From c8612c6024feb06e1806b5549ccde5384db4163d Mon Sep 17 00:00:00 2001
From: Fred Wright <fw@fwright.net>
Date: Sat, 19 Oct 2024 17:09:51 -0700
Subject: [PATCH] Makefile: Fix parallel builds.

Creating directories with "install -d" suffers from a race condition,
because, although it first-order avoids creating directories that
already exist, if multiple instances attempt to create a given
directory at the same time, the error due to a collision is not
correctly handled.  To get around this, we make separate recipes for
directory creation, with dependencies on them in the rules that
populate them.

Unfortunately, this makes the automatic variables useless for some of
the populating commands, since they include the directories.  In such
cases, we need to use explicit variables for the input files.

Maintaining the unused ability to put static and dynamic libraries in
separate directories (while not actually being separate) would have
complicated things, so that capability has been dropped.

This special treatment of directories is not applied to the
installation of headers, since that's a complicated multi-directory
target only used in a single recipe, and hence not vulnerable to
parallelism.

TESTED:
All builds now succeed with parallelism, including those that
previously exhibited a failure.
---
 Makefile | 54 ++++++++++++++++++++++++++++--------------------------
 1 file changed, 28 insertions(+), 26 deletions(-)

diff --git a/Makefile b/Makefile
index 70875b5..188269d 100644
--- a/Makefile
+++ b/Makefile
@@ -30,11 +30,10 @@ SYSLIBFILE       = lib$(SYSLIBNAME)$(SOEXT)
 DLIBPATH         = $(LIBDIR)/$(DLIBFILE)
 SLIBPATH         = $(LIBDIR)/$(SLIBFILE)
 SYSLIBPATH       = $(LIBDIR)/$(SYSLIBFILE)
-BUILDDLIBDIR     = lib
-BUILDSLIBDIR     = lib
-BUILDDLIBPATH    = $(BUILDDLIBDIR)/$(DLIBFILE)
-BUILDSLIBPATH    = $(BUILDSLIBDIR)/$(SLIBFILE)
-BUILDSYSLIBPATH  = $(BUILDDLIBDIR)/$(SYSLIBFILE)
+BUILDLIBDIR      = lib
+BUILDDLIBPATH    = $(BUILDLIBDIR)/$(DLIBFILE)
+BUILDSLIBPATH    = $(BUILDLIBDIR)/$(SLIBFILE)
+BUILDSYSLIBPATH  = $(BUILDLIBDIR)/$(SYSLIBFILE)
 SOCURVERSION    ?= 1.0
 SOCOMPATVERSION ?= 1.0
 BUILDDLIBFLAGS   = -dynamiclib -headerpad_max_install_names \
@@ -98,9 +97,12 @@ DLIBOBJEXT       = .dl.o
 SLIBOBJEXT       = .o
 DLIBOBJS        := $(patsubst %.c,%$(DLIBOBJEXT),$(LIBSRCS))
 MULTIDLIBOBJS   := $(patsubst %.c,%$(DLIBOBJEXT),$(MULTISRCS))
+ALLDLIBOBJS     := $(DLIBOBJS) $(MULTIDLIBOBJS)
 SLIBOBJS        := $(patsubst %.c,%$(SLIBOBJEXT),$(LIBSRCS))
 MULTISLIBOBJS   := $(patsubst %.c,%$(SLIBOBJEXT),$(MULTISRCS))
+ALLSLIBOBJS     := $(SLIBOBJS) $(MULTISLIBOBJS)
 ADDOBJS         := $(patsubst %.c,%$(SLIBOBJEXT),$(ADDSRCS))
+ALLSYSLIBOBJS   := $(ALLDLIBOBJS) $(ADDOBJS)
 
 # Defs for filtering out empty object files
 #
@@ -136,7 +138,7 @@ DARWINRUNS      := $(patsubst \
 TESTDIR          = test
 TESTNAMEPREFIX   = $(TESTDIR)/test_
 TESTRUNPREFIX    = run_
-TESTLDFLAGS      = -L$(BUILDDLIBDIR) $(ALLLDFLAGS)
+TESTLDFLAGS      = -L$(BUILDLIBDIR) $(ALLLDFLAGS)
 TESTLIBS         = -l$(LIBNAME)
 TESTSRCS_C      := $(wildcard $(TESTNAMEPREFIX)*.c)
 TESTOBJS_C      := $(patsubst %.c,%.o,$(TESTSRCS_C))
@@ -300,30 +302,33 @@ $(SLIBOBJS): %$(SLIBOBJEXT): %.c $(ALLHEADERS)
 $(ADDOBJS): %$(SLIBOBJEXT): %.c $(ALLHEADERS)
 	$(CC) -c -I$(SRCINCDIR) $(ALLCFLAGS) $(SLIBCFLAGS) $< -o $@
 
-dlibobjs: $(DLIBOBJS) $(MULTIDLIBOBJS)
+dlibobjs: $(ALLDLIBOBJS)
 
-syslibobjs: $(DLIBOBJS) $(MULTIDLIBOBJS) $(ADDOBJS)
+syslibobjs: $(ALLSYSLIBOBJS)
 
