Re: [Lightning] Code patching, context switching

[Paolo Bonzini]

> For instance,
> on every pusharg, increment the last allocated register by one, then
> wrap once you reach JIT_R_NUM, and push JIT_R(0) on the stack.

Are we talking about the same pusharg? :-)

> Pusharg
> can even accept an additional parameter as a hint (like C's 'register'
> storage class), to help it determine whether to allocate it to a
> register, or push it on the stack.

Whether an argument goes in a register or on the stack is mandated by 
the ABI.

> The low-level API then exposes the full register set for those who
> actually want to generate their own code.

There is already a kind of low-level ABI.  What I could do would be to 
provide a JIT_ALL_REGS_NUM macro, a jit_all_regs[] array, and three 
macros (e.g. JIT_IS_REG_CALLER_SAVE, JIT_IS_REG_CALLEE_SAVE, 
JIT_IS_REG_RESERVED) to tell you whether a register is caller save, 
callee save or reserved for use by lightning macros.  I'd prefer if you 
wrote the patch though. :-)

Paolo