1 /*
2 * Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 #include <stdio.h>
27 #include <sys/mman.h>
28 #include <dlfcn.h>
29 #include <libelf.h>
30 #include <strings.h>
31 #include <fcntl.h>
32 #include <sys/param.h>
33 #include <stdlib.h>
34 #include <thread.h>
35 #include <synch.h>
36 #include <stdarg.h>
37
38 #define TRUE 1
39 #define FALSE 0
40
41
fail(const char * err,...)42 static void fail(const char *err, ...)
43 {
44 va_list ap;
45 va_start(ap, err);
46 vfprintf(stderr, err, ap);
47 fflush(stderr);
48 va_end(ap);
49 exit(2);
50 }
51
52
find_section(Elf * elf,Elf_Data * sectionStringData,const char * name)53 static Elf_Scn *find_section(Elf *elf, Elf_Data *sectionStringData,
54 const char *name)
55 {
56 Elf_Scn *result = NULL;
57 Elf32_Shdr *symHeader;
58 const char *p;
59
60 while ((result = elf_nextscn(elf, result)) != NULL) {
61 symHeader = elf32_getshdr(result);
62 p = (const char *)(sectionStringData->d_buf) + symHeader->sh_name;
63 if (strcmp(p, name) == 0)
64 break;
65 }
66 return result;
67 }
68
69
trash_mcount(int count,Elf_Data * data,Elf_Data * stringData)70 static void trash_mcount(int count, Elf_Data *data, Elf_Data *stringData)
71 {
72 int i;
73 for (i = 0; i < count; ++i) {
74 Elf32_Sym *sym = ((Elf32_Sym *)data->d_buf) + i;
75 char *name = (char *)stringData->d_buf + sym->st_name;
76
77 if (strcmp(name, "_mcount") == 0) {
78 name[6] = 'T';
79 break;
80 }
81 }
82 if (i < count)
83 printf("Symbol _mcount found and changed.\n");
84 else
85 printf("Symbol _mcount not found.\n");
86 }
87
88
89 /*
90 * In the executable program named as the sole command line argument, find
91 * the symbol _mcount, if present, and change its name to something
92 * different. The symbol _mcount is included in Solaris/x86 programs by
93 * the compilers, and its presence prevents preloaded modules from
94 * supplying a custom implementation of that method.
95 */
96
main(int argc,char ** argv)97 int main(int argc, char **argv)
98 {
99 Elf32_Ehdr *ehdr;
100 Elf_Scn *sectionStringSection;
101 Elf_Scn *stringSection;
102 Elf_Scn *dynStringSection;
103 Elf_Scn *symSection;
104 Elf_Scn *dynSymSection;
105 Elf32_Shdr *symHeader;
106 Elf32_Shdr *dynSymHeader;
107 Elf32_Shdr *dynStringHeader;
108 Elf32_Shdr *stringHeader;
109 Elf *elf;
110 const char *p;
111 int i;
112 const char *fullName;
113 int fd;
114 Elf_Data *sectionStringData;
115 Elf_Data *symData;
116 Elf_Data *dynSymData;
117 Elf_Data *symStringData;
118 Elf_Data *dynSymStringData;
119 int symCount;
120 int dynSymCount;
121
122
123 if (argc != 2) {
124 fprintf(stderr, "Usage:\n"
125 "\t%s <file>\n", argv[0]);
126 exit(1);
127 }
128
129 fullName = argv[1];
130
131 /* Open the ELF file. Get section headers. */
132
133 elf_version(EV_CURRENT);
134 fd = open(fullName, O_RDWR);
135 if (fd < 0)
136 fail("Unable to open ELF file %s.\n", fullName);
137 elf = elf_begin(fd, ELF_C_RDWR, (Elf *)0);
138 if (elf == NULL)
139 fail("elf_begin failed.\n");
140 ehdr = elf32_getehdr(elf);
141 sectionStringSection = elf_getscn(elf, ehdr->e_shstrndx);
142 sectionStringData = elf_getdata(sectionStringSection, NULL);
143
144 /* Find the symbol table section. */
145
146 symSection = find_section(elf, sectionStringData, ".symtab");
147 if (symSection != NULL) {
148 symData = elf_getdata(symSection, NULL);
149 symCount = symData->d_size / sizeof (Elf32_Sym);
150
151 /* Find the string section, trash the _mcount symbol. */
152
153 stringSection = find_section(elf, sectionStringData, ".strtab");
154 if (stringSection == NULL)
155 fail("Unable to find string table.\n");
156 symStringData = elf_getdata(stringSection, NULL);
157 trash_mcount(symCount, symData, symStringData);
158 } else {
159 fprintf(stderr, "Unable to find symbol table.\n");
160 }
161
162 /* Find the dynamic symbol table section. */
163
164 dynSymSection = find_section(elf, sectionStringData, ".dynsym");
165 if (dynSymSection != NULL) {
166 dynSymData = elf_getdata(dynSymSection, NULL);
167 dynSymCount = dynSymData->d_size / sizeof (Elf32_Sym);
168
169 /* Find the dynamic string section, trash the _mcount symbol. */
170
171 dynStringSection = find_section(elf, sectionStringData, ".dynstr");
172 if (dynStringSection == NULL)
173 fail("Unable to find dynamic string table.\n");
174 dynSymStringData = elf_getdata(dynStringSection, NULL);
175 trash_mcount(dynSymCount, dynSymData, dynSymStringData);
176 } else {
177 fail("Unable to find dynamic symbol table.\n");
178 }
179
180 elf_update(elf, ELF_C_WRITE);
181 elf_end(elf);
182
183 exit(0);
184 }
185