137 lines
4.1 KiB
CMake
137 lines
4.1 KiB
CMake
# This function merges multiple objects into a single relocatable object
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# cc -r obj1.o obj2.o -o obj.o
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# A relocatable object is an object file that is not fully linked into an
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# executable or a shared library. It is an intermediate file format that can
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# be passed into the linker.
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# A crt object has arch-specific code and arch-agnostic code. To reduce code
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# duplication, the implementation is split into multiple units. As a result,
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# we need to merge them into a single relocatable object.
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# See also: https://maskray.me/blog/2022-11-21-relocatable-linking
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function(merge_relocatable_object name)
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set(obj_list "")
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set(fq_link_libraries "")
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get_fq_deps_list(fq_dep_list ${ARGN})
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foreach(target IN LISTS fq_dep_list)
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list(APPEND obj_list "$<TARGET_OBJECTS:${target}>")
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get_target_property(libs ${target} DEPS)
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list(APPEND fq_link_libraries "${libs}")
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endforeach()
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list(REMOVE_DUPLICATES obj_list)
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list(REMOVE_DUPLICATES fq_link_libraries)
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get_fq_target_name(${name} fq_name)
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set(relocatable_target "${fq_name}.__relocatable__")
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add_executable(
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${relocatable_target}
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${obj_list}
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)
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# Pass -r to the driver is much cleaner than passing -Wl,-r: the compiler knows it is
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# a relocatable linking and will not pass other irrelevant flags to the linker.
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target_link_options(${relocatable_target} PRIVATE -r -nostdlib)
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set_target_properties(
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${relocatable_target}
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PROPERTIES
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RUNTIME_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
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OUTPUT_NAME ${name}.o
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)
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add_library(${fq_name} OBJECT IMPORTED GLOBAL)
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add_dependencies(${fq_name} ${relocatable_target})
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target_link_libraries(${fq_name} INTERFACE ${fq_link_libraries})
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set_target_properties(
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${fq_name}
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PROPERTIES
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LINKER_LANGUAGE CXX
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IMPORTED_OBJECTS ${CMAKE_CURRENT_BINARY_DIR}/${name}.o
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TARGET_TYPE ${OBJECT_LIBRARY_TARGET_TYPE}
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DEPS "${fq_link_libraries}"
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)
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endfunction()
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function(add_startup_object name)
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cmake_parse_arguments(
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"ADD_STARTUP_OBJECT"
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"" # Option argument
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"SRC" # Single value arguments
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"DEPENDS;COMPILE_OPTIONS" # Multi value arguments
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${ARGN}
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)
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get_fq_target_name(${name} fq_target_name)
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add_object_library(
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${name}
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SRCS ${ADD_STARTUP_OBJECT_SRC}
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DEPENDS ${ADD_STARTUP_OBJECT_DEPENDS}
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COMPILE_OPTIONS ${ADD_STARTUP_OBJECT_COMPILE_OPTIONS}
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)
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set_target_properties(
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${fq_target_name}
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PROPERTIES
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OUTPUT_NAME ${name}.o
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)
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endfunction()
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check_cxx_compiler_flag("-r" LIBC_LINKER_SUPPORTS_RELOCATABLE)
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if(NOT LIBC_LINKER_SUPPORTS_RELOCATABLE)
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message(STATUS "Skipping startup for target architecture ${LIBC_TARGET_ARCHITECTURE}: linker does not support -r")
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return()
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endif()
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if(NOT (EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_ARCHITECTURE}))
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message(STATUS "Skipping startup for target architecture ${LIBC_TARGET_ARCHITECTURE}")
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return()
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endif()
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add_subdirectory(${LIBC_TARGET_ARCHITECTURE})
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add_object_library(
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do_start
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SRCS
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do_start.cpp
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HDRS
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do_start.h
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DEPENDS
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libc.config.linux.app_h
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libc.include.sys_mman
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libc.include.sys_syscall
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libc.src.__support.threads.thread
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libc.src.__support.OSUtil.osutil
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libc.src.stdlib.exit
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libc.src.stdlib.atexit
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libc.src.unistd.environ
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COMPILE_OPTIONS
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-ffreestanding # To avoid compiler warnings about calling the main function.
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-fno-builtin # avoid emit unexpected calls
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-fno-stack-protector # stack protect canary is not available yet.
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)
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# TODO: factor out crt1 into multiple objects
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merge_relocatable_object(
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crt1
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.${LIBC_TARGET_ARCHITECTURE}.start
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.${LIBC_TARGET_ARCHITECTURE}.tls
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.do_start
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)
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add_startup_object(
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crti
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SRC
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crti.cpp
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)
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add_startup_object(
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crtn
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SRC
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crtn.cpp
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)
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add_custom_target(libc-startup)
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set(startup_components crt1 crti crtn)
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foreach(target IN LISTS startup_components)
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set(fq_target_name libc.startup.linux.${target})
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add_dependencies(libc-startup ${fq_target_name})
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install(FILES $<TARGET_OBJECTS:${fq_target_name}>
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DESTINATION ${CMAKE_INSTALL_LIBDIR}
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RENAME $<TARGET_PROPERTY:${fq_target_name},OUTPUT_NAME>
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COMPONENT libc)
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endforeach()
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