# Cross-compilation toolchain for i386-elf using Clang + LLD.
#
# This targets a bare-metal i386 (80386) environment with no host OS
# libraries. lld is used as the linker because the macOS system ld does
# not support the ELF32 output format required for a GRUB-bootable kernel.

set(CMAKE_SYSTEM_NAME Generic)
set(CMAKE_SYSTEM_PROCESSOR i386)

# Use Clang for both C and assembly.
set(CMAKE_C_COMPILER   clang)
set(CMAKE_ASM_COMPILER clang)

# Prevent CMake from trying to run the cross-compiled test binaries.
set(CMAKE_TRY_COMPILE_TARGET_TYPE STATIC_LIBRARY)

# Target triple and architecture flags shared by all compilation steps.
set(CROSS_TARGET "i386-elf")
set(CROSS_ARCH_FLAGS "-target ${CROSS_TARGET} -m32 -march=i386 -mtune=i386")

# C compiler flags:
#  - ffreestanding : no hosted C runtime assumptions
#  - fno-stack-protector : no __stack_chk_fail dependency
#  - fno-builtin : avoid implicit replacements of standard functions
set(CMAKE_C_FLAGS_INIT
    "${CROSS_ARCH_FLAGS} -ffreestanding -fno-stack-protector -fno-builtin -Wall -Wextra"
)

# Assembler flags: only the flags the assembler front-end actually accepts.
# C-only flags like -ffreestanding, -fno-stack-protector, etc. must NOT be
# passed here — clang treats them as unused and errors out with -Werror.
# -Wno-unused-command-line-argument suppresses CMake's auto-added -MD/-MT/-MF
# dependency-tracking flags that clang ignores in pure assembler mode.
set(CMAKE_ASM_FLAGS_INIT
    "-target ${CROSS_TARGET} -m32 -march=i386 -Wno-unused-command-line-argument"
)

# Linking:
# On aarch64 Alpine the clang driver delegates link steps to the host gcc,
# which does not support -m32 and therefore fails.  Bypass the driver entirely
# and call ld.lld directly.  The CMake rule variables below replace the normal
# "compile-with-compiler-driver" link invocation.
#
# Rule variables use these placeholders:
#   <TARGET>         — output binary path
#   <OBJECTS>        — all compiled object files
#   <LINK_FLAGS>     — extra flags from target_link_options / CMAKE_EXE_LINKER_FLAGS
#   <LINK_LIBRARIES> — libraries to link (empty for a freestanding kernel)
set(CMAKE_LINKER "ld.lld")
set(CMAKE_C_LINK_EXECUTABLE
    "ld.lld -m elf_i386 <LINK_FLAGS> <OBJECTS> -o <TARGET> <LINK_LIBRARIES>")
set(CMAKE_ASM_LINK_EXECUTABLE
    "ld.lld -m elf_i386 <LINK_FLAGS> <OBJECTS> -o <TARGET> <LINK_LIBRARIES>")

# Keep CMake from accidentally picking up host system headers/libraries.
set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE ONLY)