gold/testsuite/plugin_new_section_layout.c

   1 /* plugin_new_section_layout.c -- Simple plugin to reorder function sections in
   2    plugin-generated objects
   3
   4    Copyright (C) 2017-2025 Free Software Foundation, Inc.
   5    Written by Stephen Crane <sjc@immunant.com>.
   6
   7    This file is part of gold.
   8
   9    This program is free software; you can redistribute it and/or modify
  10    it under the terms of the GNU General Public License as published by
  11    the Free Software Foundation; either version 3 of the License, or
  12    (at your option) any later version.
  13
  14    This program is distributed in the hope that it will be useful,
  15    but WITHOUT ANY WARRANTY; without even the implied warranty of
  16    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  17    GNU General Public License for more details.
  18
  19    You should have received a copy of the GNU General Public License
  20    along with this program; if not, write to the Free Software
  21    Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
  22    MA 02110-1301, USA.  */
  23
  24 /* This plugin tests the new_input API of the linker plugin interface that
  25  * allows plugins to modify section layout and assign sections to segments for
  26  * sections in plugin-generated object files. It assumes that another plugin is
  27  * also in use which will add new files. In practice a plugin is likely to
  28  * generate new input files itself in all_symbols_read and want to
  29  * reorder/assign sections for these files in the new_input_hook callback. */
  30
  31 #ifdef HAVE_CONFIG_H
  32 #include "config.h"
  33 #endif
  34
  35 #include <stdio.h>
  36 #include <stdlib.h>
  37 #include <string.h>
  38 #include <assert.h>
  39 #include "plugin-api.h"
  40 #include "elf/common.h"
  41
  42 static ld_plugin_get_input_section_count get_input_section_count = NULL;
  43 static ld_plugin_get_input_section_type get_input_section_type = NULL;
  44 static ld_plugin_get_input_section_name get_input_section_name = NULL;
  45 static ld_plugin_update_section_order update_section_order = NULL;
  46 static ld_plugin_allow_section_ordering allow_section_ordering = NULL;
  47 static ld_plugin_allow_unique_segment_for_sections
  48     allow_unique_segment_for_sections = NULL;
  49 static ld_plugin_unique_segment_for_sections unique_segment_for_sections = NULL;
  50
  51 enum ld_plugin_status onload(struct ld_plugin_tv *tv);
  52 enum ld_plugin_status new_input_hook(const struct ld_plugin_input_file *file);
  53
  54 /* Plugin entry point.  */
  55 enum ld_plugin_status
  56 onload(struct ld_plugin_tv *tv)
  57 {
  58   struct ld_plugin_tv *entry;
  59   for (entry = tv; entry->tv_tag != LDPT_NULL; ++entry)
  60     {
  61       switch (entry->tv_tag)
  62         {
  63         case LDPT_GET_INPUT_SECTION_COUNT:
  64           get_input_section_count = *entry->tv_u.tv_get_input_section_count;
  65           break;
  66         case LDPT_GET_INPUT_SECTION_TYPE:
  67           get_input_section_type = *entry->tv_u.tv_get_input_section_type;
  68           break;
  69         case LDPT_GET_INPUT_SECTION_NAME:
  70           get_input_section_name = *entry->tv_u.tv_get_input_section_name;
  71           break;
  72         case LDPT_UPDATE_SECTION_ORDER:
  73           update_section_order = *entry->tv_u.tv_update_section_order;
  74           break;
  75         case LDPT_ALLOW_SECTION_ORDERING:
  76           allow_section_ordering = *entry->tv_u.tv_allow_section_ordering;
  77           break;
  78         case LDPT_ALLOW_UNIQUE_SEGMENT_FOR_SECTIONS:
  79           allow_unique_segment_for_sections
  80               = *entry->tv_u.tv_allow_unique_segment_for_sections;
  81           break;
  82         case LDPT_UNIQUE_SEGMENT_FOR_SECTIONS:
  83           unique_segment_for_sections
  84               = *entry->tv_u.tv_unique_segment_for_sections;
  85           break;
  86         case LDPT_REGISTER_NEW_INPUT_HOOK:
  87           assert((*entry->tv_u.tv_register_new_input) (new_input_hook)
  88                  == LDPS_OK);
  89           break;
  90         default:
  91           break;
  92         }
  93     }
  94
  95   if (get_input_section_count == NULL
  96       || get_input_section_type == NULL
  97       || get_input_section_name == NULL
  98       || update_section_order == NULL
  99       || allow_section_ordering == NULL
 100       || allow_unique_segment_for_sections == NULL
 101       || unique_segment_for_sections == NULL)
 102     {
 103       fprintf(stderr, "Some interfaces are missing\n");
 104       return LDPS_ERR;
 105     }
 106
 107   /* Inform the linker to prepare for section reordering.  */
 108   (*allow_section_ordering)();
 109   /* Inform the linker to prepare to map some sections to unique
 110      segments.  */
 111   (*allow_unique_segment_for_sections)();
 112
 113   return LDPS_OK;
 114 }
 115
 116 inline static int is_prefix_of(const char *prefix, const char *str)
 117 {
 118   return strncmp(prefix, str, strlen (prefix)) == 0;
 119 }
 120
 121 /* This function is called by the linker when new files are added by a plugin.
 122    We can now tell the linker the desired function order since we have a file
 123    handle for the newly added file.  */
 124
 125 enum ld_plugin_status
 126 new_input_hook(const struct ld_plugin_input_file *file)
 127 {
 128   struct ld_plugin_section section_list[3];
 129   int num_entries = 0;
 130   unsigned int count;
 131
 132   if (get_input_section_count(file->handle, &count) != LDPS_OK)
 133     return LDPS_ERR;
 134
 135   unsigned int i;
 136   for (i = 0; i < count; ++i)
 137   {
 138     struct ld_plugin_section section;
 139     unsigned int type = 0;
 140     char *name = NULL;
 141     int position = 3;
 142
 143     section.handle = file->handle;
 144     section.shndx = i;
 145
 146     if (get_input_section_type(section, &type) != LDPS_OK)
 147       return LDPS_ERR;
 148     if (type != SHT_PROGBITS)
 149       continue;
 150
 151     if (get_input_section_name(section, &name))
 152       return LDPS_ERR;
 153
 154     /* As in plugin_section_order.c, order is foo() followed by bar()
 155        followed by baz() */
 156     if (is_prefix_of(".text.", name))
 157     {
 158       if (strstr(name, "_Z3foov") != NULL)
 159         position = 0;
 160       else if (strstr(name, "_Z3barv") != NULL)
 161         position = 1;
 162       else if (strstr(name, "_Z3bazv") != NULL)
 163         position = 2;
 164       else
 165         position = 3;
 166     }
 167     if (position < 3)
 168     {
 169       section_list[position] = section;
 170       num_entries++;
 171     }
 172   }
 173
 174   if (num_entries != 3)
 175     return LDPS_ERR;
 176
 177   update_section_order(section_list, num_entries);
 178   unique_segment_for_sections (".text.plugin_created_unique", 0, 0x1000,
 179                                section_list, num_entries);
 180
 181   return LDPS_OK;
 182 }