[build] make LK buildable with LLVM/Clang

Add an environment setting LLVM=1 that replaces usage of GNU tools
with the LLVM equivalents.

Current status is that it builds on arm64 for QEMU with several
warnings and then boots. I didn't hook up any other architectures but
the arm64 setup should serve as a guideline.

arch/arm64/include/arch/asm_macros.h

@@ -36,7 +36,7 @@ ldp \ra, \rb, [sp], #16
 .endif
 .endm
 
-.macro calloc_bootmem_aligned, new_ptr, new_ptr_end, tmp, size_shift, phys_offset=0
+.macro calloc_bootmem_aligned, new_ptr, new_ptr_end, tmp, size_shift, phys_offset
 .if \size_shift < 4
     .error "calloc_bootmem_aligned: Unsupported size_shift, \size_shift"
 .endif
@@ -58,11 +58,9 @@ ldp \ra, \rb, [sp], #16
     add     \new_ptr_end, \new_ptr, #(1 << \size_shift)
     str     \new_ptr_end, [\tmp, #:lo12:boot_alloc_end]
 
-.if \phys_offset != 0
     /* clear page */
     sub     \new_ptr, \new_ptr, \phys_offset
     sub     \new_ptr_end, \new_ptr_end, \phys_offset
-.endif
 
     /* clear page */
     mov     \tmp, \new_ptr

arch/arm64/rules.mk

@@ -96,7 +96,9 @@ ARCH_COMPILEFLAGS += -fno-omit-frame-pointer
 
 ARCH_LDFLAGS += -z max-page-size=4096
 
+ifeq ($(LLVM),)
 LIBGCC := $(shell $(TOOLCHAIN_PREFIX)gcc $(GLOBAL_COMPILEFLAGS) $(ARCH_COMPILEFLAGS) -print-libgcc-file-name)
+endif
 
 # make sure some bits were set up
 MEMVARS_SET := 0

arch/arm64/toolchain.mk

@@ -1,6 +1,9 @@
 ifndef ARCH_arm64_TOOLCHAIN_INCLUDED
 ARCH_arm64_TOOLCHAIN_INCLUDED := 1
 
+ifneq ($(LLVM),)
+LLVM_TARGET_TRIPLE := aarch64-elf
+else
 ifndef ARCH_arm64_TOOLCHAIN_PREFIX
 ARCH_arm64_TOOLCHAIN_PREFIX := aarch64-elf-
 FOUNDTOOL=$(shell which $(ARCH_arm64_TOOLCHAIN_PREFIX)gcc)
@@ -14,3 +17,4 @@ endif
 endif
 endif
 endif
+endif

engine.mk

@@ -63,7 +63,10 @@ GLOBAL_INCLUDES := $(BUILDDIR) $(addsuffix /include,$(LKINC))
 GLOBAL_OPTFLAGS ?= $(ARCH_OPTFLAGS)
 GLOBAL_COMPILEFLAGS := -g -include $(CONFIGHEADER)
 GLOBAL_COMPILEFLAGS += -Wextra -Wall -Werror=return-type -Wshadow -Wdouble-promotion
-GLOBAL_COMPILEFLAGS += -Wno-multichar -Wno-unused-parameter -Wno-unused-function -Wno-unused-label -Wno-nonnull-compare
+GLOBAL_COMPILEFLAGS += -Wno-multichar -Wno-unused-parameter -Wno-unused-function -Wno-unused-label
+ifeq ($(LLVM),)
+GLOBAL_COMPILEFLAGS += -Wno-nonnull-compare
+endif
 GLOBAL_COMPILEFLAGS += -fno-common
 GLOBAL_CFLAGS := --std=gnu11 -Werror-implicit-function-declaration -Wstrict-prototypes -Wwrite-strings
 GLOBAL_CPPFLAGS := --std=c++14 -fno-exceptions -fno-rtti -fno-threadsafe-statics
@@ -157,9 +160,11 @@ ifndef ARCH
 $(error couldn't find arch or platform doesn't define arch)
 endif
 include arch/$(ARCH)/rules.mk
+ifeq ($(LLVM),)
 ifndef TOOLCHAIN_PREFIX
 $(error TOOLCHAIN_PREFIX not set in the arch rules.mk)
 endif
+endif
 
