1// common.cc -- handle common symbols for gold
2
3// Copyright (C) 2006-2017 Free Software Foundation, Inc.
4// Written by Ian Lance Taylor <iant@google.com>.
5
6// This file is part of gold.
7
8// This program is free software; you can redistribute it and/or modify
9// it under the terms of the GNU General Public License as published by
10// the Free Software Foundation; either version 3 of the License, or
11// (at your option) any later version.
12
13// This program is distributed in the hope that it will be useful,
14// but WITHOUT ANY WARRANTY; without even the implied warranty of
15// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
16// GNU General Public License for more details.
17
18// You should have received a copy of the GNU General Public License
19// along with this program; if not, write to the Free Software
20// Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
21// MA 02110-1301, USA.
22
23#include "gold.h"
24
25#include <algorithm>
26
27#include "workqueue.h"
28#include "mapfile.h"
29#include "layout.h"
30#include "output.h"
31#include "symtab.h"
32#include "common.h"
33
34namespace gold
35{
36
37// Allocate_commons_task methods.
38
39// This task allocates the common symbols.  We arrange to run it
40// before anything else which needs to access the symbol table.
41
42Task_token*
43Allocate_commons_task::is_runnable()
44{
45  return NULL;
46}
47
48// Release a blocker.
49
50void
51Allocate_commons_task::locks(Task_locker* tl)
52{
53  tl->add(this, this->blocker_);
54}
55
56// Allocate the common symbols.
57
58void
59Allocate_commons_task::run(Workqueue*)
60{
61  this->symtab_->allocate_commons(this->layout_, this->mapfile_);
62}
63
64// This class is used to sort the common symbol.  We normally put the
65// larger common symbols first.  This can be changed by using
66// --sort-commons, which tells the linker to sort by alignment.
67
68template<int size>
69class Sort_commons
70{
71 public:
72  Sort_commons(const Symbol_table* symtab,
73	       Symbol_table::Sort_commons_order sort_order)
74    : symtab_(symtab), sort_order_(sort_order)
75  { }
76
77  bool operator()(const Symbol* a, const Symbol* b) const;
78
79 private:
80  // The symbol table.
81  const Symbol_table* symtab_;
82  // How to sort.
83  Symbol_table::Sort_commons_order sort_order_;
84};
85
86template<int size>
87bool
88Sort_commons<size>::operator()(const Symbol* pa, const Symbol* pb) const
89{
90  if (pa == NULL)
91    return false;
92  if (pb == NULL)
93    return true;
94
95  const Symbol_table* symtab = this->symtab_;
96  const Sized_symbol<size>* psa = symtab->get_sized_symbol<size>(pa);
97  const Sized_symbol<size>* psb = symtab->get_sized_symbol<size>(pb);
98
99  // The size.
100  typename Sized_symbol<size>::Size_type sa = psa->symsize();
101  typename Sized_symbol<size>::Size_type sb = psb->symsize();
102
103  // The alignment.
104  typename Sized_symbol<size>::Value_type aa = psa->value();
105  typename Sized_symbol<size>::Value_type ab = psb->value();
106
107  if (this->sort_order_ == Symbol_table::SORT_COMMONS_BY_ALIGNMENT_DESCENDING)
108    {
109      if (aa < ab)
110	return false;
111      else if (ab < aa)
112	return true;
113    }
114  else if (this->sort_order_
115	   == Symbol_table::SORT_COMMONS_BY_ALIGNMENT_ASCENDING)
116    {
117      if (aa < ab)
118	return true;
119      else if (ab < aa)
120	return false;
121    }
122  else
123    gold_assert(this->sort_order_
124		== Symbol_table::SORT_COMMONS_BY_SIZE_DESCENDING);
125
126  // Sort by descending size.
127  if (sa < sb)
128    return false;
129  else if (sb < sa)
130    return true;
131
132  if (this->sort_order_ == Symbol_table::SORT_COMMONS_BY_SIZE_DESCENDING)
133    {
134      // When the symbols are the same size, we sort them by
135      // alignment, largest alignment first.
136      if (aa < ab)
137	return false;
138      else if (ab < aa)
139	return true;
140    }
141
142  // Otherwise we stabilize the sort by sorting by name.
143  return strcmp(psa->name(), psb->name()) < 0;
144}
145
146// Allocate the common symbols.
147
148void
149Symbol_table::allocate_commons(Layout* layout, Mapfile* mapfile)
150{
151  Sort_commons_order sort_order;
152  if (!parameters->options().user_set_sort_common())
153    sort_order = SORT_COMMONS_BY_SIZE_DESCENDING;
154  else
155    {
156      const char* order = parameters->options().sort_common();
157      if (*order == '\0' || strcmp(order, "descending") == 0)
158	sort_order = SORT_COMMONS_BY_ALIGNMENT_DESCENDING;
159      else if (strcmp(order, "ascending") == 0)
160	sort_order = SORT_COMMONS_BY_ALIGNMENT_ASCENDING;
161      else
162	{
163	  gold_error("invalid --sort-common argument: %s", order);
164	  sort_order = SORT_COMMONS_BY_SIZE_DESCENDING;
165	}
166    }
167
168  if (parameters->target().get_size() == 32)
169    {
170#if defined(HAVE_TARGET_32_LITTLE) || defined(HAVE_TARGET_32_BIG)
171      this->do_allocate_commons<32>(layout, mapfile, sort_order);
172#else
173      gold_unreachable();
174#endif
175    }
176  else if (parameters->target().get_size() == 64)
177    {
178#if defined(HAVE_TARGET_64_LITTLE) || defined(HAVE_TARGET_64_BIG)
179      this->do_allocate_commons<64>(layout, mapfile, sort_order);
180#else
181      gold_unreachable();
182#endif
183    }
184  else
185    gold_unreachable();
186}
187
188// Allocated the common symbols, sized version.
