Memory Configurations

The new method for configuring memory is not super easy or intuitive so at least some explanation is needed. If you have any trouble, please make an issue so I can know what people might be getting stuck on.

A default config would look like:

name = Default
ident = Default_
.text = 0x400000-0x10000000
.data = 0x10000000-0x10040000
heap = 0x10040000-0x30000000
stack = 0x60000000-0x80000000
mmio = 0xffff0000-0xffffffff
gp_offset = 0x8000
extern_offset = 0x10000

name and ident may often be the same value, but there is a difference. name is what will be shown in the memory configuration list whereas ident is a unique identifier used internally.

.text and .data should be mostly self explanatory. The values are the ranges RARS will assign to the .text and .data sections. Notably, RARS will not always have enough memory to have the entire range be valid; instead RARS will shorten the range by moving the upper bound down until it fits.

heap determines the range that the sbrk system call can allocate.

stack determines the area that the stack is valid in. Unlike other sections, the stack is shrunk by moving the lower bound up.

The mmio range generally should be small enough to directly fit into RARS memory.

gp_offset is the offset from the lower bound of .data that will be assigned to the gp register on normal program execution.

extern_offset is the amount of space that should be reserved for .extern variables in the start of .data. This could presumably be left off in the future, but for now the assembler of RARS requires some constant. The default start position when the .data directive is used is the lower bound of the .data range + extern_offset