[MODERATED] Re: [PATCH v2 1/2] v2: more sampling fun 1

On Wed, Feb 26, 2020 at 11:01:36PM +0100, speck for Thomas Gleixner wrote:
> speck for Andi Kleen <[email protected]> writes:
> 
> >> > > I implemented this in the way I did to avoid modifying x86_cpu_id as
> >> > > that structure is an exported ABI and any change would impact user mode
> >> > > code using the structure.
> >> > 
> >> > Exported ABI? Which usermode code uses this? The module loading tools?
> >> 
> >> Yeah, Andi pointed it out to me on an internal review.  I don't know what tool
> >> is using it.
> >
> > Yes it's modprobe to find which module to load.
> >
> > All of mod_devicetable.h is ABI
> 
> That's simply not true.
> 
> mod_devicetable.h is a kernel internal header which gets analyzed by the
> kernel internal tool modpost which uses this header to generate the
> ALIAS entries in the .modinfo section of the .ko elf file.
> 
> The ALIAS entries are user space ABI but not the header file.

To be pedantic, it's a string sent to userspace, _but_ not really an ABI
as it depeneds entirely on the kernel that is running at the time.  It's
only used to pass back into a tool like modprobe to try to figure out
what module to load for that specific kernel.

So that string can change structure, with no side affects at all as it
is explicitly tied to that kernel version anyway.

thanks,

greg k-h