1/* plugin_section_reorder.c -- Simple plugin to reorder function sections
2
3   Copyright (C) 2011-2017 Free Software Foundation, Inc.
4   Written by Sriraman Tallam <tmsriram@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#ifdef HAVE_CONFIG_H
24#include "config.h"
25#endif
26
27#include <stdio.h>
28#include <stdlib.h>
29#include <string.h>
30#include <assert.h>
31#include "plugin-api.h"
32
33static ld_plugin_get_input_section_count get_input_section_count = NULL;
34static ld_plugin_get_input_section_type get_input_section_type = NULL;
35static ld_plugin_get_input_section_name get_input_section_name = NULL;
36static ld_plugin_get_input_section_contents get_input_section_contents = NULL;
37static ld_plugin_update_section_order update_section_order = NULL;
38static ld_plugin_allow_section_ordering allow_section_ordering = NULL;
39static ld_plugin_allow_unique_segment_for_sections
40    allow_unique_segment_for_sections = NULL;
41static ld_plugin_unique_segment_for_sections unique_segment_for_sections = NULL;
42
43enum ld_plugin_status onload(struct ld_plugin_tv *tv);
44enum ld_plugin_status claim_file_hook(const struct ld_plugin_input_file *file,
45                                      int *claimed);
46enum ld_plugin_status all_symbols_read_hook(void);
47
48/* Plugin entry point.  */
49enum ld_plugin_status
50onload(struct ld_plugin_tv *tv)
51{
52  struct ld_plugin_tv *entry;
53  for (entry = tv; entry->tv_tag != LDPT_NULL; ++entry)
54    {
55      switch (entry->tv_tag)
56        {
57        case LDPT_REGISTER_CLAIM_FILE_HOOK:
58          assert((*entry->tv_u.tv_register_claim_file) (claim_file_hook)
59		 == LDPS_OK);
60          break;
61	case LDPT_REGISTER_ALL_SYMBOLS_READ_HOOK:
62          assert((*entry->tv_u.tv_register_all_symbols_read)
63		     (all_symbols_read_hook)
64		 == LDPS_OK);
65          break;
66        case LDPT_GET_INPUT_SECTION_COUNT:
67          get_input_section_count = *entry->tv_u.tv_get_input_section_count;
68          break;
69        case LDPT_GET_INPUT_SECTION_TYPE:
70          get_input_section_type = *entry->tv_u.tv_get_input_section_type;
71          break;
72        case LDPT_GET_INPUT_SECTION_NAME:
73          get_input_section_name = *entry->tv_u.tv_get_input_section_name;
74          break;
75        case LDPT_GET_INPUT_SECTION_CONTENTS:
76          get_input_section_contents
77	      = *entry->tv_u.tv_get_input_section_contents;
78          break;
79	case LDPT_UPDATE_SECTION_ORDER:
80	  update_section_order = *entry->tv_u.tv_update_section_order;
81	  break;
82	case LDPT_ALLOW_SECTION_ORDERING:
83	  allow_section_ordering = *entry->tv_u.tv_allow_section_ordering;
84	  break;
85	case LDPT_ALLOW_UNIQUE_SEGMENT_FOR_SECTIONS:
86	  allow_unique_segment_for_sections
87	      = *entry->tv_u.tv_allow_unique_segment_for_sections;
88	case LDPT_UNIQUE_SEGMENT_FOR_SECTIONS:
89	  unique_segment_for_sections
90	      = *entry->tv_u.tv_unique_segment_for_sections;
91	  break;
92        default:
93          break;
94        }
95    }
96
97  if (get_input_section_count == NULL
98      || get_input_section_type == NULL
99      || get_input_section_name == NULL
100      || get_input_section_contents == NULL
101      || update_section_order == NULL
102      || allow_section_ordering == NULL
103      || allow_unique_segment_for_sections == NULL
104      || unique_segment_for_sections == NULL)
105    {
106      fprintf(stderr, "Some interfaces are missing\n");
107      return LDPS_ERR;
108    }
109
110  return LDPS_OK;
111}
112
113inline static int is_prefix_of(const char *prefix, const char *str)
114{
115  return strncmp(prefix, str, strlen (prefix)) == 0;
116}
117
118struct ld_plugin_section section_list[3];
119int num_entries = 0;
120
121/* This function is called by the linker for every new object it encounters.  */
122enum ld_plugin_status
123claim_file_hook(const struct ld_plugin_input_file *file, int *claimed)
124{
125  static int is_ordering_specified = 0;
126  struct ld_plugin_section section;
127  unsigned int count = 0;
128  unsigned int shndx;
129
130  *claimed = 0;
131  if (is_ordering_specified == 0)
132    {
133      /* Inform the linker to prepare for section reordering.  */
134      (*allow_section_ordering)();
135      /* Inform the linker to prepare to map some sections to unique
136	 segments.  */
137      (*allow_unique_segment_for_sections)();
138      is_ordering_specified = 1;
139    }
140
141  (*get_input_section_count)(file->handle, &count);
142
143  for (shndx = 0; shndx < count; ++shndx)
144    {
145      char *name = NULL;
146      int position = 3;
147
148      section.handle = file->handle;
149      section.shndx = shndx;
150      (*get_input_section_name)(section, &name);
151
152      /* Order is foo() followed by bar() followed by baz()  */
153      if (is_prefix_of(".text.", name))
154	{
155	  if (strstr(name, "_Z3foov") != NULL)
156	    position = 0;
157	  else if (strstr(name, "_Z3barv") != NULL)
158	    position = 1;
159	  else if (strstr(name, "_Z3bazv") != NULL)
160	    position = 2;
161	  else
162	    position = 3;
163	}
164      if (position < 3)
165	{
166	  section_list[position].handle = file->handle;
167	  section_list[position].shndx = shndx;
168	  num_entries++;
169	}
170    }
171  return LDPS_OK;
172}
173
174/* This function is called by the linker after all the symbols have been read.
175   At this stage, it is fine to tell the linker the desired function order.  */
176
177enum ld_plugin_status
178all_symbols_read_hook(void)
179{
180  if (num_entries == 3)
181    {
182      update_section_order(section_list, num_entries);
183      unique_segment_for_sections (".text.plugin_created_unique", 0, 0x1000,
184				   section_list, num_entries);
185    }
186
187  return LDPS_OK;
188}
189