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:	Thu, 23 Jul 2015 20:20:09 -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 7/23/15 1:49 PM, Alexei Starovoitov wrote:
> On 7/23/15 4:54 AM, He Kuang wrote:
>
> trimmed cc-list, since it's not related to kernel.
>
>> Thank you for your guidence, and by referencing your last mail
>> and other llvm backends, I found setting
>> BPFMCAsmInfo::SupportsDebugInformation = true in BPFMCAsmInfo.h
>
> thanks! yes. it was missing.
>
>> and fix some unhandeled switch can make llc output debug_info,
>
> what do you mean ?
>
>> but important information is missing in the result:
>
> hmm. I see slightly different picture.
> With 'clang -O2 -target bpf -g -S a.c'
> I see all the right info inside .s file.
> with '-c a.c' for some reasons it produces bogus offset:
>     Abbrev Offset: 0xffff0000
>     Pointer Size:  8
> /usr/local/bin/objdump: Warning: Debug info is corrupted, abbrev offset
> (ffff0000) is larger than abbrev section size (4b)
>
> and objdump fails to parse .o
> I'm using llvm trunk 3.8. Do you see this as well?

there were few issues related to relocations.
Fixed it up and pushed to llvm trunk r243087.
Please pull and give it a try.
AT_location should be correct, but AT_name still looks buggy.


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