gdb/minidebug.c

   1 /* Read MiniDebugInfo data from an objfile.
   2
   3    Copyright (C) 2012-2024 Free Software Foundation, Inc.
   4
   5    This file is part of GDB.
   6
   7    This program is free software; you can redistribute it and/or modify
   8    it under the terms of the GNU General Public License as published by
   9    the Free Software Foundation; either version 3 of the License, or
  10    (at your option) any later version.
  11
  12    This program is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15    GNU General Public License for more details.
  16
  17    You should have received a copy of the GNU General Public License
  18    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  19
  20 #include "gdb_bfd.h"
  21 #include "symfile.h"
  22 #include "objfiles.h"
  23 #include "gdbcore.h"
  24 #include <algorithm>
  25
  26 #ifdef HAVE_LIBLZMA
  27
  28 /* We stash a reference to the .gnu_debugdata BFD on the enclosing
  29    BFD.  */
  30 static const registry<bfd>::key<gdb_bfd_ref_ptr> gnu_debug_key;
  31
  32 #include <lzma.h>
  33
  34 /* Allocator function for LZMA.  */
  35
  36 static void *
  37 alloc_lzma (void *opaque, size_t nmemb, size_t size)
  38 {
  39   return xmalloc (nmemb * size);
  40 }
  41
  42 /* Free function for LZMA.  */
  43
  44 static void
  45 free_lzma (void *opaque, void *ptr)
  46 {
  47   xfree (ptr);
  48 }
  49
  50 /* The allocator object for LZMA.  Note that 'gdb_lzma_allocator'
  51    cannot be const due to the lzma library function prototypes.  */
  52
  53 static lzma_allocator gdb_lzma_allocator = { alloc_lzma, free_lzma, NULL };
  54
  55 /* Custom bfd_openr_iovec implementation to read compressed data from
  56    a section.  This keeps only the last decompressed block in memory
  57    to allow larger data without using to much memory.  */
  58
  59 struct gdb_lzma_stream : public gdb_bfd_iovec_base
  60 {
  61   /* Section of input BFD from which we are decoding data.  */
  62   asection *section = nullptr;
  63
  64   /* lzma library decompression state.  */
  65   lzma_index *index = nullptr;
  66
  67   /* Currently decoded block.  */
  68   bfd_size_type data_start = 0;
  69   bfd_size_type data_end = 0;
  70   gdb::byte_vector data;
  71
  72
  73   ~gdb_lzma_stream ()
  74   {
  75     lzma_index_end (index, &gdb_lzma_allocator);
  76   }
  77
  78   file_ptr read (bfd *abfd, void *buffer, file_ptr nbytes,
  79                  file_ptr offset) override;
  80
  81   int stat (struct bfd *abfd, struct stat *sb) override;
  82 };
  83
  84 /* bfd_openr_iovec implementation helper for
  85    find_separate_debug_file_in_section.  */
  86
  87 static gdb_lzma_stream *
  88 lzma_open (struct bfd *nbfd, asection *section)
  89 {
  90   bfd_size_type size, offset;
  91   lzma_stream_flags options;
  92   gdb_byte footer[LZMA_STREAM_HEADER_SIZE];
  93   lzma_index *index;
  94   uint64_t memlimit = UINT64_MAX;
  95   struct gdb_lzma_stream *lstream;
  96   size_t pos;
  97
  98   size = bfd_section_size (section);
  99   offset = section->filepos + size - LZMA_STREAM_HEADER_SIZE;
 100   if (size < LZMA_STREAM_HEADER_SIZE
 101       || bfd_seek (section->owner, offset, SEEK_SET) != 0
 102       || bfd_read (footer, LZMA_STREAM_HEADER_SIZE, section->owner)
 103          != LZMA_STREAM_HEADER_SIZE
 104       || lzma_stream_footer_decode (&options, footer) != LZMA_OK
 105       || offset < options.backward_size)
 106     {
 107       bfd_set_error (bfd_error_wrong_format);
 108       return NULL;
 109     }
 110
 111   offset -= options.backward_size;
 112   gdb::byte_vector indexdata (options.backward_size);
 113   index = NULL;
 114   pos = 0;
 115   if (bfd_seek (section->owner, offset, SEEK_SET) != 0
 116       || bfd_read (indexdata.data (), options.backward_size, section->owner)
 117          != options.backward_size
 118       || lzma_index_buffer_decode (&index, &memlimit, &gdb_lzma_allocator,
 119                                    indexdata.data (), &pos,
 120                                    options.backward_size)
 121          != LZMA_OK
 122       || lzma_index_size (index) != options.backward_size)
 123     {
 124       bfd_set_error (bfd_error_wrong_format);
 125       return NULL;
 126     }
 127
 128   lstream = new struct gdb_lzma_stream;
 129   lstream->section = section;
 130   lstream->index = index;
 131
 132   return lstream;
 133 }
 134
 135 /* bfd_openr_iovec read implementation for
 136    find_separate_debug_file_in_section.  */
 137
 138 file_ptr
 139 gdb_lzma_stream::read (struct bfd *nbfd, void *buf, file_ptr nbytes,
 140                        file_ptr offset)
 141 {
