Re: New vs Old Kernel Headers

[Marco <marco at tampabay dot rr dot com>]

Mike Frysinger wrote:
> it depends on the libc.  if you're using glibc, then glibc comes with a 
> configure option where you tell it the oldest kernel version it can run on 
> (see the --enable-kernel configure option).  that way you can compile against 
> the very latest headers (2.6.25) while still having the C library work on 
> older versions (whatever given to --enable-kernel).
> -mike
>   
So after doing some posting & reading in various places, I've come to 
the following conclusions:                    

If you have an app that uses kernel interfaces directly (sys 
call,ioctl,etc) then the new app is *not* "guaranteed" to work on an old 
kernel.  On the other hand if you have the same/similar app, created 
using older kernel headers, that abi is "guaranteed" to work in a new 
kernel version (i.e. backward compatible, but not forward compatible)

In that end, if you have a toolchain/glibc built against newer kernel 
versions, then you must be careful that when building binaries that 
interface with the kernel directly, you must compile them against older 
kernel headers if you intend to run them on that older kernel.

Or to be safe, compile glibc against older kernel headers(as old as the 
oldest kernel you intend to run).  In that way, you don't have to worry 
about compiling certain against a different set of kernel headers, but 
just compile everything with the same ones you've compiled glibc with.  
This method does have the drawback if using a newer kernel, of not being 
able to have glibc use the latest features of that kernel.


Does this sound about right?


Thanks,

Marco Fonseca        

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