gcc/config/m32c/m32c.abi

   1    Target Definitions for R8C/M16C/M32C
   2    Copyright (C) 2005-2021 Free Software Foundation, Inc.
   3    Contributed by Red Hat.
   4
   5    This file is part of GCC.
   6
   7    GCC is free software; you can redistribute it and/or modify it
   8    under the terms of the GNU General Public License as published
   9    by the Free Software Foundation; either version 3, or (at your
  10    option) any later version.
  11
  12    GCC is distributed in the hope that it will be useful, but WITHOUT
  13    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  14    or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
  15    License for more details.
  16
  17    You should have received a copy of the GNU General Public License
  18    along with GCC; see the file COPYING3.  If not see
  19    <http://www.gnu.org/licenses/>.
  20
  21
  22 These are just some random notes I used during development of this
  23 port.  Please don't consider these to be "official" specifications,
  24 just additional information to help make the code easier to
  25 understand.
  26
  27
  28 Frame
  29 =====
  30
  31         +--------------------
  32         | incoming args
  33         +--------------------
  34         | return Address
  35 osp ->  +--------------------
  36         | saved fp
  37 fp ->   +--------------------
  38         | local data
  39         +--------------------
  40         | saved regs
  41         +--------------------
  42         | outgoing args (opt)
  43 sp ->   +--------------------
  44
  45 Argument Passing
  46 ================
  47
  48 r8c, m16c
  49 ---------
  50
  51 First arg may be passed in r1l or r1 if it (1) fits (QImode or
  52 HImode), (2) is named, and (3) is an integer or pointer type (no
  53 structs, floats, etc).  Otherwise, it's passed on the stack.
  54
  55 Second arg may be passed in r2, same restrictions (but not QImode),
  56 even if the first arg is passed on the stack.
  57
  58 Third and further args are passed on the stack.  No padding is used,
  59 stack "alignment" is 8 bits.
  60
  61 m32cm, m32c
  62 -----------
  63 First arg may be passed in r0l or r0, same restrictions as above.
  64
  65 Second and further args are passed on the stack.  Padding is used
  66 after QImode parameters (i.e. lower-addressed byte is the value,
  67 higher-addressed byte is the padding), stack "alignment" is 16 bits.
  68
  69
  70 Return Value
  71 ============
  72
  73 r8c, m16c
  74 ---------
  75
  76 QImode in r0l
  77 HImode in r0
  78 near pointer in r0
  79 (desired)
  80 SImode in r2r0
  81 far pointer in r2r0
  82 (actual)
  83 Anything bigger than 16 bits is returned in memory, at mem0 (mem0
  84 through mem15 are provided by libgcc.a)
  85
  86 Aggregate values (regardless of size) are returned by pushing a
  87 pointer to a temporary area on the stack after the args are pushed.
  88 The function fills in this area with the value.  Note that this
  89 pointer on the stack does not affect how register arguments, if any,
  90 are configured.
  91
  92 m32cm, m32c
  93 -----------
  94 Same.
  95
  96
  97 Registers Preserved Across Calls
  98 ================================
  99
 100 r8c, m16c
 101 ---------
 102 sb, fb, sp (i.e. nearly all registers are call clobbered)
 103
 104 m32cm, m32c
 105 -----------
 106 r1, r2, r3, a0, a1, sb, fb, sp
 107 (except when used for return values)
 108
 109
 110 Interrupt Handlers
 111 ==================
 112
 113 The stack frame is slightly different for interrupt handlers, because
 114 (1) we don't have a usable parent frame, and (2) we have to use
 115 special instructions to return and thus must save/restore everything
 116 differently.
 117
 118         +--------------------
 119         | program state
 120 osp ->  +--------------------
 121         | return address
 122         +--------------------
 123         | saved r0..fp (pushm)
 124 fp ->   +--------------------
 125         | local data
 126         +--------------------
 127         | saved regs mem0..mem15
 128         +--------------------
 129         | outgoing args (opt)
 130 sp ->   +--------------------
 131