 142   bfd_size_type chunk_size;
 143   lzma_index_iter iter;
 144   file_ptr block_offset;
 145   lzma_filter filters[LZMA_FILTERS_MAX + 1];
 146   lzma_block block;
 147   size_t compressed_pos, uncompressed_pos;
 148   file_ptr res;
 149
 150   res = 0;
 151   while (nbytes > 0)
 152     {
 153       if (data.empty () || data_start > offset || offset >= data_end)
 154         {
 155           lzma_index_iter_init (&iter, index);
 156           if (lzma_index_iter_locate (&iter, offset))
 157             break;
 158
 159           gdb::byte_vector compressed (iter.block.total_size);
 160           block_offset = section->filepos + iter.block.compressed_file_offset;
 161           if (bfd_seek (section->owner, block_offset, SEEK_SET) != 0
 162               || bfd_read (compressed.data (), iter.block.total_size,
 163                            section->owner) != iter.block.total_size)
 164             break;
 165
 166           gdb::byte_vector uncompressed (iter.block.uncompressed_size);
 167
 168           memset (&block, 0, sizeof (block));
 169           block.filters = filters;
 170           block.header_size = lzma_block_header_size_decode (compressed[0]);
 171           if (lzma_block_header_decode (&block, &gdb_lzma_allocator,
 172                                         compressed.data ())
 173               != LZMA_OK)
 174             break;
 175
 176           compressed_pos = block.header_size;
 177           uncompressed_pos = 0;
 178           if (lzma_block_buffer_decode (&block, &gdb_lzma_allocator,
 179                                         compressed.data (), &compressed_pos,
 180                                         iter.block.total_size,
 181                                         uncompressed.data (),
 182                                         &uncompressed_pos,
 183                                         iter.block.uncompressed_size)
 184               != LZMA_OK)
 185             break;
 186
 187           data = std::move (uncompressed);
 188           data_start = iter.block.uncompressed_file_offset;
 189           data_end = (iter.block.uncompressed_file_offset
 190                       + iter.block.uncompressed_size);
 191         }
 192
 193       chunk_size = std::min (nbytes, (file_ptr) data_end - offset);
 194       memcpy (buf, data.data () + offset - data_start, chunk_size);
 195       buf = (gdb_byte *) buf + chunk_size;
 196       offset += chunk_size;
 197       nbytes -= chunk_size;
 198       res += chunk_size;
 199     }
 200
 201   return res;
 202 }
 203
 204 /* bfd_openr_iovec stat implementation for
 205    find_separate_debug_file_in_section.  */
 206
 207 int
 208 gdb_lzma_stream::stat (struct bfd *abfd, struct stat *sb)
 209 {
 210   memset (sb, 0, sizeof (struct stat));
 211   sb->st_size = lzma_index_uncompressed_size (index);
 212   return 0;
 213 }
 214
 215 #endif /* HAVE_LIBLZMA  */
 216
 217 /* This looks for a xz compressed separate debug info object file embedded
 218    in a section called .gnu_debugdata.  See
 219    http://fedoraproject.org/wiki/Features/MiniDebugInfo
 220    or the "Separate Debug Sections" of the manual for details.
 221    If we find one we create a iovec based bfd that decompresses the
 222    object data on demand.  If we don't find one, return NULL.  */
 223
 224 gdb_bfd_ref_ptr
 225 find_separate_debug_file_in_section (struct objfile *objfile)
 226 {
 227   asection *section;
 228   gdb_bfd_ref_ptr abfd;
 229
 230   if (objfile->obfd == NULL)
 231     return NULL;
 232
 233   section = bfd_get_section_by_name (objfile->obfd.get (), ".gnu_debugdata");
 234   if (section == NULL)
 235     return NULL;
 236
 237 #ifdef HAVE_LIBLZMA
 238   gdb_bfd_ref_ptr *shared = gnu_debug_key.get (objfile->obfd.get ());
 239   if (shared != nullptr)
 240     return *shared;
 241
 242   std::string filename = string_printf (_(".gnu_debugdata for %s"),
 243                                         objfile_name (objfile));
 244
 245   auto open = [&] (bfd *nbfd) -> gdb_lzma_stream *
 246   {
 247     return lzma_open (nbfd, section);
 248   };
 249
 250   abfd = gdb_bfd_openr_iovec (filename.c_str (), gnutarget, open);
 251   if (abfd == NULL)
 252     return NULL;
 253
 254   if (!bfd_check_format (abfd.get (), bfd_object))
 255     {
 256       warning (_("Cannot parse .gnu_debugdata section; not a BFD object"));
 257       return NULL;
 258     }
 259
 260   gnu_debug_key.emplace (objfile->obfd.get (), abfd);
 261
 262 #else
 263   warning (_("Cannot parse .gnu_debugdata section; LZMA support was "
 264              "disabled at compile time"));
 265 #endif /* !HAVE_LIBLZMA */
 266
 267   return abfd;
 268 }