gcc/ada/sigtramp-ios.c

   1 /****************************************************************************
   2  *                                                                          *
   3  *                         GNAT COMPILER COMPONENTS                         *
   4  *                                                                          *
   5  *                             S I G T R A M P                              *
   6  *                                                                          *
   7  *                         Asm Implementation File                          *
   8  *                                                                          *
   9  *           Copyright (C) 2015-2023, Free Software Foundation, Inc.        *
  10  *                                                                          *
  11  * GNAT is free software;  you can  redistribute it  and/or modify it under *
  12  * terms of the  GNU General Public License as published  by the Free Soft- *
  13  * ware  Foundation;  either version 3,  or (at your option) any later ver- *
  14  * sion.  GNAT is distributed in the hope that it will be useful, but WITH- *
  15  * OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY *
  16  * or FITNESS FOR A PARTICULAR PURPOSE.                                     *
  17  *                                                                          *
  18  * As a special exception under Section 7 of GPL version 3, you are granted *
  19  * additional permissions described in the GCC Runtime Library Exception,   *
  20  * version 3.1, as published by the Free Software Foundation.               *
  21  *                                                                          *
  22  * In particular,  you can freely  distribute your programs  built with the *
  23  * GNAT Pro compiler, including any required library run-time units,  using *
  24  * any licensing terms  of your choosing.  See the AdaCore Software License *
  25  * for full details.                                                        *
  26  *                                                                          *
  27  * GNAT was originally developed  by the GNAT team at  New York University. *
  28  * Extensive contributions were provided by Ada Core Technologies Inc.      *
  29  *                                                                          *
  30  ****************************************************************************/
  31
  32 /****************************************************
  33  * ARM64/IOS version of the __gnat_sigtramp service *
  34  ****************************************************/
  35
  36 #include <sys/ucontext.h>
  37
  38 #include "sigtramp.h"
  39 /* See sigtramp.h for a general explanation of functionality.  */
  40
  41 /* ----------------------
  42    -- General comments --
  43    ----------------------
  44
  45    Unfortunately the libunwind library used on this platform comes with severe
  46    limitations that make the implementation convoluted:
  47
  48      1. At each step, the stack pointer register SP is restored with the CFA.
  49         This makes it impossible to set the CFA to an arbitrary value, for
  50         example to the address of the context saved on the stack, which means
  51         that the simple CFI directives cannot be used for the registers.
  52
  53      2. For the ARM64 architecture (and only it), DWARF expressions are not
  54         supported to compute the CFA.  Only DW_CFA_def_cfa is supported, which
  55         means that the CFA (modulo offset) must be loaded into a register.
  56
  57      3. The return column cannot be changed (30 for the ARM64 architecture).
  58         Since column 30 is that of the LR register, this makes it impossible
  59         to restore both the LR register and the PC.
