netdev - Re: [PATCH v3 binutils] Add BPF support to binutils...

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Message-Id: <20170501.230323.816591707269395321.davem@davemloft.net>
Date:   Mon, 01 May 2017 23:03:23 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     ast@...com
Cc:     daniel@...earbox.net, aconole@...heb.org, netdev@...r.kernel.org,
        xdp-newbies@...r.kernel.org
Subject: Re: [PATCH v3 binutils] Add BPF support to binutils...

From: Alexei Starovoitov <ast@...com>
Date: Mon, 1 May 2017 19:49:21 -0700

> On 4/30/17 11:21 AM, David Miller wrote:
>> built with:
>>
>> 	clang -O2 -target bpfel -g -c x.c -o x.o
>>
>> readelf can see it just fine:
>>
>> [davem@...alhost binutils]$ ./readelf --debug-dump=loc ./xel.o
>> Contents of the .debug_loc section:
>>
>>     Offset   Begin            End              Expression
>>     00000000 0000000000000000 0000000000000010 (DW_OP_reg1 (r1))
>>     00000013 <End of list>
>>     00000023 0000000000000010 0000000000000020 (DW_OP_constu:
>>     590618314553; DW_OP_stack_value)
>>     0000003d 0000000000000020 0000000000000030 (DW_OP_reg1 (r1))
>>     00000050 <End of list>
>>
>> But with big-endian:
>>
>> [davem@...alhost binutils]$ ./readelf --debug-dump=loc ./xeb.o
>> readelf: Warning: Invalid pointer size (0) in compunit header, using 4
>> instead
>> readelf: Warning: Bogus end-of-siblings marker detected at offset 27
>> in .debug_info section
>> readelf: Warning: Bogus end-of-siblings marker detected at offset 28
>> in .debug_info section
>> readelf: Warning: DIE at offset 0x29 refers to abbreviation number 48
>> which does not exist
>> readelf: Warning: Unable to load/parse the .debug_info section, so
>> cannot interpret the .debug_loc section.
> 
> yeah. clang emitted dwarf for big-endian is broken.
> This dwarf stuff is too complicated for normal human beings.
> The tight packing making debugging it quite painful.

But doesn't the CLANG DWARF2 emission code look at the target
endianness?