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Commit4b53872

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Fix make rules that generate multiple output files.
For years, our makefiles have correctly observed that "there is no correctway to write a rule that generates two files". However, what we did is toprovide empty rules that "generate" the secondary output files from theprimary one, and that's not right either. Depending on the details ofthe creating process, the primary file might end up timestamped later thanone or more secondary files, causing subsequent make runs to consider thesecondary file(s) out of date. That's harmless in a plain build, sincemake will just re-execute the empty rule and nothing happens. But it'sfatal in a VPATH build, since make will expect the secondary file to berebuilt in the build directory. This would manifest as "file not found"failures during VPATH builds from tarballs, if we were ever unlucky enoughto ship a tarball with apparently out-of-date secondary files. (It's notclear 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 $@" actionnot an empty rule. Also, make sure that this rule actually gets invokedduring 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, becausethose rules are due to get replaced soon in the bootstrap data formatpatch, 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 toback-fill the changes in that one makefile from v10.Discussion:https://postgr.es/m/18556.1521668179@sss.pgh.pa.us
1 parent8694cc9 commit4b53872

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9 files changed

+58
-51
lines changed

9 files changed

+58
-51
lines changed

‎src/Makefile.shlib

Lines changed: 6 additions & 14 deletions
Original file line numberDiff line numberDiff line change
@@ -315,13 +315,9 @@ else # PORTNAME == aix
315315

316316
# AIX case
317317

318-
# There is no correct way to write a rule that generates two files.
319-
# Rules with two targets don't have that meaning, they are merely
320-
# shorthand for two otherwise separate rules. To be safe for parallel
321-
# make, we must chain the dependencies like this. The semicolon is
322-
# important, otherwise make will choose some built-in rule.
323-
324-
$(stlib): $(shlib) ;
318+
# See notes in src/backend/parser/Makefile about the following two rules
319+
$(stlib): $(shlib)
320+
touch $@
325321

326322
$(shlib): $(OBJS) | $(SHLIB_PREREQS)
327323
rm -f $(stlib)
@@ -352,13 +348,9 @@ else
352348

353349
# Win32 case
354350

355-
# There is no correct way to write a rule that generates two files.
356-
# Rules with two targets don't have that meaning, they are merely
357-
# shorthand for two otherwise separate rules. To be safe for parallel
358-
# make, we must chain the dependencies like this. The semicolon is
359-
# important, otherwise make will choose some built-in rule.
360-
361-
$(stlib): $(shlib) ;
351+
# See notes in src/backend/parser/Makefile about the following two rules
352+
$(stlib): $(shlib)
353+
touch $@
362354

363355
# XXX A backend that loads a module linked with libgcc_s_dw2-1.dll will exit
364356
# uncleanly, hence -static-libgcc. (Last verified with MinGW-w64 compilers

‎src/backend/Makefile

Lines changed: 20 additions & 13 deletions
Original file line numberDiff line numberDiff line change
@@ -70,13 +70,10 @@ ifeq ($(PORTNAME), cygwin)
7070
postgres:$(OBJS)
7171
$(CC)$(CFLAGS)$(LDFLAGS)$(LDFLAGS_EX)$(export_dynamic) -Wl,--stack,$(WIN32_STACK_RLIMIT) -Wl,--export-all-symbols -Wl,--out-implib=libpostgres.a$(call expand_subsys,$^)$(LIBS) -o$@
7272

73-
# There is no correct way to write a rule that generates two files.
74-
# Rules with two targets don't have that meaning, they are merely
75-
# shorthand for two otherwise separate rules. To be safe for parallel
76-
# make, we must chain the dependencies like this. The semicolon is
77-
# important, otherwise make will choose some built-in rule.
78-
79-
libpostgres.a: postgres ;
73+
# libpostgres.a is actually built in the preceding rule, but we need this to
74+
# ensure it's newer than postgres; see notes in src/backend/parser/Makefile
75+
libpostgres.a: postgres
76+
touch$@
8077

8178
endif# cygwin
8279

@@ -86,7 +83,10 @@ LIBS += -lsecur32
8683
postgres:$(OBJS)$(WIN32RES)
8784
$(CC)$(CFLAGS)$(LDFLAGS)$(LDFLAGS_EX) -Wl,--stack=$(WIN32_STACK_RLIMIT) -Wl,--export-all-symbols -Wl,--out-implib=libpostgres.a$(call expand_subsys,$(OBJS))$(WIN32RES)$(LIBS) -o$@$(X)
8885

