On Wed, Aug 05, 2015 at 04:59:01PM +0800, He Kuang wrote: > Hi, Alexei > > On 2015/7/30 1:13, Alexei Starovoitov wrote: > >On 7/29/15 2:38 AM, He Kuang wrote: > >>Hi, Alexei > >> > >>On 2015/7/28 10:18, Alexei Starovoitov wrote: > >>>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. > >>> > > Another thing about DW_AT_name, we've already found that the name > string is stored indirectly and needs relocation which is > architecture specific, while the e_machine info in bpf obj file > is "unknown", both objdump and libdw cannot parse DW_AT_name > correctly. > > Should we just use a known architeture for bpf object file > instead of "unknown"? If so, we can use the existing relocation > codes in libdw and get DIE name by simply invoking > dwarf_diename(). The drawback of this method is that, e.g. we > use "x86-64" instead, is hard to distinguish bpf obj file with > x86-64 elf file. Do you think this is ok?
The only clean way would be to register bpf as an architecture with elf standards committee. I have no idea who is doing that and how much such new e_machine registration may cost. So far using EM_NONE is a hack to avoid bureaucracy. Are dwarf relocation processor specific? Then simple hack to elfutils/libdw to treat EM_NONE as X64 should do the trick, right? If that indeed works, we can tweak bpf backend to use EM_X86_64, but then the danger that such .o file will be wrongly recognized by elf utils. imo it's safer to keep it as EM_NONE until real number is assigned, but even after it's assigned it will take time to propagate that value. So for now I would try to find a solution keeping EM_NONE hack. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/