1 /*
2 * vdso2c - A vdso image preparation tool
3 * Copyright (c) 2014 Andy Lutomirski and others
4 * Licensed under the GPL v2
5 *
6 * vdso2c requires stripped and unstripped input. It would be trivial
7 * to fully strip the input in here, but, for reasons described below,
8 * we need to write a section table. Doing this is more or less
9 * equivalent to dropping all non-allocatable sections, but it's
10 * easier to let objcopy handle that instead of doing it ourselves.
11 * If we ever need to do something fancier than what objcopy provides,
12 * it would be straightforward to add here.
13 *
14 * We're keep a section table for a few reasons:
15 *
16 * The Go runtime had a couple of bugs: it would read the section
17 * table to try to figure out how many dynamic symbols there were (it
18 * shouldn't have looked at the section table at all) and, if there
19 * were no SHT_SYNDYM section table entry, it would use an
20 * uninitialized value for the number of symbols. An empty DYNSYM
21 * table would work, but I see no reason not to write a valid one (and
22 * keep full performance for old Go programs). This hack is only
23 * needed on x86_64.
24 *
25 * The bug was introduced on 2012-08-31 by:
26 * https://code.google.com/p/go/source/detail?r=56ea40aac72b
27 * and was fixed on 2014-06-13 by:
28 * https://code.google.com/p/go/source/detail?r=fc1cd5e12595
29 *
30 * Binutils has issues debugging the vDSO: it reads the section table to
31 * find SHT_NOTE; it won't look at PT_NOTE for the in-memory vDSO, which
32 * would break build-id if we removed the section table. Binutils
33 * also requires that shstrndx != 0. See:
34 * https://sourceware.org/bugzilla/show_bug.cgi?id=17064
35 *
36 * elfutils might not look for PT_NOTE if there is a section table at
37 * all. I don't know whether this matters for any practical purpose.
38 *
39 * For simplicity, rather than hacking up a partial section table, we
40 * just write a mostly complete one. We omit non-dynamic symbols,
41 * though, since they're rather large.
42 *
43 * Once binutils gets fixed, we might be able to drop this for all but
44 * the 64-bit vdso, since build-id only works in kernel RPMs, and
45 * systems that update to new enough kernel RPMs will likely update
46 * binutils in sync. build-id has never worked for home-built kernel
47 * RPMs without manual symlinking, and I suspect that no one ever does
48 * that.
49 */
50
51 #include <inttypes.h>
52 #include <stdint.h>
53 #include <unistd.h>
54 #include <stdarg.h>
55 #include <stdlib.h>
56 #include <stdio.h>
57 #include <string.h>
58 #include <fcntl.h>
59 #include <err.h>
60
61 #include <sys/mman.h>
62 #include <sys/types.h>
63
64 #include <tools/le_byteshift.h>
65
66 #include <linux/elf.h>
67 #include <linux/types.h>
68
69 const char *outfilename;
70
71 /* Symbols that we need in vdso2c. */
72 enum {
73 sym_vvar_start,
74 sym_vvar_page,
75 sym_hpet_page,
76 sym_pvclock_page,
77 sym_VDSO_FAKE_SECTION_TABLE_START,
78 sym_VDSO_FAKE_SECTION_TABLE_END,
79 };
80
81 const int special_pages[] = {
82 sym_vvar_page,
83 sym_hpet_page,
84 sym_pvclock_page,
85 };
86
87 struct vdso_sym {
88 const char *name;
89 bool export;
90 };
91
92 struct vdso_sym required_syms[] = {
93 [sym_vvar_start] = {"vvar_start", true},
94 [sym_vvar_page] = {"vvar_page", true},
95 [sym_hpet_page] = {"hpet_page", true},
96 [sym_pvclock_page] = {"pvclock_page", true},
97 [sym_VDSO_FAKE_SECTION_TABLE_START] = {
98 "VDSO_FAKE_SECTION_TABLE_START", false
99 },
100 [sym_VDSO_FAKE_SECTION_TABLE_END] = {
101 "VDSO_FAKE_SECTION_TABLE_END", false
102 },
103 {"VDSO32_NOTE_MASK", true},
104 {"__kernel_vsyscall", true},
105 {"__kernel_sigreturn", true},
106 {"__kernel_rt_sigreturn", true},
107 {"int80_landing_pad", true},
108 };
109
110 __attribute__((format(printf, 1, 2))) __attribute__((noreturn))
fail(const char * format,...)111 static void fail(const char *format, ...)
