rbenv を利用した ruby のインストール中にエラーとなる場合の対応

概要
===========================
rbenv を使って ruby をインストール中に、

```
warning: implicit declaration of function 'EC_GF2m_simple_method'
```

や、

```
make[2]: *** [ossl_pkey_ec.o] Error 1
```

のようなエラーメッセージが表示される場合の対応方法です。

原因
===========================

Ruby の OpenSSL 拡張に関係する既知の問題です。

対応方法
===========================
rbenv の [wiki](https://github.com/sstephenson/ruby-build/wiki#make-error-for-200-p247-and-lower-on-fedorared-hat) に記載があるように、patch をあててやりましょう。

```
curl -fsSL https://bugs.ruby-lang.org/projects/ruby-trunk/repository/revisions/41808/diff?format=diff | \
  rbenv install --patch 1.9.3-p392
```

パッチ適用中にエラーとなる場合
===========================

以下の内容を patch.diff として保存し、適用しましょう。

```patch.diff
Index: ext/openssl/ossl_pkey_ec.c
===================================================================
--- ext/openssl/ossl_pkey_ec.c	(revision 41807)
+++ ext/openssl/ossl_pkey_ec.c	(revision 41808)
@@ -762,8 +762,10 @@
                 method = EC_GFp_mont_method();
             } else if (id == s_GFp_nist) {
                 method = EC_GFp_nist_method();
+#if !defined(OPENSSL_NO_EC2M)
             } else if (id == s_GF2m_simple) {
                 method = EC_GF2m_simple_method();
+#endif
             }

             if (method) {
@@ -817,8 +819,10 @@

             if (id == s_GFp) {
                 new_curve = EC_GROUP_new_curve_GFp;
+#if !defined(OPENSSL_NO_EC2M)
             } else if (id == s_GF2m) {
                 new_curve = EC_GROUP_new_curve_GF2m;
+#endif
             } else {
                 ossl_raise(rb_eArgError, "unknown symbol, must be :GFp or :GF2m");
             }
Index: test/openssl/test_pkey_ec.rb
===================================================================
--- test/openssl/test_pkey_ec.rb	(revision 41807)
+++ test/openssl/test_pkey_ec.rb	(revision 41808)
@@ -7,28 +7,28 @@
     @data1 = 'foo'
     @data2 = 'bar' * 1000 # data too long for DSA sig

-    @group1 = OpenSSL::PKey::EC::Group.new('secp112r1')
-    @group2 = OpenSSL::PKey::EC::Group.new('sect163k1')
-    @group3 = OpenSSL::PKey::EC::Group.new('prime256v1')
+    @groups = []
+    @keys = []

-    @key1 = OpenSSL::PKey::EC.new
-    @key1.group = @group1
-    @key1.generate_key
+    OpenSSL::PKey::EC.builtin_curves.each do |curve, comment|
+      group = OpenSSL::PKey::EC::Group.new(curve)

-    @key2 = OpenSSL::PKey::EC.new(@group2.curve_name)
-    @key2.generate_key
+      key = OpenSSL::PKey::EC.new(group)
+      key.generate_key

-    @key3 = OpenSSL::PKey::EC.new(@group3)
-    @key3.generate_key
-
-    @groups = [@group1, @group2, @group3]
-    @keys = [@key1, @key2, @key3]
+      @groups << group
+      @keys << key
+    end
   end

   def compare_keys(k1, k2)
     assert_equal(k1.to_pem, k2.to_pem)
   end

+  def test_builtin_curves
+    assert(!OpenSSL::PKey::EC.builtin_curves.empty?)
+  end
+
   def test_curve_names
     @groups.each_with_index do |group, idx|
       key = @keys[idx]
```

で、

```bash
cat /vagrant/ruby-patch.diff | rbenv install --patch 1.9.3-p392
```


参考
===========================

- [Can't install on Fedora · Issue #443 · sstephenson/ruby-build](https://github.com/sstephenson/ruby-build/issues/443)
- [Home · sstephenson/ruby-build Wiki](https://github.com/sstephenson/ruby-build/wiki#make-error-for-200-p247-and-lower-on-fedorared-hat)