1 /* VxWorks support for ELF
2    Copyright (C) 2005-2016 Free Software Foundation, Inc.
3 
4    This file is part of BFD, the Binary File Descriptor library.
5 
6    This program is free software; you can redistribute it and/or modify
7    it under the terms of the GNU General Public License as published by
8    the Free Software Foundation; either version 3 of the License, or
9    (at your option) any later version.
10 
11    This program is distributed in the hope that it will be useful,
12    but WITHOUT ANY WARRANTY; without even the implied warranty of
13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
14    GNU General Public License for more details.
15 
16    You should have received a copy of the GNU General Public License
17    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
18 
19 /* This file provides routines used by all VxWorks targets.  */
20 
21 #include "sysdep.h"
22 #include "bfd.h"
23 #include "libbfd.h"
24 #include "elf-bfd.h"
25 #include "elf-vxworks.h"
26 #include "elf/vxworks.h"
27 
28 /* Return true if symbol NAME, as defined by ABFD, is one of the special
29    __GOTT_BASE__ or __GOTT_INDEX__ symbols.  */
30 
31 static bfd_boolean
elf_vxworks_gott_symbol_p(bfd * abfd,const char * name)32 elf_vxworks_gott_symbol_p (bfd *abfd, const char *name)
33 {
34   char leading;
35 
36   leading = bfd_get_symbol_leading_char (abfd);
37   if (leading)
38     {
39       if (*name != leading)
40 	return FALSE;
41       name++;
42     }
43   return (strcmp (name, "__GOTT_BASE__") == 0
44 	  || strcmp (name, "__GOTT_INDEX__") == 0);
45 }
46 
47 /* Tweak magic VxWorks symbols as they are loaded.  */
48 bfd_boolean
elf_vxworks_add_symbol_hook(bfd * abfd,struct bfd_link_info * info,Elf_Internal_Sym * sym,const char ** namep,flagword * flagsp,asection ** secp ATTRIBUTE_UNUSED,bfd_vma * valp ATTRIBUTE_UNUSED)49 elf_vxworks_add_symbol_hook (bfd *abfd,
50 			     struct bfd_link_info *info,
51 			     Elf_Internal_Sym *sym,
52 			     const char **namep,
53 			     flagword *flagsp,
54 			     asection **secp ATTRIBUTE_UNUSED,
55 			     bfd_vma *valp ATTRIBUTE_UNUSED)
56 {
57   /* Ideally these "magic" symbols would be exported by libc.so.1
58      which would be found via a DT_NEEDED tag, and then handled
59      specially by the linker at runtime.  Except shared libraries
60      don't even link to libc.so.1 by default...
61      If the symbol is imported from, or will be put in a shared library,
62      give the symbol weak binding to get the desired samantics.
63      This transformation will be undone in
64      elf_i386_vxworks_link_output_symbol_hook. */
65   if ((bfd_link_pic (info) || abfd->flags & DYNAMIC)
66       && elf_vxworks_gott_symbol_p (abfd, *namep))
67     {
68       sym->st_info = ELF_ST_INFO (STB_WEAK, ELF_ST_TYPE (sym->st_info));
69       *flagsp |= BSF_WEAK;
70     }
71 
72   return TRUE;
73 }
74 
75 /* Perform VxWorks-specific handling of the create_dynamic_sections hook.