 $(info PROJECT = $(PROJECT))
 $(info PLATFORM = $(PLATFORM))
@@ -213,6 +218,18 @@ endif
 
 # default to no ccache
 CCACHE ?=
+
+ifneq ($(LLVM),)
+CC := $(CCACHE) clang --target=$(LLVM_TARGET_TRIPLE)
+LIBGCC := $(shell $(CC) $(GLOBAL_COMPILEFLAGS) $(ARCH_COMPILEFLAGS) -print-libgcc-file-name)
+LD := ld.lld
+OBJDUMP := llvm-objdump
+OBJCOPY := llvm-objcopy
+CPPFILT := llvm-cxxfilt
+SIZE := llvm-size
+NM := llvm-nm
+STRIP := llvm-strip
+else
 CC := $(CCACHE) $(TOOLCHAIN_PREFIX)gcc
 LD := $(TOOLCHAIN_PREFIX)ld
 OBJDUMP := $(TOOLCHAIN_PREFIX)objdump
@@ -221,6 +238,7 @@ CPPFILT := $(TOOLCHAIN_PREFIX)c++filt
 SIZE := $(TOOLCHAIN_PREFIX)size
 NM := $(TOOLCHAIN_PREFIX)nm
 STRIP := $(TOOLCHAIN_PREFIX)strip
+endif
 
 # try to have the compiler output colorized error messages if available
 export GCC_COLORS ?= 1

lib/heap/heap_wrapper.c

@@ -89,6 +89,10 @@ static inline void *HEAP_CALLOC(size_t n, size_t s) {
 #define HEAP_FREE(p) dlfree(p)
 static inline void HEAP_INIT(void) {}
 
+static inline void dump_callback(void *start, void *end, size_t used_bytes, void *arg) {
+    printf("\t\tstart %p end %p used_bytes %zu\n", start, end, used_bytes);
+}
+
 static inline void HEAP_DUMP(void) {
     struct mallinfo minfo = dlmallinfo();
 
@@ -102,10 +106,6 @@ static inline void HEAP_DUMP(void) {
     printf("\t\treleasable space 0x%zx\n", minfo.keepcost);
 
     printf("\theap block list:\n");
-    void dump_callback(void *start, void *end, size_t used_bytes, void *arg) {
-        printf("\t\tstart %p end %p used_bytes %zu\n", start, end, used_bytes);
-    }
-
     dlmalloc_inspect_all(&dump_callback, NULL);
 }
 

make/build.mk

@@ -22,8 +22,8 @@ $(OUTELF).hex: $(OUTELF)
 $(OUTELF): $(ALLMODULE_OBJS) $(EXTRA_OBJS) $(LINKER_SCRIPT) $(EXTRA_LINKER_SCRIPTS)
 	$(info linking $@)
 	$(NOECHO)$(SIZE) -t --common $(sort $(ALLMODULE_OBJS)) $(EXTRA_OBJS)
-	$(NOECHO)$(LD) $(GLOBAL_LDFLAGS) $(ARCH_LDFLAGS) -dT $(LINKER_SCRIPT) \
-		$(addprefix -T,$(EXTRA_LINKER_SCRIPTS)) \
+	$(NOECHO)$(LD) $(GLOBAL_LDFLAGS) $(ARCH_LDFLAGS) \
+		$(addprefix -T,$(EXTRA_LINKER_SCRIPTS)) -T $(LINKER_SCRIPT) \
 		$(ALLMODULE_OBJS) $(EXTRA_OBJS) $(LIBGCC) -Map=$(OUTELF).map -o $@
 
 $(OUTELF).sym: $(OUTELF)

make/help.mk

@@ -15,6 +15,8 @@ help:
 	@echo "Environment or command line variables controlling build:"
 	@echo "PROJECT = <project name>"
 	@echo "TOOLCHAIN_PREFIX = <absolute path to toolchain or relative path with prefix>"
+	@echo "LLVM = 1 # use LLVM tools instead of GCC and binutils;"
+	@echo "         # user should add tools to PATH instead of specifying TOOLCHAIN_PREFIX"
 	@echo ""
 	@echo "Special make targets:"
 	@echo "make help: This help"