SVC

System calls

Id	Name	In	Out
0x1	#svcSetHeapSize	W1=size	W0=result, X1=outaddr
0x2	#svcSetMemoryPermission	X0=addr, X1=size, W2=prot	W0=result
0x3	#svcSetMemoryAttribute	X0=addr, X1=size, W2=state0, W3=state1	W0=result
0x4	#svcMapMemory	X0=dstaddr, X1=srcaddr, X2=size	W0=result
0x5	#svcUnmapMemory	X0=dstaddr, X1=srcaddr, X2=size	W0=result
0x6	#svcQueryMemory	X0=MemoryInfo*, X2=addr	W0=result, W1=PageInfo
0x7	#svcExitProcess	None
0x8	#svcCreateThread	X1=entry, X2=arg, X3=stacktop, W4=prio, W5=processor_id	W0=result, W1=handle
0x9	#svcStartThread	W0=thread_handle	W0=result
0xA	#svcExitThread	None
0xB	#svcSleepThread	X0=nano	W0=result
0xC	#svcGetThreadPriority	W1=thread_handle	W0=result, W1=prio
0xD	#svcSetThreadPriority	W0=thread_handle, W1=prio	W0=result
0xE	#svcGetThreadCoreMask	W2=thread_handle	W0=result, W1=out, X2=out
0xF	#svcSetThreadCoreMask	W0=thread_handle, W1=in, X2=in2	W0=result
0x10	#svcGetCurrentProcessorNumber	None	W0/X0=cpuid
0x11	svcSignalEvent	W0=wevent_handle	W0=result
0x12	svcClearEvent	W0=wevent_or_revent_handle	W0=result
0x13	#svcMapSharedMemory	W0=memblk_handle, X1=addr, X2=size, W3=perm	W0=result
0x14	svcUnmapSharedMemory	W0=memblk_handle, X1=addr, X2=size	W0=result
0x15	#svcCreateTransferMemory	X1=addr, X2=size, W3=perm	W0=result, W1=handle
0x16	svcCloseHandle	W0=handle	W0=result
0x17	svcResetSignal	W0=handle	W0=result
0x18	#svcWaitSynchronization	X1=handles_ptr, W2=num_handles. X3=timeout	W0=result, W1=handle_idx
0x19	svcCancelSynchronization	W0=handle	W0=result
0x1A	svcArbitrateLock	W0=cur_thread_handle, X1=ptr, W2=req_thread_handle
0x1B	svcArbitrateUnlock	X0=ptr
0x1C	svcWaitProcessWideKeyAtomic	X0=ptr0, X1=ptr, W2=thread_handle, X3=timeout	W0=result
0x1D	svcSignalProcessWideKey	X0=ptr, W1=value	W0=result
0x1E	svcGetSystemTick		X0={value of cntpct_el0}
0x1F	svcConnectToNamedPort	X1=port_name_str	W0=result, W1=handle
0x20	svcSendSyncRequestLight
0x21	svcSendSyncRequest	X0=handle	W0=result
0x22	#svcSendSyncRequestWithUserBuffer	X0=cmdbufptr, X1=size, X2=handle	W0=result
0x23	svcSendAsyncRequestWithUserBuffer
0x24	svcGetProcessId
0x25	svcGetThreadId	W0=thread_handle	W0=result, X1=out
0x26	svcBreak	X0,X1,X2=info	?
0x27	svcOutputDebugString	X0=str, X1=size
0x28	svcReturnFromException	X0=result
0x29	#svcGetInfo	X1=info_id, X2=handle, X3=info_sub_id	W0=result, X1=out
0x2A	svcFlushEntireDataCache
0x2B	svcFlushDataCache
0x2C	[3.0.0+] svcMapPhysicalMemory
0x2D	[3.0.0+] svcUnmapPhysicalMemory
....	?	?	?
0x2F	svcGetLastThreadInfo
0x30	svcGetResourceLimitLimitValue
0x31	svcGetResourceLimitCurrentValue
0x32	svcSetThreadActivity
0x33	svcGetThreadContext3
0x3C	svcDumpInfo
0x40	svcCreateSession	W2=?, X3=?	W0=result, W1=client_handle, W2=server_handle
0x41	svcAcceptSession	W1=port_handle	W0=result, W1=session_handle
0x42	svcReplyAndReceiveLight
0x43	svcReplyAndReceive	X1=ptr_handles, W2=num_handles, X3=replytarget_handle(0=none), X4=timeout	W0=result, W1=handle_idx
0x44	svcReplyAndReceiveWithUserBuffer	X1=buf, X2=sz, X3=ptr_handles, W4=num_handles, X5=replytarget_handle(0=none), X6=timeout	W0=result, W1=handle_idx
0x45	svcCreateEvent	None	W0=result, W1=client_handle ?, W2=server_handle ?
0x4D	svcSleepSystem
