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 #include <linux/kernel.h>
69
70 const char *outfilename;
71
72 /* Symbols that we need in vdso2c. */
73 enum {
74 sym_vvar_start,
75 sym_vvar_page,
76 sym_hpet_page,
77 sym_pvclock_page,
78 sym_hvclock_page,
79 sym_VDSO_FAKE_SECTION_TABLE_START,
80 sym_VDSO_FAKE_SECTION_TABLE_END,
81 };
82
83 const int special_pages[] = {
84 sym_vvar_page,
85 sym_hpet_page,
86 sym_pvclock_page,
87 sym_hvclock_page,
88 };
89
90 struct vdso_sym {
91 const char *name;
92 bool export;
93 };
94
95 struct vdso_sym required_syms[] = {
96 [sym_vvar_start] = {"vvar_start", true},
97 [sym_vvar_page] = {"vvar_page", true},
98 [sym_hpet_page] = {"hpet_page", true},
99 [sym_pvclock_page] = {"pvclock_page", true},
100 [sym_hvclock_page] = {"hvclock_page", true},
101 [sym_VDSO_FAKE_SECTION_TABLE_START] = {
102 "VDSO_FAKE_SECTION_TABLE_START", false
103 },
104 [sym_VDSO_FAKE_SECTION_TABLE_END] = {
105 "VDSO_FAKE_SECTION_TABLE_END", false
106 },
107 {"VDSO32_NOTE_MASK", true},
108 {"__kernel_vsyscall", true},
109 {"__kernel_sigreturn", true},
110 {"__kernel_rt_sigreturn", true},
111 {"int80_landing_pad", true},
112 };
113
114 __attribute__((format(printf, 1, 2))) __attribute__((noreturn))
fail(const char * format,...)115 static void fail(const char *format, ...)
116 {
117 va_list ap;
118 va_start(ap, format);
119 fprintf(stderr, "Error: ");
120 vfprintf(stderr, format, ap);
121 if (outfilename)
122 unlink(outfilename);
123 exit(1);
124 va_end(ap);
125 }
126
127 /*
128 * Evil macros for little-endian reads and writes
129 */
130 #define GLE(x, bits, ifnot) \
131 __builtin_choose_expr( \
132 (sizeof(*(x)) == bits/8), \
133 (__typeof__(*(x)))get_unaligned_le##bits(x), ifnot)
134
135 extern void bad_get_le(void);
136 #define LAST_GLE(x) \
137 __builtin_choose_expr(sizeof(*(x)) == 1, *(x), bad_get_le())
138
139 #define GET_LE(x) \
140 GLE(x, 64, GLE(x, 32, GLE(x, 16, LAST_GLE(x))))
141
142 #define PLE(x, val, bits, ifnot) \
143 __builtin_choose_expr( \
144 (sizeof(*(x)) == bits/8), \
145 put_unaligned_le##bits((val), (x)), ifnot)
146
147 extern void bad_put_le(void);
148 #define LAST_PLE(x, val) \
149 __builtin_choose_expr(sizeof(*(x)) == 1, *(x) = (val), bad_put_le())
150
151 #define PUT_LE(x, val) \
152 PLE(x, val, 64, PLE(x, val, 32, PLE(x, val, 16, LAST_PLE(x, val))))
153
154
155 #define NSYMS ARRAY_SIZE(required_syms)
156
157 #define BITSFUNC3(name, bits, suffix) name##bits##suffix
158 #define BITSFUNC2(name, bits, suffix) BITSFUNC3(name, bits, suffix)
159 #define BITSFUNC(name) BITSFUNC2(name, ELF_BITS, )
160
161 #define INT_BITS BITSFUNC2(int, ELF_BITS, _t)
162
163 #define ELF_BITS_XFORM2(bits, x) Elf##bits##_##x
164 #define ELF_BITS_XFORM(bits, x) ELF_BITS_XFORM2(bits, x)
165 #define ELF(x) ELF_BITS_XFORM(ELF_BITS, x)
166
167 #define ELF_BITS 64
168 #include "vdso2c.h"
169 #undef ELF_BITS
170
171 #define ELF_BITS 32
172 #include "vdso2c.h"
173 #undef ELF_BITS
174
go(void * raw_addr,size_t raw_len,void * stripped_addr,size_t stripped_len,FILE * outfile,const char * name)175 static void go(void *raw_addr, size_t raw_len,
176 void *stripped_addr, size_t stripped_len,
177 FILE *outfile, const char *name)
178 {
179 Elf64_Ehdr *hdr = (Elf64_Ehdr *)raw_addr;
180
181 if (hdr->e_ident[EI_CLASS] == ELFCLASS64) {
182 go64(raw_addr, raw_len, stripped_addr, stripped_len,
183 outfile, name);
184 } else if (hdr->e_ident[EI_CLASS] == ELFCLASS32) {
185 go32(raw_addr, raw_len, stripped_addr, stripped_len,
186 outfile, name);
187 } else {
188 fail("unknown ELF class\n");
189 }
190 }
191
map_input(const char * name,void ** addr,size_t * len,int prot)192 static void map_input(const char *name, void **addr, size_t *len, int prot)
193 {
194 off_t tmp_len;
195
196 int fd = open(name, O_RDONLY);
197 if (fd == -1)
198 err(1, "%s", name);
199
200 tmp_len = lseek(fd, 0, SEEK_END);
201 if (tmp_len == (off_t)-1)
202 err(1, "lseek");
203 *len = (size_t)tmp_len;
204
205 *addr = mmap(NULL, tmp_len, prot, MAP_PRIVATE, fd, 0);
206 if (*addr == MAP_FAILED)
207 err(1, "mmap");
208
209 close(fd);
210 }
211
main(int argc,char ** argv)212 int main(int argc, char **argv)
213 {
214 size_t raw_len, stripped_len;
215 void *raw_addr, *stripped_addr;
216 FILE *outfile;
217 char *name, *tmp;
218 int namelen;
219
220 if (argc != 4) {
221 printf("Usage: vdso2c RAW_INPUT STRIPPED_INPUT OUTPUT\n");
222 return 1;
223 }
224
225 /*
226 * Figure out the struct name. If we're writing to a .so file,
227 * generate raw output insted.
228 */
229 name = strdup(argv[3]);
230 namelen = strlen(name);
231 if (namelen >= 3 && !strcmp(name + namelen - 3, ".so")) {
232 name = NULL;
233 } else {
234 tmp = strrchr(name, '/');
235 if (tmp)
236 name = tmp + 1;
237 tmp = strchr(name, '.');
238 if (tmp)
239 *tmp = '\0';
240 for (tmp = name; *tmp; tmp++)
241 if (*tmp == '-')
242 *tmp = '_';
243 }
244
245 map_input(argv[1], &raw_addr, &raw_len, PROT_READ);
246 map_input(argv[2], &stripped_addr, &stripped_len, PROT_READ);
247
248 outfilename = argv[3];
249 outfile = fopen(outfilename, "w");
250 if (!outfile)
251 err(1, "%s", argv[2]);
252
253 go(raw_addr, raw_len, stripped_addr, stripped_len, outfile, name);
254
255 munmap(raw_addr, raw_len);
256 munmap(stripped_addr, stripped_len);
257 fclose(outfile);
258
259 return 0;
260 }
261
