linux-kernel - Re: [PATCHv2 0/7] eBPF JIT for PPC64

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Date:	Thu, 30 Jun 2016 16:02:54 +0530
From:	"Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:	Denis Kirjanov <kda@...ux-powerpc.org>
Cc:	Andreas Ziegler <andreas.ziegler@....de>,
	linuxppc-dev@...ts.ozlabs.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv2 0/7] eBPF JIT for PPC64

On 2016/06/30 12:34PM, Denis Kirjanov wrote:
> On 6/30/16, Andreas Ziegler <andreas.ziegler@....de> wrote:
> > Hi Naveen,
> >
> > this patchset makes a change to arch/powerpc/net/Makefile in order to only
> > compile the previously existing bpf_jit_comp.c if !CONFIG_PPC64, and use
> > bpf_jit_comp64.c if CONFIG_PPC64 is enabled.
> >
> > Inside arch/powerpc/net/bpf_jit_comp.c, however, there is still an #ifdef
> > CONFIG_PPC64 block at line 667 (linux-next of today, i.e., next-20160630):
> >
> >   #ifdef CONFIG_PPC64
> >                   /* Function descriptor nastiness: Address + TOC */
> >                   ((u64 *)image)[0] = (u64)code_base;
> >                   ((u64 *)image)[1] = local_paca->kernel_toc;
> >   #endif
> >
> > From my understanding of the code, this #ifdef can now be removed, as there
> > is
> > no way the file could be compiled with CONFIG_PPC64 enabled. Is this
> > correct?
> 
> That was used for running classic BPF on ppc64. With eBPF on ppc64 the
> whole block can be removed.

Yes, that can be removed and so can the many 64-bit related macros in 
bpf_jit32.h. The reason I didn't remove those just yet was so that we 
could easily try out the classic BPF JIT for ppc64 BE, for 
testing/performance comparison and so on. I think it would be good to 
retain this for one kernel release.

- Naveen