Re: [PATCH] year2038: support glibc 2.34 _TIME_BITS=64

[Paul Eggert <eggert@cs.ucla.edu>]

On 7/5/21 7:32 AM, Florian Weimer wrote:

> I assume GNU clisp (at least in a full build) need to link to some
> system libraries which are not dual ABI (and probably never will be).
> If gnulib forces the use of time64 mode, then it creates a push towards
> time64 mode in those libraries, too.

Only in libraries that expose time_t (or time_t-dependent types like 
struct timespec and struct stat) directly to their users, right? For 
example, libselinux is unaffected by this issue even though it calls 
'lstat' internally, because its user-side ABI is unaffected by time_t width.

I take your point, though, that there will be a hassle with libraries 
whose user-side ABIs depend on time_t width. I expect distros will 
migrate these libraries and their users to _TIME_BITS=64 in an 
all-or-nothing way.

But again, this is not strictly a Gnulib issue. Apps like Coreutils 
should be fine even with the new Gnulib, as Coreutils doesn't use any of 
the problematic libraries. Conversely, apps that '#define _TIME_BITS 64' 
directly and use GLib (or whatever) can have the problem, even if they 
don't use Gnulib.

> It is not, gnulib is pushing things in one particular direction, a
> direction that not everyone working on the GNU toolchain agrees with.

That's OK; we needn't have universal agreement on this point, which is a 
good thing because it'd be impractical to insist on universal agreement. 
  There is a way to build with 32-bit time_t even in Gnulib-using apps, 
so distros wanting to stick with 32-bit time_t can build Gnulib-using 
apps with the appropriate flags so that they're still living in the 
32-bit time_t world for now.

> There are some major differences to _FILE_OFFSET_BITS=64:
> 
> There weren't 20+ years of backwards compatibility in 2005

Not on Linux-based platforms of course, but there were on BSD-based 
platforms with 20+ years of backwards compatibility back then (SunOS 
comes to mind). Admittedly there were fewer computers back then but the 
compatibility issues were quite extensive.

> 64-bit file offsets enabled real use cases. 

Designing devices now, that will be used past 2038, is a real use case.