[libc] Simplify integration tests by eliminating the artificial sysroot.

The test binaries are built like any other executable but with two
additional linker options -static and -nostdlib.

Reviewed By: jhuber6

Differential Revision: https://reviews.llvm.org/D145298

libc/cmake/modules/LLVMLibCTestRules.cmake

@@ -438,74 +438,54 @@ function(add_integration_test test_name)
   get_fq_target_name(${test_name}.libc fq_libc_target_name)
 
   get_fq_deps_list(fq_deps_list ${INTEGRATION_TEST_DEPENDS})
-  # All integration tests setup TLS area and the main thread's self object.
-  # So, we need to link in the threads implementation. Likewise, the startup
-  # code also has to run init_array callbacks which potentially register
-  # their own atexit callbacks. So, link in exit and atexit also with all
-  # integration tests.
-  list(
-      APPEND fq_deps_list
+  list(APPEND fq_deps_list
+      # All integration tests setup TLS area and the main thread's self object.
+      # So, we need to link in the threads implementation. Likewise, the startup
+      # code also has to run init_array callbacks which potentially register
+      # their own atexit callbacks. So, link in exit and atexit also with all
+      # integration tests.
       libc.src.__support.threads.thread
       libc.src.stdlib.atexit
       libc.src.stdlib.exit
       libc.src.unistd.environ
-      libc.test.IntegrationTest.test)
+  )
+  list(APPEND memory_functions
+      libc.src.string.bcmp
+      libc.src.string.bzero
+      libc.src.string.memcmp
+      libc.src.string.memcpy
+      libc.src.string.memmove
+      libc.src.string.memset
+  )
+  # We remove the memory function deps because we want to explicitly add the
+  # object files which include the public symbols of the memory functions.
+  list(REMOVE_ITEM fq_deps_list ${memory_functions})
   list(REMOVE_DUPLICATES fq_deps_list)
 
   # TODO: Instead of gathering internal object files from entrypoints,
   # collect the object files with public names of entrypoints.
   get_object_files_for_test(
       link_object_files skipped_entrypoints_list ${fq_deps_list})
-  if(skipped_entrypoints_list)
-    message(STATUS "Skipping ${fq_target_name} as it has skipped deps.")
-    return()
-  endif()
-
-  # Create a sysroot structure
-  set(sysroot ${CMAKE_CURRENT_BINARY_DIR}/${test_name}/sysroot)
-  file(MAKE_DIRECTORY ${sysroot})
-  file(MAKE_DIRECTORY ${sysroot}/include)
-  set(sysroot_lib ${sysroot}/lib)
-  file(MAKE_DIRECTORY ${sysroot_lib})
-  set(startup_object_file $<TARGET_OBJECTS:${INTEGRATION_TEST_STARTUP}>)
-  set(crti_object_file $<TARGET_OBJECTS:libc.startup.linux.crti>)
-  set(crtn_object_file $<TARGET_OBJECTS:libc.startup.linux.crtn>)
-  set(dummy_archive $<TARGET_PROPERTY:libc_integration_test_dummy,ARCHIVE_OUTPUT_DIRECTORY>/lib$<TARGET_PROPERTY:libc_integration_test_dummy,ARCHIVE_OUTPUT_NAME>.a)
-  # TODO: Copy the startup files to the correct target-triple directory instead
-  # of to a partly hard-coded directory.
-  set(startup_dst ${sysroot_lib}/${LIBC_TARGET_ARCHITECTURE}-linux-gnu)
-  add_custom_command(
-    OUTPUT ${startup_dst} ${sysroot}/lib/crti.o ${sysroot}/lib/crtn.o ${sysroot}/lib/libm.a ${sysroot}/lib/libc++.a
-    COMMAND cmake -E copy ${startup_object_file} ${startup_dst}/$<TARGET_PROPERTY:${INTEGRATION_TEST_STARTUP},OUTPUT_NAME>
-    COMMAND cmake -E copy ${crti_object_file} ${sysroot_lib}/$<TARGET_PROPERTY:libc.startup.linux.crti,OUTPUT_NAME>
-    COMMAND cmake -E copy ${crtn_object_file} ${sysroot_lib}/$<TARGET_PROPERTY:libc.startup.linux.crtn,OUTPUT_NAME>
-    # We copy the dummy archive as libm.a and libc++.a as the compiler drivers expect them.
-    COMMAND cmake -E copy ${dummy_archive} ${sysroot_lib}/libm.a
-    COMMAND cmake -E copy ${dummy_archive} ${sysroot_lib}/libc++.a
-    DEPENDS ${INTEGRATION_TEST_STARTUP} libc.startup.linux.crti libc.startup.linux.crtn libc_integration_test_dummy
-  )
-  add_custom_target(
-    ${fq_target_name}.__copy_startup__
-    DEPENDS ${startup_dst}
-  )
-
+  # We add the memory functions objects explicitly. Note that we
+  # are adding objects of the targets which contain the public
+  # C symbols. This is because compiler codegen can emit calls to
+  # the C memory functions.
+  foreach(func IN LISTS memory_functions)
+    list(APPEND link_object_files $<TARGET_OBJECTS:${func}>)
+  endforeach()
+  list(REMOVE_DUPLICATES link_object_files)
+
+  # Make a library of all deps
   add_library(
-    ${fq_libc_target_name}
+    ${fq_target_name}.__libc__
     STATIC
+    EXCLUDE_FROM_ALL
     ${link_object_files}
-    # We add the memory functions objects explicitly. Note that we
-    # are adding objects of the targets which contain the public
-    # C symbols. This is because compiler codegen can emit calls to
-    # the C memory functions.
-    $<TARGET_OBJECTS:libc.src.string.bcmp>
-    $<TARGET_OBJECTS:libc.src.string.bzero>
-    $<TARGET_OBJECTS:libc.src.string.memcmp>
-    $<TARGET_OBJECTS:libc.src.string.memcpy>
-    $<TARGET_OBJECTS:libc.src.string.memmove>
-    $<TARGET_OBJECTS:libc.src.string.memset>
   )
-  set_target_properties(${fq_libc_target_name} PROPERTIES ARCHIVE_OUTPUT_NAME c)
-  set_target_properties(${fq_libc_target_name} PROPERTIES ARCHIVE_OUTPUT_DIRECTORY ${sysroot_lib})
+  set_target_properties(${fq_target_name}.__libc__
+      PROPERTIES ARCHIVE_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR})
+  set_target_properties(${fq_target_name}.__libc__
+      PROPERTIES ARCHIVE_OUTPUT_NAME ${fq_target_name}.libc)
 
