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re-expand CXX_FOR_TARGET after libstdc++-v3 is configured

From: Alexandre Oliva <aoliva at redhat dot com>
To: gcc-patches at gcc dot gnu dot org
Date: Sat, 13 Nov 2010 17:19:35 -0200
Subject: re-expand CXX_FOR_TARGET after libstdc++-v3 is configured

I got a report from RTH and Aldy that libitm (in the
transactional-memory branch) would fail to build at first, but once you
retried, it would succeed.  What's new about libitm is that it expects
CXX to be a functional C++ compiler, with usual C++ headers in place.
Other libraries that require a C++ compiler don't seem to depend on the
C++ headers.

It turns out the problem is that CXX_FOR_TARGET is shell-evaluated and
passed down to sub-makes before libstdc++-v3 is configured, but it can
only get the right -I flags after libstdc++-v3 is configured.  Thus the
first build fails, but the subsequent one overrides the incorrect CXX
settings passed to libitm and it works out in the end.

This patch changes our handling of CXX_FOR_TARGET in two ways:

- before libstdc++-v3 is configured, we add an invalid flag
  (-funconfigured-libstdc++-v3) to CXX_FOR_TARGET, to make sure it isn't
  used (libstdc++-v3 and libjava use RAW_CXX_FOR_TARGET)

- we do *not* pass CXX_FOR_TARGET to a sub-make if its shell expansion
  contains -funconfigured-, so that the Makefile definition prevails and
  gets expanded at every use within the sub-make.  I considered a
  cheaper make test rather than a $(shell) expansion, but it doesn't
  have the desired effect: only the shell knows how to evaluate the
  backticks in CXX_FOR_TARGET, so we end up not ever passing down an
  expansion, because the macro definition contains the -funconfigured-*
  word within backticks.  I guess it would be possible to make it a make
  test, testing for the backticks too, but it's not as robust, and
  probably not worth it.


Here's the patch.  I'll install it soon if there aren't any objections.
Tested on x86_64-linux-gnu.

for gcc/ChangeLog
from  Alexandre Oliva  <aoliva@redhat.com>

	* configure.ac (CXX_FOR_TARGET): Add -funconfigured-libstdc++-v3.
	* Makefile.def (CXX_FOR_TARGET): Removed from flags_to_pass.
	* Makefile.tpl (CXX_FOR_TARGET_FLAG_TO_PASS): New.
	(BASE_FLAGS_TO_PASS): Use it.
	* configure: Rebuilt.
	* Makefile.in: Rebuilt.
	
Index: Makefile.def
===================================================================
--- Makefile.def.orig	2010-11-13 15:46:42.995359300 -0200
+++ Makefile.def	2010-11-13 15:46:48.553299990 -0200
@@ -280,7 +280,6 @@ flags_to_pass = { flag= AS_FOR_TARGET ; 
 flags_to_pass = { flag= CC_FOR_TARGET ; };
 flags_to_pass = { flag= CFLAGS_FOR_TARGET ; };
 flags_to_pass = { flag= CPPFLAGS_FOR_TARGET ; };
-flags_to_pass = { flag= CXX_FOR_TARGET ; };
 flags_to_pass = { flag= CXXFLAGS_FOR_TARGET ; };
 flags_to_pass = { flag= DLLTOOL_FOR_TARGET ; };
 flags_to_pass = { flag= FLAGS_FOR_TARGET ; };
Index: Makefile.in
===================================================================
--- Makefile.in.orig	2010-11-13 15:46:43.095358229 -0200
+++ Makefile.in	2010-11-13 15:46:48.981295850 -0200
@@ -632,6 +632,26 @@ HOST_LIB_PATH_libelf = \
 @endif libelf
 
