/usr/src/gcc-4.8/debian/patches/kfreebsd-boehm-gc.diff is in gcc-4.8-source 4.8.2-19ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 | # DP: boehm-gc: use mmap instead of brk also on kfreebsd-*.
--- a/src/boehm-gc/configure.host
+++ b/src/boehm-gc/configure.host
@@ -41,7 +41,7 @@
fi
case "${host}" in
- *-linux*)
+ *-linux*|*-kfreebsd*-gnu*)
gc_use_mmap=yes
;;
esac
|