adding support to global constructors

Adding suuport to global construcors as per
https://wiki.osdev.org/Calling_Global_Constructors

src/CMakeLists.txt

@@ -1,3 +1,4 @@
+# To include `version.h`
 include_directories("${CMAKE_CURRENT_SOURCE_DIR}")
 
-add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/kernel/)
+add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/kernel)

src/kernel/CMakeLists.txt

@@ -1,10 +1,34 @@
-add_executable(appa-os kernel.c)
+# Dummy `null.c` so we can create an OBJ lib from kernel.c and link in the correct order
-execute_process(COMMAND ${PROJECT_SOURCE_DIR}/scripts/versioning.sh WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
+file(WRITE "${CMAKE_CURRENT_BINARY_DIR}/null.c" "int main() { return 0; }")
-                OUTPUT_VARIABLE appa-os_VERSION)
+add_executable(${PROJECT_NAME} "${CMAKE_CURRENT_BINARY_DIR}/null.c")
 
-message(STATUS "Building [appa-os] version ${appa-os_VERSION}")
+# Execute versioning script
+execute_process(COMMAND ${PROJECT_SOURCE_DIR}/scripts/versioning.sh WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
+                OUTPUT_VARIABLE ${PROJECT_NAME}_VERSION)
+
+# Set target name to be "${PROJECT_NAME}.bin"
+set_target_properties(${PROJECT_NAME} PROPERTIES PREFIX "")
+set_target_properties(${PROJECT_NAME} PROPERTIES OUTPUT_NAME "${PROJECT_NAME}")
+set_target_properties(${PROJECT_NAME} PROPERTIES SUFFIX ".bin")
+
+message(STATUS "Building [${PROJECT_NAME}] version ${${PROJECT_NAME}_VERSION}")
+
+# Set linking options to link kernel bin
+target_link_options(
+  ${PROJECT_NAME}
+  PRIVATE
+  -T
+  ${CMAKE_CURRENT_SOURCE_DIR}/linker.ld
+  -ffreestanding
+  -O2
+  -nostdlib)
+
+# OBJ library to link in the correct order
+add_library(${PROJECT_NAME}-obj OBJECT ${CMAKE_CURRENT_SOURCE_DIR}/kernel.c)
+
+# Set compile options to have better code on .c and .h files
 target_compile_options(
-  appa-os
+  ${PROJECT_NAME}-obj
   PRIVATE
     $<$<COMPILE_LANGUAGE:C>:
     # Do not assume that libc standard is present
@@ -32,21 +56,19 @@ target_compile_options(
     "-Werror=implicit"
     "-Werror=incompatible-pointer-types"
     "-Werror=int-conversion">)
-target_link_options(
-  appa-os
-  PRIVATE
-  -T
-  ${CMAKE_CURRENT_SOURCE_DIR}/linker.ld
-  -ffreestanding
-  -O2
-  -nostdlib)
-set_target_properties(appa-os PROPERTIES PREFIX "")
-set_target_properties(appa-os PROPERTIES OUTPUT_NAME "appa-os")
-set_target_properties(appa-os PROPERTIES SUFFIX ".bin")
 
-file(GLOB ASM_FILES CONFIGURE_DEPENDS *.s)
+# Gather all .c and .h to generate kernel object files
 file(GLOB C_FILES CONFIGURE_DEPENDS *.c)
 file(GLOB H_FILES CONFIGURE_DEPENDS *.h)
 
-target_sources(appa-os PRIVATE ${C_FILES} ${ASM_FILES} PUBLIC ${H_FILES})
+target_sources(${PROJECT_NAME}-kernel PRIVATE ${C_FILES} PUBLIC ${H_FILES})
-target_include_directories(appa-os PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})
+target_include_directories(${PROJECT_NAME}-kernel PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})
+
+# Add complementary files
+add_subdirectory("${CMAKE_CURRENT_SOURCE_DIR}/boot")
+add_subdirectory("${CMAKE_CURRENT_SOURCE_DIR}/crt")
+
+# Make sure to build boot and CRT before the kernel itself
+# https://wiki.osdev.org/Calling_Global_Constructors#GNU_Compiler_Collection_-_System_V_ABI
+target_link_libraries(${PROJECT_NAME} PRIVATE ${PROJECT_NAME}-crti ${PROJECT_NAME}-crtbegin ${PROJECT_NAME}-boot
+                                              ${PROJECT_NAME}-kernel ${PROJECT_NAME}-crtend ${PROJECT_NAME}-crtn)