 
+CXX_FOR_TARGET_FLAG_TO_PASS = \
+	"CXX_FOR_TARGET=$(CXX_FOR_TARGET)"
+@if target-libstdc++-v3
+# CXX_FOR_TARGET is tricky to get right for target libs that require a
+# functional C++ compiler.  When we recurse, if we expand
+# CXX_FOR_TARGET before configuring libstdc++-v3, we won't get
+# libstdc++ include flags from the script.  Instead, we get an
+# -funconfigured-* word, so that we'll get errors if this invalid C++
+# command line is used for anything, but also so that we can use the
+# word to decide whether or not to pass on this CXX_FOR_TARGET.  If we
+# don't pass it on, sub-make will use the default definition, that
+# re-expands it at the time of use, so we'll get it right when we need
+# it.  One potential exception is the expansion of CXX_FOR_TARGET
+# passed down as part of CXX within TARGET_FLAGS, but this wouldn't
+# really work, for C++ host programs can't depend on the current-stage
+# C++ target library.
+CXX_FOR_TARGET_FLAG_TO_PASS = \
+	$(shell if echo "$(CXX_FOR_TARGET)" | grep " -funconfigured-" > /dev/null; then :; else echo '"CXX_FOR_TARGET=$(CXX_FOR_TARGET)"'; fi)
+@endif target-libstdc++-v3
+
 # Flags to pass down to all sub-makes.
 BASE_FLAGS_TO_PASS = \
 	"DESTDIR=$(DESTDIR)" \
@@ -699,7 +719,6 @@ BASE_FLAGS_TO_PASS = \
 	"CC_FOR_TARGET=$(CC_FOR_TARGET)" \
 	"CFLAGS_FOR_TARGET=$(CFLAGS_FOR_TARGET)" \
 	"CPPFLAGS_FOR_TARGET=$(CPPFLAGS_FOR_TARGET)" \
-	"CXX_FOR_TARGET=$(CXX_FOR_TARGET)" \
 	"CXXFLAGS_FOR_TARGET=$(CXXFLAGS_FOR_TARGET)" \
 	"DLLTOOL_FOR_TARGET=$(DLLTOOL_FOR_TARGET)" \
 	"FLAGS_FOR_TARGET=$(FLAGS_FOR_TARGET)" \
@@ -737,6 +756,7 @@ BASE_FLAGS_TO_PASS = \
 	"STAGEfeedback_CFLAGS=$(STAGEfeedback_CFLAGS)" \
 	"STAGEfeedback_CXXFLAGS=$(STAGEfeedback_CXXFLAGS)" \
 	"STAGEfeedback_TFLAGS=$(STAGEfeedback_TFLAGS)" \
+	$(CXX_FOR_TARGET_FLAG_TO_PASS) \
 	"TFLAGS=$(TFLAGS)" \
 	"CONFIG_SHELL=$(SHELL)" \
 	"MAKEINFO=$(MAKEINFO) $(MAKEINFOFLAGS)" 
Index: Makefile.tpl
===================================================================
--- Makefile.tpl.orig	2010-11-13 15:46:43.514353755 -0200
+++ Makefile.tpl	2010-11-13 15:46:49.604288725 -0200
@@ -543,6 +543,26 @@ HOST_LIB_PATH_[+module+] = \
 @endif [+module+]
 [+ ENDIF lib_path +][+ ENDFOR host_modules +]
 
