WIP: build Linux on MacOS

I just built the ARCH=arm64 defconfig Linux kernel on MacOS Monterey
12.5.1!

$ make LLVM=1 -j8

Hacked up patch for now, will need to clean these up and break them up
into individual patches before sending.

Issues Encountered:

1. SUBARCH defaults to arm rather than arm64; fix regex in
   scripts/subarch.include.
2. MacOS doesn't distribute elf.h and neither does Homebrew. I used
   gelf.h from libelf from Homebrew, but then had to muck up a bunch of
   build flags to invoke pkg-config via HOSTPKG_CONFIG. I think a better
   approach would be just to include a minimal elf.h in the kernel
   sources for MacOS hosts, similar to
   https://gist.github.com/mlafeldt/3885346 but smaller.
3. MacOS doesn't distribute endian.h. I used a combination of
   machine/endian.h and https://gist.github.com/yinyin/2027912, but
   probably should include a minimal copy in kernel sources similar to
   elf.h above.
4. pkg-config doesn't detect libcrypto from openssl from HomeBrew
   because MacOS uses LibreSSL or something. brew install openssl prints
   a warning about it.
5. MacOS' FORTIFY_SOURCE implementation seems broken wrt.
   scripts/mod/file2alias.c.
6. MacOS sys/types.h defines uuid_t, which conflicts with
   scripts/mod/file2alias.c.

For the build, I built the following from source:
1. clang
2. lld
3. llvm-nm
4. llvm-objcopy
5. llvm-objdump
6. llvm-strip

From Homebrew I needed to install:
1. libelf (probably not necessary)
2. pkg-config
3. bash (the one that ships with macos is too old, doesn't understand
   lastpipe)
4. md5sha1sum
5. openssl

Before all of the above I needed to create a case-sensitive volume to
check out the kernel sources.

It probably wouldn't hurt to add the above to some documentation.

Signed-off-by: Nick Desaulniers <nick.desaulniers@gmail.com>

Author: nickdesaulniers

Makefile

@@ -385,6 +385,7 @@ include $(srctree)/scripts/subarch.include
 # Default value for CROSS_COMPILE is not to prefix executables
 # Note: Some architectures assign CROSS_COMPILE in their arch/*/Makefile
 ARCH		?= $(SUBARCH)
+$(info $$SUBARCH is [${SUBARCH}])
 
 # Architecture as present in compile.h
 UTS_MACHINE 	:= $(ARCH)

arch/arm/vdso/vdsomunge.c

@@ -32,7 +32,7 @@
  * it does.
  */
 
-#include <elf.h>
+#include <gelf.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <stdarg.h>

arch/arm64/kernel/vdso32/Makefile

@@ -111,6 +111,7 @@ VDSO_LDFLAGS += --orphan-handling=warn
 # We have to use a relative path because scripts/Makefile.host prefixes
 # $(hostprogs) with $(obj)
 munge := ../../../arm/vdso/vdsomunge
+HOST_EXTRACFLAGS	+= $(shell $(HOSTPKG_CONFIG) --cflags libelf) -include $(obj)/elf_helper.h
 hostprogs := $(munge)
 
 c-obj-vdso := note.o

arch/arm64/kernel/vdso32/elf_helper.h

@@ -0,0 +1,2 @@
+#define EF_ARM_EABIMASK 0XFF000000
+#define EF_ARM_EABI_VERSION(flags) ((flags) & EF_ARM_EABIMASK)

arch/arm64/kvm/hyp/nvhe/Makefile

@@ -13,6 +13,8 @@ ccflags-y := -D__KVM_NVHE_HYPERVISOR__ -D__DISABLE_EXPORTS -D__DISABLE_TRACE_MMI
 
 hostprogs := gen-hyprel
 HOST_EXTRACFLAGS += -I$(objtree)/include
+HOST_EXTRACFLAGS += $(shell $(HOSTPKG_CONFIG) --cflags libelf)
+HOST_EXTRACFLAGS += -include $(obj)/endian_helper.h
 
 lib-objs := clear_page.o copy_page.o memcpy.o memset.o
 lib-objs := $(addprefix ../../../lib/, $(lib-objs))

arch/arm64/kvm/hyp/nvhe/endian_helper.h

@@ -0,0 +1,5 @@
+#include <libkern/OSByteOrder.h>
+#define le16toh(x) OSSwapLittleToHostInt16(x)
+#define le32toh(x) OSSwapLittleToHostInt32(x)
+#define le64toh(x) OSSwapLittleToHostInt64(x)
+#define EM_AARCH64 183

arch/arm64/kvm/hyp/nvhe/gen-hyprel.c

@@ -24,8 +24,8 @@
  * However, those are only generated if CONFIG_RELOCATABLE=y.
  */
 
-#include <elf.h>
-#include <endian.h>
+#include <gelf.h>
+#include <machine/endian.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <stdbool.h>

certs/Makefile

@@ -85,4 +85,6 @@ targets += x509_revocation_list
 hostprogs := extract-cert
 
 HOSTCFLAGS_extract-cert.o = $(shell $(HOSTPKG_CONFIG) --cflags libcrypto 2> /dev/null)
+HOSTCFLAGS_extract-cert.o += -I/opt/homebrew/opt/openssl@3/include
+HOSTCFLAGS_extract-cert.o += -L/opt/homebrew/opt/openssl@3/lib
 HOSTLDLIBS_extract-cert = $(shell $(HOSTPKG_CONFIG) --libs libcrypto 2> /dev/null || echo -lcrypto)

scripts/Makefile

@@ -11,7 +11,7 @@ hostprogs-always-$(CONFIG_ASN1)				+= asn1_compiler
 hostprogs-always-$(CONFIG_MODULE_SIG_FORMAT)		+= sign-file
 hostprogs-always-$(CONFIG_SYSTEM_EXTRA_CERTIFICATE)	+= insert-sys-cert
 
-HOSTCFLAGS_sorttable.o = -I$(srctree)/tools/include
+HOSTCFLAGS_sorttable.o = -I$(srctree)/tools/include $(shell $(HOSTPKG_CONFIG) --cflags libelf)
 HOSTLDLIBS_sorttable = -lpthread
 HOSTCFLAGS_asn1_compiler.o = -I$(srctree)/include
 HOSTCFLAGS_sign-file.o = $(shell $(HOSTPKG_CONFIG) --cflags libcrypto 2> /dev/null)

scripts/mod/Makefile

@@ -3,6 +3,12 @@ OBJECT_FILES_NON_STANDARD := y
 CFLAGS_REMOVE_empty.o += $(CC_FLAGS_LTO)
 
 hostprogs-always-y	+= modpost mk_elfconfig
+libelf_flags	:= $(shell $(HOSTPKG_CONFIG) --cflags libelf)
+HOSTCFLAGS_mk_elfconfig.o	+= $(libelf_flags)
+HOSTCFLAGS_modpost.o	+= $(libelf_flags) -include $(obj)/elf_helper.h
+HOSTCFLAGS_sumversion.o	+= $(libelf_flags)
+#HOSTCFLAGS_file2alias.o	+= $(libelf_flags) -U_FORTIFY_SOURCE
+HOSTCFLAGS_file2alias.o	+= $(libelf_flags) -D_FORTIFY_SOURCE=0
 always-y		+= empty.o
 
 modpost-objs	:= modpost.o file2alias.o sumversion.o