C++ : Add the -stdlib= option.

This option allows the user to specifiy alternate C++ runtime libraries,
for example when a platform uses libc++ as the installed C++ runtime.

We introduce the command line option: -stdlib= which is the user-facing
mechanism to select the C++ runtime to be used when compiling and linking
code.  This is the same option spelling as that used by clang to allow the
use of libstdc++.

The availability (and thus function) of the option are a configure-time
choice using the configuration control:
--with-gxx-libcxx-include-dir=

Specification of the path for the libc++ headers, enables the -stdlib=
option (using the path as given), default values are set when the path
is unconfigured.

If --with-gxx-libcxx-include-dir is given together with --with-sysroot=,
then we test to see if the include path starts with the sysroot and, if so,
record the sysroot-relative component as the local path.  At runtime, we
prepend the sysroot that is actually active.

At link time, we use the C++ runtime in force and (if that is libc++) also
append the libc++abi ABI library. As for other cases, if a target sets the
name pointer for the ABI library to NULL the G++ driver will omit it from
the link line.

gcc/ChangeLog:

	* configure.ac: Add gxx-libcxx-include-dir handled
	in the same way as the regular cxx header directory.
	* Makefile.in: Regenerated.
	* config.in: Likewise.
	* configure: Likewise.
	* cppdefault.c: Pick up libc++ headers if the option
	is enabled.
	* cppdefault.h (struct default_include): Amend comments
	to reflect the extended use of the cplusplus field.
	* incpath.c (add_standard_paths): Allow for multiple
	c++ header include path variants.
	* doc/invoke.texi: Document the -stdlib= option.

gcc/c-family/ChangeLog:

	* c.opt: Add -stdlib= option and enumerations for
	libstdc++ and libc++.

gcc/cp/ChangeLog:

	* g++spec.c (LIBCXX, LIBCXX_PROFILE, LIBCXX_STATIC): New.
	(LIBCXXABI, LIBCXXABI_PROFILE, LIBCXXABI_STATIC): New.
	(enum stdcxxlib_kind): New.
	(lang_specific_driver): Allow selection amongst multiple
	c++ runtime libraries.

1 files changed, 66 insertions, 8 deletions

diff --git a/gcc/cp/g++spec.c b/gcc/cp/g++spec.c
index 0f17148..a8254cd 100644
--- a/gcc/cp/g++spec.c
+++ b/gcc/cp/g++spec.c
@@ -49,6 +49,34 @@ along with GCC; see the file COPYING3.  If not see
 #define LIBSTDCXX_STATIC NULL
 #endif
 
+#ifndef LIBCXX
+#define LIBCXX "c++"
+#endif
+#ifndef LIBCXX_PROFILE
+#define LIBCXX_PROFILE LIBCXX
+#endif
+#ifndef LIBCXX_STATIC
+#define LIBCXX_STATIC NULL
+#endif
+
+#ifndef LIBCXXABI
+#define LIBCXXABI "c++abi"
+#endif
+#ifndef LIBCXXABI_PROFILE
+#define LIBCXXABI_PROFILE LIBCXXABI
+#endif
+#ifndef LIBCXXABI_STATIC
+#define LIBCXXABI_STATIC NULL
+#endif
+
+/* The values used here must match those of the stdlib_kind enumeration
+   in c.opt.  */
+enum stdcxxlib_kind
+{
+  USE_LIBSTDCXX = 1,
+  USE_LIBCXX = 2
+};
+
 void
 lang_specific_driver (struct cl_decoded_option **in_decoded_options,
 		      unsigned int *in_decoded_options_count,
@@ -59,13 +87,16 @@ lang_specific_driver (struct cl_decoded_option **in_decoded_options,
   /* If nonzero, the user gave us the `-p' or `-pg' flag.  */
   int saw_profile_flag = 0;
 
-  /* What do with libstdc++:
-     -1 means we should not link in libstdc++
-     0  means we should link in libstdc++ if it is needed
-     1  means libstdc++ is needed and should be linked in.
-     2  means libstdc++ is needed and should be linked statically.  */
+  /* What action to take for the c++ runtime library:
+    -1  means we should not link it in.
+     0  means we should link it if it is needed.
+     1  means it is needed and should be linked in.
+     2  means it is needed but should be linked statically.  */
   int library = 0;
 
+  /* Which c++ runtime library to link.  */
+  stdcxxlib_kind which_library = USE_LIBSTDCXX;
+
   /* The number of arguments being added to what's in argv, other than
      libraries.  We use this to track the number of times we've inserted
      -xc++/-xnone.  */
@@ -194,6 +225,10 @@ lang_specific_driver (struct cl_decoded_option **in_decoded_options,
 	  args[i] |= SKIPOPT;
 	  break;
 
+	case OPT_stdlib_:
+	  which_library = (stdcxxlib_kind) decoded_options[i].value;
+	  break;
+
 	case OPT_SPECIAL_input_file:
 	  {
 	    int len;
@@ -250,6 +285,13 @@ lang_specific_driver (struct cl_decoded_option **in_decoded_options,
 
   /* Add one for shared_libgcc or extra static library.  */
   num_args = argc + added + need_math + (library > 0) * 4 + 1;
+  /* For libc++, on most platforms, the ABI library (usually called libc++abi)
+     is provided as a separate DSO, which we must also append.
+     However, a platform might have the ability to forward the ABI library
+     from libc++, or combine it in some other way; in that case, LIBCXXABI
+     should be set to NULL to signal that it need not be appended.  */
+  if (which_library == USE_LIBCXX && LIBCXXABI != NULL)
+    num_args += 4;
   new_decoded_options = XNEWVEC (struct cl_decoded_option, num_args);
 
   i = 0;
@@ -323,9 +365,25 @@ lang_specific_driver (struct cl_decoded_option **in_decoded_options,
 	  j++;
 	}
 #endif
-      generate_option (OPT_l,
-		       saw_profile_flag ? LIBSTDCXX_PROFILE : LIBSTDCXX, 1,
-		       CL_DRIVER, &new_decoded_options[j]);
+      if (which_library == USE_LIBCXX)
+	{
+	  generate_option (OPT_l,
+			 saw_profile_flag ? LIBCXX_PROFILE : LIBCXX, 1,
+			 CL_DRIVER, &new_decoded_options[j]);
+	  if (LIBCXXABI != NULL)
+	    {
+	      j++;
+	      added_libraries++;
+	      generate_option (OPT_l,
+			       saw_profile_flag ? LIBCXXABI_PROFILE
+						: LIBCXXABI, 1,
+			       CL_DRIVER, &new_decoded_options[j]);
+	    }
+	}
+      else
+	generate_option (OPT_l,
+			 saw_profile_flag ? LIBSTDCXX_PROFILE : LIBSTDCXX, 1,
+			 CL_DRIVER, &new_decoded_options[j]);
       added_libraries++;
       j++;
       /* Add target-dependent static library, if necessary.  */