sysdeps/generic/unwind-dw2-fde-glibc.c

   1 /* Copyright (C) 2001-2024 Free Software Foundation, Inc.
   2
   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 /* Locate the FDE entry for a given address, using PT_GNU_EH_FRAME ELF
  20    segment and dl_iterate_phdr to avoid register/deregister calls at
  21    DSO load/unload.  */
  22
  23 #ifdef _LIBC
  24 # include <shlib-compat.h>
  25 #endif
  26
  27 #if !defined _LIBC || SHLIB_COMPAT (libc, GLIBC_2_0, GLIBC_2_2_5)
  28
  29 #include <link.h>
  30 #include <stddef.h>
  31
  32 #define _Unwind_Find_FDE _Unwind_Find_registered_FDE
  33
  34 #include <unwind-dw2-fde.c>
  35
  36 #undef _Unwind_Find_FDE
  37
  38 extern fde * _Unwind_Find_registered_FDE (void *pc,
  39                                           struct dwarf_eh_bases *bases);
  40 extern fde * _Unwind_Find_FDE (void *, struct dwarf_eh_bases *);
  41
  42 struct unw_eh_callback_data
  43 {
  44   _Unwind_Ptr pc;
  45   void *tbase;
  46   void *dbase;
  47   void *func;
  48   fde *ret;
  49 };
  50
  51 struct unw_eh_frame_hdr
  52 {
  53   unsigned char version;
  54   unsigned char eh_frame_ptr_enc;
  55   unsigned char fde_count_enc;
  56   unsigned char table_enc;
  57 };
  58
  59 /* Like base_of_encoded_value, but take the base from a struct object
  60    instead of an _Unwind_Context.  */
  61
  62 static _Unwind_Ptr
  63 base_from_cb_data (unsigned char encoding, struct unw_eh_callback_data *data)
  64 {
  65   if (encoding == DW_EH_PE_omit)
  66     return 0;
  67
  68   switch (encoding & 0x70)
  69     {
  70     case DW_EH_PE_absptr:
  71     case DW_EH_PE_pcrel:
  72     case DW_EH_PE_aligned:
  73       return 0;
  74
  75     case DW_EH_PE_textrel:
  76       return (_Unwind_Ptr) data->tbase;
  77     case DW_EH_PE_datarel:
  78       return (_Unwind_Ptr) data->dbase;
  79     }
  80   abort ();
  81 }
  82
  83 static int
  84 _Unwind_IteratePhdrCallback (struct dl_phdr_info *info, size_t size, void *ptr)
  85 {
  86   struct unw_eh_callback_data *data = (struct unw_eh_callback_data *) ptr;
  87   const ElfW(Phdr) *phdr, *p_eh_frame_hdr;
  88   const ElfW(Phdr) *p_dynamic __attribute__ ((unused));
  89   long n, match;
  90   _Unwind_Ptr load_base;
  91   const unsigned char *p;
  92   const struct unw_eh_frame_hdr *hdr;
  93   _Unwind_Ptr eh_frame;
  94   struct object ob;
  95
  96   /* Make sure struct dl_phdr_info is at least as big as we need.  */
  97   if (size < offsetof (struct dl_phdr_info, dlpi_phnum)
  98              + sizeof (info->dlpi_phnum))
  99     return -1;
 100
 101   match = 0;
 102   phdr = info->dlpi_phdr;
 103   load_base = info->dlpi_addr;
 104   p_eh_frame_hdr = NULL;
 105   p_dynamic = NULL;
 106
 107   /* See if PC falls into one of the loaded segments.  Find the eh_frame
 108      segment at the same time.  */
 109   for (n = info->dlpi_phnum; --n >= 0; phdr++)
 110     {
 111       if (phdr->p_type == PT_LOAD)
 112         {
 113           _Unwind_Ptr vaddr = phdr->p_vaddr + load_base;
 114           if (data->pc >= vaddr && data->pc < vaddr + phdr->p_memsz)
 115             match = 1;
 116         }
 117       else if (phdr->p_type == PT_GNU_EH_FRAME)
 118         p_eh_frame_hdr = phdr;
 119       else if (phdr->p_type == PT_DYNAMIC)
 120         p_dynamic = phdr;
 121     }
 122   if (!match || !p_eh_frame_hdr)
 123     return 0;
 124
 125   /* Read .eh_frame_hdr header.  */
 126   hdr = (const struct unw_eh_frame_hdr *)
 127         (p_eh_frame_hdr->p_vaddr + load_base);
 128   if (hdr->version != 1)
 129     return 1;
 130
 131 #ifdef CRT_GET_RFIB_DATA
 132 # ifdef __i386__
 133   data->dbase = NULL;
 134   if (p_dynamic)
 135     {
 136       /* For dynamically linked executables and shared libraries,
 137          DT_PLTGOT is the gp value for that object.  */
 138       ElfW(Dyn) *dyn = (ElfW(Dyn) *)(p_dynamic->p_vaddr + load_base);
 139       for (; dyn->d_tag != DT_NULL ; dyn++)
 140         if (dyn->d_tag == DT_PLTGOT)
 141           {
 142             /* On IA-32, _DYNAMIC is writable and GLIBC has relocated it.  */
 143             data->dbase = (void *) dyn->d_un.d_ptr;
 144             break;
 145           }
 146     }
 147 # else
 148 #  error What is DW_EH_PE_datarel base on this platform?