0x4E	#svcReadWriteRegister	X1=reg_addr, W2=rw_mask, W3=in_val	W0=result, W1=out_val
0x4F	svcSetProcessActivity
0x50	#svcCreateSharedMemory	W1=size?, W2=myperm, W3=otherperm	W0=result, W1=handle
0x51	#svcMapTransferMemory	X0=mirror_handle, X1=addr, X2=size, W3=perm	W0=result
0x52	#svcUnmapTransferMemory	W0=mirror_handle, X1=addr, X2=size	W0=result
0x53	svcCreateInterruptEvent	X1=irq_id, W2=flag	W0=result, W1=handle
0x54	#svcQueryPhysicalAddress
0x55	#svcQueryIoMapping	X1=physaddr, X2=size	W0=result, X1=virtaddr
0x56	#svcCreateDeviceAddressSpace	X1=dev_as_start_addr, X2=dev_as_end_addr	W0=result, W1=dev_as_handle
0x57	#svcAttachDeviceAddressSpace	W0=device, X1=dev_as_handle	W0=result
0x58	#svcDetachDeviceAddressSpace	W0=device, X1=dev_as_handle	W0=result
0x59	#svcMapDeviceAddressSpaceByForce	W0=dev_as_handle, W1=proc_handle, X2=dev_map_addr, X3=dev_as_size, X4=dev_as_addr, W5=perm	W0=result
0x5A	#svcMapDeviceAddressSpaceAligned	W0=dev_as_handle, W1=proc_handle, X2=dev_map_addr, X3=dev_as_size, X4=dev_as_addr, W5=perm	W0=result
0x5B	svcMapDeviceAddressSpace
0x5C	#svcUnmapDeviceAddressSpace	W0=dev_as_handle, W1=proc_handle, X2=dev_map_addr, X3=dev_as_size, X4=dev_as_addr	W0=result
0x5D	svcInvalidateProcessDataCache
0x5E	svcStoreProcessDataCache
0x5F	svcFlushProcessDataCache
0x60	svcDebugActiveProcess	X1=processID	W0=result, W1=out_debughandle
0x61	svcBreakDebugProcess
0x62	svcTerminateDebugProcess
0x63	svcGetDebugEvent	X0=DebugEventInfo*, W1=debughandle	W0=result
0x64	svcContinueDebugEvent	W0=debughandle, W1=flags, X2=?	W0=result
0x65	svcGetProcessList
0x66	svcGetThreadList
0x67	svcGetDebugThreadContext	X0=ThreadContext*, X1=debughandle, X2=?, W3=?	W0=result
0x68	svcSetDebugThreadContext
0x69	svcQueryDebugProcessMemory	X0=MemoryInfo*, X2=debughandle, X3=addr	W0=result, W1=PageInfo
0x6A	svcReadDebugProcessMemory	X0=buffer*, X1=debughandle, X2=src_addr, X3=size	W0=result
0x6B	svcWriteDebugProcessMemory	X0=debughandle, X1=buffer*, X2=dst_addr, X3=size	W0=result
0x6C	svcSetHardwareBreakPoint
0x6D	svcGetDebugThreadParam	X2=debughandle, X3=?, W4=DebugThreadParam	W0=result, X1=out0, W2=out1
0x70	svcCreatePort
0x71	svcManageNamedPort	X1=namestr*, W2=maxsessions(?)	W0=result, W1=outhandle
0x72	svcConnectToPort	W1=inhandle	W0=result, W1=outhandle
0x73	svcSetProcessMemoryPermission
0x74	#svcMapProcessMemory	X0=srcaddr, W1=process_handle, X2=dstaddr, X3=size	W0=result
0x75	#svcUnmapProcessMemory	W0=process_handle, X1=dstaddr, X2=srcaddr, X3=size	W0=result
0x76	#svcQueryProcessMemory	X0=meminfo_ptr, W2=process_handle, X3=addr	W0=result, W1=pageinfo
0x77	#svcMapProcessCodeMemory	W0=process_handle, X2=dstaddr, X2=srcaddr, X3=size	W0=result
0x78	#svcUnmapProcessCodeMemory	W0=process_handle, X1=dstaddr, X2=srcaddr, X3=size	W0=result
0x79	#svcCreateProcess	X1=procinfo_ptr, X2=caps_ptr, W3=cap_num	W0=result, W1=process_handle
0x7A	svcStartProcess	W0=process_handle, W1=main_thread_prio, W2=default_cpuid, W3=main_thread_stacksz	W0=result
0x7B	svcTerminateProcess	W0=process_handle	W0=result
0x7C	#svcGetProcessInfo	W0=process_handle	W0=result, X1=process_state
0x7D	svcCreateResourceLimit
0x7E	svcSetResourceLimitLimitValue
0x7F	svcCallSecureMonitor