112 {
113 va_list ap;
114 va_start(ap, format);
115 fprintf(stderr, "Error: ");
116 vfprintf(stderr, format, ap);
117 if (outfilename)
118 unlink(outfilename);
119 exit(1);
120 va_end(ap);
121 }
122
123 /*
124 * Evil macros for little-endian reads and writes
125 */
126 #define GLE(x, bits, ifnot) \
127 __builtin_choose_expr( \
128 (sizeof(*(x)) == bits/8), \
129 (__typeof__(*(x)))get_unaligned_le##bits(x), ifnot)
130
131 extern void bad_get_le(void);
132 #define LAST_GLE(x) \
133 __builtin_choose_expr(sizeof(*(x)) == 1, *(x), bad_get_le())
134
135 #define GET_LE(x) \
136 GLE(x, 64, GLE(x, 32, GLE(x, 16, LAST_GLE(x))))
137
138 #define PLE(x, val, bits, ifnot) \
139 __builtin_choose_expr( \
140 (sizeof(*(x)) == bits/8), \
141 put_unaligned_le##bits((val), (x)), ifnot)
142
143 extern void bad_put_le(void);
144 #define LAST_PLE(x, val) \
145 __builtin_choose_expr(sizeof(*(x)) == 1, *(x) = (val), bad_put_le())
146
147 #define PUT_LE(x, val) \
148 PLE(x, val, 64, PLE(x, val, 32, PLE(x, val, 16, LAST_PLE(x, val))))
149
150
151 #define NSYMS (sizeof(required_syms) / sizeof(required_syms[0]))
152
153 #define BITSFUNC3(name, bits, suffix) name##bits##suffix
154 #define BITSFUNC2(name, bits, suffix) BITSFUNC3(name, bits, suffix)
155 #define BITSFUNC(name) BITSFUNC2(name, ELF_BITS, )
156
157 #define INT_BITS BITSFUNC2(int, ELF_BITS, _t)
158
159 #define ELF_BITS_XFORM2(bits, x) Elf##bits##_##x
160 #define ELF_BITS_XFORM(bits, x) ELF_BITS_XFORM2(bits, x)
161 #define ELF(x) ELF_BITS_XFORM(ELF_BITS, x)
162
163 #define ELF_BITS 64
164 #include "vdso2c.h"
165 #undef ELF_BITS
166
167 #define ELF_BITS 32
168 #include "vdso2c.h"
169 #undef ELF_BITS
170
go(void * raw_addr,size_t raw_len,void * stripped_addr,size_t stripped_len,FILE * outfile,const char * name)171 static void go(void *raw_addr, size_t raw_len,
172 void *stripped_addr, size_t stripped_len,
173 FILE *outfile, const char *name)
174 {
175 Elf64_Ehdr *hdr = (Elf64_Ehdr *)raw_addr;
176
177 if (hdr->e_ident[EI_CLASS] == ELFCLASS64) {
178 go64(raw_addr, raw_len, stripped_addr, stripped_len,
179 outfile, name);
180 } else if (hdr->e_ident[EI_CLASS] == ELFCLASS32) {
181 go32(raw_addr, raw_len, stripped_addr, stripped_len,
182 outfile, name);
183 } else {
184 fail("unknown ELF class\n");
185 }
186 }
187
map_input(const char * name,void ** addr,size_t * len,int prot)188 static void map_input(const char *name, void **addr, size_t *len, int prot)
189 {
190 off_t tmp_len;
191
192 int fd = open(name, O_RDONLY);
193 if (fd == -1)
194 err(1, "%s", name);
195
196 tmp_len = lseek(fd, 0, SEEK_END);
197 if (tmp_len == (off_t)-1)
198 err(1, "lseek");
199 *len = (size_t)tmp_len;
200
201 *addr = mmap(NULL, tmp_len, prot, MAP_PRIVATE, fd, 0);
202 if (*addr == MAP_FAILED)
203 err(1, "mmap");
204
205 close(fd);
206 }
207
main(int argc,char ** argv)208 int main(int argc, char **argv)
209 {
210 size_t raw_len, stripped_len;
211 void *raw_addr, *stripped_addr;
212 FILE *outfile;
213 char *name, *tmp;
214 int namelen;
215
216 if (argc != 4) {
217 printf("Usage: vdso2c RAW_INPUT STRIPPED_INPUT OUTPUT\n");
218 return 1;
219 }
220
221 /*
222 * Figure out the struct name. If we're writing to a .so file,
223 * generate raw output insted.
224 */
225 name = strdup(argv[3]);
226 namelen = strlen(name);
227 if (namelen >= 3 && !strcmp(name + namelen - 3, ".so")) {
228 name = NULL;
229 } else {
230 tmp = strrchr(name, '/');
231 if (tmp)
232 name = tmp + 1;
233 tmp = strchr(name, '.');
234 if (tmp)
235 *tmp = '\0';
236 for (tmp = name; *tmp; tmp++)
237 if (*tmp == '-')
238 *tmp = '_';
239 }
240
241 map_input(argv[1], &raw_addr, &raw_len, PROT_READ);
242 map_input(argv[2], &stripped_addr, &stripped_len, PROT_READ);
243
244 outfilename = argv[3];
245 outfile = fopen(outfilename, "w");
246 if (!outfile)
247 err(1, "%s", argv[2]);
248
249 go(raw_addr, raw_len, stripped_addr, stripped_len, outfile, name);
250
251 munmap(raw_addr, raw_len);
252 munmap(stripped_addr, stripped_len);
253 fclose(outfile);
254
255 return 0;
256 }
257