8000 Fix make rules that generate multiple output files. · tomdcc/postgres@3bd5009 · GitHub
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Fix make rules that generate multiple output files.
For years, our makefiles have correctly observed that "there is no correct way to write a rule that generates two files". However, what we did is to provide empty rules that "generate" the secondary output files from the primary one, and that's not right either. Depending on the details of the creating process, the primary file might end up timestamped later than one or more secondary files, causing subsequent make runs to consider the secondary file(s) out of date. That's harmless in a plain build, since make will just re-execute the empty rule and nothing happens. But it's fatal in a VPATH build, since make will expect the secondary file to be rebuilt in the build directory. This would manifest as "file not found" failures during VPATH builds from tarballs, if we were ever unlucky enough to ship a tarball with apparently out-of-date secondary files. (It's not clear whether that has ever actually happened, but it definitely could.) To ensure that secondary output files have timestamps >= their primary's, change our makefile convention to be that we provide a "touch $@" action not an empty rule. Also, make sure that this rule actually gets invoked during a distprep run, else the hazard remains. It's been like this a long time, so back-patch to all supported branches. In HEAD, I skipped the changes in src/backend/catalog/Makefile, because those rules are due to get replaced soon in the bootstrap data format patch, and there seems no need to create a merge issue for that patch. If for some reason we fail to land that patch in v11, we'll need to back-fill the changes in that one makefile from v10. Discussion: https://postgr.es/m/18556.1521668179@sss.pgh.pa.us
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9 files changed

+43
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lines changed

‎src/Makefile.shlib

Lines changed: 3 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -358,13 +358,9 @@ else # PORTNAME == aix
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# AIX case
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361-
# There is no correct way to write a rule that generates two files.
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# Rules with two targets don't have that meaning, they are merely
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# shorthand for two otherwise separate rules. To be safe for parallel
364-
# make, we must chain the dependencies like this. The semicolon is
365-
# important, otherwise make will choose some built-in rule.
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$(stlib): $(shlib) ;
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# See notes in src/backend/parser/Makefile about the following two rules
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$(stlib): $(shlib)
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touch $@
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$(shlib): $(OBJS) | $(SHLIB_PREREQS)
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rm -f $(stlib)

‎src/backend/Makefile

Lines changed: 6 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -141,6 +141,12 @@ postgres.o: $(OBJS)
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# The following targets are specified in make commands that appear in
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# the make files in our subdirectories. Note that it's important we
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# match the dependencies shown in the subdirectory makefiles!
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# Also, in cases where a subdirectory makefile generates two files in
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# what's really one step, such as bison producing both gram.h and gram.c,
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# we must request making the one that is shown as the secondary (dependent)
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# output, else the timestamp on it might be wrong. By project convention,
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# the .h file is the dependent one for bison output, so we need only request
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# that; but in other cases, request both for safety.
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parser/gram.h: parser/gram.y
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$(MAKE) -C parser gram.h

‎src/backend/catalog/Makefile

Lines changed: 8 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -21,7 +21,7 @@ BKIFILES = postgres.bki postgres.description postgres.shdescription
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include $(top_srcdir)/src/backend/common.mk
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24-
all: $(BKIFILES) schemapg.h
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all: $(BKIFILES) schemapg.h postgres.description postgres.shdescription
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# Note: there are some undocumented dependencies on the ordering in which
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# the catalog header files are assembled into postgres.bki. In particular,
@@ -50,12 +50,15 @@ catalogdir = $(top_srcdir)/src/backend/catalog
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# locations of headers that genbki.pl needs to read
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pg_includes = -I$(top_srcdir)/src/include/catalog -I$(top_builddir)/src/include/catalog
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53-
# see explanation in ../parser/Makefile
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postgres.description: postgres.bki ;
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# see notes in src/backend/parser/Makefile about multiple output files
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postgres.description: postgres.bki
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touch $@
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56-
postgres.shdescription: postgres.bki ;
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postgres.shdescription: postgres.bki
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touch $@
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schemapg.h: postgres.bki ;
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schemapg.h: postgres.bki
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touch $@
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# Technically, this should depend on Makefile.global, but then
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# postgres.bki would need to be rebuilt after every configure run,

