Merge pull request #381 from public/compile-openssl-docs

Document compiling OpenSSL to avoid conflicts

1 files changed, 27 insertions, 0 deletions

diff --git a/docs/hazmat/backends/openssl.rst b/docs/hazmat/backends/openssl.rst
index 5e51c75e..99b327d9 100644
--- a/docs/hazmat/backends/openssl.rst
+++ b/docs/hazmat/backends/openssl.rst
@@ -21,5 +21,32 @@ These are `CFFI`_ bindings to the `OpenSSL`_ C library.
         and access constants.
 
 
+Using your own OpenSSL on Linux
+-------------------------------
+
+Python links to OpenSSL for its own purposes and this can sometimes cause
+problems when you wish to use a different version of OpenSSL with cryptography.
+If you want to use cryptography with your own build of OpenSSL you will need to
+make sure that the build is configured correctly so that your version of
+OpenSSL doesn't conflict with Python's.
+
+The options you need to add allow the linker to identify every symbol correctly
+even when multiple versions of the library are linked into the same program. If
+you are using your distribution's source packages these will probably be
+patched in for you already, otherwise you'll need to use options something like
+this when configuring OpenSSL::
+
+    ./config -Wl,--version-script=openssl.ld -Wl,-Bsymbolic-functions -fPIC shared
+
+You'll also need to generate your own ``openssl.ld`` file. For example::
+
+    OPENSSL_1.0.1F_CUSTOM {
+        global:
+            *;
+    };
+
+You should replace the version string on the first line as appropriate for your
+build.
+
 .. _`CFFI`: https://cffi.readthedocs.org/
 .. _`OpenSSL`: https://www.openssl.org/