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Diffstat (limited to 'gcc/config/stormy16/stormy-abi')
| -rw-r--r-- | gcc/config/stormy16/stormy-abi | 174 |
1 files changed, 174 insertions, 0 deletions
diff --git a/gcc/config/stormy16/stormy-abi b/gcc/config/stormy16/stormy-abi new file mode 100644 index 000000000..887e7d76e --- /dev/null +++ b/gcc/config/stormy16/stormy-abi @@ -0,0 +1,174 @@ +xStormy16 ABI +************ + +!!!!! NOTE !!!!! +This document is a draft and is subject to change. +!!!!! NOTE !!!!! + +This part of the file describes the conventions required to write +ELF object files that are link-compatible with the ones produced +by the GNU toolchains. + +Bit and Byte Ordering +===================== + +This implementation is little-endian. Bits are numbered starting +from 0 being the LSB. + +In this document, 'word' means 16 bits. + +Calling Sequence +================ + +The registers are allocated as follows: + +Register Purpose +------------------------------------------------------------------- +r0, r1 Call-volatile. May be changed during the execution + of a call instruction. +r2 through r7 Argument passing; call-clobbered. +r8, r9 Call-volatile. May be changed during the execution + of a call instruction. +r10 through r13 Call-saved. +r14 Program status word. +r15 Stack pointer. + + +Scalar values are returned in register r2-r7 if the value fits. +Otherwise, a pointer is passed as a 'hidden' first argument and +the return value is placed there. + +Arguments are passed in registers starting in r2, then on the stack. +Arguments of size not a multiple of a word are padded to whole words. +If an argument would otherwise be passed partially in registers, and +partially on the stack, the whole of it is passed on the stack. The +last argument is pushed on the stack first. + +After a procedure's arguments are pushed on the stack, +the return address is pushed on the stack, as if by the call +instruction. The return address is on the top of the stack when +a procedure is called. + +Objects whose size is a multiple of 16 bits are aligned to a 16-bit +boundary. + +Pointers are 16 bits, referencing addresses between 0 and 0xFFFF. + +Procedure pointers are also implemented as 16-bit pointers. + +Variable Argument Functions +=========================== + +The C type 'va_list' is implemented as a structure, as follows: + +struct { + char *base; + unsigned count; +} + +Both fields are 16 bits. An argument of size N bytes +(N will be even) is accessed as if by the following code: + +char *result; +/* count = #bytes non-variable arguments */ +/* 12 = #bytes for register arguments */ +if (count + N > 12) + { + if (count < 12) + count = 12; + result = base - (count + N - 12 + 4); + } +else + { + result = base + count; + } +count += N; +/* The argument is at `*result'. */ + + +One implementation of this is if a variadic function first +pushes registers 2 through 7 in sequence at entry, and +sets 'base' to the address of the first word pushed, +producing a stack that appears like: + +SP -> + [other data] + r7 + r6 + r5 + r4 + r3 +count-> r2 + Return address (two words) + 7th procedure parameter word + 8th procedure parameter word + ... + last procedure parameter word + +and initializes 'count' to be the number of bytes of non-variable +arguments to the function. + +ELF File Format +=============== + +ELF file header +--------------- + +xStormy16 ELF files are distinguished by the value EM_XSTORMY16 in +the e_machine field of the ELF file header: + +#define EM_XSTORMY16 0xad45 + +DWARF Register Number Mapping +----------------------------- + +Registers r0 through r15 are mapped to numbers 0 through 15. + +Relocations +----------- + +RELA relocs are used exclusively. The relocation types defined are: + +Name Value Field Calculation Overflow +---------------------------------------------------------------- +R_XSTORMY16_NONE 0 none none none +R_XSTORMY16_32 1 32 S + A none +R_XSTORMY16_16 2 16 S + A either +R_XSTORMY16_8 3 8 S + A unsigned +R_XSTORMY16_PC32 4 32 S + A - P none +R_XSTORMY16_PC16 5 16 S + A - P signed +R_XSTORMY16_PC8 6 8 S + A - P signed +R_XSTORMY16_REL_12 7 16:12:0 S + A - P signed +R_XSTORMY16_24 8 32:23:1 (S + A) >> 1 unsigned +R_XSTORMY16_FPTR16 9 16 S + A either +R_XSTORMY16_LO16 10 16 S + A none +R_XSTORMY16_HI16 11 32:16:16 S + A none +R_XSTORMY16_12 12 16:12:0 S + A signed +R_XSTORMY16_GNU_VTINHERIT 128 n/a n/a n/a +R_XSTORMY16_GNU_VTENTRY 129 n/a n/a n/a + +In the 'Field' column, the first number indicates whether the +relocation refers to a byte, word or doubleword. The second number, +if any, indicates the size of the bit-field into which the relocation +is to occur (and also the size for overflow checking). The third +number indicates the first bit of the bit-field in the word or +doubleword, counting the LSB as bit 0. + +In the 'Calculation' column, 'S' is the value of the symbol to which +the reloc refers, 'A' is the addend, and 'P' represents the place of +the storage unit being relocated. + +In the 'Overflow' column, 'none' means that any overflow of the +computation performed in the 'Calculation' column is ignored. +'signed' means that the overflow is only reported if it happens when +the values are treated as signed quantities. 'unsigned' is the same, +except that the values are treated as unsigned quantities. 'either' +means that overflow is reported for either signed or unsigned +overflow. + + +Copyright (C) 2001, 2002, 2003, 2005 Free Software Foundation, Inc. + +Copying and distribution of this file, with or without modification, +are permitted in any medium without royalty provided the copyright +notice and this notice are preserved. |