[llvm-dev] [iovisor-dev] [PATCH, BPF 1/5] BPF: Use a provisional ELF e_machine value
Daniel Borkmann via llvm-dev
llvm-dev at lists.llvm.org
Thu Jun 16 12:55:22 PDT 2016
On 06/16/2016 06:57 PM, Richard Henderson via iovisor-dev wrote:
> On 06/15/2016 10:14 PM, Alexei Starovoitov wrote:
>> On Wed, Jun 15, 2016 at 2:37 PM, Richard Henderson via iovisor-dev
>> <iovisor-dev at lists.iovisor.org> wrote:
>>> This same value for EM_BPF is being propagated to glibc,
>>> elfutils, and binutils.
>> Can you share the link to glibc and the other patches?
> I haven't sent one yet for binutils.
>>> + EM_BPF = 0xeb9f, // Linux kernel bpf virtual machine
Great, can that be assumed the final magic e_machine number for the ELF
header that eBPF loaders can check for as well then (I do like 0xeb9f ;))?
>> was this id reserved this with whoever managing the numbers ?
>> The only reason bpf backend used em_none is that we were couldn't
>> figure out who's responsible for keeping these records.
> No, it's an unofficial number. But there's history for this.
> In binutils there's a comment
> /* If it is necessary to assign new unofficial EM_* values, please pick large
> random numbers (0x8523, 0xa7f2, etc.) to minimize the chances of collision
> with official or non-GNU unofficial values.
> NOTE: Do not just increment the most recent number by one.
> Somebody else somewhere will do exactly the same thing, and you
> will have a collision. Instead, pick a random number.
> Normally, each entity or maintainer responsible for a machine with an
> unofficial e_machine number should eventually ask registry at sco.com for
> an officially blessed number to be added to the list above. */
> It used to take years to get sco to answer such emails.
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