Prevent accidental linking of system-supplied copies of libpq.so etc.

We were being careless in some places about the order of -L switches in
link command lines, such that -L switches referring to external directories
could come before those referring to directories within the build tree.
This made it possible to accidentally link a system-supplied library, for
example /usr/lib/libpq.so, in place of the one built in the build tree.
Hilarity ensued, the more so the older the system-supplied library is.

To fix, break LDFLAGS into two parts, a sub-variable LDFLAGS_INTERNAL
and the main LDFLAGS variable, both of which are "recursively expanded"
so that they can be incrementally adjusted by different makefiles.
Establish a policy that -L switches for directories in the build tree
must always be added to LDFLAGS_INTERNAL, while -L switches for external
directories must always be added to LDFLAGS.  This is sufficient to
ensure a safe search order.  For simplicity, we typically also put -l
switches for the respective libraries into those same variables.
(Traditional make usage would have us put -l switches into LIBS, but
cleaning that up is a project for another day, as there's no clear
need for it.)

This turns out to also require separating SHLIB_LINK into two variables,
SHLIB_LINK and SHLIB_LINK_INTERNAL, with a similar rule about which
switches go into which variable.  And likewise for PG_LIBS.

Although this change might appear to affect external users of pgxs.mk,
I think it doesn't; they shouldn't have any need to touch the _INTERNAL
variables.

In passing, tweak src/common/Makefile so that the value of CPPFLAGS
recorded in pg_config lacks "-DFRONTEND" and the recorded value of
LDFLAGS lacks "-L../../../src/common".  Both of those things are
mistakes, apparently introduced during prior code rearrangements,
as old versions of pg_config don't print them.  In general we don't
want anything that's specific to the src/common subdirectory to
appear in those outputs.

This is certainly a bug fix, but in view of the lack of field
complaints, I'm unsure whether it's worth the risk of back-patching.
In any case it seems wise to see what the buildfarm makes of it first.

Discussion: https://postgr.es/m/[email protected]

1 files changed, 1 insertions, 1 deletions

diff --git a/contrib/jsonb_plpython/Makefile b/contrib/jsonb_plpython/Makefile
index 8c7090a8846..b3c98e6db00 100644
--- a/contrib/jsonb_plpython/Makefile
+++ b/contrib/jsonb_plpython/Makefile
@@ -26,7 +26,7 @@ endif
 # We must link libpython explicitly
 ifeq ($(PORTNAME), win32)
 # ... see silliness in plpython Makefile ...
-SHLIB_LINK += $(sort $(wildcard ../../src/pl/plpython/libpython*.a))
+SHLIB_LINK_INTERNAL += $(sort $(wildcard ../../src/pl/plpython/libpython*.a))
 else
 rpathdir = $(python_libdir)
 SHLIB_LINK += $(python_libspec) $(python_additional_libs)