Kernel Application Binary Interface (kABI) support in FreeBSD

[Julian Elischer]

On 7/21/15 2:02 PM, Venkat Duvvuru wrote:
> Yes, my question was about kernel module compatibililty with FreeBSD's
> major releases of a particular version.
> For example, will FreeBSD makes sure that the driver built on 10.0 version
> of Freebsd seamlessly load on all other 10.x versions of FreeBSD?
> Does it make sure that the symbols and their parameters are not blindly
> changed without considering the binary compatibility with other FreeBSD
> version binaries?
Our aim is that a module compiled on X.0 should be loadable on X.Y for 
all values of Y.
This is true for most of the subsystems that people expect to touch 
with modules.
i.e. the network stack, driver framework, IO paths, system call 
interfaces, scheduler exported calls.
and the structures  they use. Note, a module compiled on X.Y is not 
guaranteed (or expected) to run
on systems with smaller values of Y.

>
> RHEL kABI whitelist makes sure that once the symbol is added into the
> whitelist, it will never be changed during the major releases of that
> kernel.
>
>
> Thanks,
> Venkat.
>
> On Fri, Jul 17, 2015 at 8:29 PM, Allan Jude <allanjude at freebsd.org> wrote:
>
>> On 2015-07-17 10:47, Julian Elischer wrote:
>>> On 7/17/15 9:02 PM, Venkat Duvvuru wrote:
>>>> Hi,
>>>>
>>>> Is there kABI (Kabi-whitelist) equivalent feature in FreeBSD?
>>> well, yes and no.
>>>
>>> Firstly, FreeBSD maintains a backwards compatible kABI (with the
>>> exception of programs that hunt around in kernel memory).
>>> We also use symbol versioning on the libc. so depending on what you want
>>> to do. the answer may be useful to you or not.
>>> Basically any binary should continue to run on a newer kernel, even if
>>> the syscalls change, because we should still support the old abi.
>>>
>>> tell us more about what you need and we can be more specific.
>>>
>>> I have run Freebsd 1.1 binaries on a Freebsd 8  system, in fact I have
>>> done a system build in a freebsd 1.1 chroot on an 8 system.
>>> I haven't tried it on 9 or 10 but I'd expect it to work..
>>>
>>>
>>>>
>>>>
>>>> Thanks,
>>>>
>>>> Venkat.
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>>
>> I think the question related to drivers (kernel modules).
>>
>> In which case, they should be compatible across major versions (module
>> from 10.0 works in 10.2, but not 9.3 or 11.0)
>>
>> --
>> Allan Jude
>>
>>
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