cmake: add support for versioned symbols option

Implement the `--enable-versioned-symbols` feature available in
`./configure` for CMake.

Enable with `-DCURL_LIBCURL_VERSIONED_SYMBOLS=ON`. Customize the version
prefix with `-DCURL_LIBCURL_VERSIONED_SYMBOLS_PREFIX=MYPREFIX_`. By
default the prefix matches what autotools uses.

When enabled, the feature is detected and a warning shown if
unavailable. (E.g. on Apple and Windows, it isn't.)

Included `HIDDEN {};` to match autotools, though I don't know if it's
necessary, useful or making any difference.

Differences from the autotools implementation:
- soversion is dynamic instead of hard-coded.
- omits referencing non-curl symbols.
- allows prefix/flavour override.
- more universal feature detection.
- doesn't rely on the in-repo `lib/libcurl.vers.in` file.

Also:
- add mbedTLS and BearSSL versioned symbol prefix support to autotools.
- enable this option in an old-linux job.

Follow-up to 7cc2e8b349
Fixes #14349
Closes #14378

.github/workflows/linux-old.yml

@@ -81,7 +81,8 @@ jobs:
         run: |
           mkdir bld-1
           cd bld-1
-          cmake .. -DCMAKE_UNITY_BUILD=ON -DCURL_WERROR=ON -DBUILD_SHARED_LIBS=ON -DENABLE_ARES=OFF -DCURL_ZSTD=OFF -DCURL_USE_GSSAPI=OFF -DCURL_USE_LIBSSH2=ON -DCURL_USE_LIBSSH=OFF
+          cmake .. -DCMAKE_UNITY_BUILD=ON -DCURL_WERROR=ON -DBUILD_SHARED_LIBS=ON \
+            -DENABLE_ARES=OFF -DCURL_ZSTD=OFF -DCURL_USE_GSSAPI=OFF -DCURL_USE_LIBSSH2=ON -DCURL_USE_LIBSSH=OFF
           make install
           src/curl --disable --version
 
@@ -89,7 +90,9 @@ jobs:
         run: |
           mkdir bld-cares
           cd bld-cares
-          cmake .. -DCMAKE_UNITY_BUILD=ON -DCURL_WERROR=ON -DBUILD_SHARED_LIBS=ON -DENABLE_ARES=ON -DCURL_ZSTD=ON -DCURL_USE_GSSAPI=ON -DCURL_USE_LIBSSH2=OFF -DCURL_USE_LIBSSH=ON
+          cmake .. -DCMAKE_UNITY_BUILD=ON -DCURL_WERROR=ON -DBUILD_SHARED_LIBS=ON \
+            -DENABLE_ARES=ON -DCURL_ZSTD=ON -DCURL_USE_GSSAPI=ON -DCURL_USE_LIBSSH2=OFF -DCURL_USE_LIBSSH=ON \
+            -DCURL_LIBCURL_VERSIONED_SYMBOLS=ON
 
       - name: 'build'
         run: |

configure.ac

@@ -2495,6 +2495,10 @@ AS_HELP_STRING([--disable-versioned-symbols], [Disable versioned symbols in shar
           versioned_symbols_flavour="MULTISSL_"
         elif test "x$OPENSSL_ENABLED" = "x1"; then
           versioned_symbols_flavour="OPENSSL_"
+        elif test "x$MBEDTLS_ENABLED" = "x1"; then
+          versioned_symbols_flavour="MBEDTLS_"
+        elif test "x$BEARSSL_ENABLED" = "x1"; then
+          versioned_symbols_flavour="BEARSSL_"
         elif test "x$GNUTLS_ENABLED" = "x1"; then
           versioned_symbols_flavour="GNUTLS_"
         elif test "x$WOLFSSL_ENABLED" = "x1"; then

lib/CMakeLists.txt

@@ -212,18 +212,59 @@ if(BUILD_SHARED_LIBS)
   endif()
 
   option(CURL_LIBCURL_SOVERSION "Enable libcurl SOVERSION" ${_soversion_default})
+  option(CURL_LIBCURL_VERSIONED_SYMBOLS "Enable libcurl versioned symbols" OFF)
 
-  if(CURL_LIBCURL_SOVERSION)
+  if(CURL_LIBCURL_SOVERSION OR CURL_LIBCURL_VERSIONED_SYMBOLS)
     # Get 'VERSIONCHANGE', 'VERSIONADD', 'VERSIONDEL', 'VERSIONINFO' variables
     transform_makefile_inc("Makefile.soname" "${CMAKE_CURRENT_BINARY_DIR}/Makefile.soname.cmake")
     include(${CMAKE_CURRENT_BINARY_DIR}/Makefile.soname.cmake)
 
     math(EXPR _cmakesoname "${VERSIONCHANGE} - ${VERSIONDEL}")
     set(_cmakeversion "${_cmakesoname}.${VERSIONDEL}.${VERSIONADD}")
+  endif()
 
+  if(CURL_LIBCURL_SOVERSION)
     set_target_properties(${LIB_SHARED} PROPERTIES
       VERSION "${_cmakeversion}" SOVERSION "${_cmakesoname}")
   endif()
+
+  ## Versioned symbols
+
+  if(CURL_LIBCURL_VERSIONED_SYMBOLS)
+    if(NOT DEFINED CURL_LIBCURL_VERSIONED_SYMBOLS_PREFIX)
+      # Default to prefixes used by autotools
+      if(CURL_WITH_MULTI_SSL)
+        set(CURL_LIBCURL_VERSIONED_SYMBOLS_PREFIX "MULTISSL_")
+      elseif(CURL_USE_OPENSSL)
+        set(CURL_LIBCURL_VERSIONED_SYMBOLS_PREFIX "OPENSSL_")
+      elseif(CURL_USE_MBEDTLS)
+        set(CURL_LIBCURL_VERSIONED_SYMBOLS_PREFIX "MBEDTLS_")
+      elseif(CURL_USE_BEARSSL)
+        set(CURL_LIBCURL_VERSIONED_SYMBOLS_PREFIX "BEARSSL_")
+      elseif(CURL_USE_WOLFSSL)
+        set(CURL_LIBCURL_VERSIONED_SYMBOLS_PREFIX "WOLFSSL_")
+      elseif(CURL_USE_GNUTLS)
+        set(CURL_LIBCURL_VERSIONED_SYMBOLS_PREFIX "GNUTLS_")
+      endif()
+    endif()
+    file(WRITE "${CMAKE_CURRENT_BINARY_DIR}/libcurl.vers" "
+      HIDDEN {};
+      CURL_${CURL_LIBCURL_VERSIONED_SYMBOLS_PREFIX}${_cmakesoname}
+      {
+        global: curl_*;
+        local: *;
+      };")
+    include(CheckCSourceCompiles)
+    set(CMAKE_REQUIRED_LINK_OPTIONS "-Wl,--version-script=${CMAKE_CURRENT_BINARY_DIR}/libcurl.vers")
+    check_c_source_compiles("int main(void) { return 0; }" HAVE_VERSIONED_SYMBOLS)
+    if(HAVE_VERSIONED_SYMBOLS)
+      # Superseded by LINK_OPTIONS in CMake 3.13 and later.
+      set_target_properties(${LIB_SHARED} PROPERTIES LINK_FLAGS "${CMAKE_REQUIRED_LINK_OPTIONS}")
+    else()
+      message(WARNING "Versioned symbols requested, but not supported by the toolchain.")
+    endif()
+    unset(CMAKE_REQUIRED_LINK_OPTIONS)
+  endif()
 endif()
 
 add_library(${LIB_NAME} ALIAS ${LIB_SELECTED})