linux-kernel - Re: [RFC PATCH v3 06/37] bpf tools: Introduce 'bpf' library to tools

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Date:	Thu, 21 May 2015 15:10:23 +0800
From:	"Wangnan (F)" <wangnan0@...wei.com>
To:	Alexei Starovoitov <ast@...mgrid.com>, <paulus@...ba.org>,
	<a.p.zijlstra@...llo.nl>, <mingo@...hat.com>, <acme@...nel.org>,
	<namhyung@...nel.org>, <jolsa@...nel.org>, <dsahern@...il.com>,
	<daniel@...earbox.net>, <brendan.d.gregg@...il.com>,
	<masami.hiramatsu.pt@...achi.com>
CC:	<lizefan@...wei.com>, <linux-kernel@...r.kernel.org>,
	<pi3orama@....com>
Subject: Re: [RFC PATCH v3 06/37] bpf tools: Introduce 'bpf' library to tools



在 2015/5/19 1:35, Alexei Starovoitov 写道:
> On 5/17/15 3:56 AM, Wang Nan wrote:
>> This is the first patch of libbpf. The goal of libbpf is to create a
>> standard way for accessing eBPF object files. This patch creates
>> Makefile and Build for it, allows 'make' to build libbpf.a and
>> libbpf.so, 'make install' to put them into proper directories.
>> Most part of Makefile is borrowed from traceevent. Before building,
>> it checks the existance of libelf in Makefile, and deny to build if
>> not found. Instead of throw an error if libelf not found, the error
>> raises in a phony target "elfdep". This design is to ensure
>> 'make clean' still workable even if libelf is not found.
>>
>> Signed-off-by: Wang Nan <wangnan0@...wei.com>
>> ---
> ...
>> +
>> +# Version of eBPF elf file
>> +FILE_VERSION = 1
>
> what that comment suppose to mean?
>
>> +# Makefiles suck: This macro sets a default value of $(2) for the
>> +# variable named by $(1), unless the variable has been set by
>> +# environment or command line. This is necessary for CC and AR
>> +# because make sets default values, so the simpler ?= approach
>> +# won't work as expected.
>
> what this for? copy-paste?
>
>> +# Allow setting CC and AR, or setting CROSS_COMPILE as a prefix.
>> +$(call allow-override,CC,$(CROSS_COMPILE)gcc)
>> +$(call allow-override,AR,$(CROSS_COMPILE)ar)
>
> was cross-compile tested or just copy-pasted?
>

Cross compiling is tested on aarch64.

>> +EXT = -std=gnu99
>
> I guess it was copy-pasted from libtraceevent, but please double
> check that it's actually needed.
>

Will remove.

>> +# Append required CFLAGS
>> +override CFLAGS += -fPIC
>> +override CFLAGS += $(INCLUDES)
>> +override CFLAGS += -D_GNU_SOURCE
>
> _GNU_SOURCE actually needed?
> Please sanitize the file.
>
>> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
>> new file mode 100644
>> index 0000000..bebe99a
>> --- /dev/null
>> +++ b/tools/lib/bpf/libbpf.c
>> @@ -0,0 +1,15 @@
>> +/*
>> + * common eBPF ELF loading operations.
>> + *
>> + * Copyright (C) 2015, Wang Nan <wangnan0@...wei.com>
>> + * Copyright (C) 2015, Huawei Inc.
>
> since it borrows heavily from samples/bpf/bpf_load.c, libbpf.h
> would be nice if you mention the source and/or copyright in the header.
>

Will change. Could you please provide copyright information so I can add 
it here?

>> + *
>> + * Released under the GPL v2. (and only v2, not any later version)
>> + */
>
> are you sure about this restriction? libtracevent is LGPL, for example.
>

Will change.

Thank you.


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