Embedded heap allocation?

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I've done a number of embedded ARM7 projects using ADS1.2 without much
trouble.  Now all of a sudden I can't get the heap to allocate correctly.

My entry.s code does some standard startup things like setting the stacks,
clocks, etc.  It ends by branching to __main as usual. When I make the first
call to malloc() looking for about 24Kbytes, it doesn't have enough space.
There should be 3 MB.  I am using a simple stackheap.s shown below.

__main calls _init_alloc to create the heap.   I have some old code that
shows that it puts the bottom of the heap in R0 and the bottom of the stack
in R1.  If I make a manual call to this with the values filled in I get a
3MB heap.  If I break on __main calling this, it has the bottom of heap in
both registers and I get no heap.

Anyone have any suggestions?


        AREA    stacks, DATA, NOINIT

        EXPORT top_of_stacks
        EXPORT  top_of_memory
; Physical location of our memory system

MEMORY_Limit    EQU     0x20400000

top_of_memory   equ     MEMORY_Limit
; = Total 4M SDRAM on Pixter2005 board,  end of memory is 0x003f, ffff
; We will mirror the memory 0x20000000 to 0x203fffff at 0x00000000 to
; with the MMU.  This is done so that we have a copy of the interrupt
vectors at
; 0x0 as required for the ARM
Stack_Limit     EQU     MEMORY_Limit - 0x100
SVC_Stack       EQU     Stack_Limit             ; = 0x400 bytes
ABT_Stack       EQU     SVC_Stack - 0x100       ; = 0x200 bytes
UNDEF_Stack     EQU     ABT_Stack - 0x100       ; = 0x200 bytes
IRQ_Stack       EQU     UNDEF_Stack - 0x100     ; = 0x200 bytes
FIQ_Stack       EQU     IRQ_Stack - 0x100       ; = 0x200

; Create dummy variable used to locate stacks in memory

top_of_stacks    SPACE   1

        AREA   heap, DATA, NOINIT

        EXPORT bottom_of_heap

; Create dummy variable used to locate bottom of heap

bottom_of_heap    SPACE   1


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