svcSetHeapSize

Argument	Type	Name	Direction
X0	u64	Size	In
W0	#Result	Ret	Out
X1	u64	OutAddr	Out

Description: Set the process heap to a given Size. It can both extend and shrink the heap.

Size must be a multiple of 0x2000000.

On success, the heap base-address (which is fixed by kernel, aslr'd) is written to OutAddr.

[2.0.0+] Size must be less than 0x18000000.

svcSetMemoryPermission

Description: Change permission of page-aligned memory region.

Bit2 of permission (exec) is not allowed. Setting write-only is not allowed either (bit1).

This can be used to move back and forth between ---, r-- and rw-.

svcSetMemoryAttribute

Description: Change attribute of page-aligned memory region.

This is used to turn on/off caching for a given memory area. Useful when talking to devices such as the GPU.

What happens "under the hood" is the "Memory Attribute Indirection Register" index is changed from 2 to 3 in the MMU descriptor.

State0	State1	Action
0	0	Clear bit3 in #MemoryAttribute.
8	0	Clear bit3 in #MemoryAttribute.
8	8	Set bit3 in #MemoryAttribute.

svcMapMemory

Description: Maps a memory range into a different range.

Mainly used for adding guard pages around stack.

Source range gets reprotected to --- (it can no longer be accessed), and bit0 is set in the source #MemoryAttribute.

If dstaddr >= LowerTreshold, the dst-range is enforced to be within the process' "MapRegion". Code can get the range of this region from #svcGetInfo id0=2,3.

In this case, the mapped memory will have state 0x5C3C0B.

As long as (dstaddr+size) < LowerThreshold, then you can map anywhere but the mapped memory will have state 0x482907 instead.

LowerTreshold is 0x80000000 for 36-bit address spaces, and 0x40000000 for 32-bit ones.

[2.0.0+] Support for the 0x482907 mappings outside the "MapRegion" were removed.

svcUnmapMemory

Description: Unmaps a region that was previously mapped with #svcMapMemory.

It's possible to unmap ranges partially, you don't need to unmap the entire range "in one go".

The srcaddr/dstaddr must match what was given when the pages were originally mapped.

svcQueryMemory

Description: Query information about an address. Will always fetch the lowest page-aligned mapping that contains the provided address.

Outputs a #MemoryInfo struct.

svcExitProcess

Description: Exits the current process.

svcCreateThread

Description: Create a thread in the current process.

Processor_id must be 0,1,2,3 or -2, where -2 uses the default cpuid for process.

svcStartThread

Description: Starts the thread for the provided handle.

svcExitThread

Description: Exits the current thread.

svcSleepThread

Description: Sleep for a specified amount of time, or yield thread.

Setting nano=0 means "yield thread".

svcGetThreadPriority

Description: Get priority of provided thread handle.

svcSetThreadPriority

Description: Set priority of provided thread handle.

Priority is a number 0-0x3F. Lower value means higher priority.

svcGetThreadCoreMask

Description: Get affinity mask of provided thread handle.

svcSetThreadCoreMask

Description: Set affinity mask of provided thread handle.

svcGetCurrentProcessorNumber

Description: Get which cpu is executing the current thread.

Cpu-id is an integer in the range 0-3.

svcMapSharedMemory

Maps the block supplied by the handle. The required permissions are different for the process that created the handle and all other processes.

