Rask Ingemann Lambertsen <[EMAIL PROTECTED]> writes: > 4. Stack and argument passing. > > PicoBlaze has an internal call/return stack which can't be used for > passing arguments. How will the STACK_POINTER_REGNUM macro and the > "push<mode>" instruction pattern be specified?
For STACK_POINTER_REGNUM you just pick one of the general purpose registers and don't use it for anything else. You don't have to define the push<mode> instructions, so you don't. Instead you define ACCUMULATE_OUTGOING_ARGS. If you want some registers to be callee saved, which you probably do, then you hand generate the prologue and epilogue instructions; with the limited address space, you will probably want to jump to a library routine to do it. > Very simple. An address is taken from a register or an immediate. As an > "interesting" feature, function address can only be immediate values. I.e. > jump tables and function pointers can't be used. Note that the GCC Internals > documentation, says (in the section "Standard Pattern Names For > Generation"): Processors without jump to register indirect suck. If instructions and data are in the same address space, you can use self-modifying code. Making that both thread-safe and small is a pain, but you probably don't have to worry about threads. > The PicoBlaze has a program storage of at most 1024 instructions and a data > storage of 64 bytes. Is it really necessary and useful to port GCC to such a > target? 1024 instructions? That is small. Ian