-slibobjs: $(SLIBOBJS) $(MULTISLIBOBJS)
+slibobjs: $(ALLSLIBOBJS)
 
 allobjs: dlibobjs slibobjs syslibobjs
 
-$(SOBJLIST): $(SLIBOBJS) $(MULTISLIBOBJS)
+# Create a list of nonempty static object files.
+$(SOBJLIST): $(ALLSLIBOBJS)
 	$(CC) -c $(ALLCFLAGS) $(SLIBCFLAGS) -xc /dev/null -o $(EMPTYSOBJ)
 	for f in $^; do cmp -s $(EMPTYSOBJ) $$f || echo $$f; done > $@
 
-$(BUILDDLIBPATH): $(DLIBOBJS) $(MULTIDLIBOBJS)
-	$(MKINSTALLDIRS) $(BUILDDLIBDIR)
-	$(CC) $(BUILDDLIBFLAGS) $(ALLLDFLAGS) $^ -o $@
+# Make the directories separate targets to avoid collisions in parallel builds.
+$(BUILDLIBDIR) $(DESTDIR)$(LIBDIR):
+	$(MKINSTALLDIRS) $@
 
-$(BUILDSYSLIBPATH): $(DLIBOBJS) $(MULTIDLIBOBJS) $(ADDOBJS)
-	$(MKINSTALLDIRS) $(BUILDDLIBDIR)
-	$(CC) $(BUILDSYSLIBFLAGS) $(ALLLDFLAGS) $(SYSREEXPORTFLAG) $^ -o $@
+$(BUILDDLIBPATH): $(ALLDLIBOBJS) $(BUILDLIBDIR)
+	$(CC) $(BUILDDLIBFLAGS) $(ALLLDFLAGS) $(ALLDLIBOBJS) -o $@
 
-$(BUILDSLIBPATH): $(SOBJLIST)
-	$(MKINSTALLDIRS) $(BUILDSLIBDIR)
+$(BUILDSYSLIBPATH): $(ALLSYSLIBOBJS) $(BUILDLIBDIR)
+	$(CC) $(BUILDSYSLIBFLAGS) $(ALLLDFLAGS) $(SYSREEXPORTFLAG) \
+	      $(ALLSYSLIBOBJS) -o $@
+
+$(BUILDSLIBPATH): $(SOBJLIST) $(BUILDLIBDIR)
 	$(RM) $@
-	$(AR) $(BUILDSLIBFLAGS) $@ $$(cat $^)
+	$(AR) $(BUILDSLIBFLAGS) $@ $$(cat $<)
 
 $(TESTOBJS_C): %.o: %.c $(ALLHEADERS)
 	$(CC) -c -std=c99 -I$(SRCINCDIR) $(ALLCFLAGS) $< -o $@
@@ -440,18 +445,15 @@ install-headers:
 
 install-lib: install-dlib install-slib install-syslib
 
-install-dlib: $(BUILDDLIBPATH)
-	$(MKINSTALLDIRS) $(DESTDIR)$(LIBDIR)
+install-dlib: $(BUILDDLIBPATH) $(DESTDIR)$(LIBDIR)
 	$(INSTALL_PROGRAM) $(BUILDDLIBPATH) $(DESTDIR)$(LIBDIR)
 	$(POSTINSTALL) -id $(DLIBPATH) $(DESTDIR)$(DLIBPATH)
 
-install-syslib: $(BUILDSYSLIBPATH)
-	$(MKINSTALLDIRS) $(DESTDIR)$(LIBDIR)
+install-syslib: $(BUILDSYSLIBPATH) $(DESTDIR)$(LIBDIR)
 	$(INSTALL_PROGRAM) $(BUILDSYSLIBPATH) $(DESTDIR)$(LIBDIR)
 	$(POSTINSTALL) -id $(SYSLIBPATH) $(DESTDIR)$(SYSLIBPATH)
 
-install-slib: $(BUILDSLIBPATH)
-	$(MKINSTALLDIRS) $(DESTDIR)$(LIBDIR)
+install-slib: $(BUILDSLIBPATH) $(DESTDIR)$(LIBDIR)
 	$(INSTALL_DATA) $(BUILDSLIBPATH) $(DESTDIR)$(LIBDIR)
 
 install-tiger: $(TIGERBINS)
@@ -475,7 +477,7 @@ test_clean: xtest_clean $(MANRUNPREFIX)clean
 clean: $(MANRUNPREFIX)clean test_clean
 	$(RM) $(foreach D,$(SRCDIR),$D/*.o $D/*.o.* $D/*.d)
 	$(RM) $(BUILDDLIBPATH) $(BUILDSLIBPATH) $(BUILDSYSLIBPATH) $(TESTPRGS) test/test_cmath_* test/test_faccessat_setuid
-	@$(RMDIR) $(BUILDDLIBDIR) $(BUILDSLIBDIR)
+	@$(RMDIR) $(BUILDLIBDIR)
 
 .PHONY: all dlib syslib slib clean check test test_cmath xtest test_static
 .PHONY: $(TESTRUNS) $(XTESTRUNS) $(MANTESTRUNS)
-- 
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