Re: [PATCH] linux: add support for uname26 personality

[Florian Weimer <fweimer at redhat dot com>]

On 12/03/2015 09:32 PM, Aurelien Jarno wrote:

>>> +/* When the kernel is running under the uname26 personality (for programs
>>> +   that cannot handle "Linux 3.0"), it maps version 3.x to 2.6.40+x and
>>> +   4.x to 2.6.60+x.  We need to convert that back to the standard version
>>> +   numbering to be able to compare versions.  */
>>> +static int
>>> +convert_from_uname26 (int version)
>>> +{
>>> +  if ((version & 0xffff00) == 0x020600)
>>> +    {
>>> +      /* 2.6.40+x to 3.x */
>>> +      if ((version & 0xff) >= 60)
>>> +	version += 0x020000 - 60;
>>> +      /* 2.6.60+x to 4.x */
>>> +      else if ((version & 0xff) >= 40)
>>> +	version += 0x010000 - 40;
>>> +    }
>>> +
>>> +  return version;
>>> +}
>>
>> â this function will have to be changed again for Linux 5.0.
>>
>> A long-term solution would map the minimum required version hard-coded
>> into libc to its 2.6 equivalent, and check that if the kernel reports a
>> 2.6 version.  This is solves the forward compatibility issue because the
>> 2.6 mapping for the minimum version is known at the time glibc is compiled.
> 
> So you mean that we should have for example two defines in our code, one
> for the standard version and the other for the 2.6 version and that both
> would be defined at compilation time. Correct?

Essentially, yes.

> That still means we need to do the conversion at compile time to be able
> to define both values.

Or you could write the inverse function convert_from_uname26 as an
inline function or macro, and apply it to the (constant) minimum
version.  I don't have a preference in either direction.

Florian