76    When creating an executable, set *SRELPLT2_OUT to the .rel(a).plt.unloaded
77    section.  */
78 
79 bfd_boolean
elf_vxworks_create_dynamic_sections(bfd * dynobj,struct bfd_link_info * info,asection ** srelplt2_out)80 elf_vxworks_create_dynamic_sections (bfd *dynobj, struct bfd_link_info *info,
81 				     asection **srelplt2_out)
82 {
83   struct elf_link_hash_table *htab;
84   const struct elf_backend_data *bed;
85   asection *s;
86 
87   htab = elf_hash_table (info);
88   bed = get_elf_backend_data (dynobj);
89 
90   if (!bfd_link_pic (info))
91     {
92       s = bfd_make_section_anyway_with_flags (dynobj,
93 					      bed->default_use_rela_p
94 					      ? ".rela.plt.unloaded"
95 					      : ".rel.plt.unloaded",
96 					      SEC_HAS_CONTENTS | SEC_IN_MEMORY
97 					      | SEC_READONLY
98 					      | SEC_LINKER_CREATED);
99       if (s == NULL
100 	  || !bfd_set_section_alignment (dynobj, s, bed->s->log_file_align))
101 	return FALSE;
102 
103       *srelplt2_out = s;
104     }
105 
106   /* Mark the GOT and PLT symbols as having relocations; they might
107      not, but we won't know for sure until we build the GOT in
108      finish_dynamic_symbol.  Also make sure that the GOT symbol
109      is entered into the dynamic symbol table; the loader uses it
110      to initialize __GOTT_BASE__[__GOTT_INDEX__].  */
111   if (htab->hgot)
112     {
113       htab->hgot->indx = -2;
114       htab->hgot->other &= ~ELF_ST_VISIBILITY (-1);
115       htab->hgot->forced_local = 0;
116       if (!bfd_elf_link_record_dynamic_symbol (info, htab->hgot))
117 	return FALSE;
118     }
119   if (htab->hplt)
120     {
121       htab->hplt->indx = -2;
122       htab->hplt->type = STT_FUNC;
123     }
124 
125   return TRUE;
126 }
127 
128 /* Tweak magic VxWorks symbols as they are written to the output file.  */
129 int
elf_vxworks_link_output_symbol_hook(struct bfd_link_info * info ATTRIBUTE_UNUSED,const char * name,Elf_Internal_Sym * sym,asection * input_sec ATTRIBUTE_UNUSED,struct elf_link_hash_entry * h)130 elf_vxworks_link_output_symbol_hook (struct bfd_link_info *info
131 				       ATTRIBUTE_UNUSED,
132 				     const char *name,
133 				     Elf_Internal_Sym *sym,
134 				     asection *input_sec ATTRIBUTE_UNUSED,
135 				     struct elf_link_hash_entry *h)
136 {
137   /* Reverse the effects of the hack in elf_vxworks_add_symbol_hook.  */
138   if (h
139       && h->root.type == bfd_link_hash_undefweak
140       && elf_vxworks_gott_symbol_p (h->root.u.undef.abfd, name))
141     sym->st_info = ELF_ST_INFO (STB_GLOBAL, ELF_ST_TYPE (sym->st_info));
142 
143   return 1;
144 }
145 
146 /* Copy relocations into the output file.  Fixes up relocations against PLT
147    entries, then calls the generic routine.  */
148 
149 bfd_boolean
elf_vxworks_emit_relocs(bfd * output_bfd,asection * input_section,Elf_Internal_Shdr * input_rel_hdr,Elf_Internal_Rela * internal_relocs,struct elf_link_hash_entry ** rel_hash)150 elf_vxworks_emit_relocs (bfd *output_bfd,
151 			 asection *input_section,
152 			 Elf_Internal_Shdr *input_rel_hdr,
153 			 Elf_Internal_Rela *internal_relocs,
154 			 struct elf_link_hash_entry **rel_hash)
155 {
156   const struct elf_backend_data *bed;
157   int j;
158 
159   bed = get_elf_backend_data (output_bfd);
160 
161   if (output_bfd->flags & (DYNAMIC|EXEC_P))
162     {
163       Elf_Internal_Rela *irela;
164       Elf_Internal_Rela *irelaend;
165       struct elf_link_hash_entry **hash_ptr;
166 
167       for (irela = internal_relocs,
168 	     irelaend = irela + (NUM_SHDR_ENTRIES (input_rel_hdr)
169 				 * bed->s->int_rels_per_ext_rel),
170 	     hash_ptr = rel_hash;
171 	   irela < irelaend;
172 	   irela += bed->s->int_rels_per_ext_rel,
173 	     hash_ptr++)
174 	{
175 	  if (*hash_ptr
176 	      && (*hash_ptr)->def_dynamic
177 	      && !(*hash_ptr)->def_regular
178 	      && ((*hash_ptr)->root.type == bfd_link_hash_defined
179 		  || (*hash_ptr)->root.type == bfd_link_hash_defweak)
180 	      && (*hash_ptr)->root.u.def.section->output_section != NULL)
181 	    {
182 	      /* This is a relocation from an executable or shared
183 	         library against a symbol in a different shared
184 	         library.  We are creating a definition in the output
185 	         file but it does not come from any of our normal (.o)
186 	         files. ie. a PLT stub.  Normally this would be a
187 	         relocation against against SHN_UNDEF with the VMA of
188 	         the PLT stub.  This upsets the VxWorks loader.
