Re: [PATCH v2 bpf-next 03/17] bpf: Introduce BPF trampoline

On Nov 7, 2019, at 3:09 PM, Alexei Starovoitov [off-list ref] wrote:

On Thu, Nov 07, 2019 at 11:07:21PM +0000, Song Liu wrote:

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+static int bpf_trampoline_update(struct bpf_prog *prog)

Seems argument "prog" is not used at all? 

like one below ? ;)

e... I was really dumb... sorry..

Maybe we should just pass the tr in? 

that would be imbalanced.

Hmm.. what do you mean by imbalanced?

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+{
+	struct bpf_trampoline *tr = prog->aux->trampoline;
+	void *old_image = tr->image + ((tr->selector + 1) & 1) * PAGE_SIZE/2;
+	void *new_image = tr->image + (tr->selector & 1) * PAGE_SIZE/2;
+	if (err)
+		goto out;
+	tr->selector++;

Shall we do selector-- for unlink?

It's a bit flip. I think it would be more confusing with --

Right.. Maybe should use int instead of u64 for selector? 

No, since int can overflow.

I guess it is OK to overflow, no?