Platform/GNU: Add Debian shared library permissions policy

Copy the `CMAKE_INSTALL_SO_NO_EXE` setting from `Platform/Linux`.

Fixes: #18376

1 files changed, 27 insertions, 0 deletions

diff --git a/Modules/Platform/GNU.cmake b/Modules/Platform/GNU.cmake
index e8c3b65..fac29a8 100644
--- a/Modules/Platform/GNU.cmake
+++ b/Modules/Platform/GNU.cmake
@@ -8,6 +8,33 @@ set(CMAKE_SHARED_LIBRARY_RPATH_LINK_C_FLAG "-Wl,-rpath-link,")
 set(CMAKE_SHARED_LIBRARY_SONAME_C_FLAG "-Wl,-soname,")
 set(CMAKE_EXE_EXPORTS_C_FLAG "-Wl,--export-dynamic")
 
+# Debian policy requires that shared libraries be installed without
+# executable permission.  Fedora policy requires that shared libraries
+# be installed with the executable permission.  Since the native tools
+# create shared libraries with execute permission in the first place a
+# reasonable policy seems to be to install with execute permission by
+# default.  In order to support debian packages we provide an option
+# here.  The option default is based on the current distribution, but
+# packagers can set it explicitly on the command line.
+if(DEFINED CMAKE_INSTALL_SO_NO_EXE)
+  # Store the decision variable in the cache.  This preserves any
+  # setting the user provides on the command line.
+  set(CMAKE_INSTALL_SO_NO_EXE "${CMAKE_INSTALL_SO_NO_EXE}" CACHE INTERNAL
+    "Install .so files without execute permission.")
+else()
+  # Store the decision variable as an internal cache entry to avoid
+  # checking the platform every time.  This option is advanced enough
+  # that only package maintainers should need to adjust it.  They are
+  # capable of providing a setting on the command line.
+  if(EXISTS "/etc/debian_version")
+    set(CMAKE_INSTALL_SO_NO_EXE 1 CACHE INTERNAL
+      "Install .so files without execute permission.")
+  else()
+    set(CMAKE_INSTALL_SO_NO_EXE 0 CACHE INTERNAL
+      "Install .so files without execute permission.")
+  endif()
+endif()
+
 set(CMAKE_LIBRARY_ARCHITECTURE_REGEX "[a-z0-9_]+(-[a-z0-9_]+)?-gnu[a-z0-9_]*")
 
 include(Platform/UnixPaths)