src/kernel/boot/CMakeLists.txt

@@ -0,0 +1,6 @@
+add_library(${PROJECT_NAME}-boot OBJECT)
+
+file(GLOB ASM_FILES CONFIGURE_DEPENDS *.s)
+
+target_sources(${PROJECT_NAME}-boot PRIVATE ${ASM_FILES})
+target_include_directories(${PROJECT_NAME}-boot PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})

src/kernel/crt/CMakeLists.txt

@@ -0,0 +1,28 @@
+# Gather crtbegin.o and crtend.o from toolchain
+execute_process(
+  COMMAND ${CMAKE_C_COMPILER} -print-file-name=crtbegin.o
+  WORKING_DIRECTORY ${PROJECT_SOURCE_DIR}
+  OUTPUT_VARIABLE CRTBEGIN_O
+  OUTPUT_STRIP_TRAILING_WHITESPACE)
+message(STATUS "Using crtbegin.o as ${CRTBEGIN_O}")
+add_library(${PROJECT_NAME}-crtbegin OBJECT IMPORTED GLOBAL)
+set_property(TARGET ${PROJECT_NAME}-crtbegin PROPERTY IMPORTED_OBJECTS ${CRTBEGIN_O})
+
+execute_process(
+  COMMAND ${CMAKE_C_COMPILER} -print-file-name=crtend.o
+  WORKING_DIRECTORY ${PROJECT_SOURCE_DIR}
+  OUTPUT_VARIABLE CRTEND_O
+  OUTPUT_STRIP_TRAILING_WHITESPACE)
+message(STATUS "Using crtend.o as ${CRTEND_O}")
+add_library(${PROJECT_NAME}-crtend OBJECT IMPORTED GLOBAL)
+set_property(TARGET ${PROJECT_NAME}-crtend PROPERTY IMPORTED_OBJECTS ${CRTEND_O})
+
+# Build own crt
+if(CMAKE_SYSTEM_PROCESSOR MATCHES "(i686)|(x86)|(X86)|(amd64)|(AMD64)")
+  add_subdirectory("${CMAKE_CURRENT_SOURCE_DIR}/x86")
+  add_library(${PROJECT_NAME}-crti ALIAS ${PROJECT_NAME}-crti-x86)
+  add_library(${PROJECT_NAME}-crtn ALIAS ${PROJECT_NAME}-crtn-x86)
+else()
+  message(FATAL_ERROR "Unsupported CRT for ${CMAKE_SYSTEM_PROCESSOR}")
+endif()
+

src/kernel/crt/x86/CMakeLists.txt

@@ -0,0 +1,2 @@
+add_library(${PROJECT_NAME}-crti-x86 OBJECT crti.s)
+add_library(${PROJECT_NAME}-crtn-x86 OBJECT crtn.s)

src/kernel/crt/x86/crti.s

@@ -0,0 +1,20 @@
+// x86 crti.s
+.section .init
+.global  _init
+.type    _init, @function
+
+_init:
+	push %ebp
+	movl %esp, %ebp
+
+	// gcc will nicely put the contents of crtbegin.o's .init section here.
+
+	.section .fini
+	.global  _fini
+	.type    _fini, @function
+
+_fini:
+	push %ebp
+	movl %esp, %ebp
+
+	// gcc will nicely put the contents of crtbegin.o's .fini section here.

src/kernel/crt/x86/crtn.s

@@ -0,0 +1,12 @@
+// x86 crtn.s
+.section .init
+
+	// gcc will nicely put the contents of crtend.o's .init section here.
+	popl %ebp
+	ret
+
+.section .fini
+
+	// gcc will nicely put the contents of crtend.o's .fini section here.
+	popl %ebp
+	ret

toolchain.cmake

@@ -13,5 +13,5 @@ set(CMAKE_CXX_COMPILER_WORKS TRUE)
 
 set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
 set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
-set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE BOTH)
+set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
 set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE ONLY)