Found the code, and it's actually part of python (as of 2.4).
Gentoo sets aliased to 1 when printing the system uname.
/usr/lib/python2.{4,5,6}/platform.py:

def _platform(*args):

   """ Helper to format the platform string in a filename
       compatible format e.g. "system-version-machine".
   """
   # Format the platform string
   platform = string.join(
       map(string.strip,
           filter(len,args)),
       '-')

   # Cleanup some possible filename obstacles...
   replace = string.replace
   platform = replace(platform,' ','_')
   platform = replace(platform,'/','-')
   platform = replace(platform,'\\','-')
   platform = replace(platform,':','-')
   platform = replace(platform,';','-')
   platform = replace(platform,'"','-')
   platform = replace(platform,'(','-')
   platform = replace(platform,')','-')

   # No need to report 'unknown' information...
   platform = replace(platform,'unknown','')

   # Fold '--'s and remove trailing '-'
   while 1:
       cleaned = replace(platform,'--','-')
       if cleaned == platform:
           break
       platform = cleaned
   while platform[-1] == '-':
       platform = platform[:-1]

   return platform

def platform(aliased=0, terse=0):

   """ Returns a single string identifying the underlying platform
       with as much useful information as possible (but no more :).

       The output is intended to be human readable rather than
       machine parseable. It may look different on different
       platforms and this is intended.

       If "aliased" is true, the function will use aliases for
       various platforms that report system names which differ from
       their common names, e.g. SunOS will be reported as
       Solaris. The system_alias() function is used to implement
       this.

       Setting terse to true causes the function to return only the
       absolute minimum information needed to identify the platform.

   """
   result = _platform_cache.get((aliased, terse), None)
   if result is not None:
       return result

   # Get uname information and then apply platform specific cosmetics
   # to it...
   system,node,release,version,machine,processor = uname()
   if machine == processor:
       processor = ''
   if aliased:
       system,release,version = system_alias(system,release,version)

   if system == 'Windows':
       # MS platforms
       rel,vers,csd,ptype = win32_ver(version)
       if terse:
           platform = _platform(system,release)
       else:
           platform = _platform(system,release,version,csd)

   elif system in ('Linux',):
       # Linux based systems
       distname,distversion,distid = dist('')
       if distname and not terse:
           platform = _platform(system,release,machine,processor,
                                'with',
                                distname,distversion,distid)
       else:
           # If the distribution name is unknown check for libc vs. glibc
           libcname,libcversion = libc_ver(sys.executable)
           platform = _platform(system,release,machine,processor,
                                'with',
                                libcname+libcversion)
   elif system == 'Java':
       # Java platforms
       r,v,vminfo,(os_name,os_version,os_arch) = java_ver()
       if terse:
           platform = _platform(system,release,version)
       else:
           platform = _platform(system,release,version,
                                'on',
                                os_name,os_version,os_arch)

   elif system == 'MacOS':
       # MacOS platforms
       if terse:
           platform = _platform(system,release)
       else:
           platform = _platform(system,release,machine)

   else:
       # Generic handler
       if terse:
           platform = _platform(system,release)
       else:
           bits,linkage = architecture(sys.executable)
           platform = _platform(system,release,machine,processor,bits,linkage)

   _platform_cache[(aliased, terse)] = platform
   return platform


Proof: run /usr/lib/python2.{4,5,6}/platform.py
aliased and terse have no effect wrt output (kernel_version-with-libc_version)

--
Andrey Vul

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