Increases reference count for the KSharedMemory object. Thus in order to release the memory associated with the object, all handles to it must be closed and all mappings must be unmapped.

svcCreateTransferMemory

This one reprotects the src block with perms you give it. It also sets bit0 into #MemoryAttribute.

Executable bit perm not allowed.

Closing all handles automatically causes the bit0 in #MemoryAttribute to clear, and the permission to reset.

svcWaitSynchronization

Works with num_handles <= 0x40, error on num_handles == 0.

Does not accept 0xFFFF8001 or 0xFFFF8000 as handles.

svcSendSyncRequestWithUserBuffer

Size must be 0x1000-aligned.

svcBreak

When used on retail where inx0 bit31 is clear, the system will throw a fatal-error. Otherwise when bit31 is set, it will return 0.

svcGetInfo

Handle type	Id0	Id1	Description
Process	0	0	AllowedCpuIdBitmask
Process	1	0	AllowedThreadPrioBitmask
Process	2	0	ReservedMapRegionBaseAddress
Process	3	0	ReservedMapRegionSize
Process	4	0	ReservedHeapRegionBaseAddress
Process	5	0	ReservedHeapRegionSize
Process	6	0	TotalMemoryUsage
Process	7	0	TotalHeapUsage
Zero	8	0	IsCurrentProcessBeingDebugged
Zero	9	0	Returns ResourceLimit handle for current process. Used by PM.
Zero	10	-1, {current coreid}	Unknown. Output data changes each time this SVC is used. Global and core-specific tick-count?
Zero	11	0-3	RandomEntropy from current process. TRNG. Used to seed usermode PRNGs.
Process	12	0	[2.0.0+] AddressSpaceStart
Process	13	0	[2.0.0+] AddressSpaceSize
Process	14	0	[2.0.0+] NewReservedRegionStartAddr
Process	15	0	[2.0.0+] NewReservedRegionSize
Process	18	0	[3.0.0+] Title-id.
Thread	0xF0000002	0	Performance counter related.

svcDumpInfo

Does nothing, just returns with registers set to all-zero.

svcReadWriteRegister

Read/write IO registers with a hardcoded whitelist. Input address is physical-address and must be aligned to 4.

rw_mask is 0 for reading and 0xffffffff for writing. You can also write individual bits by using a mask value.

You can only write to registers inside physical pages 0x70019000 (MC), 0x7001C000 (MC0), 0x7001D000 (MC1), and they all share the same whitelist.

The whitelist is same for writing as for reading.

The whitelist is: 0x054, 0x090, 0x094, 0x098, 0x09c, 0x0a0, 0x0a4, 0x0a8, 0x0ac, 0x0b0, 0x0b4, 0x0b8, 0x0bc, 0x0c0, 0x0c4, 0x0c8, 0x0d0, 0x0d4, 0x0d8, 0x0dc, 0x0e0, 0x100, 0x108, 0x10c, 0x118, 0x11c, 0x124, 0x128, 0x12c, 0x130, 0x134, 0x138, 0x13c, 0x158, 0x15c, 0x164, 0x168, 0x16c, 0x170, 0x174, 0x178, 0x17c, 0x200, 0x204, 0x2e4, 0x2e8, 0x2ec, 0x2f4, 0x2f8, 0x310, 0x314, 0x320, 0x328, 0x344, 0x348, 0x370, 0x374, 0x37c, 0x380, 0x390, 0x394, 0x398, 0x3ac, 0x3b8, 0x3bc, 0x3c0, 0x3c4, 0x3d8, 0x3e8, 0x41c, 0x420, 0x424, 0x428, 0x42c, 0x430, 0x44c, 0x47c, 0x480, 0x484, 0x50c, 0x554, 0x558, 0x55c, 0x670, 0x674, 0x690, 0x694, 0x698, 0x69c, 0x6a0, 0x6a4, 0x6c0, 0x6c4, 0x6f0, 0x6f4, 0x960, 0x970, 0x974, 0xa20, 0xa24, 0xb88, 0xb8c, 0xbc4, 0xbc8, 0xbcc, 0xbd0, 0xbd4, 0xbd8, 0xbdc, 0xbe0, 0xbe4, 0xbe8, 0xbec, 0xc00, 0xc5c, 0xcac

[2.0.0+] Whitelist was extended with 0x4c4, 0x4c8, 0x4cc, 0x584, 0x588, 0x58c.