89-
libpostgres.a: postgres ;
86+
# libpostgres.a is actually built in the preceding rule, but we need this to
87+
# ensure it's newer than postgres; see notes in src/backend/parser/Makefile
88+
libpostgres.a: postgres
89+
touch$@
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9191
endif# win32
9292

@@ -130,21 +130,28 @@ postgres.o: $(OBJS)
130130
# The following targets are specified in make commands that appear in
131131
# the make files in our subdirectories. Note that it's important we
132132
# match the dependencies shown in the subdirectory makefiles!
133+
# Also, in cases where a subdirectory makefile generates two files in
134+
# what's really one step, such as bison producing both gram.h and gram.c,
135+
# we must request making the one that is shown as the secondary (dependent)
136+
# output, else the timestamp on it might be wrong. By project convention,
137+
# the .h file is the dependent one for bison output, so we need only request
138+
# that; but in other cases, request both for safety.
133139

134140
parser/gram.h: parser/gram.y
135141
$(MAKE) -C parser gram.h
136142

137143
storage/lmgr/lwlocknames.h: storage/lmgr/generate-lwlocknames.pl storage/lmgr/lwlocknames.txt
138-
$(MAKE) -C storage/lmgr lwlocknames.h
144+
$(MAKE) -C storage/lmgr lwlocknames.h lwlocknames.c
139145

140146
utils/errcodes.h: utils/generate-errcodes.pl utils/errcodes.txt
141147
$(MAKE) -C utils errcodes.h
142148

143-
# see explanation in parser/Makefile
144-
utils/fmgrprotos.h: utils/fmgroids.h ;
149+
# see notes in src/backend/parser/Makefile
150+
utils/fmgrprotos.h: utils/fmgroids.h
151+
touch$@
145152

146153
utils/fmgroids.h: utils/Gen_fmgrtab.pl catalog/Catalog.pm$(top_srcdir)/src/include/catalog/pg_proc.h
147-
$(MAKE) -C utils$(notdir$@)
154+
$(MAKE) -C utilsfmgroids.h fmgrprotos.h
148155

149156
utils/probes.h: utils/probes.d
150157
$(MAKE) -C utils probes.h
@@ -219,7 +226,7 @@ distprep:
219226
$(MAKE) -C bootstrapbootparse.c bootscanner.c
220227
$(MAKE) -C catalogschemapg.h postgres.bki postgres.description postgres.shdescription
221228
$(MAKE) -C replicationrepl_gram.c repl_scanner.c syncrep_gram.c syncrep_scanner.c
222-
$(MAKE) -C storage/lmgrlwlocknames.h
229+
$(MAKE) -C storage/lmgrlwlocknames.h lwlocknames.c
223230
$(MAKE) -C utilsfmgrtab.c fmgroids.h fmgrprotos.h errcodes.h
224231
$(MAKE) -C utils/miscguc-file.c
225232
$(MAKE) -C utils/sortqsort_tuple.c

‎src/backend/parser/Makefile

Lines changed: 11 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -23,12 +23,17 @@ include $(top_srcdir)/src/backend/common.mk
2323

2424
# There is no correct way to write a rule that generates two files.
2525
# Rules with two targets don't have that meaning, they are merely
26-
# shorthand for two otherwise separate rules. To be safe for parallel
27-
# make, we must chain the dependencies like this. The semicolon is
28-
# important, otherwise make will choose the built-in rule for
29-
# gram.y=>gram.c.
30-
31-
gram.h: gram.c ;
26+
# shorthand for two otherwise separate rules. If we have an action
27+
# that in fact generates two or more files, we must choose one of them
28+
# as primary and show it as the action's output, then make all of the
29+
# other output files dependent on the primary, like this. Furthermore,
30+
# the "touch" action is essential, because it ensures that gram.h is
31+
# marked as newer than (or at least no older than) gram.c. Without that,
32+
# make is likely to try to rebuild gram.h in subsequent runs, which causes
33+
# failures in VPATH builds from tarballs.
34+
35+
gram.h: gram.c
36+
touch$@
3237

3338
gram.c: BISONFLAGS += -d
3439
gram.c: BISON_CHECK_CMD =$(PERL)$(srcdir)/check_keywords.pl$<$(top_srcdir)/src/include/parser/kwlist.h

