linux-kernel - Re: [PATCH 2/2 v2] perf tools: Enable bpf prologue for arm64

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Date:   Thu, 26 Jan 2017 16:31:22 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Will Deacon <will.deacon@....com>
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        He Kuang <hekuang@...wei.com>, peterz@...radead.org,
        mingo@...hat.com, alexander.shishkin@...ux.intel.com,
        jolsa@...hat.com, wangnan0@...wei.com, bintian.wang@...wei.com,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 2/2 v2] perf tools: Enable bpf prologue for arm64

Em Thu, Jan 26, 2017 at 04:52:12PM +0000, Will Deacon escreveu:
> On Thu, Jan 26, 2017 at 10:49:16AM +0900, Masami Hiramatsu wrote:
> > On Wed, 25 Jan 2017 13:32:01 +0000
> > Will Deacon <will.deacon@....com> wrote:
> > 
> > > On Wed, Jan 25, 2017 at 07:23:11AM +0000, He Kuang wrote:
> > > > Since HAVE_KPROBES can be enabled in arm64, this patch introduces
> > > > regs_query_register_offset() to convert register name to offset for
> > > > arm64, so the BPF prologue feature is ready to use.
> > > > 
> > > > This patch also changes the 'dwarfnum' to 'offset' in register table,
> > > > so the related functions are consistent with x86.
> > > 
> > > Wouldn't it be an awful lot simpler just to leave the code as-is, and
> > > implement regs_query_register_offset in the same way that we implement
> > > get_arch_regstr but return the dwarfnum?
> > 
> > No, since the offset is not same as dwarfnum.
> > 
> > With this style, the index of array becomes the dwarfnum (the index of
> > each register defined by DWARF) and the "offset" member means the
> > byte-offset of the register in (user_)pt_regs. Those should be different.
> 
> Ok, then do it as two patches then, rather than introduce functionality
> along with the renaming.
> 
> > > I don't really see the point of all the refactoring.
> > 
> > Also, from the maintenance point of view, this rewrite work makes
> > the code simply similar to x86 implementation, that will be easier to
> > maintain :)
> 
> Right, apart from the two howling bugs in the version that was nearly merged
> initially :p. I tend to err on the "if it ain't broke, don't fix it" side
> of the argument but if you really want the refactoring lets keep it as a
> separate change.

So, He, can you do that? How do we proceed?

- Arnaldo