gmake && file time precision of 1 second

[Tim Kientzle]

On Oct 13, 2014, at 2:20 AM, Matthias Apitz <guru at unixarea.de> wrote:

> 
> Hello,
> 
> I have a large project where a shell script fires up
> gmake runs in subdirs as:
> 
> for dir in src norm print ....; do 
>   cd $dir
>   gmake
>   cd ..
> done
> 
> in each subdir *.c are compiled to *.o and the resulting *.o are ar'ed
> into all the same lib.a; based on normal Makefile rules like:
> 
> SRCS = f1.c f2.c
> OBJS = $(SRCS:.c=.o)
> 
> .c.o:
> 	$(CC) -c ... $*.c
> 
> lib.a:: $(OBJS)
> 	$(AR) $@ $(OBJS)
> 
> 
> after moving to a faster server it turned out that gmake sometimes forget
> to ar the *.o into the lib; I investigated it and it turned out that the
> *.o files have the same modification time (in seconds) as the target
> lib.a (which was produced/updated in the last directory worked on) and
> gmake thinks that the lib.a is uptodate.
> 
> Any idea how to address this in the Makefiles?

Instead of updating the same lib.a from every makefile, instead consider creating a separate lib.a in each directory and then combining them at the end.

Combining .a libraries is a little tricky:  Try creating a dir, extracting each lib.a into that same directory, then creating a new lib.a.  It might be possible to combine them directly using tar —format=ar but I’ve not tried it.

Cheers,

Tim