+CXX_FOR_TARGET_FLAG_TO_PASS = \
+	"CXX_FOR_TARGET=$(CXX_FOR_TARGET)"
+@if target-libstdc++-v3
+# CXX_FOR_TARGET is tricky to get right for target libs that require a
+# functional C++ compiler.  When we recurse, if we expand
+# CXX_FOR_TARGET before configuring libstdc++-v3, we won't get
+# libstdc++ include flags from the script.  Instead, we get an
+# -funconfigured-* word, so that we'll get errors if this invalid C++
+# command line is used for anything, but also so that we can use the
+# word to decide whether or not to pass on this CXX_FOR_TARGET.  If we
+# don't pass it on, sub-make will use the default definition, that
+# re-expands it at the time of use, so we'll get it right when we need
+# it.  One potential exception is the expansion of CXX_FOR_TARGET
+# passed down as part of CXX within TARGET_FLAGS, but this wouldn't
+# really work, for C++ host programs can't depend on the current-stage
+# C++ target library.
+CXX_FOR_TARGET_FLAG_TO_PASS = \
+	$(shell if echo "$(CXX_FOR_TARGET)" | grep " -funconfigured-" > /dev/null; then :; else echo '"CXX_FOR_TARGET=$(CXX_FOR_TARGET)"'; fi)
+@endif target-libstdc++-v3
+
 # Flags to pass down to all sub-makes.
 BASE_FLAGS_TO_PASS =[+ FOR flags_to_pass +][+ IF optional +] \
 	"`echo '[+flag+]=$([+flag+])' | sed -e s'/[^=][^=]*=$$/XFOO=/'`"[+ ELSE optional +] \
@@ -550,6 +570,7 @@ BASE_FLAGS_TO_PASS =[+ FOR flags_to_pass
 	"STAGE[+id+]_CFLAGS=$(STAGE[+id+]_CFLAGS)" \
 	"STAGE[+id+]_CXXFLAGS=$(STAGE[+id+]_CXXFLAGS)" \
 	"STAGE[+id+]_TFLAGS=$(STAGE[+id+]_TFLAGS)"[+ ENDFOR bootstrap-stage +] \
+	$(CXX_FOR_TARGET_FLAG_TO_PASS) \
 	"TFLAGS=$(TFLAGS)" \
 	"CONFIG_SHELL=$(SHELL)" \
 	"MAKEINFO=$(MAKEINFO) $(MAKEINFOFLAGS)" 
Index: configure
===================================================================
--- configure.orig	2010-11-13 15:46:43.387355189 -0200
+++ configure	2010-11-13 15:46:49.762287562 -0200
@@ -13119,7 +13119,7 @@ else
   esac
   if test $ok = yes; then
     # An in-tree tool is available and we can use it
-    CXX_FOR_TARGET='$$r/$(HOST_SUBDIR)/gcc/g++ -B$$r/$(HOST_SUBDIR)/gcc/ -nostdinc++ `test ! -f $$r/$(TARGET_SUBDIR)/libstdc++-v3/scripts/testsuite_flags || $(SHELL) $$r/$(TARGET_SUBDIR)/libstdc++-v3/scripts/testsuite_flags --build-includes` -L$$r/$(TARGET_SUBDIR)/libstdc++-v3/src -L$$r/$(TARGET_SUBDIR)/libstdc++-v3/src/.libs'
+    CXX_FOR_TARGET='$$r/$(HOST_SUBDIR)/gcc/g++ -B$$r/$(HOST_SUBDIR)/gcc/ -nostdinc++ `if test -f $$r/$(TARGET_SUBDIR)/libstdc++-v3/scripts/testsuite_flags; then $(SHELL) $$r/$(TARGET_SUBDIR)/libstdc++-v3/scripts/testsuite_flags --build-includes; else echo -funconfigured-libstdc++-v3 ; fi` -L$$r/$(TARGET_SUBDIR)/libstdc++-v3/src -L$$r/$(TARGET_SUBDIR)/libstdc++-v3/src/.libs'
     { $as_echo "$as_me:${as_lineno-$LINENO}: result: just compiled" >&5
 $as_echo "just compiled" >&6; }
   elif expr "x$CXX_FOR_TARGET" : "x/" > /dev/null; then
Index: configure.ac
===================================================================
--- configure.ac.orig	2010-11-13 15:46:43.244356651 -0200
+++ configure.ac	2010-11-13 15:46:49.937285702 -0200
@@ -3162,7 +3162,7 @@ GCC_TARGET_TOOL(ar, AR_FOR_TARGET, AR, [
 GCC_TARGET_TOOL(as, AS_FOR_TARGET, AS, [gas/as-new])
 GCC_TARGET_TOOL(cc, CC_FOR_TARGET, CC, [gcc/xgcc -B$$r/$(HOST_SUBDIR)/gcc/])
 GCC_TARGET_TOOL(c++, CXX_FOR_TARGET, CXX,
-		[gcc/g++ -B$$r/$(HOST_SUBDIR)/gcc/ -nostdinc++ `test ! -f $$r/$(TARGET_SUBDIR)/libstdc++-v3/scripts/testsuite_flags || $(SHELL) $$r/$(TARGET_SUBDIR)/libstdc++-v3/scripts/testsuite_flags --build-includes` -L$$r/$(TARGET_SUBDIR)/libstdc++-v3/src -L$$r/$(TARGET_SUBDIR)/libstdc++-v3/src/.libs],
+		[gcc/g++ -B$$r/$(HOST_SUBDIR)/gcc/ -nostdinc++ `if test -f $$r/$(TARGET_SUBDIR)/libstdc++-v3/scripts/testsuite_flags; then $(SHELL) $$r/$(TARGET_SUBDIR)/libstdc++-v3/scripts/testsuite_flags --build-includes; else echo -funconfigured-libstdc++-v3 ; fi` -L$$r/$(TARGET_SUBDIR)/libstdc++-v3/src -L$$r/$(TARGET_SUBDIR)/libstdc++-v3/src/.libs],dnl see comments for CXX_FOR_TARGET_FLAG_TO_PASS
 		c++)
 GCC_TARGET_TOOL(c++ for libstdc++, RAW_CXX_FOR_TARGET, CXX,
 		[gcc/xgcc -shared-libgcc -B$$r/$(HOST_SUBDIR)/gcc -nostdinc++ -L$$r/$(TARGET_SUBDIR)/libstdc++-v3/src -L$$r/$(TARGET_SUBDIR)/libstdc++-v3/src/.libs],

-- 
Alexandre Oliva, freedom fighter    http://FSFLA.org/~lxoliva/
You must be the change you wish to see in the world. -- Gandhi
Be Free! -- http://FSFLA.org/   FSF Latin America board member
Free Software Evangelist      Red Hat Brazil Compiler Engineer

Follow-Ups:
- Re: re-expand CXX_FOR_TARGET after libstdc++-v3 is configured
  - From: Ralf Wildenhues
- Re: re-expand CXX_FOR_TARGET after libstdc++-v3 is configured
  - From: Paolo Bonzini

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