189
190template<int size>
191void
192Symbol_table::do_allocate_commons(Layout* layout, Mapfile* mapfile,
193				  Sort_commons_order sort_order)
194{
195  if (!this->commons_.empty())
196    this->do_allocate_commons_list<size>(layout, COMMONS_NORMAL,
197					 &this->commons_, mapfile,
198					 sort_order);
199  if (!this->tls_commons_.empty())
200    this->do_allocate_commons_list<size>(layout, COMMONS_TLS,
201					 &this->tls_commons_, mapfile,
202					 sort_order);
203  if (!this->small_commons_.empty())
204    this->do_allocate_commons_list<size>(layout, COMMONS_SMALL,
205					 &this->small_commons_, mapfile,
206					 sort_order);
207  if (!this->large_commons_.empty())
208    this->do_allocate_commons_list<size>(layout, COMMONS_LARGE,
209					 &this->large_commons_, mapfile,
210					 sort_order);
211}
212
213// Allocate the common symbols in a list.  IS_TLS indicates whether
214// these are TLS common symbols.
215
216template<int size>
217void
218Symbol_table::do_allocate_commons_list(
219    Layout* layout,
220    Commons_section_type commons_section_type,
221    Commons_type* commons,
222    Mapfile* mapfile,
223    Sort_commons_order sort_order)
224{
225  // We've kept a list of all the common symbols.  But the symbol may
226  // have been resolved to a defined symbol by now.  And it may be a
227  // forwarder.  First remove all non-common symbols.
228  bool any = false;
229  uint64_t addralign = 0;
230  for (Commons_type::iterator p = commons->begin();
231       p != commons->end();
232       ++p)
233    {
234      Symbol* sym = *p;
235      if (sym->is_forwarder())
236	{
237	  sym = this->resolve_forwards(sym);
238	  *p = sym;
239	}
240      if (!sym->is_common())
241	*p = NULL;
242      else
243	{
244	  any = true;
245	  Sized_symbol<size>* ssym = this->get_sized_symbol<size>(sym);
246	  if (ssym->value() > addralign)
247	    addralign = ssym->value();
248	}
249    }
250  if (!any)
251    return;
252
253  // Sort the common symbols.
254  std::sort(commons->begin(), commons->end(),
255	    Sort_commons<size>(this, sort_order));
256
257  // Place them in a newly allocated BSS section.
258  elfcpp::Elf_Xword flags = elfcpp::SHF_WRITE | elfcpp::SHF_ALLOC;
259  const char* name;
260  const char* ds_name;
261  switch (commons_section_type)
262    {
263    case COMMONS_NORMAL:
264      name = ".bss";
265      ds_name = "** common";
266      break;
267    case COMMONS_TLS:
268      flags |= elfcpp::SHF_TLS;
269      name = ".tbss";
270      ds_name = "** tls common";
271      break;
272    case COMMONS_SMALL:
273      flags |= parameters->target().small_common_section_flags();
274      name = ".sbss";
275      ds_name = "** small common";
276      break;
277    case COMMONS_LARGE:
278      flags |= parameters->target().large_common_section_flags();
279      name = ".lbss";
280      ds_name = "** large common";
281      break;
282    default:
283      gold_unreachable();
284    }
285
286  Output_data_space* poc;
287  Output_section* os;
288
289  if (!parameters->incremental_update())
290    {
291      poc = new Output_data_space(addralign, ds_name);
292      os = layout->add_output_section_data(name, elfcpp::SHT_NOBITS, flags,
293					   poc, ORDER_INVALID, false);
294    }
295  else
296    {
297      // When doing an incremental update, we need to allocate each common
298      // directly from the output section's free list.
299      poc = NULL;
300      os = layout->find_output_section(name);
301    }
302
303  if (os != NULL)
304    {
305      if (commons_section_type == COMMONS_SMALL)
306	os->set_is_small_section();
307      else if (commons_section_type == COMMONS_LARGE)
308	os->set_is_large_section();
309    }
310
311  // Allocate them all.
312
313  off_t off = 0;
314  for (Commons_type::iterator p = commons->begin();
315       p != commons->end();
316       ++p)
317    {
318      Symbol* sym = *p;
319      if (sym == NULL)
320	break;
321
322      // Because we followed forwarding symbols above, but we didn't
323      // do it reliably before adding symbols to the list, it is
324      // possible for us to have the same symbol on the list twice.
325      // This can happen in the horrible case where a program defines
326      // a common symbol with the same name as a versioned libc
327      // symbol.  That will show up here as a symbol which has already
328      // been allocated and is therefore no longer a common symbol.
329      if (!sym->is_common())
330	continue;
331
332      Sized_symbol<size>* ssym = this->get_sized_symbol<size>(sym);
333
334      // Record the symbol in the map file now, before we change its
335      // value.  Pass the size in separately so that we don't have to
336      // templatize the map code, which is not performance sensitive.
337      if (mapfile != NULL)
338	mapfile->report_allocate_common(sym, ssym->symsize());
339
340      if (poc != NULL)
341	{
342	  off = align_address(off, ssym->value());
343	  ssym->allocate_common(poc, off);
344	  off += ssym->symsize();
345	}
346      else
347	{
348	  // For an incremental update, allocate from the free list.
349	  off = os->allocate(ssym->symsize(), ssym->value());
350	  if (off == -1)
351	    gold_fallback(_("out of patch space in section %s; "
352			    "relink with --incremental-full"),
353			  os->name());
354	  ssym->allocate_common(os, off);
355	}
356    }
357
358  if (poc != NULL)
359    poc->set_current_data_size(off);
360
361  commons->clear();
362}
363
364} // End namespace gold.
365