Problem: overriding postgres symbols

Solution: add a target that checks if Postgres and a Postgres extension have
conflicting symbols. If conflicting symbols are detected the build shall fail.

cmake/PostgreSQLExtension.cmake

@@ -165,7 +165,7 @@ function(add_postgresql_extension NAME)
         add_library(${_ext_TARGET} MODULE ${_ext_SOURCES})
     endif()
 
-    # inja ia a default target dependency for all extensions    
+    # inja ia a default target dependency for all extensions
     if(NOT TARGET inja)
         add_subdirectory("${CMAKE_CURRENT_SOURCE_DIR}/../../misc/inja" "${CMAKE_CURRENT_BINARY_DIR}/inja")
     endif()
@@ -255,6 +255,16 @@ function(add_postgresql_extension NAME)
                 PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})
     endif()
 
+    # Check that the extension has no conflicting symbols with the Postgres binary
+    # otherwise the linker might use the symbols from Postgres
+    find_package(Python COMPONENTS Interpreter REQUIRED)
+    execute_process(COMMAND dirname ${PG_CTL} OUTPUT_VARIABLE POSTGRES_BINARY)
+    get_filename_component(POSTGRES_BINARY ${PG_CTL}/../postgres ABSOLUTE)
+    set(SO_FILE "${CMAKE_CURRENT_BINARY_DIR}/${_ext_TARGET}${_suffix}")
+    add_custom_target(omni_check_symbol_conflict_${_ext_TARGET} ALL
+            WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
+            COMMAND ${Python_EXECUTABLE} ${CMAKE_CURRENT_FUNCTION_LIST_DIR}/check_symbol_conflict.py ${POSTGRES_BINARY} ${SO_FILE})
+
     set(_pkg_dir "${CMAKE_BINARY_DIR}/packaged")
 
     if(_ext_SOURCES)

cmake/check_symbol_conflict.py

@@ -0,0 +1,35 @@
+import platform
+import subprocess
+import sys
+
+
+def get_symbols(binary):
+    symbols = set()
+    args = ["nm"]
+    if platform.system() == "Darwin":
+        args += ["-g", "-U", binary]
+    elif platform.system() == "Linux":
+        args += ["-g", "--defined-only", binary]
+    else:
+        raise Exception("Unsupported platform %s" % platform.system())
+    res = subprocess.run(args, stdout=subprocess.PIPE)
+    for line in res.stdout.decode("utf-8").split("\n"):
+        # skip over empty lines and lines that are not symbols
+        if line.strip() and "for architecture" not in line:
+            symbols.add(line.split(" ")[2])
+    return symbols
+
+
+
+if __name__ == "__main__":
+    if len(sys.argv) < 3:
+        print("Usage: %s <binary1> <binary2>" % sys.argv[0])
+        sys.exit(1)
+    binary1, binary2 = sys.argv[1:]
+    symbols1 = get_symbols(binary1)
+    symbols2 = get_symbols(binary2)
+    intersection = symbols1 & symbols2
+    if symbols1 & symbols2:
+        sys.stderr.write("Found symbols that are present in both binaries:\n")
+        sys.stderr.write("\n".join(intersection))
+        sys.exit(1)