No custom board, it's the tm4c1294-launchpad. Seems no general problem with heap allocation, so I guess it's not in the linker script, it's rather directly linked to the usage of the elf- binary loader, and there are only two configs in the nuttx repo which use the CONFIG_ELF stuff.
That part has 256Kb of SRAM. That is more that many, but it could be that you are using too much SRAM and just cannot run ELF reliably. It does want a lot of SRAM.
