Re: [bug-gnulib] Re: [patch] byteswap module fails when building from subdir

[Ben Pfaff]

Bruno Haible <address@hidden> writes:

> Oskar Liljeblad wrote:
>> >  byteswap.h: byteswap_.h
>> > -       cp $(srcdir)/$< address@hidden
>> > +       cp $(srcdir)/byteswap_.h address@hidden
>> >         mv address@hidden $@
>>
>> Can you please explain why this is necessary,
>> so that I won't make the same mistake in the future again?
>
> See the POSIX specification of "make", at
> http://www.opengroup.org/onlinepubs/009695399/utilities/make.html :
> $< is defined for inference rules only. Not for target rules.
> GNU make implements $< also for target rules, but other "make" programs
> don't.

That is one reason, but there is another also.  When the build
directory is different from the source directory, $< expands to
the file name in the source directory, e.g. ../../gl/byteswap_.h.
Thus, $(srcdir)/$< expands to something like
../../gl/../../gl/byteswap_.h, which will fail.  This is the
actual problem that I encountered.
-- 
"MONO - Monochrome Emulation
 This field is used to store your favorite bit."
--FreeVGA Attribute Controller Reference