‎src/backend/parser/Makefile

Lines changed: 11 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -28,12 +28,17 @@ endif
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# There is no correct way to write a rule that generates two files.
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# Rules with two targets don't have that meaning, they are merely
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# shorthand for two otherwise separate rules. To be safe for parallel
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# make, we must chain the dependencies like this. The semicolon is
33-
# important, otherwise make will choose the built-in rule for
34-
# gram.y=>gram.c.
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gram.h: gram.c ;
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# shorthand for two otherwise separate rules. If we have an action
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# that in fact generates two or more files, we must choose one of them
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# as primary and show it as the action's output, then make all of the
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# other output files dependent on the primary, like this. Furthermore,
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# the "touch" action is essential, because it ensures that gram.h is
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# marked as newer than (or at least no older than) gram.c. Without that,
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# make is likely to try to rebuild gram.h in subsequent runs, which causes
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# failures in VPATH builds from tarballs.
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gram.h: gram.c
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touch $@
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gram.c: BISONFLAGS += -d
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gram.c: BISON_CHECK_CMD = $(PERL) $(srcdir)/check_keywords.pl $< $(top_srcdir)/src/include/parser/kwlist.h

‎src/backend/utils/Makefile

Lines changed: 3 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -20,8 +20,9 @@ all: errcodes.h fmgroids.h probes.h
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$(SUBDIRS:%=%-recursive): fmgroids.h
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23-
# see explanation in ../parser/Makefile
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fmgroids.h: fmgrtab.c ;
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# see notes in src/backend/parser/Makefile
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fmgroids.h: fmgrtab.c
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touch $@
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fmgrtab.c: Gen_fmgrtab.pl $(catalogdir)/Catalog.pm $(top_srcdir)/src/include/catalog/pg_proc.h
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$(PERL) -I $(catalogdir) $< $(top_srcdir)/src/include/catalog/pg_proc.h

‎src/bin/psql/Makefile

Lines changed: 5 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -40,7 +40,10 @@ dumputils.c keywords.c: % : $(top_srcdir)/src/bin/pg_dump/%
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kwlookup.c: % : $(top_srcdir)/src/backend/parser/%
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rm -f $@ && $(LN_S) $< .
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43-
sql_help.c: sql_help.h ;
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# See notes in src/backend/parser/Makefile about the following two rules
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sql_help.c: sql_help.h
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touch $@
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sql_help.h: create_help.pl $(wildcard $(REFDOCDIR)/*.sgml)
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$(PERL) $< $(REFDOCDIR) $*
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@@ -50,7 +53,7 @@ mainloop.o: psqlscan.c
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psqlscan.c: FLEXFLAGS = -Cfe -p -p
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psqlscan.c: FLEX_NO_BACKUP=yes
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53-
distprep: sql_help.h psqlscan.c
56+
distprep: sql_help.h sql_help.c psqlscan.c
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install: all installdirs
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$(INSTALL_PROGRAM) psql$(X) '$(DESTDIR)$(bindir)/psql$(X)'

‎src/interfaces/ecpg/preproc/Makefile

Lines changed: 4 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -44,7 +44,10 @@ ecpg: $(OBJS) | submake-libpgport
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../ecpglib/typename.o: ../ecpglib/typename.c
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$(MAKE) -C $(dir $@) $(notdir $@)
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47-
preproc.h: preproc.c ;
47+
# See notes in src/backend/parser/Makefile about the following two rules
48+
preproc.h: preproc.c
49+
touch $@
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4851
preproc.c: BISONFLAGS += -d
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5053
preproc.y: ../../../backend/parser/gram.y parse.pl ecpg.addons ecpg.header ecpg.tokens ecpg.trailer ecpg.type

‎src/pl/plpgsql/src/Makefile

Lines changed: 3 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -55,7 +55,9 @@ uninstall-headers:
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pl_gram.o pl_handler.o pl_comp.o pl_exec.o pl_funcs.o pl_scanner.o: plpgsql.h pl_gram.h plerrcodes.h
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5757
# See notes in src/backend/parser/Makefile about the following two rules
58-
pl_gram.h: pl_gram.c ;
58+
pl_gram.h: pl_gram.c
59+
touch $@
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pl_gram.c: BISONFLAGS += -d
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# generate plerrcodes.h from src/backend/utils/errcodes.txt

‎src/test/isolation/Makefile

Lines changed: 0 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -29,15 +29,6 @@ isolationtester$(X): $(OBJS) | submake-libpq submake-libpgport
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distprep: specparse.c specscanner.c
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32-
# There is no correct way to write a rule that generates two files.
33-
# Rules with two targets don't have that meaning, they are merely
34-
# shorthand for two otherwise separate rules. To be safe for parallel
35-
# make, we must chain the dependencies like this. The semicolon is
36-
# important, otherwise make will choose the built-in rule for
37-
# gram.y=>gram.c.
38-
39-
specparse.h: specparse.c ;
40-
4132
# specscanner is compiled as part of specparse
4233
specparse.o: specscanner.c
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