Old build problem: unpack200 failure when setting OTHER_CXXFLAGS in environment

[David Holmes]

This is a blast from the past:

http://mail.openjdk.java.net/pipermail/build-dev/2007-May/000026.html

but the above issue and patch seem to have been ignored. I just ran into 
this myself.

/export/users/dh198349/jdk8/builds/b01/se8-linux-i586-ea/tmp/sun/com.sun.java.util.jar.pack/unpack-cmd/obj/main.o: 
In function `unpacker::run(int, char**)':
main.cpp:(.text+0xe0b): undefined reference to `gunzip::init(unpacker*)'
main.cpp:(.text+0xe1d): undefined reference to `gunzip::start(int)'
collect2: ld returned 1 exit status
make[7]: *** 
[/export/users/dh198349/jdk8/builds/b01/se8-linux-i586-ea/bin/unpack200] 
Error 1

The basic issue is one of recursive makes, with conditionally set 
variables that might also be set externally in the environment. Here's 
an example Makefile:

build: unpack

ifdef STANDALONE
   FLAGS+=-XstandAlone
else
   FLAGS+=-Xcombined
endif

unpack:
         @make STANDALONE=true unpack_exe

build:
         @echo build FLAGS = $(FLAGS)
unpack_exe:
         @echo unpack_exe FLAGS = $(FLAGS)

.phony: build unpack unpack_exe

---

Here's a normal run:

  > make build
make[1]: Entering directory `/scratch/dh198349'
unpack_exe FLAGS = -XstandAlone
make[1]: Leaving directory `/scratch/dh198349'
build FLAGS = -Xcombined

which is what we would expect. But if you now give FLAGS an initial 
external value:

 > FLAGS=external make build
make[1]: Entering directory `/scratch/dh198349'
unpack_exe FLAGS = external -Xcombined -XstandAlone
make[1]: Leaving directory `/scratch/dh198349'
build FLAGS = external -Xcombined

Yikes! Now unpack_exe sees both the STANDALONE and non-STANDALONE value 
of FLAGS. This is because make re-exports any variable that came in from 
the environment. So when the top-level make is called, FLAGS==external, 
and to that the Makefile adds -Xcombined, so the sub-make effectively 
becomes:

make FLAGS="external -Xcombined" STANDALONE=true unpack_exe

Here's one way to fix this:

# save original incoming FLGS
ORIG_FLAGS := $(FLAGS)
# hide any locally modified value of FLAGS
unexport FLAGS

build: unpack

ifdef STANDALONE
   # override to allow sub-make to add to FLAGS
   override FLAGS+=-XstandAlone
else
   FLAGS+=-Xcombined
endif

unpack:
         # Send in ORIG_FLAGS as FLAGS
         @make FLAGS=$(ORIG_FLAGS) STANDALONE=true unpack_exe

build:
         @echo build FLAGS = $(FLAGS)
unpack_exe:
         @echo unpack_exe FLAGS = $(FLAGS)

.phony: build unpack unpack_exe

----

Or as per the original Patch, use a different variable in the Makefile 
to that set in the environment.

David
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