CCS linker won't allow data segment or heap bigger than 0x20000 bytes?

I'm using Code Composer Studio 5.2.0.69 to build, load and run a simple C program on the A8 processor of a DM8148.  The program is intended to test changes to the timing parameters of the DDR3 RAM on a custom board.  To avoid testiing the caches instead of the RAM, I seem to have two choices - disable both L1 and L2 caches in software, which means I need to learn ARM assembler, or run the test over a range of memory addresses that's too big to fit in either cache.  I'm trying the second approach, which means the program must access a chunk of memory significantly bigger than the 512KB L2 cache.  I can't get the linker to build such a program.  I've tried both defining a global array of 1MB and allocating it from heap (using malloc() and the "--heap-size 0x100000" linker option).  Both result in linker errors like:

'Invoking: ARM Linker'

"C:/ti/ccsv5/tools/compiler/tms470_4.9.1/bin/cl470" -mv7A8 --code_state=32 --abi=eabi -me -g --define=dm8146 --define=dm8148 --diag_warning=225 --display_error_number -z --stack_size=0x800 -m"Memory_performance_test.map" --heap_size=0x100000 -i"C:/ti/ccsv5/tools/compiler/tms470_4.9.1/lib" -i"C:/ti/ccsv5/tools/compiler/tms470_4.9.1/include" --reread_libs --warn_sections --display_error_number --rom_model -o "Memory_performance_test.out"  "./ptr_rw.obj" -l"libc.a" "../DM8148.cmd"

<Linking>

"../DM8148.cmd", line 49: error #10099-D: run placement fails for object

   ".sysmem", size 0x100000 (page 0).  Available ranges:

   L3OCMC0      size: 0x20000      unused: 0x1a91b      max hole: 0x1a917  

How do I get the linker to allow a data segment or heap of a several megabytes?

Thanks!

- Dave Beal