linux-kernel - Re: [RFC PATCH v6 25/32] perf tools: Add 'bpf.' config section to perf default config

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Date:	Thu, 11 Jun 2015 23:50:40 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	"Wangnan (F)" <wangnan0@...wei.com>
Cc:	Alexei Starovoitov <ast@...mgrid.com>, acme@...nel.org,
	brendan.d.gregg@...il.com, daniel@...earbox.net,
	masami.hiramatsu.pt@...achi.com, paulus@...ba.org,
	a.p.zijlstra@...llo.nl, mingo@...hat.com, jolsa@...nel.org,
	dsahern@...il.com, linux-kernel@...r.kernel.org,
	lizefan@...wei.com, hekuang@...wei.com, xiakaixu@...wei.com,
	pi3orama@....com
Subject: Re: [RFC PATCH v6 25/32] perf tools: Add 'bpf.' config section to
 perf default config

On Thu, Jun 11, 2015 at 04:09:36PM +0800, Wangnan (F) wrote:
> On 2015/6/11 15:45, Namhyung Kim wrote:
> >On Tue, Jun 09, 2015 at 04:43:19PM -0700, Alexei Starovoitov wrote:
> >>On 6/8/15 10:50 PM, Wang Nan wrote:
> >>>perf_bpf_config() is added to parse 'bpf' section in perf config file.
> >>>Following is an example:
> >>>
> >>>  [bpf]
> >>>    clang-path = /llvm/bin/x86_64-linux-clang"
> >>>    llc-path = /llvm/bin/x86_64-linux-llc"
> >>>    clang-opt = "-nostdinc -isystem /llvm/lib/clang/include -I/kernel/arch/x86/include ..."
> >>>    llc-opt = ""
> >>a section to specify -I flags to compile prog.c is useful,
> >>but users shouldn't be populating it manually for kernel headers.
> >>How about adding a script that can figure out $(LINUXINCLUDE)
> >>automatically ?
> >Maybe a dummy question.  For what reason it needs such headers?  Is it
> >possible to have a (part of?) copy of needed bits in the perf source?
> >
> >Thanks,
> >Namhyung
> 
> It is improtant for eBPF script that it should be able to extract
> information
> from kernel pointers. For example: to extract registers from 'struct
> pt_regs' and
> to extract fields from 'struct page *'. I believe this is an improtant
> reason
> why we decide to use C-like language instead of designing a DLS. Therefore,
> when
> compiling .c to .o, kernel source is mandatory. Since we don't want to limit
> the
> ability of data accessing of eBPF scripts, we have to give it ability to
> access all
> kernel headers.

Understood, thank you for the explanation!
Namhyung
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