[Qemu-devel] [PATCH] fix tool/libuser makefile race

[Paolo Bonzini <pbonzini@redhat.com>]

I just had this race happen on me while building qemu.  The problematic
file in my case was cutils.o.  I'm using GNU make's order-only
dependencies to avoid that "make recurse-all" builds the tools as well.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 Makefile |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/Makefile b/Makefile
index d555bb2..373a861 100644
--- a/Makefile
+++ b/Makefile
@@ -79,7 +79,10 @@ romsubdir-%:
 
 ALL_SUBDIRS=$(TARGET_DIRS) $(patsubst %,pc-bios/%, $(ROMS))
 
-recurse-all: $(SUBDIR_RULES) $(ROMSUBDIR_RULES)
+# Some files are shared between the tools and the emulators.  So there
+# can be a race when the main makefile starts building xyz.o, while
+# the recursive make sees a partially built xyz.o and ar(1) fails.
+recurse-all: $(SUBDIR_RULES) $(ROMSUBDIR_RULES) | $(TOOLS)
 
 #######################################################################
 # QObject
-- 
1.6.5.2