1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * vdso2c - A vdso image preparation tool
4 * Copyright (c) 2014 Andy Lutomirski and others
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 struct vdso_sym {
73 const char *name;
74 bool export;
75 };
76
77 struct vdso_sym required_syms[] = {
78 {"VDSO32_NOTE_MASK", true},
79 {"__kernel_vsyscall", true},
80 {"__kernel_sigreturn", true},
81 {"__kernel_rt_sigreturn", true},
82 {"int80_landing_pad", true},
83 {"vdso32_rt_sigreturn_landing_pad", true},
84 {"vdso32_sigreturn_landing_pad", true},
85 };
86
87 __attribute__((format(printf, 1, 2))) __attribute__((noreturn))
fail(const char * format,...)88 static void fail(const char *format, ...)
89 {
90 va_list ap;
91 va_start(ap, format);
92 fprintf(stderr, "Error: ");
93 vfprintf(stderr, format, ap);
94 if (outfilename)
95 unlink(outfilename);
96 exit(1);
97 va_end(ap);
98 }
99
100 /*
101 * Evil macros for little-endian reads and writes
102 */
103 #define GLE(x, bits, ifnot) \
104 __builtin_choose_expr( \
105 (sizeof(*(x)) == bits/8), \
106 (__typeof__(*(x)))get_unaligned_le##bits(x), ifnot)
107
108 extern void bad_get_le(void);
109 #define LAST_GLE(x) \
110 __builtin_choose_expr(sizeof(*(x)) == 1, *(x), bad_get_le())
111
112 #define GET_LE(x) \
113 GLE(x, 64, GLE(x, 32, GLE(x, 16, LAST_GLE(x))))
114
115 #define PLE(x, val, bits, ifnot) \
116 __builtin_choose_expr( \
117 (sizeof(*(x)) == bits/8), \
118 put_unaligned_le##bits((val), (x)), ifnot)
119
120 extern void bad_put_le(void);
121 #define LAST_PLE(x, val) \
122 __builtin_choose_expr(sizeof(*(x)) == 1, *(x) = (val), bad_put_le())
123
124 #define PUT_LE(x, val) \
125 PLE(x, val, 64, PLE(x, val, 32, PLE(x, val, 16, LAST_PLE(x, val))))
126
127
128 #define NSYMS ARRAY_SIZE(required_syms)
129
130 #define BITSFUNC3(name, bits, suffix) name##bits##suffix
131 #define BITSFUNC2(name, bits, suffix) BITSFUNC3(name, bits, suffix)
132 #define BITSFUNC(name) BITSFUNC2(name, ELF_BITS, )
133
134 #define INT_BITS BITSFUNC2(int, ELF_BITS, _t)
135
136 #define ELF_BITS_XFORM2(bits, x) Elf##bits##_##x
137 #define ELF_BITS_XFORM(bits, x) ELF_BITS_XFORM2(bits, x)
138 #define ELF(x) ELF_BITS_XFORM(ELF_BITS, x)
139
140 #define ELF_BITS 64
141 #include "vdso2c.h"
142 #undef ELF_BITS
143
144 #define ELF_BITS 32
145 #include "vdso2c.h"
146 #undef ELF_BITS
147
go(void * raw_addr,size_t raw_len,void * stripped_addr,size_t stripped_len,FILE * outfile,const char * name)148 static void go(void *raw_addr, size_t raw_len,
149 void *stripped_addr, size_t stripped_len,
150 FILE *outfile, const char *name)
151 {
152 Elf64_Ehdr *hdr = (Elf64_Ehdr *)raw_addr;
153
154 if (hdr->e_ident[EI_CLASS] == ELFCLASS64) {
155 go64(raw_addr, raw_len, stripped_addr, stripped_len,
156 outfile, name);
157 } else if (hdr->e_ident[EI_CLASS] == ELFCLASS32) {
158 go32(raw_addr, raw_len, stripped_addr, stripped_len,
159 outfile, name);
160 } else {
161 fail("unknown ELF class\n");
162 }
163 }
164
map_input(const char * name,void ** addr,size_t * len,int prot)165 static void map_input(const char *name, void **addr, size_t *len, int prot)
166 {
167 off_t tmp_len;
168
169 int fd = open(name, O_RDONLY);
170 if (fd == -1)
171 err(1, "open(%s)", name);
172
173 tmp_len = lseek(fd, 0, SEEK_END);
174 if (tmp_len == (off_t)-1)
175 err(1, "lseek");
176 *len = (size_t)tmp_len;
177
178 *addr = mmap(NULL, tmp_len, prot, MAP_PRIVATE, fd, 0);
179 if (*addr == MAP_FAILED)
180 err(1, "mmap");
181
182 close(fd);
183 }
184
main(int argc,char ** argv)185 int main(int argc, char **argv)
186 {
187 size_t raw_len, stripped_len;
188 void *raw_addr, *stripped_addr;
189 FILE *outfile;
190 char *name, *tmp;
191 int namelen;
192
193 if (argc != 4) {
194 printf("Usage: vdso2c RAW_INPUT STRIPPED_INPUT OUTPUT\n");
195 return 1;
196 }
197
198 /*
199 * Figure out the struct name. If we're writing to a .so file,
200 * generate raw output instead.
201 */
202 name = strdup(argv[3]);
203 namelen = strlen(name);
204 if (namelen >= 3 && !strcmp(name + namelen - 3, ".so")) {
205 name = NULL;
206 } else {
207 tmp = strrchr(name, '/');
208 if (tmp)
209 name = tmp + 1;
210 tmp = strchr(name, '.');
211 if (tmp)
212 *tmp = '\0';
213 for (tmp = name; *tmp; tmp++)
214 if (*tmp == '-')
215 *tmp = '_';
216 }
217
218 map_input(argv[1], &raw_addr, &raw_len, PROT_READ);
219 map_input(argv[2], &stripped_addr, &stripped_len, PROT_READ);
220
221 outfilename = argv[3];
222 outfile = fopen(outfilename, "w");
223 if (!outfile)
224 err(1, "fopen(%s)", outfilename);
225
226 go(raw_addr, raw_len, stripped_addr, stripped_len, outfile, name);
227
228 munmap(raw_addr, raw_len);
229 munmap(stripped_addr, stripped_len);
230 fclose(outfile);
231
232 return 0;
233 }
234