linux-kernel - Re: llvm bpf debug info. Re: [RFC PATCH v4 3/3] bpf: Introduce function for outputing data to perf event

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Date:	Mon, 27 Jul 2015 19:18:45 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	He Kuang <hekuang@...wei.com>, "Wangnan (F)" <wangnan0@...wei.com>,
	pi3orama <pi3orama@....com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: llvm bpf debug info. Re: [RFC PATCH v4 3/3] bpf: Introduce
 function for outputing data to perf event

On 7/25/15 3:04 AM, He Kuang wrote:
> I noticed that for 64-bit elf format, the reloc sections have
> 'Addend' in the entry, but there's no 'Addend' info in bpf elf
> file(64bit). I think there must be something wrong in the process
> of .s -> .o, which related to 64bit/32bit. Anyway, we can parse out the
> AT_name now, DW_AT_LOCATION still missed and need your help.

looks like objdump/llvm-dwarfdump can only read known EM,
but that that shouldn't be the problem for your dwarf reader right?
It should be able to recognize id-s of ELF::R_X86_64_* relo used right?
As far as AT_location for testprog.c it seems there is no info for
local variables because they were optimized away.
With -O0 I see AT_location being emitted.
Also line number info seems to be good in both cases.
But in our case, we don't need this anyway, no? we need to see
the types of structs mainly or you have some other use cases?
I think line number info would be great to correlate the error reported
by verifier into specific line in C.

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