--- /dev/null
+ IQ2000 ABI
+ =========
+
+Sizes and alignments
+--------------------
+
+ Type Size (bytes) Alignment (bytes)
+
+ char 1 1
+ short 2 2
+ int 4 4
+ unsigned 4 4
+ long 4 4
+ long long 8 8
+ float 4 4
+ double 8 8
+ pointers 4 4
+
+* alignment within aggregates (structs and unions) is as above, with
+ padding added if needed
+* aggregates have alignment equal to that of their most aligned
+ member
+* aggregates have sizes which are a multiple of their alignment
+
+
+Floating point
+--------------
+
+All emulated using IEEE floating point conventions.
+
+Registers
+----------------
+
+%0 always zero
+%1 call clobbered
+%2 return value
+%3 return value
+%4 argument register 1
+%5 argument register 2
+%6 argument register 3
+%7 argument register 4
+%8 argument register 5
+%9 argument register 6
+%10 argument register 7
+%11 argument register 8
+%12 call clobbered
+%13 call clobbered
+%14 call clobbered
+%15 call clobbered
+%16 call saved
+%17 call saved
+%18 call saved
+%19 call saved
+%20 call saved
+%21 call saved
+%22 call saved
+%23 call saved
+%24 call clobbered
+%25 call clobbered
+%26 reserved
+%27 frame ptr
+%28 global ptr
+%29 stack ptr
+%30 reserved
+%31 return address
+
+Stack alignment 8 bytes
+
+Structures passed <= 32 bits as values, else as pointers
+
+The IQ2000 Stack
+---------------
+
+Space is allocated as needed in the stack frame for the following at compile
+time:
+
+* Outgoing parameters beyond the eighth
+
+* All automatic arrays, automatic data aggregates, automatic
+ scalars which must be addressable, and automatic scalars for
+ which there is no room in registers
+
+* Compiler-generated temporary values (typically when there are
+ too many for the compiler to keep them all in registers)
+
+Space can be allocated dynamically (at runtime) in the stack frame for the
+following:
+
+* Memory allocated using the alloca() function of the C library
+
+Addressable automatic variables on the stack are addressed with positive
+offsets relative to %27; dynamically allocated space is addressed with positive
+offsets from the pointer returned by alloca().
+
+Stack Frame
+-----------
+
+ +-----------------------+
+ | Caller memory args |
+ +-----------------------+ <-sp
+ | Return address |
+ +-----------------------+
+ | Previous FP |
+ +-----------------------+
+ | Saved Registers |
+ +-----------------------+
+ | ... |
+ +-----------------------+
+ | Local Variables |
+ +-----------------------+ <-fp
+ | Alloca |
+ +-----------------------+
+ | ... |
+ +-----------------------+
+ | Parameter Word 2 |
+ +-----------------------+
+ | Parameter Word 1 |
+ +-----------------------+ <-sp
+
+
+Parameter Assignment to Registers
+---------------------------------
+
+Consider the parameters in a function call as ordered from left (first
+parameter) to right. GR contains the number of the next available
+general-purpose register. STARG is the address of the next available stack
+parameter word.
+
+INITIALIZE:
+ Set GR=r4 and STARG to point to parameter word 1.
+
+SCAN:
+ If there are no more parameters, terminate.
+ Otherwise, select one of the following depending on the type
+ of the next parameter:
+
+ SIMPLE ARG:
+
+ A SIMPLE ARG is one of the following:
+
+ * One of the simple integer types which will fit into a
+ general-purpose register,
+ * A pointer to an object of any type,
+ * A struct or union small enough to fit in a register (<= 32 bits)
+ * A larger struct or union, which shall be treated as a
+ pointer to the object or to a copy of the object.
+ (See below for when copies are made.)
+
+ If GR > r11, go to STACK. Otherwise, load the parameter value into
+ general-purpose register GR and advance GR to the next general-purpose
+ register. Values shorter than the register size are sign-extended or
+ zero-extended depending on whether they are signed or unsigned. Then
+ go to SCAN.
+
+ DOUBLE or LONG LONG
+
+ If GR > r10, go to STACK. Otherwise, if GR is odd, advance GR to the
+ next register. Load the 64-bit long long or double value into register
+ pair GR and GR+1. Advance GR to GR+2 and go to SCAN.
+
+ STACK:
+
+ Parameters not otherwise handled above are passed in the parameter
+ words of the caller's stack frame. SIMPLE ARGs, as defined above, are
+ considered to have size and alignment equal to the size of a
+ general-purpose register, with simple argument types shorter than this
+ sign- or zero-extended to this width. Round STARG up to a multiple of
+ the alignment requirement of the parameter and copy the argument
+ byte-for-byte into STARG, STARG+1, ... STARG+size-1. Set STARG to
+ STARG+size and go to SCAN.
+
+
+Structure passing
+-----------------
+
+As noted above, code which passes structures and unions by value is implemented
+specially. (In this section, "struct" will refer to structs and unions
+inclusively.) Structs small enough to fit in a register are passed by value in
+a single register or in a stack frame slot the size of a register. Structs
+containing a single double or long long component are passed by value in two
+registers or in a stack frame slot the size of two registers. Other structs
+are handled by passing the address of the structure. In this case, a copy of
+the structure will be made if necessary in order to preserve the pass-by-value
+semantics.
+
+Copies of large structs are made under the following rules:
+
+ ANSI mode K&R Mode
+ --------- --------
+Normal param Callee copies if needed Caller copies
+Varargs (...) param Caller copies Caller copies
+
+In the case of normal (non-varargs) large-struct parameters in ANSI mode, the
+callee is responsible for producing the same effect as if a copy of the
+structure were passed, preserving the pass-by-value semantics. This may be
+accomplished by having the callee make a copy, but in some cases the callee may
+be able to determine that a copy is not necessary in order to produce the same
+results. In such cases, the callee may choose to avoid making a copy of the
+parameter.
+
+
+Varargs handling
+----------------
+
+No special changes are needed for handling varargs parameters other than the
+caller knowing that a copy is needed on struct parameters larger than a
+register (see above).
+
+The varargs macros set up a register save area for the general-purpose
+registers to be saved. Because the save area lies between the caller and
+callee stack frames, the saved register parameters are contiguous with
+parameters passed on the stack. A pointer advances from the register save area
+into the caller's stack frame.
+
+
+Function return values
+----------------------
+
+ Type Register
+ ---- --------
+ int r2
+ short r2
+ long r2
+ long long r2-r3
+ float r2
+ double r2-r3
+ struct/union see below
+
+Structs/unions which will fit into two general-purpose registers are returned
+in r2, or in r2-r3 if necessary. Larger structs/unions are handled by the
+caller passing as a "hidden" first argument a pointer to space allocated to
+receive the return value.
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