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

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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/25214.1522604295@sss.pgh.pa.us
This commit is contained in:
Tom Lane
2018-04-03 16:26:05 -04:00
parent d4a4c3d5b4
commit dddfc4cb2e
32 changed files with 66 additions and 49 deletions
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8
src/common/Makefile
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@@ -24,12 +24,9 @@ subdir = src/common
top_builddir = ../..
include $(top_builddir)/src/Makefile.global
override CPPFLAGS := -DFRONTEND $(CPPFLAGS)
LIBS += $(PTHREAD_LIBS)
# don't include subdirectory-path-dependent -I and -L switches
STD_CPPFLAGS := $(filter-out -I$(top_srcdir)/src/include -I$(top_builddir)/src/include,$(CPPFLAGS))
STD_LDFLAGS := $(filter-out -L$(top_builddir)/src/port,$(LDFLAGS))
STD_LDFLAGS := $(filter-out -L$(top_builddir)/src/common -L$(top_builddir)/src/port,$(LDFLAGS))
override CPPFLAGS += -DVAL_CONFIGURE="\"$(configure_args)\""
override CPPFLAGS += -DVAL_CC="\"$(CC)\""
override CPPFLAGS += -DVAL_CPPFLAGS="\"$(STD_CPPFLAGS)\""
@@ -40,6 +37,9 @@ override CPPFLAGS += -DVAL_LDFLAGS_EX="\"$(LDFLAGS_EX)\""
override CPPFLAGS += -DVAL_LDFLAGS_SL="\"$(LDFLAGS_SL)\""
override CPPFLAGS += -DVAL_LIBS="\"$(LIBS)\""
override CPPFLAGS := -DFRONTEND $(CPPFLAGS)
LIBS += $(PTHREAD_LIBS)
OBJS_COMMON = base64.o config_info.o controldata_utils.o exec.o ip.o \
keywords.o md5.o pg_lzcompress.o pgfnames.o psprintf.o relpath.o \
rmtree.o saslprep.o scram-common.o string.o unicode_norm.o \