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

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Date:   Tue, 18 Apr 2017 14:37:32 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     alexei.starovoitov@...il.com
Cc:     sparclinux@...r.kernel.org, netdev@...r.kernel.org, ast@...nel.org,
        daniel@...earbox.net
Subject: Re: [PATCH RFC] sparc64: eBPF JIT

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"