   set(fq_build_target_name ${fq_target_name}.__build__)
   add_executable(
@@ -523,16 +503,13 @@ function(add_integration_test test_name)
       ${LIBC_BUILD_DIR}
       ${LIBC_BUILD_DIR}/include
   )
-  target_compile_options(${fq_build_target_name} PRIVATE -ffreestanding ${INTEGRATION_TEST_COMPILE_OPTIONS})
-  # We set a number of link options to prevent picking up system libc binaries.
-  # Also, we restrict the integration tests to fully static executables. The
-  # rtlib is set to compiler-rt to make the compiler drivers pick up the compiler
-  # runtime binaries using full paths. Otherwise, files like crtbegin.o are passed
-  # as is (and not as paths like /usr/lib/.../crtbegin.o).
-  target_link_options(${fq_build_target_name} PRIVATE --sysroot=${sysroot} -static -stdlib=libc++ --rtlib=compiler-rt)
+  target_compile_options(${fq_build_target_name}
+                         PRIVATE -ffreestanding ${INTEGRATION_TEST_COMPILE_OPTIONS})
+  target_link_options(${fq_build_target_name} PRIVATE -nostdlib -static)
+  target_link_libraries(${fq_build_target_name}
+                        ${INTEGRATION_TEST_STARTUP} ${fq_target_name}.__libc__
+                        libc.test.IntegrationTest.test)
   add_dependencies(${fq_build_target_name}
-                   ${fq_target_name}.__copy_startup__
-                   ${fq_libc_target_name}
                    libc.test.IntegrationTest.test
                    ${INTEGRATION_TEST_DEPENDS})
 
@@ -541,6 +518,5 @@ function(add_integration_test test_name)
     COMMAND ${INTEGRATION_TEST_ENV} $<TARGET_FILE:${fq_build_target_name}> ${INTEGRATION_TEST_ARGS}
     COMMENT "Running integration test ${fq_target_name}"
   )
-
   add_dependencies(${INTEGRATION_TEST_SUITE} ${fq_target_name})
 endfunction(add_integration_test)

libc/startup/linux/aarch64/start.cpp

@@ -23,6 +23,9 @@
 #include <unistd.h>
 
 extern "C" int main(int, char **, char **);
+// The BFD linker requires a reference to __dso_handle to trigger creating
+// a symbol for it when -nostdlib is used..
+extern "C" void *__dso_handle = nullptr;
 
 // Source documentation:
 // https://github.com/ARM-software/abi-aa/tree/main/sysvabi64

libc/startup/linux/x86_64/start.cpp

@@ -22,6 +22,9 @@
 #include <unistd.h>
 
 extern "C" int main(int, char **, char **);
+// The BFD linker requires a reference to __dso_handle to trigger creating
+// a symbol for it when -nostdlib is used..
+extern "C" void *__dso_handle = nullptr;
 
 namespace __llvm_libc {