Restore PIE support being dropped on Linux (osquery#6611)

CMake ignores the sysroot when testing the support of PIE,
so the link test fails when it tries to check for PIE support
and decides that it's not supported.
Therefore we tell CMake that PIE is supported when using the
osquery-toolchain and leave the automatic test for other toolchains.

Temporarily disable PIE on executables built with the
osquery-toolchain libFuzzer, since it has not been compiled with PIE/PIC
support.

cmake/flags.cmake

@@ -1,5 +1,10 @@
-include(CheckPIESupported)
-check_pie_supported()
+if(NOT DEFINED OSQUERY_TOOLCHAIN_SYSROOT)
+    include(CheckPIESupported)
+    check_pie_supported()
+    if(NOT CMAKE_C_LINK_PIE_SUPPORT OR NOT CMAKE_CXX_LINK_PIE_SUPPORT)
+        message(FATAL_ERROR "The linker for the current compiler do not support -fPIE or -pie")
+    endif()
+endif()
 set(CMAKE_POSITION_INDEPENDENT_CODE ON)
 
 # The function creates the osquery_<c|cxx>_settings targets with compiler and linker flags

cmake/toolchain.cmake

@@ -6,6 +6,10 @@ if(OSQUERY_TOOLCHAIN_SYSROOT)
   overwrite_cache_variable("CMAKE_SYSROOT" "PATH" "${OSQUERY_TOOLCHAIN_SYSROOT}")
   overwrite_cache_variable("CMAKE_LINK_SEARCH_START_STATIC" "BOOL" "ON")
   overwrite_cache_variable("CMAKE_LINK_SEARCH_END_STATIC" "BOOL" "ON")
+  overwrite_cache_variable("CMAKE_CXX_LINK_NO_PIE_SUPPORTED" "INTERNAL" "TRUE")
+  overwrite_cache_variable("CMAKE_CXX_LINK_PIE_SUPPORTED" "INTERNAL" "TRUE")
+  overwrite_cache_variable("CMAKE_C_LINK_NO_PIE_SUPPORTED" "INTERNAL" "TRUE")
+  overwrite_cache_variable("CMAKE_C_LINK_PIE_SUPPORTED" "INTERNAL" "TRUE")
 else()
   option(OSQUERY_STATIC_BUILD "Whether to prefer linking static libraries or not")
 

osquery/main/harnesses/CMakeLists.txt

@@ -67,7 +67,11 @@ endfunction()
 
 function(generateOsqueryFuzzHarness harness_name source_files)
   add_osquery_executable(${harness_name} ${source_files})
-  set_target_properties(${harness_name} PROPERTIES POSITION_INDEPENDENT_CODE true)
+  # TODO: osquery-toolchain libFuzzer is not compiled with -fPIC support,
+  # temporarily disable PIE until the toolchain is fixed.
+  if(DEFINED OSQUERY_TOOLCHAIN_SYSROOT)
+    set_target_properties(${harness_name} PROPERTIES POSITION_INDEPENDENT_CODE OFF)
+  endif()
   target_link_libraries(${harness_name} PRIVATE osquery_harnesses)
   target_link_options(${harness_name} PRIVATE -fsanitize=fuzzer)
 endfunction()