  60
  61    Therefore we need 2 distinct call-saved registers in the trampoline and
  62    we resort to manual encoding of CFI byte sequences.  */
  63
  64 /* -----------------------------------------
  65    -- Protypes for our internal asm stubs --
  66    -----------------------------------------
  67
  68    Even though our symbols will remain local, the prototype claims "extern"
  69    and not "static" to prevent compiler complaints about a symbol used but
  70    never defined.  */
  71
  72 /* sigtramp stub providing unwind info for common registers.  */
  73
  74 #if defined(__cplusplus)
  75 extern "C" {
  76 #endif
  77
  78 extern void __gnat_sigtramp_common
  79   (int signo, void *siginfo, void *sigcontext,
  80    __sigtramphandler_t * handler);
  81
  82 void __gnat_sigtramp (int signo, void *si, void *ucontext,
  83                       __sigtramphandler_t * handler)
  84      __attribute__((optimize(2)));
  85
  86 void __gnat_sigtramp (int signo, void *si, void *ucontext,
  87                       __sigtramphandler_t * handler)
  88 {
  89   mcontext_t mcontext = ((ucontext_t *) ucontext)->uc_mcontext;
  90
  91   __gnat_sigtramp_common (signo, si, mcontext, handler);
  92 }
  93
  94 #if defined(__cplusplus)
  95 }
  96 #endif
  97
  98 /* asm string construction helpers.  */
  99
 100 #define STR(TEXT) #TEXT
 101 /* stringify expanded TEXT, surrounding it with double quotes.  */
 102
 103 #define S(E) STR(E)
 104 /* stringify E, which will resolve as text but may contain macros
 105    still to be expanded.  */
 106
 107 /* asm (TEXT) outputs <tab>TEXT. These facilitate the output of
 108    multiline contents:  */
 109 #define TAB(S) "\t" S
 110 #define CR(S)  S "\n"
 111
 112 #undef TCR
 113 #define TCR(S) TAB(CR(S))
 114
 115 /* Offset in uc_mcontext of the __ss structure containing the registers.  */
 116 #define UC_MCONTEXT_SS 16
 117
 118 #define CFA_REG  19
 119 #define BASE_REG 20
 120
 121 #define DW_CFA_def_cfa    0x0c
 122 #define DW_CFA_expression 0x10
 123
 124 #define DW_OP_breg(n)     0x70+(n)
 125
 126 #define REG_REGNO_GR(n)   n
 127 #define REG_REGNO_PC      30
 128
 129 /* The first byte of the SLEB128 value of the offset.  */
 130 #define REG_OFFSET_GR(n)         (UC_MCONTEXT_SS + n * 8)
 131 #define REG_OFFSET_LONG_GR(n)    (UC_MCONTEXT_SS + n * 8 + 128)
 132 #define REG_OFFSET_LONG128_GR(n) (UC_MCONTEXT_SS + (n - 16) * 8 + 128)
 133 #define REG_OFFSET_LONG256_GR(n) (UC_MCONTEXT_SS + (n - 32) * 8 + 128)
 134
 135 #define REG_OFFSET_LONG256_PC    REG_OFFSET_LONG256_GR(32)
 136
 137 #define CFI_DEF_CFA \
 138   TCR(".cfi_def_cfa " S(CFA_REG) ", 0")
 139
 140 /* We need 4 variants depending on the offset: 0+, 64+, 128+, 256+.  */
 141 #define COMMON_CFI(REG) \
 142   ".cfi_escape " S(DW_CFA_expression) "," S(REG_REGNO_##REG) ",2," \
 143   S(DW_OP_breg(BASE_REG)) "," S(REG_OFFSET_##REG)
 144
 145 #define COMMON_LONG_CFI(REG) \
 146   ".cfi_escape " S(DW_CFA_expression) "," S(REG_REGNO_##REG) ",3," \
 147   S(DW_OP_breg(BASE_REG)) "," S(REG_OFFSET_LONG_##REG) ",0"
 148
 149 #define COMMON_LONG128_CFI(REG) \
 150   ".cfi_escape " S(DW_CFA_expression) "," S(REG_REGNO_##REG) ",3," \
