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Re: 32 bits time_t and Y2038 issue

From David Brown <david.brown@hesbynett.no>
Newsgroups comp.arch.embedded
Subject Re: 32 bits time_t and Y2038 issue
Date 2025-03-21 13:54 +0100
Organization A noiseless patient Spider
Message-ID <vrjnig$1hmmn$1@dont-email.me> (permalink)
References (3 earlier) <vrbado$2133a$1@dont-email.me> <vrbi79$2a30t$1@dont-email.me> <vrc74l$2133a$2@dont-email.me> <vrchj2$35fbp$1@dont-email.me> <slrnvtqbq4.566.news-1513678000@a-tuin.ms.intern>

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On 21/03/2025 10:20, Michael Schwingen wrote:
> On 2025-03-18, David Brown <david.brown@hesbynett.no> wrote:
>>
>> These days I happily use it on Windows with recursive make (done
>> /carefully/, as all recursive makes should be), automatic dependency
>> generation, multiple makefiles, automatic file discovery, parallel
>> builds, host-specific code (for things like the toolchain installation
>> directory), and all sorts of other bits and pieces.
> 
> I converted to the "recursive make considered harmful" group long ago.
> Having one makefile for the whole build makes it possible to have
> dependencies crossing directories, and gives better performance in parallel
> builds - with recursive make, the overhead for entering/exiting directories
> and waiting for sub-makes to finish piles up.  If a compile takes 30 minutes
> on a fast 16-cpu machine, that does make a difference.
> 
> using ninja instead of make works even better in such a scenario.
> 
> cu
> Michael

I fully agree with the points in "recursive make considered harmful", 
which I also read long ago.  But that does not mean that recursive make 
can't be used well - it just means you have to use it appropriately, and 
carefully.

In particular, using one "outer" make to run make on makefiles in 
different directories is asking for trouble - you can easily get 
dependencies wrong or miss cross-directory dependencies.  And it is 
often difficult to figure out what is happening if something fails in 
one of the builds.  And with older makes (from the days when that paper 
was written), there was no inter-make job server meaning you either had 
to give each submake too few parallel jobs (and thus wait for some to 
finish), or too many (and slow the system down).

The way I use recursive makes is /really/ recursive - the main make 
(typically split into a few include makefiles for convenience, but only 
one real make) handles everything, and it does some of that be calling 
/itself/ recursively.  It is quite common for me to build multiple 
program images from one set of source - perhaps for different variants 
of a board, with different features enabled, and so on.  So I might use 
"make prog=board_a" to build the image for board a, and "make 
prog=board_b" for board b.  Each build will be done in its own directory 
- builds/build_a or builds/build_b.  Often I will want to build for both 
boards - then I will do "make prog="board_a board_b"" (with a default 
setting for the most common images).

These different boards can require different settings for compiler 
flags, directories, and various other options.  Rather than having to 
track multiple sets of variables in the makefiles for when multiple 
board images are being handled within the one make, I have a far simpler 
solution - if there is more than one image being build, I simply spin 
off recursive makes for each build - thus after "make prog="board_a 
board_b"", I start "make prog=board_a" and "make prog=board_b".  Each 
make instance lives on its own, so I only need one set of flags at a 
time, compiling into one build directory - but they share a job server, 
and all the dependencies are correct.

It is not the only way to handle such things, but it is definitely a 
convenient and efficient method.