 149 # endif
 150 #endif
 151 #ifdef CRT_GET_RFIB_TEXT
 152 # error What is DW_EH_PE_textrel base on this platform?
 153 #endif
 154
 155   p = read_encoded_value_with_base (hdr->eh_frame_ptr_enc,
 156                                     base_from_cb_data (hdr->eh_frame_ptr_enc,
 157                                                        data),
 158                                     (const unsigned char *) (hdr + 1),
 159                                     &eh_frame);
 160
 161   /* We require here specific table encoding to speed things up.
 162      Also, DW_EH_PE_datarel here means using PT_GNU_EH_FRAME start
 163      as base, not the processor specific DW_EH_PE_datarel.  */
 164   if (hdr->fde_count_enc != DW_EH_PE_omit
 165       && hdr->table_enc == (DW_EH_PE_datarel | DW_EH_PE_sdata4))
 166     {
 167       _Unwind_Ptr fde_count;
 168
 169       p = read_encoded_value_with_base (hdr->fde_count_enc,
 170                                         base_from_cb_data (hdr->fde_count_enc,
 171                                                            data),
 172                                         p, &fde_count);
 173       /* Shouldn't happen.  */
 174       if (fde_count == 0)
 175         return 1;
 176       if ((((_Unwind_Ptr) p) & 3) == 0)
 177         {
 178           struct fde_table {
 179             signed initial_loc __attribute__ ((mode (SI)));
 180             signed fde __attribute__ ((mode (SI)));
 181           };
 182           const struct fde_table *table = (const struct fde_table *) p;
 183           size_t lo, hi, mid;
 184           _Unwind_Ptr data_base = (_Unwind_Ptr) hdr;
 185           fde *f;
 186           unsigned int f_enc, f_enc_size;
 187           _Unwind_Ptr range;
 188
 189           mid = fde_count - 1;
 190           if (data->pc < table[0].initial_loc + data_base)
 191             return 1;
 192           else if (data->pc < table[mid].initial_loc + data_base)
 193             {
 194               lo = 0;
 195               hi = mid;
 196
 197               while (lo < hi)
 198                 {
 199                   mid = (lo + hi) / 2;
 200                   if (data->pc < table[mid].initial_loc + data_base)
 201                     hi = mid;
 202                   else if (data->pc >= table[mid + 1].initial_loc + data_base)
 203                     lo = mid + 1;
 204                   else
 205                     break;
 206                 }
 207
 208               if (lo >= hi)
 209                 __gxx_abort ();
 210             }
 211
 212           f = (fde *) (table[mid].fde + data_base);
 213           f_enc = get_fde_encoding (f);
 214           f_enc_size = size_of_encoded_value (f_enc);
 215           read_encoded_value_with_base (f_enc & 0x0f, 0,
 216                                         &f->pc_begin[f_enc_size], &range);
 217           if (data->pc < table[mid].initial_loc + data_base + range)
 218             data->ret = f;
 219           data->func = (void *) (table[mid].initial_loc + data_base);
 220           return 1;
 221         }
 222     }
 223
 224   /* We have no sorted search table, so need to go the slow way.
 225      As soon as GLIBC will provide API so to notify that a library has been
 226      removed, we could cache this (and thus use search_object).  */
 227   ob.pc_begin = NULL;
 228   ob.tbase = data->tbase;
 229   ob.dbase = data->dbase;
 230   ob.u.single = (fde *) eh_frame;
 231   ob.s.i = 0;
 232   ob.s.b.mixed_encoding = 1;  /* Need to assume worst case.  */
 233   data->ret = linear_search_fdes (&ob, (fde *) eh_frame, (void *) data->pc);
 234   if (data->ret != NULL)
 235     {
 236       unsigned int encoding = get_fde_encoding (data->ret);
 237       _Unwind_Ptr func;
 238       read_encoded_value_with_base (encoding,
 239                                     base_from_cb_data (encoding, data),
 240                                     data->ret->pc_begin, &func);
 241       data->func = (void *) func;
 242     }
 243   return 1;
 244 }
 245
 246 # ifdef _LIBC
 247 # define dl_iterate_phdr __dl_iterate_phdr
 248 # endif
 249
 250 fde *
 251 _Unwind_Find_FDE (void *pc, struct dwarf_eh_bases *bases)
 252 {
 253   struct unw_eh_callback_data data;
 254   fde *ret;
 255
 256   ret = _Unwind_Find_registered_FDE (pc, bases);
 257   if (ret != NULL)
 258     return ret;
 259
 260   data.pc = (_Unwind_Ptr) pc;
 261   data.tbase = NULL;
 262   data.dbase = NULL;
 263   data.func = NULL;
 264   data.ret = NULL;
 265
 266   if (dl_iterate_phdr (_Unwind_IteratePhdrCallback, &data) < 0)
 267     return NULL;
 268
 269   if (data.ret)
 270     {
 271       bases->tbase = data.tbase;
 272       bases->dbase = data.dbase;
 273       bases->func = data.func;
 274     }
 275   return data.ret;
 276 }
 277
 278 #endif