Both the Debug and Release builds try to write .o and .a files to WebKit/chromium/out/WebCore/* . Trying to switch between the two can cause problems for the linker. The Makefile generated by gyp assumes that it is at the root of the build tree. We generate the Makefile in WebKit/chromium/, but build files in WebCore, so this causes targets like this: OBJS := $(obj).target/$(TARGET)/../../WebCore/accessibility/AXObjectCache.o \ $(obj).target/$(TARGET)/../../WebCore/accessibility/AccessibilityARIAGrid.o \ $(obj).target/$(TARGET)/../../WebCore/accessibility/AccessibilityARIAGridCell.o \ The fix would be to try to generate something like Makefile.chromium in the root of the checkout so all the paths would be below the Makefile.
*** This bug has been marked as a duplicate of bug 40285 ***