‎src/backend/storage/lmgr/Makefile

Lines changed: 3 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -25,8 +25,9 @@ s_lock_test: s_lock.c $(top_builddir)/src/port/libpgport.a
2525
$(CC)$(CPPFLAGS)$(CFLAGS) -DS_LOCK_TEST=1$(srcdir)/s_lock.c\
2626
$(TASPATH) -L$(top_builddir)/src/port -lpgport -o s_lock_test
2727

28-
# see explanation in ../../parser/Makefile
29-
lwlocknames.c: lwlocknames.h ;
28+
# see notes in src/backend/parser/Makefile
29+
lwlocknames.c: lwlocknames.h
30+
touch$@
3031

3132
lwlocknames.h:$(top_srcdir)/src/backend/storage/lmgr/lwlocknames.txt generate-lwlocknames.pl
3233
$(PERL)$(srcdir)/generate-lwlocknames.pl$<

‎src/backend/utils/Makefile

Lines changed: 6 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -20,9 +20,12 @@ all: errcodes.h fmgroids.h fmgrprotos.h probes.h
2020

2121
$(SUBDIRS:%=%-recursive): fmgroids.h fmgrprotos.h
2222

23-
# see explanation in ../parser/Makefile
24-
fmgrprotos.h: fmgroids.h ;
25-
fmgroids.h: fmgrtab.c ;
23+
# see notes in src/backend/parser/Makefile
24+
fmgrprotos.h: fmgroids.h
25+
touch$@
26+
27+
fmgroids.h: fmgrtab.c
28+
touch$@
2629

2730
fmgrtab.c: Gen_fmgrtab.pl$(catalogdir)/Catalog.pm$(top_srcdir)/src/include/catalog/pg_proc.h
2831
$(PERL) -I$(catalogdir)$< -I$(top_srcdir)/src/include/$(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
@@ -35,15 +35,18 @@ psql: $(OBJS) | submake-libpq submake-libpgport submake-libpgfeutils
3535

3636
help.o: sql_help.h
3737

38-
sql_help.c: sql_help.h ;
38+
# See notes in src/backend/parser/Makefile about the following two rules
39+
sql_help.c: sql_help.h
40+
touch$@
41+
3942
sql_help.h: create_help.pl$(wildcard$(REFDOCDIR)/*.sgml)
4043
$(PERL)$<$(REFDOCDIR)$*
4144

4245
psqlscanslash.c: FLEXFLAGS = -Cfe -p -p
4346
psqlscanslash.c: FLEX_NO_BACKUP=yes
4447
psqlscanslash.c: FLEX_FIX_WARNING=yes
4548

46-
distprep: sql_help.h psqlscanslash.c
49+
distprep: sql_help.hsql_help.cpsqlscanslash.c
4750

4851
install: all installdirs
4952
$(INSTALL_PROGRAM) psql$(X)'$(DESTDIR)$(bindir)/psql$(X)'

‎src/interfaces/ecpg/preproc/Makefile

Lines changed: 4 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -39,7 +39,10 @@ ecpg: $(OBJS) | submake-libpgport
3939
../ecpglib/typename.o: ../ecpglib/typename.c
4040
$(MAKE) -C$(dir$@)$(notdir$@)
4141

42-
preproc.h: preproc.c ;
42+
# See notes in src/backend/parser/Makefile about the following two rules
43+
preproc.h: preproc.c
44+
touch$@
45+
4346
preproc.c: BISONFLAGS += -d
4447

4548
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
@@ -63,7 +63,9 @@ uninstall-headers:
6363
pl_gram.opl_handler.opl_comp.opl_exec.opl_funcs.opl_scanner.o: plpgsql.h pl_gram.h plerrcodes.h
6464

6565
# See notes in src/backend/parser/Makefile about the following two rules
66-
pl_gram.h: pl_gram.c ;
66+
pl_gram.h: pl_gram.c
67+
touch$@
68+
6769
pl_gram.c: BISONFLAGS += -d
6870

6971
# 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
@@ -36,15 +36,6 @@ isolationtester$(X): $(OBJS) | submake-libpq submake-libpgport
3636

3737
distprep: specparse.c specscanner.c
3838

39-
# There is no correct way to write a rule that generates two files.
40-
# Rules with two targets don't have that meaning, they are merely
41-
# shorthand for two otherwise separate rules. To be safe for parallel
42-
# make, we must chain the dependencies like this. The semicolon is
43-
# important, otherwise make will choose the built-in rule for
44-
# gram.y=>gram.c.
45-
46-
specparse.h: specparse.c ;
47-
4839
# specscanner is compiled as part of specparse
4940
specparse.o: specscanner.c
5041

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