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)) 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 174 175 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 } 191 192 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 } 211 212 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