linux-kernel - Re: [PATCH 11/13] perf bpf: Add helper header files

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Message-ID: <20180312223234.GB14525@krava>
Date:   Mon, 12 Mar 2018 23:32:34 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Jiri Olsa <jolsa@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        David Ahern <dsahern@...il.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Daniel Borkmann <daniel@...earbox.net>,
        Wangnan <wangnan0@...wei.com>
Subject: Re: [PATCH 11/13] perf bpf: Add helper header files

On Mon, Mar 12, 2018 at 04:25:51PM -0300, Arnaldo Carvalho de Melo wrote:

SNIP

> > 
> > right, I kept this way, because it was already there for kernel,
> > so it was fast to write ;-)
> > 
> > but it's true we could leave it symbol based and have some sort of
> > dynamic loader behaviour.. but we'd need to sort out passing the
> > arguments in some generic form.. I'll check on that
> 
> Does this answer it or am I missing something?
> 
> Documentation/bpf/bpf_design_QA.txt
> 
> Q: Is BPF a generic virtual machine ?
> A: NO.
> 
> BPF is generic instruction set _with_ C calling convention.
> 
> Q: Why C calling convention was chosen?
> A: Because BPF programs are designed to run in the linux kernel
>    which is written in C, hence BPF defines instruction set compatible
>    with two most used architectures x64 and arm64 (and takes into
>    consideration important quirks of other architectures) and
>    defines calling convention that is compatible with C calling
>    convention of the linux kernel on those architectures.

hm right, but still we interpret the calls.. so we have to call
the function at the end

jirka