[dpdk-dev] [PATCH] bpf: fix to allow ptr stack program type

[Jerin Jacob Kollanukkaran]

> -----Original Message-----
> From: Ananyev, Konstantin <konstantin.ananyev at intel.com>
> Sent: Monday, August 12, 2019 5:08 PM
> To: Jerin Jacob Kollanukkaran <jerinj at marvell.com>; dev at dpdk.org
> Cc: thomas at monjalon.net; stable at dpdk.org
> Subject: [EXT] RE: [dpdk-dev] [PATCH] bpf: fix to allow ptr stack program
> type
> 
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> 
> ----------------------------------------------------------------------
> 
> > > Hi Jerin,
> >
> > Hi Konstantin,
> >
> > >
> > > >
> > > > bpf_validate does not allow to execute RTE_BPF_ARG_PTR_STACK for
> > > > no reason.
> > >
> > > I believe there is a reason,
> > > ARG_PTR_STACK is reserved for memory within BPF program internal
> > > stack only.
> > > User that calls BPF program should never pass parameter with that type.
> >
> > OK.
> > Shouldn't we remove that from public header file
> > (lib/librte_bpf/rte_bpf.h) then ?
> 
> Probably... or might be just put extra comments to mark it as internal?
> The reason I left it here, so we can add new public values for enum here,
> before RTE_BPF_ARG_PTR_STACK.
> Of course in theory we can use for RTE_BPF_ARG_PTR_STACK some
> reserved value instead.
> 
> >
> > > If the user allocates parameter for bpf function on the stack, he
> > > can still use RTE_BPF_ARG_PTR for it.
> >
> > I see the _stack_ is only allocated under RTE_BPF_ARG_PTR_STACK checks
> in bpf_validate.c.
> > Can you check? I agree that stack should be allocated for
> RTE_BPF_ARG_PTR as well.
> 
> Not sure I understand your query here...
> Each BPF program can use up to MAX_BPF_STACK_SIZE bytes for stack.
> Though to avoid JIT to allocate unused space for the stack, in bpf_validate.c
> we figure out does given BPF program really allocate things on the stack and
> if yes, how many bytes is needed.
> This info is stored in rte_bpf.stack_sz and can be used later by the JIT.
> Let say for x86 jit is used in  emit_prolog().

I thought, stack will be allocated only when user gives
RTE_BPF_ARG_PTR_STACK.
I tested following program with RTE_BPF_ARG_PTR. It allocates stacks
Properly. So everything is good.

stdw [r10-64], 0xab
mov r0, 0
exit

I will modify this patch to following to avoid any confusion to user:
1) Change RTE_BPF_ARG_PTR_STACK to RTE_BPF_ARG_RESERVED in public header file
2) In the implementation #define RTE_BPF_ARG_RESERVED BPF_ARG_PTR_STACK

Is it OK?