Re: About make manual 11.3 a(m) syntax in prerequisite

[Paul Smith]

On Fri, 2024-12-27 at 17:03 +0800, lijh8 wrote:
> but if i use ` a(m) ` syntax in the prerequisites, 
> it rebuilds the archive even i did not change the `*.c` source files
> or the `*.o` object files.

You didn't give us any indication of your operating system or
distribution, or what version of ar(1) you're using.  I will assume
you're using a version of GNU/Linux or, at least, using the version of
ar(1) provided by GNU binutils.

In that case I suspect that your distribution has fallen under the sway
of the "reproducible builds at all costs" cult and has set the default
format of ar(1) to be "reproducible" instead of the traditional
behavior of ar(1) since it was created over 50 years ago.

This setting breaks make.

You should file a bug report with your distribution and request that
they remove the --enable-deterministic-archives option from their
configuration of GNU binutils.  Personally I believe adding that option
as a configuration default was a mistake and the GNU binutils
maintainers should remove it.

In the meantime, you will have to add the "U" option to your invocation
of ar(1) to disable "reproducible" archives, if you want to see the
correct behavior from make when using a(m) syntax.  For example:

    ARFLAGS := rvU

-- 
Paul D. Smith <psmith@gnu.org>            Find some GNU Make tips at:
https://www.gnu.org                       http://make.mad-scientist.net
"Please remain calm...I may be mad, but I am a professional." --Mad
Scientist