[2.0.0+] The IO registers in range 0x7000E400 (PMC) size 0xC00 skip the whitelist, and do a TrustZone call using SMC Id1 0xC3000008(ReadWriteRegister).

svcCreateSharedMemory

Other perm can be used to enforce permission 1, 3, or 0x10000000 if don't care.

svcMapTransferMemory

The newly mapped pages will have #MemoryState type 0xE.

You must pass same size and permissions as given in svcCreateMemoryMirror, otherwise error.

svcUnmapTransferMemory

Size must match size given in map syscall, otherwise there's an invalid-size error.

svcQueryPhysicalAddress

The inverse operation of #svcQueryIoMapping.

svcQueryIoMapping

Description: Returns a virtual address mapped to a given IO range.

svcCreateDeviceAddressSpace

Description: Creates a virtual address space for binding device address spaces and returns a handle.

dev_as_start_addr is normally set to 0 and dev_as_end_addr is normally set to 0xFFFFFFFF.

svcAttachDeviceAddressSpace

Description: Attaches a device address space to a device.

svcDetachDeviceAddressSpace

Description: Detaches a device address space from a device.

svcMapDeviceAddressSpaceByForce

Description: Maps an attached device address space to an userspace address.

dev_map_addr is the userspace destination address, while dev_as_addr is the source address between dev_as_start_addr and dev_as_end_addr (passed to #svcCreateDeviceAddressSpace).

The userspace destination address must have the MapDeviceAllowed bit set. Bit IsDeviceMapped will be set after mapping.

svcMapDeviceAddressSpaceAligned

Description: Maps an attached device address space to an userspace address.

Same as #svcMapDeviceAddressSpaceByForce, but the userspace destination address must have the MapDeviceAlignedAllowed bit set instead.

svcUnmapDeviceAddressSpace

Description: Unmaps an attached device address space from an userspace address.

svcMapProcessMemory

Maps the src address from the supplied process handle into the current process.

This allows mapping code and rodata with RW- permission.

svcUnmapProcessMemory

Unmaps what was mapped by #svcMapProcessMemory.

svcQueryProcessMemory

Equivalent to #svcQueryMemory except takes a process handle.

svcMapProcessCodeMemory

Takes a process handle, and maps normal heap in that process as executable code in that process. Used when loading NROs.

svcUnmapProcessCodeMemory

Unmaps what was mapped by #svcMapProcessCodeMemory.

svcCreateProcess

Takes a #CreateProcessInfo as input.

svcGetProcessInfo

Returns an enum with value 0-7.

Debugging

[2.0.0+] Exactly 6 debug SVCs require that IsDebugMode is non-zero. Error 0x4201 is returned otherwise.

• svcBreakDebugProcess
• svcContinueDebugEvent
• svcWriteDebugProcessMemory
• svcSetDebugThreadContext
• svcTerminateDebugProcess
• svcSetHardwareBreakPoint

svcDebugActiveProcess stops execution of the target process, the normal method for resuming it requires svcContinueDebugEvent(see above). Closing the debug handle also results in execution being resumed.

Structures

DeviceName

Value	Name
0	DeviceName_AFI
1	DeviceName_AVPC
2	DeviceName_DC
3	DeviceName_DCB
4	DeviceName_HC
5	DeviceName_HDA
6	DeviceName_ISP2
7	DeviceName_MSENCNVENC
8	DeviceName_NV
9	DeviceName_NV2
10	DeviceName_PPCS
11	DeviceName_SATA
12	DeviceName_VI
13	DeviceName_VIC
14	DeviceName_XUSB_HOST
15	DeviceName_XUSB_DEV
16	DeviceName_TSEC
17	DeviceName_PPCS1
18	DeviceName_DC1
19	DeviceName_SDMMC1A
20	DeviceName_SDMMC2A
21	DeviceName_SDMMC3A
22	DeviceName_SDMMC4A
23	DeviceName_ISP2B
24	DeviceName_GPU
25	DeviceName_GPUB
26	DeviceName_PPCS2
27	DeviceName_NVDEC
28	DeviceName_APE
29	DeviceName_SE
30	DeviceName_NVJPG
31	DeviceName_HC1
32	DeviceName_SE1
33	DeviceName_AXIAP
34	DeviceName_ETR
35	DeviceName_TSECB
36	DeviceName_TSEC1
37	DeviceName_TSECB1
38	DeviceName_NVDEC1

