Basic Stack Layout
------------------
Here is the basic stack layout.
`STACK_GROWS_DOWNWARD'
Define this macro if pushing a word onto the stack moves the stack
pointer to a smaller address.
When we say, "define this macro if ...," it means that the
compiler checks this macro only with `#ifdef' so the precise
definition used does not matter.
`FRAME_GROWS_DOWNWARD'
Define this macro if the addresses of local variable slots are at
negative offsets from the frame pointer.
`ARGS_GROW_DOWNWARD'
Define this macro if successive arguments to a function occupy
decreasing addresses on the stack.
`STARTING_FRAME_OFFSET'
Offset from the frame pointer to the first local variable slot to
be allocated.
If `FRAME_GROWS_DOWNWARD', find the next slot's offset by
subtracting the first slot's length from `STARTING_FRAME_OFFSET'.
Otherwise, it is found by adding the length of the first slot to
the value `STARTING_FRAME_OFFSET'.
`STACK_POINTER_OFFSET'
Offset from the stack pointer register to the first location at
which outgoing arguments are placed. If not specified, the
default value of zero is used. This is the proper value for most
machines.
If `ARGS_GROW_DOWNWARD', this is the offset to the location above
the first location at which outgoing arguments are placed.
`FIRST_PARM_OFFSET (FUNDECL)'
Offset from the argument pointer register to the first argument's
address. On some machines it may depend on the data type of the
function.
If `ARGS_GROW_DOWNWARD', this is the offset to the location above
the first argument's address.
`STACK_DYNAMIC_OFFSET (FUNDECL)'
Offset from the stack pointer register to an item dynamically
allocated on the stack, e.g., by `alloca'.
The default value for this macro is `STACK_POINTER_OFFSET' plus the
length of the outgoing arguments. The default is correct for most
machines. See `function.c' for details.
`DYNAMIC_CHAIN_ADDRESS (FRAMEADDR)'
A C expression whose value is RTL representing the address in a
stack frame where the pointer to the caller's frame is stored.
Assume that FRAMEADDR is an RTL expression for the address of the
stack frame itself.
If you don't define this macro, the default is to return the value
of FRAMEADDR--that is, the stack frame address is also the address
of the stack word that points to the previous frame.
`SETUP_FRAME_ADDRESSES'
If defined, a C expression that produces the machine-specific code
to setup the stack so that arbitrary frames can be accessed. For
example, on the Sparc, we must flush all of the register windows
to the stack before we can access arbitrary stack frames. You
will seldom need to define this macro.
`BUILTIN_SETJMP_FRAME_VALUE'
If defined, a C expression that contains an rtx that is used to
store the address of the current frame into the built in `setjmp'
buffer. The default value, `virtual_stack_vars_rtx', is correct
for most machines. One reason you may need to define this macro
is if `hard_frame_pointer_rtx' is the appropriate value on your
machine.
`RETURN_ADDR_RTX (COUNT, FRAMEADDR)'
A C expression whose value is RTL representing the value of the
return address for the frame COUNT steps up from the current
frame, after the prologue. FRAMEADDR is the frame pointer of the
COUNT frame, or the frame pointer of the COUNT - 1 frame if
`RETURN_ADDR_IN_PREVIOUS_FRAME' is defined.
The value of the expression must always be the correct address when
COUNT is zero, but may be `NULL_RTX' if there is not way to
determine the return address of other frames.
`RETURN_ADDR_IN_PREVIOUS_FRAME'
Define this if the return address of a particular stack frame is
accessed from the frame pointer of the previous stack frame.
`INCOMING_RETURN_ADDR_RTX'
A C expression whose value is RTL representing the location of the
incoming return address at the beginning of any function, before
the prologue. This RTL is either a `REG', indicating that the
return value is saved in `REG', or a `MEM' representing a location
in the stack.
You only need to define this macro if you want to support call
frame debugging information like that provided by DWARF 2.
`INCOMING_FRAME_SP_OFFSET'
A C expression whose value is an integer giving the offset, in
bytes, from the value of the stack pointer register to the top of
the stack frame at the beginning of any function, before the
prologue. The top of the frame is defined to be the value of the
stack pointer in the previous frame, just before the call
instruction.
You only need to define this macro if you want to support call
frame debugging information like that provided by DWARF 2.
`ARG_POINTER_CFA_OFFSET'
A C expression whose value is an integer giving the offset, in
bytes, from the argument pointer to the canonical frame address
(cfa). The final value should coincide with that calculated by
`INCOMING_FRAME_SP_OFFSET'. Which is unfortunately not usable
during virtual register instantiation.
You only need to define this macro if you want to support call
frame debugging information like that provided by DWARF 2.