From 59d2e56811a01ed543010b93109017f03e8881bc Mon Sep 17 00:00:00 2001
From: Ryan Lovelett <ryan@lovelett.me>
Date: Mon, 4 Apr 2016 21:28:40 -0400
Subject: [PATCH] Work around relocation R_X86_64_PC32 link error

A more complete discussion of the error and its background can be found
in SR-1023.

The brief overview is that in versions of `ld` that would be effected by
this dynamic relocation issue there are two flags: `-z nocopyreloc` and
`-z noextern-protected-data`. If `ld` supports the flags then they are
sento to the linker. This patch checks that the linker supports the
flags and then optionally sets them.

The code to check if `ld` supports the flags is inspired by this CMake
mailing list entry.

https://cmake.org/pipermail/cmake/2011-July/045525.html
---
 CMakeLists.txt                                        |  7 +++++++
 cmake/modules/AddSwift.cmake                          |  8 ++++++++
 cmake/modules/CheckLinkerDynamicRelocationFlags.cmake | 11 +++++++++++
 3 files changed, 26 insertions(+)
 create mode 100644 cmake/modules/CheckLinkerDynamicRelocationFlags.cmake

diff --git a/CMakeLists.txt b/CMakeLists.txt
index cae3647..b1ef7b6 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -277,6 +277,7 @@ option(SWIFT_BUILD_SOURCEKIT
 #
 
 include(CheckCXXSourceRuns)
+include(CheckLinkerDynamicRelocationFlags)
 include(CMakeParseArguments)
 include(SwiftTranslateFlag)
 include(SwiftHandleGybSources)
@@ -437,6 +438,12 @@ if("${CMAKE_SYSTEM_NAME}" STREQUAL "Linux")
   set(SWIFT_HOST_VARIANT_SDK "LINUX")
   set(SWIFT_PRIMARY_VARIANT_SDK_default "LINUX")
 
+  # Support relative relocation against protected symbols in binutils 2.26
+  check_linker_supports_flag("-Wl,-z,nocopyreloc"
+    "SWIFT_LINKER_SUPPORTS_NOCOPYRELOC")
+  check_linker_supports_flag("-Wl,-z,noextern-protected-data"
+    "SWIFT_LINKER_SUPPORTS_NOEXTERN_PROTECTED_DATA")
+
   # FIXME: This will not work while trying to cross-compile.
   if("${CMAKE_SYSTEM_PROCESSOR}" STREQUAL "x86_64")
     set(SWIFT_HOST_VARIANT_ARCH "x86_64")
diff --git a/cmake/modules/AddSwift.cmake b/cmake/modules/AddSwift.cmake
index 7294dd4..f6dae01 100644
--- a/cmake/modules/AddSwift.cmake
+++ b/cmake/modules/AddSwift.cmake
@@ -1189,6 +1189,14 @@ function(_add_swift_library_single target name)
     list(APPEND link_flags "-fuse-ld=gold")
   endif()
 
+  # Support relative relocation against protected symbols in binutils 2.26
+  if(SWIFT_LINKER_SUPPORTS_NOCOPYRELOC)
+    list(APPEND link_flags "-Wl,-z,nocopyreloc")
+  endif()
+  if(SWIFT_LINKER_SUPPORTS_NOEXTERN_PROTECTED_DATA)
+    list(APPEND link_flags "-Wl,-z,noextern-protected-data")
+  endif()
+
   # Configure plist creation for OS X.
   set(PLIST_INFO_PLIST "Info.plist" CACHE STRING "Plist name")
   if(APPLE AND SWIFTLIB_SINGLE_IS_STDLIB)
diff --git a/cmake/modules/CheckLinkerDynamicRelocationFlags.cmake b/cmake/modules/CheckLinkerDynamicRelocationFlags.cmake
new file mode 100644
index 0000000..0a53f77
--- /dev/null
+++ b/cmake/modules/CheckLinkerDynamicRelocationFlags.cmake
@@ -0,0 +1,11 @@
+include(CheckCXXCompilerFlag)
+
+function(check_linker_supports_flag flag_to_test var_name)
+  set(CMAKE_REQUIRED_FLAGS "${flag_to_test}")
+  check_cxx_compiler_flag("" LINKER_SUPPORTS_NOEXTERN_PROTECTED_DATA)
+  if(LINKER_SUPPORTS_NOEXTERN_PROTECTED_DATA)
+    set("${var_name}" TRUE PARENT_SCOPE)
+  else()
+    set("${var_name}" FALSE PARENT_SCOPE)
+  endif()
+endfunction()