sysdeps/unix/sysv/linux/x86_64/libc_sigaction.c

   1 /* POSIX.1 `sigaction' call for Linux/x86-64.
   2    Copyright (C) 2001-2021 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <signal.h>
  20 #define SA_RESTORER 0x04000000
  21
  22 extern void restore_rt (void) asm ("__restore_rt") attribute_hidden;
  23
  24 #define SET_SA_RESTORER(kact, act)                      \
  25   (kact)->sa_flags = (act)->sa_flags | SA_RESTORER;     \
  26   (kact)->sa_restorer = &restore_rt
  27
  28 #define RESET_SA_RESTORER(act, kact)                    \
  29   (act)->sa_restorer = (kact)->sa_restorer
  30
  31 #include <kernel_sigaction.h>
  32
  33 #include <sysdeps/unix/sysv/linux/libc_sigaction.c>
  34
  35 /* NOTE: Please think twice before making any changes to the bits of
  36    code below.  GDB needs some intimate knowledge about it to
  37    recognize them as signal trampolines, and make backtraces through
  38    signal handlers work right.  Important are both the names
  39    (__restore_rt) and the exact instruction sequence.
  40    If you ever feel the need to make any changes, please notify the
  41    appropriate GDB maintainer.
  42
  43    The unwind information starts a byte before __restore_rt, so that
  44    it is found when unwinding, to get an address the unwinder assumes
  45    will be in the middle of a call instruction.  See the Linux kernel
  46    (the i386 vsyscall, in particular) for an explanation of the complex
  47    unwind information used here in order to get the traditional CFA.
  48    We do not restore cs - it's only stored as two bytes here so that's
  49    a bit tricky.  We don't use the gas cfi directives, so that we can
  50    reliably add .cfi_signal_frame.  */
  51
  52 #include "ucontext_i.h"
  53
  54 #define do_cfa_expr                                             \
  55   "     .byte 0x0f\n"           /* DW_CFA_def_cfa_expression */ \
  56   "     .uleb128 2f-1f\n"       /* length */                    \
  57   "1:   .byte 0x77\n"           /* DW_OP_breg7 */               \
  58   "     .sleb128 " CFI_STRINGIFY (oRSP) "\n"                    \
  59   "     .byte 0x06\n"           /* DW_OP_deref */               \
  60   "2:"
  61
  62 #define do_expr(regno, offset)                                  \
  63   "     .byte 0x10\n"           /* DW_CFA_expression */         \
  64   "     .uleb128 " CFI_STRINGIFY (regno) "\n"                   \
  65   "     .uleb128 2f-1f\n"       /* length */                    \
  66   "1:   .byte 0x77\n"           /* DW_OP_breg7 */               \
  67   "     .sleb128 " CFI_STRINGIFY (offset) "\n"                  \
  68   "2:"
  69
  70 #define RESTORE(name, syscall) RESTORE2 (name, syscall)
  71 # define RESTORE2(name, syscall) \
  72 asm                                                                     \
  73   (                                                                     \
  74    /* `nop' for debuggers assuming `call' should not disalign the code.  */ \
  75    "    nop\n"                                                          \
  76    ".align 16\n"                                                        \
  77    ".LSTART_" #name ":\n"                                               \
  78    "    .type __" #name ",@function\n"                                  \
  79    "__" #name ":\n"                                                     \
  80    "    movq $" #syscall ", %rax\n"                                     \
  81    "    syscall\n"                                                      \
  82    ".LEND_" #name ":\n"                                                 \
  83    ".section .eh_frame,\"a\",@progbits\n"                               \
  84    ".LSTARTFRAME_" #name ":\n"                                          \
  85    "    .long .LENDCIE_" #name "-.LSTARTCIE_" #name "\n"                \
  86    ".LSTARTCIE_" #name ":\n"                                            \
  87    "    .long 0\n"      /* CIE ID */                                    \
  88    "    .byte 1\n"      /* Version number */                            \
  89    "    .string \"zRS\"\n" /* NUL-terminated augmentation string */     \
  90    "    .uleb128 1\n"   /* Code alignment factor */                     \
  91    "    .sleb128 -8\n"  /* Data alignment factor */                     \
  92    "    .uleb128 16\n"  /* Return address register column (rip) */      \
  93    /* Augmentation value length */                                      \
  94    "    .uleb128 .LENDAUGMNT_" #name "-.LSTARTAUGMNT_" #name "\n"       \
  95    ".LSTARTAUGMNT_" #name ":\n"                                         \
  96    "    .byte 0x1b\n"   /* DW_EH_PE_pcrel|DW_EH_PE_sdata4. */           \
  97    ".LENDAUGMNT_" #name ":\n"                                           \
  98    "    .align " LP_SIZE "\n"                                           \
  99    ".LENDCIE_" #name ":\n"                                              \
 100    "    .long .LENDFDE_" #name "-.LSTARTFDE_" #name "\n" /* FDE len */  \
 101    ".LSTARTFDE_" #name ":\n"                                            \
 102    "    .long .LSTARTFDE_" #name "-.LSTARTFRAME_" #name "\n" /* CIE */  \
 103    /* `LSTART_' is subtracted 1 as debuggers assume a `call' here.  */  \
 104    "    .long (.LSTART_" #name "-1)-.\n" /* PC-relative start addr.  */ \
 105    "    .long .LEND_" #name "-(.LSTART_" #name "-1)\n"                  \
 106    "    .uleb128 0\n"                   /* FDE augmentation length */   \
 107    do_cfa_expr                                                          \
 108    do_expr (8 /* r8 */, oR8)                                            \
 109    do_expr (9 /* r9 */, oR9)                                            \
 110    do_expr (10 /* r10 */, oR10)                                         \
 111    do_expr (11 /* r11 */, oR11)                                         \
 112    do_expr (12 /* r12 */, oR12)                                         \
 113    do_expr (13 /* r13 */, oR13)                                         \
 114    do_expr (14 /* r14 */, oR14)                                         \
 115    do_expr (15 /* r15 */, oR15)                                         \
 116    do_expr (5 /* rdi */, oRDI)                                          \
 117    do_expr (4 /* rsi */, oRSI)                                          \
 118    do_expr (6 /* rbp */, oRBP)                                          \
 119    do_expr (3 /* rbx */, oRBX)                                          \
 120    do_expr (1 /* rdx */, oRDX)                                          \
 121    do_expr (0 /* rax */, oRAX)                                          \
 122    do_expr (2 /* rcx */, oRCX)                                          \
 123    do_expr (7 /* rsp */, oRSP)                                          \
 124    do_expr (16 /* rip */, oRIP)                                         \
 125    /* libgcc-4.1.1 has only `DWARF_FRAME_REGISTERS == 17'.  */          \
 126    /* do_expr (49 |* rflags *|, oEFL) */                                \
 127    /* `cs'/`ds'/`fs' are unaligned and a different size.  */            \
 128    /* gas: Error: register save offset not a multiple of 8  */          \
 129    "    .align " LP_SIZE "\n"                                           \
 130    ".LENDFDE_" #name ":\n"                                              \
 131    "    .previous\n"                                                    \
 132    );
 133 /* The return code for realtime-signals.  */
 134 RESTORE (restore_rt, __NR_rt_sigreturn)