1 /* plugin_section_reorder.c -- Simple plugin to reorder function sections
2
3 Copyright (C) 2011-2020 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
33 static ld_plugin_get_input_section_count get_input_section_count = NULL;
34 static ld_plugin_get_input_section_type get_input_section_type = NULL;
35 static ld_plugin_get_input_section_name get_input_section_name = NULL;
36 static ld_plugin_get_input_section_contents get_input_section_contents = NULL;
37 static ld_plugin_update_section_order update_section_order = NULL;
38 static ld_plugin_allow_section_ordering allow_section_ordering = NULL;
39 static ld_plugin_allow_unique_segment_for_sections
40 allow_unique_segment_for_sections = NULL;
41 static ld_plugin_unique_segment_for_sections unique_segment_for_sections = NULL;
42
43 enum ld_plugin_status onload(struct ld_plugin_tv *tv);
44 enum ld_plugin_status claim_file_hook(const struct ld_plugin_input_file *file,
45 int *claimed);
46 enum ld_plugin_status all_symbols_read_hook(void);
47
48 /* Plugin entry point. */
49 enum ld_plugin_status
onload(struct ld_plugin_tv * tv)50 onload(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 break;
89 case LDPT_UNIQUE_SEGMENT_FOR_SECTIONS:
90 unique_segment_for_sections
91 = *entry->tv_u.tv_unique_segment_for_sections;
92 break;
93 default:
94 break;
95 }
96 }
97
98 if (get_input_section_count == NULL
99 || get_input_section_type == NULL
100 || get_input_section_name == NULL
101 || get_input_section_contents == NULL
102 || update_section_order == NULL
103 || allow_section_ordering == NULL
104 || allow_unique_segment_for_sections == NULL
105 || unique_segment_for_sections == NULL)
106 {
107 fprintf(stderr, "Some interfaces are missing\n");
108 return LDPS_ERR;
109 }
110
111 return LDPS_OK;
112 }
113
is_prefix_of(const char * prefix,const char * str)114 inline static int is_prefix_of(const char *prefix, const char *str)
115 {
116 return strncmp(prefix, str, strlen (prefix)) == 0;
117 }
118
119 struct ld_plugin_section section_list[3];
120 int num_entries = 0;
121
122 /* This function is called by the linker for every new object it encounters. */
123 enum ld_plugin_status
claim_file_hook(const struct ld_plugin_input_file * file,int * claimed)124 claim_file_hook(const struct ld_plugin_input_file *file, int *claimed)
125 {
126 static int is_ordering_specified = 0;
127 struct ld_plugin_section section;
128 unsigned int count = 0;
129 unsigned int shndx;
130
131 *claimed = 0;
132 if (is_ordering_specified == 0)
133 {
134 /* Inform the linker to prepare for section reordering. */
135 (*allow_section_ordering)();
136 /* Inform the linker to prepare to map some sections to unique
137 segments. */
138 (*allow_unique_segment_for_sections)();
139 is_ordering_specified = 1;
140 }
141
142 (*get_input_section_count)(file->handle, &count);
143
144 for (shndx = 0; shndx < count; ++shndx)
145 {
146 char *name = NULL;
147 int position = 3;
148
149 section.handle = file->handle;
150 section.shndx = shndx;
151 (*get_input_section_name)(section, &name);
152
153 /* Order is foo() followed by bar() followed by baz() */
154 if (is_prefix_of(".text.", name))
155 {
156 if (strstr(name, "_Z3foov") != NULL)
157 position = 0;
158 else if (strstr(name, "_Z3barv") != NULL)
159 position = 1;
160 else if (strstr(name, "_Z3bazv") != NULL)
161 position = 2;
162 else
163 position = 3;
164 }
165 if (position < 3)
166 {
167 section_list[position].handle = file->handle;
168 section_list[position].shndx = shndx;
169 num_entries++;
170 }
171 }
172 return LDPS_OK;
173 }
174
175 /* This function is called by the linker after all the symbols have been read.
176 At this stage, it is fine to tell the linker the desired function order. */
177
178 enum ld_plugin_status
all_symbols_read_hook(void)179 all_symbols_read_hook(void)
180 {
181 if (num_entries == 3)
182 {
183 update_section_order(section_list, num_entries);
184 unique_segment_for_sections (".text.plugin_created_unique", 0, 0x1000,
185 section_list, num_entries);
186 }
187
188 return LDPS_OK;
189 }
190