Fix erroneous (and circular) implied pattern rule for linkobj/libc.so.

[BZ #15915] As described in the bug, the pattern rule for lib%.so files
in Makerules includes linkobj/libc.so as a dependency.  However, the
explicit rule for linkobj/libc.so is in the top-level Makefile.

Thus, the subdirectory makefiles that include Makerules end up with an
erroneous makefile pattern rule for linkobj/libc.so that includes
itself as a dependency.  The result is make warnings whenever rules
for other .so files are resolved -- and, on occasion, actual makefile
failures when a race condition causes the implicit rule to actually be
used.

This patch moves the explicit rules for linkobj/libc.so into Makerules
to clear up this problem.  It also elaborates a couple of comments
that I'd initially found confusing.

3 files changed, 41 insertions, 33 deletions

diff --git a/ChangeLog b/ChangeLog
index beba952cb4..12c2417679 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2013-10-03  Brooks Moses  <bmoses@google.com>
+
+	[BZ #15915]
+	* Makefile (linkobj/libc_pic.a, linkobj/libc.so): Move rules to...
+	* Makerules: ...here, and adjust associated comments.
+
 2013-10-02  Will Newton  <will.newton@linaro.org>
 
 	* malloc/Makefile: Add tst-pvalloc.
diff --git a/Makefile b/Makefile
index ba1820d2b2..302a300d48 100644
--- a/Makefile
+++ b/Makefile
@@ -123,36 +123,7 @@ lib-noranlib: subdir_lib
 
 ifeq (yes,$(build-shared))
 # Build the shared object from the PIC object library.
-lib: $(common-objpfx)libc.so
-
-lib: $(common-objpfx)linkobj/libc.so
-
-# Do not filter ld.so out of libc.so link.
-$(common-objpfx)linkobj/libc.so: link-libc-deps = # empty
-
-$(common-objpfx)linkobj/libc.so: $(elfobjdir)/soinit.os \
-				 $(common-objpfx)linkobj/libc_pic.a \
-				 $(elfobjdir)/sofini.os \
-				 $(elfobjdir)/interp.os \
-				 $(elfobjdir)/ld.so \
-				 $(shlib-lds)
-	$(build-shlib)
-
-ifeq (,$(filter sunrpc,$(subdirs)))
-$(common-objpfx)linkobj/libc_pic.a: $(common-objpfx)libc_pic.a
-	$(make-target-directory)
-	ln -f $< $@
-else
-$(common-objpfx)linkobj/libc_pic.a: $(common-objpfx)libc_pic.a \
-				    $(common-objpfx)sunrpc/librpc_compat_pic.a
-	$(make-target-directory)
-	(cd $(common-objpfx)linkobj; \
-	 $(AR) x ../libc_pic.a; \
-	 rm $$($(AR) t ../sunrpc/librpc_compat_pic.a | sed 's/^compat-//'); \
-	 $(AR) x ../sunrpc/librpc_compat_pic.a; \
-	 $(AR) cr libc_pic.a *.os; \
-	 rm *.os)
-endif # $(subdirs) contains sunrpc
+lib: $(common-objpfx)libc.so $(common-objpfx)linkobj/libc.so
 endif # $(build-shared)
 
 
diff --git a/Makerules b/Makerules
index cca3f82799..92c2872612 100644
--- a/Makerules
+++ b/Makerules
@@ -565,16 +565,47 @@ generated += libc_pic.opts libc_pic.os.clean
 libc_pic_clean := .clean
 endif
 
-# Do not filter ld.so out of libc.so link.
+# Build a possibly-modified version of libc_pic.a for use in building
+# linkobj/libc.so.
+ifeq (,$(filter sunrpc,$(subdirs)))
+$(common-objpfx)linkobj/libc_pic.a: $(common-objpfx)libc_pic.a
+	$(make-target-directory)
+	ln -f $< $@
+else
+$(common-objpfx)linkobj/libc_pic.a: $(common-objpfx)libc_pic.a \
+				    $(common-objpfx)sunrpc/librpc_compat_pic.a
+	$(make-target-directory)
+	(cd $(common-objpfx)linkobj; \
+	 $(AR) x ../libc_pic.a; \
+	 rm $$($(AR) t ../sunrpc/librpc_compat_pic.a | sed 's/^compat-//'); \
+	 $(AR) x ../sunrpc/librpc_compat_pic.a; \
+	 $(AR) cr libc_pic.a *.os; \
+	 rm *.os)
+endif # $(subdirs) contains sunrpc
+
+# Clear link-libc-deps for the libc.so libraries so build-shlibs does not
+# filter ld.so out of the list of linked objects.
 $(common-objpfx)libc.so: link-libc-deps = # empty
+$(common-objpfx)linkobj/libc.so: link-libc-deps = # empty
 
-# Use our own special initializer and finalizer files for libc.so.
+# Use our own special initializer and finalizer files for the libc.so
+# libraries.
 $(common-objpfx)libc.so: $(elfobjdir)/soinit.os \
 			 $(common-objpfx)libc_pic.os$(libc_pic_clean) \
 			 $(elfobjdir)/sofini.os \
-			 $(elfobjdir)/interp.os $(elfobjdir)/ld.so \
+			 $(elfobjdir)/interp.os \
+			 $(elfobjdir)/ld.so \
+			 $(shlib-lds)
+	$(build-shlib)
+
+$(common-objpfx)linkobj/libc.so: $(elfobjdir)/soinit.os \
+			 $(common-objpfx)linkobj/libc_pic.a \
+			 $(elfobjdir)/sofini.os \
+			 $(elfobjdir)/interp.os \
+			 $(elfobjdir)/ld.so \
 			 $(shlib-lds)
 	$(build-shlib)
+
 ifeq ($(build-shared),yes)
 $(common-objpfx)libc.so: $(common-objpfx)libc.map
 endif