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 keep a section table for a few reasons: 15 * 16 * Binutils has issues debugging the vDSO: it reads the section table to 17 * find SHT_NOTE; it won't look at PT_NOTE for the in-memory vDSO, which 18 * would break build-id if we removed the section table. Binutils 19 * also requires that shstrndx != 0. See: 20 * https://sourceware.org/bugzilla/show_bug.cgi?id=17064 21 * 22 * elfutils might not look for PT_NOTE if there is a section table at 23 * all. I don't know whether this matters for any practical purpose. 24 * 25 * For simplicity, rather than hacking up a partial section table, we 26 * just write a mostly complete one. We omit non-dynamic symbols, 27 * though, since they're rather large. 28 * 29 * Once binutils gets fixed, we might be able to drop this for all but 30 * the 64-bit vdso, since build-id only works in kernel RPMs, and 31 * systems that update to new enough kernel RPMs will likely update 32 * binutils in sync. build-id has never worked for home-built kernel 33 * RPMs without manual symlinking, and I suspect that no one ever does 34 * that. 35 */ 36 37 /* 38 * Copyright (c) 2017 Oracle and/or its affiliates. All rights reserved. 39 */ 40 41 #include <inttypes.h> 42 #include <stdint.h> 43 #include <unistd.h> 44 #include <stdarg.h> 45 #include <stdlib.h> 46 #include <stdio.h> 47 #include <string.h> 48 #include <fcntl.h> 49 #include <err.h> 50 51 #include <sys/mman.h> 52 #include <sys/types.h> 53 #include <tools/be_byteshift.h> 54 55 #include <linux/elf.h> 56 #include <linux/types.h> 57 #include <linux/kernel.h> 58 59 const char *outfilename; 60 61 /* Symbols that we need in vdso2c. */ 62 enum { 63 sym_vvar_start, 64 sym_VDSO_FAKE_SECTION_TABLE_START, 65 sym_VDSO_FAKE_SECTION_TABLE_END, 66 sym_vread_tick, 67 sym_vread_tick_patch_start, 68 sym_vread_tick_patch_end 69 }; 70 71 struct vdso_sym { 72 const char *name; 73 int export; 74 }; 75 76 struct vdso_sym required_syms[] = { 77 [sym_vvar_start] = {"vvar_start", 1}, 78 [sym_VDSO_FAKE_SECTION_TABLE_START] = { 79 "VDSO_FAKE_SECTION_TABLE_START", 0 80 }, 81 [sym_VDSO_FAKE_SECTION_TABLE_END] = { 82 "VDSO_FAKE_SECTION_TABLE_END", 0 83 }, 84 [sym_vread_tick] = {"vread_tick", 1}, 85 [sym_vread_tick_patch_start] = {"vread_tick_patch_start", 1}, 86 [sym_vread_tick_patch_end] = {"vread_tick_patch_end", 1} 87 }; 88 89 __attribute__((format(printf, 1, 2))) __attribute__((noreturn)) 90 static void fail(const char *format, ...) 91 { 92 va_list ap; 93 94 va_start(ap, format); 95 fprintf(stderr, "Error: "); 96 vfprintf(stderr, format, ap); 97 if (outfilename) 98 unlink(outfilename); 99 exit(1); 100 va_end(ap); 101 } 102 103 /* 104 * Evil macros for big-endian reads and writes 105 */ 106 #define GBE(x, bits, ifnot) \ 107 __builtin_choose_expr( \ 108 (sizeof(*(x)) == bits/8), \ 109 (__typeof__(*(x)))get_unaligned_be##bits(x), ifnot) 110 111 #define LAST_GBE(x) \ 112 __builtin_choose_expr(sizeof(*(x)) == 1, *(x), (void)(0)) 113 114 #define GET_BE(x) \ 115 GBE(x, 64, GBE(x, 32, GBE(x, 16, LAST_GBE(x)))) 116 117 #define PBE(x, val, bits, ifnot) \ 118 __builtin_choose_expr( \ 119 (sizeof(*(x)) == bits/8), \ 120 put_unaligned_be##bits((val), (x)), ifnot) 121 122 #define LAST_PBE(x, val) \ 123 __builtin_choose_expr(sizeof(*(x)) == 1, *(x) = (val), (void)(0)) 124 125 #define PUT_BE(x, val) \ 126 PBE(x, val, 64, PBE(x, val, 32, PBE(x, val, 16, LAST_PBE(x, val)))) 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 147 148 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 } 164 165 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); 170 171 if (fd == -1) 172 err(1, "%s", name); 173 174 tmp_len = lseek(fd, 0, SEEK_END); 175 if (tmp_len == (off_t)-1) 176 err(1, "lseek"); 177 *len = (size_t)tmp_len; 178 179 *addr = mmap(NULL, tmp_len, prot, MAP_PRIVATE, fd, 0); 180 if (*addr == MAP_FAILED) 181 err(1, "mmap"); 182 183 close(fd); 184 } 185 186 int main(int argc, char **argv) 187 { 188 size_t raw_len, stripped_len; 189 void *raw_addr, *stripped_addr; 190 FILE *outfile; 191 char *name, *tmp; 192 int namelen; 193 194 if (argc != 4) { 195 printf("Usage: vdso2c RAW_INPUT STRIPPED_INPUT OUTPUT\n"); 196 return 1; 197 } 198 199 /* 200 * Figure out the struct name. If we're writing to a .so file, 201 * generate raw output insted. 202 */ 203 name = strdup(argv[3]); 204 namelen = strlen(name); 205 if (namelen >= 3 && !strcmp(name + namelen - 3, ".so")) { 206 name = NULL; 207 } else { 208 tmp = strrchr(name, '/'); 209 if (tmp) 210 name = tmp + 1; 211 tmp = strchr(name, '.'); 212 if (tmp) 213 *tmp = '\0'; 214 for (tmp = name; *tmp; tmp++) 215 if (*tmp == '-') 216 *tmp = '_'; 217 } 218 219 map_input(argv[1], &raw_addr, &raw_len, PROT_READ); 220 map_input(argv[2], &stripped_addr, &stripped_len, PROT_READ); 221 222 outfilename = argv[3]; 223 outfile = fopen(outfilename, "w"); 224 if (!outfile) 225 err(1, "%s", argv[2]); 226 227 go(raw_addr, raw_len, stripped_addr, stripped_len, outfile, name); 228 229 munmap(raw_addr, raw_len); 230 munmap(stripped_addr, stripped_len); 231 fclose(outfile); 232 233 return 0; 234 } 235