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Thread

32 bits time_t and Y2038 issue pozz <pozzugno@gmail.com> - 2025-03-11 16:22 +0100
  Re: 32 bits time_t and Y2038 issue David Brown <david.brown@hesbynett.no> - 2025-03-11 17:32 +0100
    Re: 32 bits time_t and Y2038 issue pozz <pozzugno@gmail.com> - 2025-03-11 23:21 +0100
      Re: 32 bits time_t and Y2038 issue David Brown <david.brown@hesbynett.no> - 2025-03-12 10:33 +0100
        Re: 32 bits time_t and Y2038 issue pozz <pozzugno@gmail.com> - 2025-03-12 16:48 +0100
          Re: 32 bits time_t and Y2038 issue David Brown <david.brown@hesbynett.no> - 2025-03-12 17:39 +0100
            Re: 32 bits time_t and Y2038 issue pozz <pozzugno@gmail.com> - 2025-03-12 18:13 +0100
              Re: 32 bits time_t and Y2038 issue David Brown <david.brown@hesbynett.no> - 2025-03-12 19:18 +0100
                Re: 32 bits time_t and Y2038 issue pozz <pozzugno@gmail.com> - 2025-03-13 09:57 +0100
                Re: 32 bits time_t and Y2038 issue David Brown <david.brown@hesbynett.no> - 2025-03-13 16:51 +0100
                Re: 32 bits time_t and Y2038 issue pozz <pozzugno@gmail.com> - 2025-03-14 13:27 +0100
                Re: 32 bits time_t and Y2038 issue David Brown <david.brown@hesbynett.no> - 2025-03-14 14:20 +0100
    Re: 32 bits time_t and Y2038 issue pozz <pozzugno@gmail.com> - 2025-03-12 08:44 +0100
      Re: 32 bits time_t and Y2038 issue David Brown <david.brown@hesbynett.no> - 2025-03-12 11:14 +0100
      Re: 32 bits time_t and Y2038 issue antispam@fricas.org (Waldek Hebisch) - 2025-03-14 01:48 +0000
        Re: 32 bits time_t and Y2038 issue pozz <pozzugno@gmail.com> - 2025-03-14 08:36 +0100
    Re: 32 bits time_t and Y2038 issue Michael Schwingen <news-1513678000@discworld.dascon.de> - 2025-03-15 16:30 +0000
      Re: 32 bits time_t and Y2038 issue Grant Edwards <invalid@invalid.invalid> - 2025-03-15 17:02 +0000
        Re: 32 bits time_t and Y2038 issue Michael Schwingen <news-1513678000@discworld.dascon.de> - 2025-03-15 23:26 +0000
      Re: 32 bits time_t and Y2038 issue pozz <pozzugno@gmail.com> - 2025-03-18 09:21 +0100
        Re: 32 bits time_t and Y2038 issue David Brown <david.brown@hesbynett.no> - 2025-03-18 11:34 +0100
          Re: 32 bits time_t and Y2038 issue pozz <pozzugno@gmail.com> - 2025-03-18 17:31 +0100
            Re: 32 bits time_t and Y2038 issue David Brown <david.brown@hesbynett.no> - 2025-03-18 20:29 +0100
              Re: 32 bits time_t and Y2038 issue Michael Schwingen <news-1513678000@discworld.dascon.de> - 2025-03-21 09:20 +0000
                Re: 32 bits time_t and Y2038 issue David Brown <david.brown@hesbynett.no> - 2025-03-21 13:54 +0100
                Re: 32 bits time_t and Y2038 issue Michael Schwingen <news-1513678000@discworld.dascon.de> - 2025-03-21 20:53 +0000
                Re: 32 bits time_t and Y2038 issue David Brown <david.brown@hesbynett.no> - 2025-03-22 11:19 +0100
                Re: 32 bits time_t and Y2038 issue antispam@fricas.org (Waldek Hebisch) - 2025-03-21 14:35 +0000
          Re: 32 bits time_t and Y2038 issue Michael Schwingen <news-1513678000@discworld.dascon.de> - 2025-03-18 18:28 +0000
            Re: 32 bits time_t and Y2038 issue David Brown <david.brown@hesbynett.no> - 2025-03-18 20:43 +0100
              Re: 32 bits time_t and Y2038 issue Grant Edwards <invalid@invalid.invalid> - 2025-03-18 20:58 +0000
                Re: 32 bits time_t and Y2038 issue Hans-Bernhard Bröker <HBBroeker@gmail.com> - 2025-03-18 23:31 +0100
                Re: 32 bits time_t and Y2038 issue David Brown <david.brown@hesbynett.no> - 2025-03-19 11:24 +0100
                Re: 32 bits time_t and Y2038 issue Grant Edwards <invalid@invalid.invalid> - 2025-03-19 14:27 +0000
                Re: 32 bits time_t and Y2038 issue David Brown <david.brown@hesbynett.no> - 2025-03-19 17:33 +0100
                Re: 32 bits time_t and Y2038 issue Grant Edwards <invalid@invalid.invalid> - 2025-03-19 19:08 +0000
                Re: 32 bits time_t and Y2038 issue David Brown <david.brown@hesbynett.no> - 2025-03-19 21:14 +0100
                Re: 32 bits time_t and Y2038 issue Michael Schwingen <news-1513678000@discworld.dascon.de> - 2025-03-21 09:48 +0000
                Re: 32 bits time_t and Y2038 issue Grant Edwards <invalid@invalid.invalid> - 2025-03-21 13:27 +0000
                Re: 32 bits time_t and Y2038 issue antispam@fricas.org (Waldek Hebisch) - 2025-03-19 22:09 +0000
                Re: 32 bits time_t and Y2038 issue David Brown <david.brown@hesbynett.no> - 2025-03-20 09:26 +0100
                Re: 32 bits time_t and Y2038 issue pozz <pozzugno@gmail.com> - 2025-03-21 22:40 +0100
                Re: 32 bits time_t and Y2038 issue Michael Schwingen <news-1513678000@discworld.dascon.de> - 2025-03-21 09:23 +0000
                Re: 32 bits time_t and Y2038 issue Hans-Bernhard Bröker <HBBroeker@gmail.com> - 2025-03-21 22:38 +0100
                Re: 32 bits time_t and Y2038 issue David Brown <david.brown@hesbynett.no> - 2025-03-19 08:24 +0100
              Re: 32 bits time_t and Y2038 issue antispam@fricas.org (Waldek Hebisch) - 2025-03-21 14:04 +0000
                Re: 32 bits time_t and Y2038 issue David Brown <david.brown@hesbynett.no> - 2025-03-21 16:45 +0100
                Re: 32 bits time_t and Y2038 issue pozz <pozzugno@gmail.com> - 2025-03-21 22:51 +0100
                Re: 32 bits time_t and Y2038 issue Hans-Bernhard Bröker <HBBroeker@gmail.com> - 2025-03-22 00:00 +0100
                Re: 32 bits time_t and Y2038 issue David Brown <david.brown@hesbynett.no> - 2025-03-22 14:29 +0100
                Re: 32 bits time_t and Y2038 issue Michael Schwingen <news-1513678000@discworld.dascon.de> - 2025-03-22 14:46 +0000
                Re: 32 bits time_t and Y2038 issue David Brown <david.brown@hesbynett.no> - 2025-03-22 17:57 +0100
                Re: 32 bits time_t and Y2038 issue antispam@fricas.org (Waldek Hebisch) - 2025-03-22 15:57 +0000
                Re: 32 bits time_t and Y2038 issue David Brown <david.brown@hesbynett.no> - 2025-03-22 18:02 +0100
        Re: 32 bits time_t and Y2038 issue Michael Schwingen <news-1513678000@discworld.dascon.de> - 2025-03-18 18:44 +0000

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