = _SDA_BASE_:

    lis  13,_SDA_BASE_@ha
    addi 13,13,_SDA_BASE_@l

On Friday 20 September 2002 10:35 am, mwette@grover.jpl.nasa.gov wrote:
> I am looking for insight/help in working with the GNU loader.  I am
> trying to work with my own versions of startup code, etc to understand
> how _start, _eabi, main, crt0, ... all work together.  I am using
> gcc-2.95.3, binutils-2.12.1, gdb-5.2, all compiled on suse-linux 7.2
> for target powerpc-eabi.  I am running against the (psim) simulator
> in gdb via "run -e bug".
>
> Here is the problem.  I want to initialize r13 with the address of the
> start of .sdata segment.  If I look in the map file that is generated
> by the loader, this address, given by _SDA_BASE_, is 0xa5a8.  When I
> copy _SDA_BASE_ to "v1" and print it out from the program I get 0x125a8.
> Bitwise these are
>
> 	0xa5a8		0000 0000 0000 0000 1010 0101 1010 0100
> 	0x125a8		0000 0000 0000 0001 0010 0101 1010 0100
>                                           ^ ^
> Does anyone have a clue what is going on here and what I might be going
> wrong?   Any help would be appreciated.  Relevant snippets of code
> included below.
>
> Thanks,
> Matt
>
>
> --- run ---
>
> 	albacore$ powerpc-eabi-run -e bug load4
> 	v1=0x125a8 (_SDA_BASE_)
>
>
> --- load4.map ---
>
> .sdata          0x0000a5a8      0x120
>                 0x0000a5a8                PROVIDE (__sda_base, .)
>                 0x0000a5a8                __sdata_start = .
>
>
> --- main.c ---
>
> 	unsigned long v1;
>
> 	printf("v1=0x%x (_SDA_BASE_)\n", v1);
>
>
> --- Makefile ---
> load4: main.o kos.o kos1.o kos0.o kos_i.o kos_n.o kos4b.ld
>         powerpc-eabi-ld -o load4 \
>                 -M >load4.map \
>                 -g -N -Bstatic -T kos4b.ld \
>                 -L/usr/local/powerpc-eabi/lib \
>                 kos_i.o \
>                 main.o kos.o kos1.o kos0.o \
>                 -lucos1 --start-group -lmvme -lc --end-group \
>                 kos_n.o
>
>
> --- kos_i.S ---
>
> 	.section ".sdata","aw"
> 	.weak	_SDA_BASE_
> 	.type	_SDA_BASE_,@object
> _SDA_BASE_:
>
>
> --- kos1.S (startup code) ---
>
> 	.section ".got"
> 	.align 2
> .LCTOC1 = .
> .Ltable = .-.LCTOC1
> .Lsda   = .-.LCTOC1
> 	.long	_SDA_BASE_
>
> _start:
> 	...
> 	.extern v1
> 	lwz	%r7,.Lsda(%r5)
> 	lis	%r6,v1@ha
> 	stw	%r7,v1@l(%r6)
>
>
> --- kos4b.ld ---
>
> PHDRS
> {
>   headers PT_PHDR FILEHDR PHDRS ;
>   text PT_LOAD ;			/* text */
>   data PT_LOAD ;			/* data */
> }
>
> SECTIONS
> {
>   .text :
>   {
>     . = 0x0000;
>     kos0.o(.text)
>     . = 0x3000;
>     kos1.o(.text)
>     kos.o(.text)
>     *(.text)
>   } :text =0
>   PROVIDE (__etext = .); PROVIDE (_etext = .); PROVIDE (etext = .);
>   .sdata : {
>     PROVIDE(__sda_base = . );
>     __sdata_start = . ;
>     *(.sdata)
>     __sdata_end = . ;
>     kos*(.sbss)
>     *(.sbss)
>   } :data = 0
>   ...
>
>
>
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