19f5946001
Fix various typos in documentation txts. Signed-off-by: Matt LaPlante <kernel1@cyberdogtech.com> Signed-off-by: Jiri Kosina <jkosina@suse.cz>
149 lines
3.9 KiB
Text
149 lines
3.9 KiB
Text
=========================
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MN10300 FUNCTION CALL ABI
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=========================
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=======
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GENERAL
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=======
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The MN10300/AM33 kernel runs in little-endian mode; big-endian mode is not
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supported.
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The stack grows downwards, and should always be 32-bit aligned. There are
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separate stack pointer registers for userspace and the kernel.
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================
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ARGUMENT PASSING
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================
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The first two arguments (assuming up to 32-bits per argument) to a function are
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passed in the D0 and D1 registers respectively; all other arguments are passed
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on the stack.
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If 64-bit arguments are being passed, then they are never split between
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registers and the stack. If the first argument is a 64-bit value, it will be
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passed in D0:D1. If the first argument is not a 64-bit value, but the second
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is, the second will be passed entirely on the stack and D1 will be unused.
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Arguments smaller than 32-bits are not coalesced within a register or a stack
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word. For example, two byte-sized arguments will always be passed in separate
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registers or word-sized stack slots.
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=================
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CALLING FUNCTIONS
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=================
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The caller must allocate twelve bytes on the stack for the callee's use before
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it inserts a CALL instruction. The CALL instruction will write into the TOS
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word, but won't actually modify the stack pointer; similarly, the RET
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instruction reads from the TOS word of the stack, but doesn't move the stack
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pointer beyond it.
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Stack:
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|---------------| SP+20
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| 4th Arg |
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|---------------| SP+16
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| 3rd Arg |
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|---------------| SP+12
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| D1 Save Slot |
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|---------------| SP+8
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| D0 Save Slot |
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|---------------| SP+4
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| Return Addr |
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|---------------| SP
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The caller must leave space on the stack (hence an allocation of twelve bytes)
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in which the callee may store the first two arguments.
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============
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RETURN VALUE
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============
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The return value is passed in D0 for an integer (or D0:D1 for a 64-bit value),
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or A0 for a pointer.
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If the return value is a value larger than 64-bits, or is a structure or an
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array, then a hidden first argument will be passed to the callee by the caller:
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this will point to a piece of memory large enough to hold the result of the
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function. In this case, the callee will return the value in that piece of
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memory, and no value will be returned in D0 or A0.
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===================
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REGISTER CLOBBERING
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===================
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The values in certain registers may be clobbered by the callee, and other
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values must be saved:
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Clobber: D0-D1, A0-A1, E0-E3
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Save: D2-D3, A2-A3, E4-E7, SP
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All other non-supervisor-only registers are clobberable (such as MDR, MCRL,
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MCRH).
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=================
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SPECIAL REGISTERS
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=================
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Certain ordinary registers may carry special usage for the compiler:
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A3: Frame pointer
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E2: TLS pointer
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==========
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KERNEL ABI
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==========
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The kernel may use a slightly different ABI internally.
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(*) E2
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If CONFIG_MN10300_CURRENT_IN_E2 is defined, then the current task pointer
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will be kept in the E2 register, and that register will be marked
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unavailable for the compiler to use as a scratch register.
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Normally the kernel uses something like:
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MOV SP,An
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AND 0xFFFFE000,An
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MOV (An),Rm // Rm holds current
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MOV (yyy,Rm) // Access current->yyy
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To find the address of current; but since this option permits current to
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be carried globally in an register, it can use:
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MOV (yyy,E2) // Access current->yyy
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instead.
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===============
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SYSTEM CALL ABI
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===============
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System calls are called with the following convention:
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REGISTER ENTRY EXIT
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=============== ======================= =======================
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D0 Syscall number Return value
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A0 1st syscall argument Saved
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D1 2nd syscall argument Saved
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A3 3rd syscall argument Saved
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A2 4th syscall argument Saved
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D3 5th syscall argument Saved
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D2 6th syscall argument Saved
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All other registers are saved. The layout is a consequence of the way the MOVM
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instruction stores registers onto the stack.
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