✘64-bit time_t on glibc 2.34 and up

[Gary E. Miller]

Yo Greg!

On Sun, 15 Jan 2023 09:42:06 -0500
Greg Troxel <gdt at lexort.com> wrote:

> > You can always build bad .o.  But good practice is to build all .o
> > in a program or binary with the same setting.  Otherwise a huge
> > number of ways to fail.  That is why all gpsd c files start with:
> >
> > #include "../include/gpsd_config.h"  // must be before all includes
> >  
> 
> I was asking about an installed library built one way, and a program
> built another.  It seems like they will have DT_NEEDED on two
> different libc versions, which will end up somewhere between erroring
> at start and UB.

Um, lost me.  The new _TIME_SIZE_BITS means only one libc is needed.
You keep thinking it needs two.

> How are you going to manage building gpsd to match the time_t size
> choice made in dbus and libusb?

Don't need to. dbus can use whatever time_t it wants, different from the
one gpsd uses, as long as time_t is not passed as a binary between the
two.

gpsd does not pass binary time_t to either one.  Unless you can point
out somewhere I miised a bianry call?

gpsd passes dbus time as a double:

         DBUS_TYPE_DOUBLE, &dtime,

gpsd only uses libusb for the Garmin 18usb which only speaks native usd.
But the protocol is Garmin Binary.  No time_t anywhere.

> How is anyone else going to manage
> this in the world of individual compilation unit choice?

Linux has been doing this a long time.  Not my first choice, but
rare that glibc or Linus takes what I say seriously.  If you are sure
they are wrong, I'd love to watch you convince them the error of their
ways.  I'll get popcorn.

> The only
> paths I can see are
> 
>   a distribution choosing a setting for all programs

Like all the BSDs.  Except, they don't always.

>   setting up two hierarchies of lib/bin for building each way

And yet, the folks at glibc disagree, at least as far as time_t.

For other things, yes, my Gentoo has many separate /usr/lib depending on
all sorts of things.  All installed at the same time, and it just works.
Close to a dozen on one of my hosts.  Could be much more.

So it can be done, is very frequently done, but is irrelevant to the
gpsd issue at hand.

RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
	gem at rellim.com  Tel:+1 541 382 8588

	    Veritas liberabit vos. -- Quid est veritas?
    "If you can't measure it, you can't improve it." - Lord Kelvin
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