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"Conv" is ambiguous. Perhaps "CallConv" is not, but the full name is still more helpful for those of us browsing or searching for targeted info.
213 lines
13 KiB
ReStructuredText
213 lines
13 KiB
ReStructuredText
:orphan:
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Calling Convention Summary
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==========================
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Below is a summary of the calling conventions used on macOS and iOS.
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The `ABI stability manifesto <../ABIStabilityManifesto.md>`_ gives more details
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on the use of the Swift error return and ``self`` registers, while `The Swift
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Calling Convention <CallingConvention.rst>`_ covers the specifics in more
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details. (The Swift ``self`` register is known in other documents as the
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"Context register".)
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x86-64
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------
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See `Apple x86-64 Documentation`_, `System V ABI AMD64 Processor Supplement`_.
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.. _Apple x86-64 Documentation: https://developer.apple.com/library/archive/documentation/DeveloperTools/Conceptual/LowLevelABI/140-x86-64_Function_Calling_Conventions/x86_64.html
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.. _System V ABI AMD64 Processor Supplement: https://www.uclibc.org/docs/psABI-x86_64.pdf
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Register usage
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^^^^^^^^^^^^^^
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+-----------+----------------------------------+----------+----------+----------+
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| Register | Purpose | C++ | ObjC | Swift |
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+===========+==================================+==========+==========+==========+
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| ``rax`` | Return value; also, for varargs, | | | |
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| | number of ``xmm`` registers used | | | |
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+-----------+----------------------------------+----------+----------+----------+
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| ``rbx`` | Callee-saved register | | | |
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+-----------+----------------------------------+----------+----------+----------+
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| ``rdi`` | Integer argument 1 | ``this`` | ``self`` | |
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+-----------+----------------------------------+----------+----------+----------+
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| ``rsi`` | Integer argument 2 | | ``_cmd`` | |
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+-----------+----------------------------------+----------+----------+----------+
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| ``rdx`` | Integer argument 3 | | | |
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| | (2nd return value) | | | |
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+-----------+----------------------------------+----------+----------+----------+
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| ``rcx`` | Integer argument 4 | | | |
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| | (3rd return value) | | | |
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+-----------+----------------------------------+----------+----------+----------+
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| ``r8`` | Integer argument 5 | | | |
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| | (4th return value) | | | |
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+-----------+----------------------------------+----------+----------+----------+
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| ``r9`` | Integer argument 6 | | | |
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+-----------+----------------------------------+----------+----------+----------+
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| ``r12`` | Callee-saved register | | | Error |
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| | | | | return |
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+-----------+----------------------------------+----------+----------+----------+
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| ``r13`` | Callee-saved register | | | ``self`` |
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+-----------+----------------------------------+----------+----------+----------+
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| ``r14`` | Callee-saved register | | | Async |
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| | | | | context |
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+-----------+----------------------------------+----------+----------+----------+
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| ``r15`` | Callee-saved register | | | |
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| | (other platforms use as GOT ptr) | | | |
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+-----------+----------------------------------+----------+----------+----------+
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| ``st0`` | Used to return ``long double`` | | | |
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| | values | | | |
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+-----------+----------------------------------+----------+----------+----------+
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| ``st1`` | Used to return ``long double`` | | | |
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| | values | | | |
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+-----------+----------------------------------+----------+----------+----------+
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| ``xmm0``- | Floating point arguments 1-8 | | | |
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| ``xmm7`` | (``xmm0``-``xmm3`` also used | | | |
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| | for return) | | | |
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+-----------+----------------------------------+----------+----------+----------+
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| ``rsp`` | Stack pointer | | | |
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+-----------+----------------------------------+----------+----------+----------+
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| ``rbp`` | Callee-saved register, | | | |
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| | used as frame pointer | | | |
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+-----------+----------------------------------+----------+----------+----------+
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Stack frame
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^^^^^^^^^^^
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On function entry, ``rsp+8`` is **16-byte aligned**, i.e. the start of the memory
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arguments is 16-byte aligned; the initial stack pointer is shown below as "entry
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``rsp``", but a typical non-leaf function will start by doing::
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push %rbp
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mov %rsp, %rbp
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sub <local-size>, %rsp
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Frameless leaf functions, however, will often not set up the frame pointer,
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``rbp``, in which case they may refer to arguments relative to ``rsp`` instead.
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+---------------+---------------+------------------------+
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| | ``rbp+8n+16`` | memory argument *n* |
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| | | |
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| | ... | ... |
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| | | |
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| | ``rbp+16`` | memory argument 0 |
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+---------------+-----------+---+------------------------+
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| ↓ Current Frame | ↑ Previous Frame |
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+---------------+-----------+---+------------------------+
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| | ``rbp+8`` | return address |
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| | | |
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+---------------+---------------+------------------------+
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| entry ``rsp`` | ``rbp`` | previous ``rbp`` value |
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+---------------+---------------+------------------------+
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| | ``rbp-8`` | |
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| | | |
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| | ... | local storage |
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| | | |
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| | ``rsp`` | |
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+---------------+---------------+------------------------+
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| | ``rsp-8`` | |
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| | | |
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| | ... | red zone |
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| | ``rsp-128`` | |
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+---------------+---------------+------------------------+
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ARM64
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-----
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See `Apple ARM64 Documentation`_, `Procedure Call Standard for the Arm 64-bit Architecture`_.
