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

Alexei Starovoitov <ast@xxxxxx> · Mon, 1 May 2017 20:14:57 -0700

On 5/1/17 8:03 PM, David Miller wrote:

From: Alexei Starovoitov <ast@xxxxxx>
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@localhost 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@localhost 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?

it certainly does and on bpf backend side I'm not doing
anything special comparing to what other bi-endian architectures
like ppc and mips are doing. Obviously I missed something.