Add TOOLCHAIN{,_PREFIX} make options

README.md

@@ -12,6 +12,19 @@ It is recommended to build this project using a standard UNIX-like system, using
 
 Additionally, building an ISO with `make all` requires `xorriso`, and building a HDD/USB image with `make all-hdd` requires `sgdisk` (usually from `gdisk` or `gptfdisk` packages) and `mtools`.
 
+### Toolchain selection
+
+The `TOOLCHAIN` and `TOOLCHAIN_PREFIX` `make` variables can be used to set the toolchain. `TOOLCHAIN` can be set to `llvm` to use Clang/LLVM.
+
+For example:
+```
+make TOOLCHAIN=llvm
+```
+or:
+```
+make TOOLCHAIN_PREFIX=x86_64-elf-
+```
+
 ### Architectural targets
 
 The `ARCH` make variable determines the target architecture to build the kernel and image for.

kernel/GNUmakefile

@@ -17,11 +17,30 @@ ifeq ($(filter $(ARCH),aarch64 loongarch64 riscv64 x86_64),)
     $(error Architecture $(ARCH) not supported)
 endif
 
+# User controllable toolchain and toolchain prefix.
+TOOLCHAIN :=
+TOOLCHAIN_PREFIX :=
+ifneq ($(TOOLCHAIN),)
+    ifeq ($(TOOLCHAIN_PREFIX),)
+        TOOLCHAIN_PREFIX := $(TOOLCHAIN)-
+    endif
+endif
+
 # User controllable C compiler command.
-CC := cc
+ifneq ($(TOOLCHAIN_PREFIX),)
+    CC := $(TOOLCHAIN_PREFIX)gcc
+else
+    CC := cc
+endif
 
 # User controllable linker command.
-LD := ld
+LD := $(TOOLCHAIN_PREFIX)ld
+
+# Defaults overrides for variables if using "llvm" as toolchain.
+ifeq ($(TOOLCHAIN),llvm)
+    CC := clang
+    LD := ld.lld
+endif
 
 # User controllable C flags.
 CFLAGS := -g -O2 -pipe