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.. _Apple ARM64 Documentation: https://developer.apple.com/documentation/xcode/writing-arm64-code-for-apple-platforms
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.. _Procedure Call Standard for the Arm 64-bit Architecture: https://github.com/ARM-software/abi-aa/blob/main/aapcs64/aapcs64.rst
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Register usage
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^^^^^^^^^^^^^^
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+----------+---------+-------------------------+----------+----------+----------+
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| Register | Special | Purpose | C++ | ObjC | Swift |
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+==========+=========+=========================+==========+==========+==========+
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| ``x0`` | | Integer argument 1 | ``this`` | ``self`` | |
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| | | (1st return value) | | | |
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+----------+---------+-------------------------+----------+----------+----------+
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| ``x1`` | | Integer argument 2 | | ``_cmd`` | |
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| | | (2nd return value) | | | |
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+----------+---------+-------------------------+----------+----------+----------+
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| ``x2``- | | Integer arguments 3-8 | | | |
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| ``x7`` | | (3rd-8th return values) | | | |
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+----------+---------+-------------------------+----------+----------+----------+
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| ``x8`` | | Indirect result | | | |
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| | | location register | | | |
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+----------+---------+-------------------------+----------+----------+----------+
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| ``x16``, | ``ip0``,| Scratch registers (used | | | |
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| ``x17`` | ``ip1`` | by dyld, can be used | | | |
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| | | freely otherwise) | | | |
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+----------+---------+-------------------------+----------+----------+----------+
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| ``x18`` | | RESERVED **DO NOT USE** | | | |
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+----------+---------+-------------------------+----------+----------+----------+
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| ``x19`` | | Callee-saved register | | | |
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+----------+---------+-------------------------+----------+----------+----------+
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| ``x20`` | | Callee-saved register | | | ``self`` |
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+----------+---------+-------------------------+----------+----------+----------+
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| ``x21`` | | Callee-saved register | | | Error |
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| | | | | | return |
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+----------+---------+-------------------------+----------+----------+----------+
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| ``x22`` | | Callee-saved register | | | Async |
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| | | | | | context |
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+----------+---------+-------------------------+----------+----------+----------+
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| ``x23``- | | Callee-saved registers | | | |
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| ``x28`` | | | | | |
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+----------+---------+-------------------------+----------+----------+----------+
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| ``x29`` | ``fp`` | Frame pointer | | | |
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+----------+---------+-------------------------+----------+----------+----------+
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| ``x30`` | ``lr`` | Link register | | | |
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+----------+---------+-------------------------+----------+----------+----------+
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| ``sp`` | | Stack pointer | | | |
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+----------+---------+-------------------------+----------+----------+----------+
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| ``v0``- | | Floating point/SIMD | | | |
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| ``v7`` | | arguments 1-8 | | | |
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| | | (also for return) | | | |
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+----------+---------+-------------------------+----------+----------+----------+
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| ``v8``- | | Callee-saved registers | | | |
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| ``v15`` | | (**lower 64-bits only**)| | | |
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+----------+---------+-------------------------+----------+----------+----------+
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Stack frame
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^^^^^^^^^^^
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The stack pointer is **16-byte aligned**; on function entry, ``sp`` points at
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the location shown by "entry ``sp``" below. As with x86, frameless leaf
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functions may not set up ``fp``, in which case they will use ``sp`` relative
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accesses.
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+--------------+---------------+------------------------+
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| | ``fp+8n+16`` | last memory argument |
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| | | |
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| | ... | ... |
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| | ``fp+16`` | memory argument 0 [1]_ |
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+--------------+------------+--+------------------------+
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| ↓ Current Frame | ↑ Previous Frame |
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+--------------+------------+--+------------------------+
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| entry ``sp`` | ``fp+8`` | saved ``lr`` |
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| | | (return address) |
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+--------------+---------------+------------------------+
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| | ``fp`` | previous ``fp`` value |
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+--------------+---------------+------------------------+
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| | ``fp-8`` | |
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| | | |
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| | ... | local storage |
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| | ``sp`` | |
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+--------------+---------------+------------------------+
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| | ``sp-8`` | |
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| | | |
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| | ... | red zone |
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| | ``sp-128`` | |
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+--------------+---------------+------------------------+
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.. [1] See Apple documentation, however. Unlike the official ARM64 ABI, we pack
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arguments, so this might also hold argument 1, argument 2 and so on.
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