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)) 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 170 171 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 } 187 188 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 } 207 208 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