189 	         Convert it to a section-relative relocation.  This
190 	         gets some other symbols (for instance .dynbss), but
191 	         is conservatively correct.  */
192 	      for (j = 0; j < bed->s->int_rels_per_ext_rel; j++)
193 		{
194 		  asection *sec = (*hash_ptr)->root.u.def.section;
195 		  int this_idx = sec->output_section->target_index;
196 
197 		  irela[j].r_info
198 		    = ELF32_R_INFO (this_idx, ELF32_R_TYPE (irela[j].r_info));
199 		  irela[j].r_addend += (*hash_ptr)->root.u.def.value;
200 		  irela[j].r_addend += sec->output_offset;
201 		}
202 	      /* Stop the generic routine adjusting this entry.  */
203 	      *hash_ptr = NULL;
204 	    }
205 	}
206     }
207   return _bfd_elf_link_output_relocs (output_bfd, input_section,
208 				      input_rel_hdr, internal_relocs,
209 				      rel_hash);
210 }
211 
212 
213 /* Set the sh_link and sh_info fields on the static plt relocation secton.  */
214 
215 void
elf_vxworks_final_write_processing(bfd * abfd,bfd_boolean linker ATTRIBUTE_UNUSED)216 elf_vxworks_final_write_processing (bfd *abfd,
217 				    bfd_boolean linker ATTRIBUTE_UNUSED)
218 {
219   asection * sec;
220   struct bfd_elf_section_data *d;
221 
222   sec = bfd_get_section_by_name (abfd, ".rel.plt.unloaded");
223   if (!sec)
224     sec = bfd_get_section_by_name (abfd, ".rela.plt.unloaded");
225   if (!sec)
226     return;
227   d = elf_section_data (sec);
228   d->this_hdr.sh_link = elf_onesymtab (abfd);
229   sec = bfd_get_section_by_name (abfd, ".plt");
230   if (sec)
231     d->this_hdr.sh_info = elf_section_data (sec)->this_idx;
232 }
233 
234 /* Add the dynamic entries required by VxWorks.  These point to the
235    tls sections.  */
236 
237 bfd_boolean
elf_vxworks_add_dynamic_entries(bfd * output_bfd,struct bfd_link_info * info)238 elf_vxworks_add_dynamic_entries (bfd *output_bfd, struct bfd_link_info *info)
239 {
240   if (bfd_get_section_by_name (output_bfd, ".tls_data"))
241     {
242       if (!_bfd_elf_add_dynamic_entry (info, DT_VX_WRS_TLS_DATA_START, 0)
243 	  || !_bfd_elf_add_dynamic_entry (info, DT_VX_WRS_TLS_DATA_SIZE, 0)
244 	  || !_bfd_elf_add_dynamic_entry (info, DT_VX_WRS_TLS_DATA_ALIGN, 0))
245 	return FALSE;
246     }
247   if (bfd_get_section_by_name (output_bfd, ".tls_vars"))
248     {
249       if (!_bfd_elf_add_dynamic_entry (info, DT_VX_WRS_TLS_VARS_START, 0)
250 	  || !_bfd_elf_add_dynamic_entry (info, DT_VX_WRS_TLS_VARS_SIZE, 0))
251 	return FALSE;
252     }
253   return TRUE;
254 }
255 
256 /* If *DYN is one of the VxWorks-specific dynamic entries, then fill
257    in the value now  and return TRUE.  Otherwise return FALSE.  */
258 
259 bfd_boolean
elf_vxworks_finish_dynamic_entry(bfd * output_bfd,Elf_Internal_Dyn * dyn)260 elf_vxworks_finish_dynamic_entry (bfd *output_bfd, Elf_Internal_Dyn *dyn)
261 {
262   asection *sec;
263 
264   switch (dyn->d_tag)
265     {
266     default:
267       return FALSE;
268 
269     case DT_VX_WRS_TLS_DATA_START:
270       sec = bfd_get_section_by_name (output_bfd, ".tls_data");
271       dyn->d_un.d_ptr = sec->vma;
272       break;
273 
274     case DT_VX_WRS_TLS_DATA_SIZE:
275       sec = bfd_get_section_by_name (output_bfd, ".tls_data");
276       dyn->d_un.d_val = sec->size;
277       break;
278 
279     case DT_VX_WRS_TLS_DATA_ALIGN:
280       sec = bfd_get_section_by_name (output_bfd, ".tls_data");
281       dyn->d_un.d_val
282 	= (bfd_size_type)1 << bfd_get_section_alignment (output_bfd,
283 							 sec);
284       break;
285 
286     case DT_VX_WRS_TLS_VARS_START:
287       sec = bfd_get_section_by_name (output_bfd, ".tls_vars");
288       dyn->d_un.d_ptr = sec->vma;
289       break;
290 
291     case DT_VX_WRS_TLS_VARS_SIZE:
292       sec = bfd_get_section_by_name (output_bfd, ".tls_vars");
293       dyn->d_un.d_val = sec->size;
294       break;
295     }
296   return TRUE;
297 }
298 
299 
300