netdev - Re: [PATCH RFC] sparc64: eBPF JIT

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Date:   Tue, 18 Apr 2017 15:57:09 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     David Miller <davem@...emloft.net>
Cc:     sparclinux@...r.kernel.org, netdev@...r.kernel.org, ast@...nel.org,
        daniel@...earbox.net
Subject: Re: [PATCH RFC] sparc64: eBPF JIT

On Tue, Apr 18, 2017 at 02:37:32PM -0400, David Miller wrote:
> From: Alexei Starovoitov <alexei.starovoitov@...il.com>
> Date: Mon, 17 Apr 2017 22:44:47 -0700
> 
> > The way llvm generates stack access is:
> > rX = r10
> > rX += imm
> > and that's the only thing verifier recognizes as valid ptr_to_stack.
> > Like rX -= imm will not be recognized as proper stack offset,
> > since llvm never does it.
> 
> That simplifies things significantly for me.
> 
> I only allow moves from the frame pointer to another register,
> and when I see that I rewrite it to "add FP, STACK_BIAS, DST_REG"

Sounds good to me. Alternative idea: can the above
'add FP, STACK_BIAS, one_of_local_regs' be done once in prologue
and that register used as substitue for R10 ?
(assuming non-leaf function)
I completely forgot by now how 2047 magic works.