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) $(srcdir)/mkconfig.sh config.h
+ @echo "config.h generated `date`"
cs-bconfig.h: Makefile
TARGET_CPU_DEFAULT="" \
...
2) compiling gcc
2. Analysis
Most C source files included config.h which was generated by a rule.
But no related prerequisites was added to the C source compiling rule.
There was potential building failure while makefile enabled parallel.
The C source compiling rule used suffix rule '.c.o', but the suffix
rule doesn't support prerequisites.
https://www.gnu.org/software/make/manual/html_node/Suffix-Rules.html
We used the pattern rule '%.o : %.c' to instead, and add the config.h
as its prerequisite
We also moved the '%.o : %.c' rule down to the 'build/%.o :' rule, which
makes '%.o : %.c' rule doesn't override 'build/%.o :'.
For more detail:
https://bugzilla.yoctoproject.org/show_bug.cgi?id=6568
Signed-off-by: Hongxu Jia <hongxu....@windriver.com>
---
gcc/Makefile.in | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)
diff --git gcc-4.9.0/gcc/Makefile.in gcc-4.9.0/gcc/Makefile.in
index 6475cba..04889fe 100644
--- gcc-4.9.0/gcc/Makefile.in
+++ gcc-4.9.0/gcc/Makefile.in
@@ -1054,10 +1054,6 @@ COMPILE = source='$<' 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
