Re: [PATCH] Cygwin: Speed up mkimport

[Jon Turney <jon.turney@dronecode.org.uk>]

On 26/11/2020 09:56, Mark Geisert wrote:
> Cut mkimport elapsed time in half by forking each iteration of the two
> time-consuming loops within.  Only do this if more than one CPU is
> present.  In the second loop, combine the two 'objdump' calls into one
> system() invocation to avoid a system() invocation per iteration.

Nice.  Thanks for looking into this.

> @@ -86,8 +94,18 @@ for my $f (keys %text) {
>       if (!$text{$f}) {
>   	unlink $f;
>       } else {
> -	system $objcopy, '-R', '.text', $f and exit 1;
> -	system $objcopy, '-R', '.bss', '-R', '.data', "t-$f" and exit 1;
> +	if ($forking && fork) {
> +	    # Testing shows parent does need to sleep a short time here,
> +	    # otherwise system is inundated with hundreds of objcopy processes
> +	    # and the forked perl processes that launched them.
> +	    my $delay = 0.01; # NOTE: Slower systems may need to raise this
> +	    select(undef, undef, undef, $delay); # Supports fractional seconds
> +	} else {
> +	    # Do two objcopy calls at once to avoid one system() call overhead
> +	    system '(', $objcopy, '-R', '.text', $f, ')', '||',
> +		$objcopy, '-R', '.bss', '-R', '.data', "t-$f" and exit 1;
> +	    exit 0 if $forking;
> +	}
>       }
>   }
>   

Hmm... not so sure about this.  This seems racy, as nothing ensures that 
these objcopies have finished before we combine all the produced .o 
files into a library.

I'm pretty sure with more understanding, this whole thing could be done 
better:  For example, from a brief look, it seems that the t-*.o files 
are produced by gas, and then we remove .bss and .data sections.  Could 
we not arrange to assemble these objects without those sections in the 
first place?