CreateProcessInfo

Offset	Length	Bits	Description
0	12		ProcessName (doesn't have to be null-terminated)
0xC	4
0x10	8		TitleId
0x18	8		CodeAddr
0x20	4		CodeNumPages
0x24	4		MmuFlags
		Bit0	Is64bit
		Bit3-1	#AddressSpaceType
		Bit4
		Bit5	EnableAslr
		Bit6	IsSystem
0x28	4		ResourceLimitHandle
0x2C	4

AddressSpaceType

Type	Name	Width	Description
0	Normal_32Bit	32
1	Normal_36Bit	36
2	WithoutMap_32Bit	32	Appears to be missing map region [?]
3	[2.0.0+] Normal_39Bit	39

MemoryInfo

Offset	Length	Description
0	8	BaseAddress
8	8	Size
0x10	4	MemoryType: lower 8 bits of #MemoryState
0x14	4	#MemoryAttribute
0x18	4	Permission (bit0: R, bit1: W, bit2: X)
0x1C	4	DeviceRefCount
0x20	4	IpcRefCount
0x24	4	Padding: always zero

MemoryAttribute

Bits	Description
0	IsBorrowed
1	IsIpcMapped: when IpcRefCount > 0.
2	IsDeviceMapped: when DeviceRefCount > 0.
3	IsUncached

MemoryState

Bits	Description
7-0	Type
8	PermissionChangeAllowed
9	IsUserWritable [?]
10	IpcSendAllowed_Type0
11	IpcSendAllowed_Type3
12	IpcSendAllowed_Type1
14	ProcessPermissionChangeAllowed
15	MapAllowed
16	UnmapProcessCodeMemoryAllowed
17	TransferMemoryAllowed
19	MapDeviceAllowed (#svcMapDeviceAddressSpace and #svcMapDeviceAddressSpaceByForce)
20	MapDeviceAlignedAllowed
21	IpcBufferAllowed
22	IsPoolAllocated/IsReferenceCounted
23	MapProcessAllowed
24	AttributeChangeAllowed

Value	Type	Meaning
0x00000000	Unmapped
0x00002001	IO	Mapped by kernel capability parsing in #svcCreateProcess.
0x00042002	Normal	Mapped by kernel capability parsing in #svcCreateProcess.
0x00DC7E03	Code static	Mapped during #svcCreateProcess.
0x01FEBD04	Code	Transition from 0xDC7E03 performed by #svcSetProcessMemoryPermission.
0x017EBD05	Heap	Mapped using #svcSetHeapSize.
0x00402006	Shared memory block	Mapped using #svcMapSharedMemory.
0x00482907	[1.0.0] Weird mapped memory	Mapped using #svcMapMemory.
0x00DD7E08	Module code static	Mapped using #svcMapProcessCodeMemory.
0x01FFBD09	Module code mutable	Transition from 0xDD7E08 performed by #svcSetProcessMemoryPermission.
0x005C3C0A	IPC buffers	IPC buffers with descriptor flags=0.
0x005C3C0B	Mapped memory	Mapped using #svcMapMemory.
0x0040200C	Thread local storage	Mapped during #svcCreateThread.
0x015C3C0D	Isolated transfer memory	Mapped using #svcMapTransferMemory when the owning process has perm=0.
0x005C380E	Transfer memory	Mapped using #svcMapTransferMemory when the owning process has perm!=0.
0x0040380F	Process memory	Mapped using #svcMapProcessMemory.
0x00000010	Reserved
0x005C3811	IPC buffers	IPC buffers with descriptor flags=1.
0x004C2812	IPC buffers	IPC buffers with descriptor flags=3.
0x00002013	Kernel per-thread stack	Mapped in kernel during #svcCreateThread.

Exception handling

There is userland code for handling exceptions, however this doesn't seem to be executed on retail mode.

When a usermode exception occurs, it jumps to the main code binary entrypoint (main_binary_address + 0 == _start).

During normal boot _start is invoked with X0=0 and X1=main_thread_handle (triggering normal crt0 setup). During an usermode exception _start is invoked with X0=exception_info0_ptr and X1=exception_info1_ptr instead.

The _start method determines whether to boot normally or handle an exception if X0 is set to 0 or not.

ResourceLimit

For regular-applications, the reslimit(?) seems to only allow 1 NamedPort handle to be open at a time?