GCC has two runtime libraries: The static library libgcc.a (-lgcc) and

the shared library libgcc_s.so (-lgcc_s).  Both implement many of the
same functions but they also each have their unique functions.  When
GCC links programs and libraries there are three possibilities:

1. gcc -static-libgcc or gcc -static: -lgcc
   => Just use libgcc.a.

2. gcc -shared-libgcc: -lgcc_s -lgcc
   => Link with libgcc_s first, so libgcc.a is only used for its unique
      functions.

3. gcc: -lgcc -Wl,--as-needed -lgcc_s -Wl,--no-as-needed
   => Link with libgcc.a first so libgcc_s is only used for its unique
      functions (_Unwind_* functions).

Approach 3 is the default for gcc and it's also what clang and clang++ use;
approach 2 is the default for gfortran, g++ and probably other front ends.

This patch makes 3 the default for gfortran.  It significantly reduces
the use of libgcc_s.  The _Unwind_* functions are also available in the
old base system libgcc_s which means this reduces the need for
-rpath /usr/local/lib/gccN in ports that depend on libraries built with
gfortran.  Consider a dependency tree like this:

  prog -> libA -> libgcc_s (old base system libgcc_s is fine)
       -> libB -> libgcc_s (libB built with gfortran, needs new libgcc_s)

Here prog needs to be linked with -rpath /usr/local/lib/gccN even if it's
a normal C program compiled with clang.  Without -rpath it will fail to
start because it loads old libgcc_s first as a dependency of libA and then
it fails to load libB.  With this patch libB works with old base system
libgcc_s or may not need libgcc_s at all, so prog does not need to be
linked with -rpath.

PR:		208120
Submitted by:	tijl
MFH:		2019Q2 (important user visible improvement)

2 files changed, 71 insertions, 1 deletions

diff --git a/lang/gcc8/Makefile b/lang/gcc8/Makefile
index 6b46544fc7c7..b91c0934c1a4 100644
--- a/lang/gcc8/Makefile
+++ b/lang/gcc8/Makefile
@@ -3,7 +3,7 @@
 
 PORTNAME=	gcc
 PORTVERSION=	8.3.0
-PORTREVISION=	1
+PORTREVISION=	2
 CATEGORIES=	lang
 MASTER_SITES=	GCC
 PKGNAMESUFFIX=	${SUFFIX}
diff --git a/lang/gcc8/files/patch-gfortran-libgcc b/lang/gcc8/files/patch-gfortran-libgcc
new file mode 100644
index 000000000000..89c6cb902c42
--- /dev/null
+++ b/lang/gcc8/files/patch-gfortran-libgcc
@@ -0,0 +1,70 @@
+GCC has two runtime libraries:  The static library libgcc.a (-lgcc) and
+the shared library libgcc_s.so (-lgcc_s).  Both implement many of the
+same functions but they also each have their unique functions.  When
+gcc links programs and libraries there are three possibilities:
+
+1. gcc -static-libgcc or gcc -static: -lgcc
+   => Just use libgcc.a.
+
+2. gcc -shared-libgcc: -lgcc_s -lgcc
+   => Link with libgcc_s first, so libgcc.a is only used for its unique
+      functions.
+
+3. gcc: -lgcc -Wl,--as-needed -lgcc_s -Wl,--no-as-needed
+   => Link with libgcc.a first so libgcc_s is only used for its unique
+      functions (_Unwind_* functions).
+
+Approach 3 is the default for gcc and it's also what clang and clang++ use;
+approach 2 is the default for gfortran, g++ and probably other front ends.
+
+This patch makes 3 the default for gfortran.  It significantly reduces
+the use of libgcc_s.  The _Unwind_* functions are also available in the
+old base system libgcc_s which means this reduces the need for
+-rpath /usr/local/lib/gccN in ports that depend on libraries built with
+gfortran.  Consider a dependency tree like this:
+
+  prog -> libA -> libgcc_s (old base system libgcc_s is fine)
+       -> libB -> libgcc_s (libB built with gfortran, needs new libgcc_s)
+
+Here prog needs to be linked with -rpath /usr/local/lib/gccN even if it's
+a normal C program compiled with clang.  Without -rpath it will fail to
+start because it loads old libgcc_s first as a dependency of libA and then
+it fails to load libB.  With this patch libB works with old base system
+libgcc_s or may not need libgcc_s at all, so prog does not need to be
+linked with -rpath.
+
+Upstream is unlikely accept a patch like this because libgfortran calls
+some _Unwind_* functions and so always needs libgcc_s.  Also because
+every Fortran program and library links to libgfortran it makes sense
+that option 2 above is the default.  On FreeBSD where clang and GCC
+compiled code can be mixed and where multiple libgcc_s may be installed,
+option 3 is just a lot easier to deal with.
+
+The bug that sparked this is PR 208120 (but note there's a lot of
+misleading information in that bug.  CMake is not actually doing
+anything wrong.)
+
+--- UTC
+--- gcc/fortran/gfortranspec.c.orig	2015-06-26 17:47:23 UTC
++++ gcc/fortran/gfortranspec.c
+@@ -404,7 +404,7 @@ For more information about these matters
+ 	}
+     }
+ 
+-#ifdef ENABLE_SHARED_LIBGCC
++#if 0
+   if (library)
+     {
+       unsigned int i;
+
+--- libgfortran/Makefile.in.orig	2019-02-22 14:22:13.000000000 +0000
++++ libgfortran/Makefile.in	2019-02-27 16:27:08.856408000 +0000
+@@ -625,7 +625,7 @@
+ 	$(LTLDFLAGS) $(LIBQUADLIB) ../libbacktrace/libbacktrace.la \
+ 	$(HWCAP_LDFLAGS) \
+ 	-lm $(extra_ldflags_libgfortran) \
+-	$(version_arg) -Wc,-shared-libgcc
++	$(version_arg)
+ 
+ libgfortran_la_DEPENDENCIES = $(version_dep) libgfortran.spec $(LIBQUADLIB_DEP)
+ cafexeclib_LTLIBRARIES = libcaf_single.la