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author | Schrodinger ZHU Yifan <yifanzhu@rochester.edu> | 2023-12-20 11:18:51 -0500 |
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committer | GitHub <noreply@github.com> | 2023-12-20 08:18:51 -0800 |
commit | 8bbeed05c4da832a2abf532fee8665c0d6576cbc (patch) | |
tree | 54ca161edf3fc736d29da437ff6cfc3c534a7b34 /libc/startup | |
parent | e4f4022b7044b135a950a5fdc033af13fee9f6fa (diff) | |
download | llvm-8bbeed05c4da832a2abf532fee8665c0d6576cbc.zip llvm-8bbeed05c4da832a2abf532fee8665c0d6576cbc.tar.gz llvm-8bbeed05c4da832a2abf532fee8665c0d6576cbc.tar.bz2 |
[libc] [startup] add cmake function to merge separated crt1 objects (#75413)
As part of startup refactoring, this patch adds a function to merge
multiple objects into a single relocatable object:
cc -r obj1.o obj2.o -o obj.o
A relocatable object is an object file that is not fully linked into an
executable or a shared library. It is an intermediate file format that
can be passed into the linker.
A crt object can have arch-specific code and arch-agnostic code. To
reduce code cohesion, the implementation is splitted into multiple
units. As a result, we need to merge them into a single relocatable
object.
Diffstat (limited to 'libc/startup')
-rw-r--r-- | libc/startup/linux/CMakeLists.txt | 71 |
1 files changed, 60 insertions, 11 deletions
diff --git a/libc/startup/linux/CMakeLists.txt b/libc/startup/linux/CMakeLists.txt index 007aa30..d81c7db 100644 --- a/libc/startup/linux/CMakeLists.txt +++ b/libc/startup/linux/CMakeLists.txt @@ -1,19 +1,62 @@ +# This function merges multiple objects into a single relocatable object +# cc -r obj1.o obj2.o -o obj.o +# A relocatable object is an object file that is not fully linked into an +# executable or a shared library. It is an intermediate file format that can +# be passed into the linker. +# A crt object has arch-specific code and arch-agnostic code. To reduce code +# duplication, the implementation is split into multiple units. As a result, +# we need to merge them into a single relocatable object. +# See also: https://maskray.me/blog/2022-11-21-relocatable-linking +function(merge_relocatable_object name) + set(obj_list "") + set(fq_link_libraries "") + get_fq_deps_list(fq_dep_list ${ARGN}) + foreach(target IN LISTS fq_dep_list) + list(APPEND obj_list "$<TARGET_OBJECTS:${target}>") + get_target_property(libs ${target} DEPS) + list(APPEND fq_link_libraries "${libs}") + endforeach() + list(REMOVE_DUPLICATES obj_list) + list(REMOVE_DUPLICATES fq_link_libraries) + get_fq_target_name(${name} fq_name) + set(relocatable_target "${fq_name}.__relocatable__") + add_executable( + ${relocatable_target} + ${obj_list} + ) + # Pass -r to the driver is much cleaner than passing -Wl,-r: the compiler knows it is + # a relocatable linking and will not pass other irrelevant flags to the linker. + target_link_options(${relocatable_target} PRIVATE -r) + set_target_properties( + ${relocatable_target} + PROPERTIES + RUNTIME_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR} + OUTPUT_NAME ${name}.o + ) + add_library(${fq_name} OBJECT IMPORTED GLOBAL) + add_dependencies(${fq_name} ${relocatable_target}) + target_link_libraries(${fq_name} INTERFACE ${fq_link_libraries}) + set_target_properties( + ${fq_name} + PROPERTIES + LINKER_LANGUAGE CXX + IMPORTED_OBJECTS ${CMAKE_CURRENT_BINARY_DIR}/${name}.o + TARGET_TYPE ${OBJECT_LIBRARY_TARGET_TYPE} + DEPS "${fq_link_libraries}" + ) +endfunction() + function(add_startup_object name) cmake_parse_arguments( "ADD_STARTUP_OBJECT" - "ALIAS" # Option argument + "" # Option argument "SRC" # Single value arguments "DEPENDS;COMPILE_OPTIONS" # Multi value arguments ${ARGN} ) get_fq_target_name(${name} fq_target_name) - if(ADD_STARTUP_OBJECT_ALIAS) - get_fq_deps_list(fq_dep_list ${ADD_STARTUP_OBJECT_DEPENDS}) - add_library(${fq_target_name} ALIAS ${fq_dep_list}) - return() - endif() - + add_object_library( ${name} SRCS ${ADD_STARTUP_OBJECT_SRC} @@ -27,6 +70,13 @@ function(add_startup_object name) ) endfunction() +check_cxx_compiler_flag("-r" LIBC_LINKER_SUPPORTS_RELOCATABLE) + +if(NOT LIBC_LINKER_SUPPORTS_RELOCATABLE) + message(STATUS "Skipping startup for target architecture ${LIBC_TARGET_ARCHITECTURE}: linker does not support -r") + return() +endif() + if(NOT (EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_ARCHITECTURE})) message(STATUS "Skipping startup for target architecture ${LIBC_TARGET_ARCHITECTURE}") return() @@ -34,11 +84,10 @@ endif() add_subdirectory(${LIBC_TARGET_ARCHITECTURE}) -add_startup_object( +# TODO: factor out crt1 into multiple objects +merge_relocatable_object( crt1 - ALIAS - DEPENDS - .${LIBC_TARGET_ARCHITECTURE}.crt1 + .${LIBC_TARGET_ARCHITECTURE}.crt1 ) add_startup_object( |