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.

1 files changed, 34 insertions, 3 deletions

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