cygwin strangeness installing glibc: "mv: foo and foo.new are thesame file"

[Daniel Kegel <dank at kegel dot com>]

Installing glibc-2.1.3 under cygwin was giving me trouble.  Here's the error:

/usr/bin/install -c /tmp/toolchain.whitejl/crosstool-0.28-pre8c/build/i686-unknown-linux-gnu/gcc-2.95.3-glibc-2.1.3/build-glibc/db2/makedb /home/dkegel/experimental/i686-pc-cygwin/i686-unknown-linux-gnu/gcc-2.95.3-glibc-2.1.3/i686-unknown-l
inux-gnu/bin/makedb.new
mv -f /home/dkegel/experimental/i686-pc-cygwin/i686-unknown-linux-gnu/gcc-2.95.3-glibc-2.1.3/i686-unknown-linux-gnu/bin/makedb.new /home/dkegel/experimental/i686-pc-cygwin/i686-unknown-linux-gnu/gcc-2.95.3-glibc-2.1.3/i686-unknown-linux-gnu
/bin/makedb
mv: `/home/dkegel/experimental/i686-pc-cygwin/i686-unknown-linux-gnu/gcc-2.95.3-glibc-2.1.3/i686-unknown-linux-gnu/bin/makedb.new' and `/home/dkegel/experimental/i686-pc-cygwin/i686-unknown-linux-gnu/gcc-2.95.3-glibc-2.1.3/i686-unknown-linu
x-gnu/bin/makedb' are the same file
make[2]: *** [/home/dkegel/experimental/i686-pc-cygwin/i686-unknown-linux-gnu/gcc-2.95.3-glibc-2.1.3/i686-unknown-linux-gnu/bin/makedb] Error 1
make[2]: Leaving directory `/tmp/toolchain.whitejl/crosstool-0.28-pre8c/build/i686-unknown-linux-gnu/gcc-2.95.3-glibc-2.1.3/glibc-2.1.3/db2'
make[1]: *** [db2/subdir_install] Error 2
make[1]: Leaving directory `/tmp/toolchain.whitejl/crosstool-0.28-pre8c/build/i686-unknown-linux-gnu/gcc-2.95.3-glibc-2.1.3/glibc-2.1.3'
make: *** [install] Error 2

Investigating a bit, I found that this is a general problem
with cygwin when referring to programs without the implicit
.exe suffix.  For instance,
 $ cp /usr/bin/ls.exe foo.new.exe
 $ cp foo.new foo
will yield the same error message, whereas
 $ cp foo.new.exe foo.exe
will work just fine.

I'm not quite sure why installing *any* glibc executable has ever
worked for my under Cygwin now... glibc-2.3.2 still uses the
same idiom for installing executables.  You can see this by doing
 $ grep "mv.*new" Makerules

I think the chief offender is

define do-install-program
$(make-target-directory)
$(INSTALL_PROGRAM) $< $@.new
mv -f $@.new $@
endef

but only in the context of rules like

ifdef install-bin
$(addprefix $(inst_bindir)/,$(install-bin)): \
    $(inst_bindir)/%: $(objpfx)% $(+force)
        $(do-install-program)
endif

(it's also used to install shared libraries, which don't need the .exe suffix.)

I'm sure that mv is there to keep the update atomic, which might be important for parallel builds.

I guess the real question is, why is makedb.exe built for cygwin?
It's probably a target system thing that should be built with the
cross-compiler.   I'm not going to worry about it too much,
since db2 isn't part of later glibc's anyway; I'm just going to
disable the install of makedb.exe.  But now I'm slightly more aware of the issue,
and if it comes up on something I care about, maybe I'll think
about a real fix.
- Dan

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