Re: touch and utimens troubles on new/old software combinations

[Bob Proulx]

Daniel Jacobowitz wrote:
> Bob Proulx wrote:
> > Most common systems only support backward compatibility.  I have not
> > heard of a system which supported forward compatibility.
> > 
> > In other words, compiling on a platform usually results in an
> > executable that only runs on that version or later of components of
> > the system and not usually older versions.  That has always been true
> > of unix-like systems.  Sometimes it happens to work anyway simply by
> > the happy chance that nothing in the call graph changed.  But it isn't
> > generally possible when new interfaces are added to the system.
> 
> FYI, this is not how glibc handles kernel headers, and that's worked
> fine for many years.  You compile against the newest version you would
> like to take advantage of, and specify the oldest version to be
> supported separately.

I don't understand and would appreciate clarification.  Are you saying
that this is how glibc is compiled?  Or are you saying this is how
programs are compiled against glibc?

For example I compile hello.c into a hello program.  How do I specify
an older version of libc that I want the program to use so that it can
run on older systems?  If my hello.c program uses new interfaces
introduced in glibc X.Y how does this program function when linked
with a glibc prior to the introduction of the interface?

I am really surprised that you tell me that this works with glibc (it
does not work on traditional Unix systems such as say HP-UX) and I am
very interested to know how this is accomplished with glibc.

Bob