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[PATCH][gcc-4.9.0] gcc/Makefile.in: fix parallel building failure


1. How to reproduce the issue:

1) manually modify gcc/Makefile.in to delay the generation of config.h:
...
diff --git gcc-4.9.0/gcc/Makefile.in gcc-4.9.0/gcc/Makefile.in
--- gcc-4.9.0/gcc/Makefile.in
+++ gcc-4.9.0/gcc/Makefile.in
@@ -1622,9 +1622,12 @@ tm.h: cs-tm.h ; @true
 tm_p.h: cs-tm_p.h ; @true
 
 cs-config.h: Makefile
+   @echo "start to generate config.h `date`"
+   sleep 10
    TARGET_CPU_DEFAULT="" \
    HEADERS="$(host_xm_include_list)" DEFINES="$(host_xm_defines)" \
    $(SHELL) $(srcdir)/mkconfig.sh config.h
+   @echo "config.h generated `date`"
 
 cs-bconfig.h: Makefile
    TARGET_CPU_DEFAULT="" \
...

2) compiling gcc

2. Analysis

Most C source files included config.h which was generated by a rule.
But no related prerequisites was added to the C source compiling rule.
There was potential building failure while makefile enabled parallel.

The C source compiling rule used suffix rule '.c.o', but the suffix
rule doesn't support prerequisites.
https://www.gnu.org/software/make/manual/html_node/Suffix-Rules.html

We used the pattern rule '%.o : %.c' to instead, and add the config.h
as its prerequisite

We also moved the '%.o : %.c' rule down to the 'build/%.o :' rule, which
makes '%.o : %.c' rule doesn't override 'build/%.o :'.

For more detail:
https://bugzilla.yoctoproject.org/show_bug.cgi?id=6568

Signed-off-by: Hongxu Jia <hongxu.jia@windriver.com>
---
 gcc/Makefile.in | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git gcc-4.9.0/gcc/Makefile.in gcc-4.9.0/gcc/Makefile.in
index 6475cba..04889fe 100644
--- gcc-4.9.0/gcc/Makefile.in
+++ gcc-4.9.0/gcc/Makefile.in
@@ -1054,10 +1054,6 @@ COMPILE = source='$<' object='$@' libtool=no \
 POSTCOMPILE =
 endif
 
-.cc.o .c.o:
-	$(COMPILE) $<
-	$(POSTCOMPILE)
-
 #
 # Support for additional languages (other than C).
 # C can be supported this way too (leave for later).
@@ -2342,6 +2338,14 @@ build/%.o :  # dependencies provided by explicit rule later
 	$(COMPILER_FOR_BUILD) -c $(BUILD_COMPILERFLAGS) $(BUILD_CPPFLAGS) \
 		-o $@ $<
 
+%.o: %.c $(CONFIG_H)
+	$(COMPILE) $<
+	$(POSTCOMPILE)
+
+%.o: %.cc $(CONFIG_H)
+	$(COMPILE) $<
+	$(POSTCOMPILE)
+
 ## build/version.o is compiled by the $(COMPILER_FOR_BUILD) but needs
 ## several C macro definitions, just like version.o
 build/version.o:  version.c version.h \
-- 
1.8.1.2


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