XNU-7195.81.3.md

Steps for building XNU 7195.81.3 (macOS 11.0)

The kernel can be found at Apple Open Source. We show here how to build this XNU version for Raspberry Pi 3(BCM2837).

Preparation

TBC.

Patch

There are some files to modify to get the build successful.

Force to use arm64 arch rather than arm64e

Change the arm64e(compiling target for M1) in makedefs/MakeInc.def to arm64:

ifneq ($(findstring _Sim,$(RC_ProjectName)),)
ARCH_FLAGS_ARM64          = -arch arm64e
else ifneq ($(findstring _host,$(RC_ProjectName)),)
ARCH_FLAGS_ARM64          = -arch arm64e
...
export ARCH_STRING_FOR_CURRENT_MACHINE_CONFIG := arm64e
...
LDFLAGS_KERNEL_ONLY_SUBARCH_arm64e = \
	-Wl,-add_split_seg_info \
	-Wl,-kernel

to

ifneq ($(findstring _Sim,$(RC_ProjectName)),)
ARCH_FLAGS_ARM64          = -arch arm64
else ifneq ($(findstring _host,$(RC_ProjectName)),)
ARCH_FLAGS_ARM64          = -arch arm64
...
export ARCH_STRING_FOR_CURRENT_MACHINE_CONFIG := arm64
...
LDFLAGS_KERNEL_ONLY_SUBARCH_arm64 = \
	-Wl,-add_split_seg_info \
	-Wl,-kernel

This disables Pointer Authentication(PAC) extension, because Raspberry Pi has an ARMv8 kernel without such extension in ARMv8.3(M1).

Patch Makefile to disable "-Werror" flag

Comment out the WERROR flag in makedefs/MakeInc.def like this:

ifeq ($(USE_WERROR),1)
# WERROR := -Werror
endif

Patch 'vm_pageout_*'

Find any refereces of vm_pageout_wait in the source code (you can also try to compile the kernel and let the compiler find them for you). Foe example, there is one in iokit/Kernel/IOPMrootDomain.cpp:

#if defined(XNU_TARGET_OS_OSX)
  vm_pageout_wait(AbsoluteTime_to_scalar(&deadline));
#endif /* defined(XNU_TARGET_OS_OSX) */

Add !CONFIG_EMBEDDED into the condition:

#if defined(XNU_TARGET_OS_OSX) && !CONFIG_EMBEDDED
  vm_pageout_wait(AbsoluteTime_to_scalar(&deadline));
#endif /* defined(XNU_TARGET_OS_OSX) */

This will suppress the line when compiling for Raspberry Pi, which is an embedded device.

Patch 'vmmap_high_start`

Raspberry Pi is declared as an embedded service in the makefile, which explicitly disables some features. But apparently, Apple does not handle them well.

We need to add !CONFIG_EMBEDDED in osfmk/vm/vm_map.c to comment out all the vmmap_high_start field. The field is not defined under an embedded enviroment.

For instance, we should change:

#if XNU_TARGET_OS_OSX
	result->vmmap_high_start = 0;
#endif

to

#if XNU_TARGET_OS_OSX && !CONFIG_EMBEDDED
	result->vmmap_high_start = 0;
#endif

Remove PAC extension header

We need to remove any PAC extension code. To do so, comment out the #include <arm64/pac_asm.h> in the files that compiler conplains.

For instance, in osfmk/arm64/exception_asm.h:

// #include <arm64/pac_asm.h>
#include <pexpert/arm64/board_config.h>
#include "assym.s"

Remove PAC extension reference

Remove ml_enable_monitor in osfmk/arm64/arm_vm_init.c, replace pmap_cs_allow_invalid(vm_map_pmap(map)) in osfmk/arm64/vm_map.c with 0.

Both of them disable the unintentional calling to PAC-related functions.

Fix GPIO Base for UART output

In pexpert/arm/pe_serial.c, change the base address to the one that belongs to Raspberry Pi 3:

vm_offset_t pi3_gpio_base_vaddr = 0x3F200000;
vm_offset_t pi3_aux_base_vaddr = 0x3F215000;

Comment out the base address detection from Apple Device Tree:

#ifdef PI3_UART
	/*
	if (SecureDTFindEntry("name", "gpio", &entryP) == kSuccess) {
		SecureDTGetProperty(entryP, "reg", (void const **)&reg_prop, &prop_size);
		pi3_gpio_base_vaddr = ml_io_map(soc_base + *reg_prop, *(reg_prop + 1));
	}
	if (SecureDTFindEntry("name", "aux", &entryP) == kSuccess) {
		SecureDTGetProperty(entryP, "reg", (void const **)&reg_prop, &prop_size);
		pi3_aux_base_vaddr = ml_io_map(soc_base + *reg_prop, *(reg_prop + 1));
	}
	*/
	if ((pi3_gpio_base_vaddr != 0) && (pi3_aux_base_vaddr != 0)) {
		register_serial_functions(&pi3_uart_serial_functions);
	}
#endif /* PI3_UART */

Build command

Only run this on a Mac:

make SDKROOT=macosx ARCH_CONFIGS=ARM64 MACHINE_CONFIGS=BCM2837 KERNEL_CONFIGS=DEVELOPMENT

You can also replace the DEVELOPMENT config to RELEASE.

Post-build

Finally, there will be a kernel file kernel.<CONFIGS>.bcm2837 in BUILD/obj/<CONFIGS>_ARM64_BCM2837 directory.

Any other problems

Please create an issue if you have any other problems when building XNU.