 151   S(DW_OP_breg(BASE_REG)) "," S(REG_OFFSET_LONG128_##REG) ",1"
 152
 153 #define COMMON_LONG256_CFI(REG) \
 154   ".cfi_escape " S(DW_CFA_expression) "," S(REG_REGNO_##REG) ",3," \
 155   S(DW_OP_breg(BASE_REG)) "," S(REG_OFFSET_LONG256_##REG) ",2"
 156
 157 #define CFI_COMMON_REGS \
 158   CR("# CFI for common registers\n") \
 159   TCR(COMMON_CFI(GR(0)))  \
 160   TCR(COMMON_CFI(GR(1)))  \
 161   TCR(COMMON_CFI(GR(2)))  \
 162   TCR(COMMON_CFI(GR(3)))  \
 163   TCR(COMMON_CFI(GR(4)))  \
 164   TCR(COMMON_CFI(GR(5)))  \
 165   TCR(COMMON_LONG_CFI(GR(6)))  \
 166   TCR(COMMON_LONG_CFI(GR(7)))  \
 167   TCR(COMMON_LONG_CFI(GR(8)))  \
 168   TCR(COMMON_LONG_CFI(GR(9)))  \
 169   TCR(COMMON_LONG_CFI(GR(10))) \
 170   TCR(COMMON_LONG_CFI(GR(11))) \
 171   TCR(COMMON_LONG_CFI(GR(12))) \
 172   TCR(COMMON_LONG_CFI(GR(13))) \
 173   TCR(COMMON_LONG128_CFI(GR(14))) \
 174   TCR(COMMON_LONG128_CFI(GR(15))) \
 175   TCR(COMMON_LONG128_CFI(GR(16))) \
 176   TCR(COMMON_LONG128_CFI(GR(17))) \
 177   TCR(COMMON_LONG128_CFI(GR(18))) \
 178   TCR(COMMON_LONG128_CFI(GR(19))) \
 179   TCR(COMMON_LONG128_CFI(GR(20))) \
 180   TCR(COMMON_LONG128_CFI(GR(21))) \
 181   TCR(COMMON_LONG128_CFI(GR(22))) \
 182   TCR(COMMON_LONG128_CFI(GR(23))) \
 183   TCR(COMMON_LONG128_CFI(GR(24))) \
 184   TCR(COMMON_LONG128_CFI(GR(25))) \
 185   TCR(COMMON_LONG128_CFI(GR(26))) \
 186   TCR(COMMON_LONG128_CFI(GR(27))) \
 187   TCR(COMMON_LONG128_CFI(GR(28))) \
 188   TCR(COMMON_LONG128_CFI(GR(29))) \
 189   TCR(COMMON_LONG256_CFI(PC))
 190
 191 /* Trampoline body block
 192    ---------------------  */
 193
 194 #define SIGTRAMP_BODY \
 195   TCR("stp fp, lr, [sp, #-32]!") \
 196   TCR("stp x" S(CFA_REG) ", x" S(BASE_REG) ", [sp, #16]") \
 197   TCR("mov fp, sp") \
 198   TCR("# Load the saved value of the stack pointer as CFA") \
 199   TCR("ldr x" S(CFA_REG) ", [x2, #" S(REG_OFFSET_GR(31)) "]") \
 200   TCR("# Use x" S(BASE_REG) " as base register for the CFI") \
 201   TCR("mov x" S(BASE_REG) ", x2") \
 202   TCR("# Call the handler") \
 203   TCR("blr x3") \
 204   TCR("# Release our frame and return (should never get here!).") \
 205   TCR("ldp x" S(CFA_REG) ", x" S(BASE_REG)" , [sp, #16]") \
 206   TCR("ldp fp, lr, [sp], 32") \
 207   TCR("ret")
 208
 209 /* -----------------------------
 210    -- Symbol definition block --
 211    ----------------------------- */
 212
 213 #define SIGTRAMP_START(SYM) \
 214   CR("# " S(SYM) " signal trampoline") \
 215   CR(S(SYM) ":") \
 216   TCR(".cfi_startproc") \
 217   TCR(".cfi_signal_frame")
 218
 219 /* ------------------------------
 220    -- Symbol termination block --
 221    ------------------------------ */
 222
 223 #define SIGTRAMP_END(SYM) \
 224   TCR(".cfi_endproc")
 225
 226 /*----------------------------
 227   -- And now, the real code --
 228   ---------------------------- */
 229
 230 asm(".text\n"
 231     TCR(".align 2"));
 232
 233 /* sigtramp stub for common registers.  */
 234
 235 #define TRAMP_COMMON ___gnat_sigtramp_common
 236
 237 asm (SIGTRAMP_START(TRAMP_COMMON));
 238 asm (CFI_DEF_CFA);
 239 asm (CFI_COMMON_REGS);
 240 asm (SIGTRAMP_BODY);
 241 asm (SIGTRAMP_END(TRAMP_COMMON));