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

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Date:	Mon, 18 May 2015 10:35:23 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	Wang Nan <wangnan0@...wei.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

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?

> +EXT = -std=gnu99

I guess it was copy-pasted from libtraceevent, but please double
check that it's actually needed.

> +# 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.

> + *
> + * Released under the GPL v2. (and only v2, not any later version)
> + */

are you sure about this restriction? libtracevent is LGPL, for example.

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