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 }; 67 68 struct vdso_sym { 69 const char *name; 70 int export; 71 }; 72 73 struct vdso_sym required_syms[] = { 74 [sym_vvar_start] = {"vvar_start", 1}, 75 [sym_VDSO_FAKE_SECTION_TABLE_START] = { 76 "VDSO_FAKE_SECTION_TABLE_START", 0 77 }, 78 [sym_VDSO_FAKE_SECTION_TABLE_END] = { 79 "VDSO_FAKE_SECTION_TABLE_END", 0 80 }, 81 }; 82 83 __attribute__((format(printf, 1, 2))) __attribute__((noreturn)) 84 static void fail(const char *format, ...) 85 { 86 va_list ap; 87 88 va_start(ap, format); 89 fprintf(stderr, "Error: "); 90 vfprintf(stderr, format, ap); 91 if (outfilename) 92 unlink(outfilename); 93 exit(1); 94 va_end(ap); 95 } 96 97 /* 98 * Evil macros for big-endian reads and writes 99 */ 100 #define GBE(x, bits, ifnot) \ 101 __builtin_choose_expr( \ 102 (sizeof(*(x)) == bits/8), \ 103 (__typeof__(*(x)))get_unaligned_be##bits(x), ifnot) 104 105 #define LAST_GBE(x) \ 106 __builtin_choose_expr(sizeof(*(x)) == 1, *(x), (void)(0)) 107 108 #define GET_BE(x) \ 109 GBE(x, 64, GBE(x, 32, GBE(x, 16, LAST_GBE(x)))) 110 111 #define PBE(x, val, bits, ifnot) \ 112 __builtin_choose_expr( \ 113 (sizeof(*(x)) == bits/8), \ 114 put_unaligned_be##bits((val), (x)), ifnot) 115 116 #define LAST_PBE(x, val) \ 117 __builtin_choose_expr(sizeof(*(x)) == 1, *(x) = (val), (void)(0)) 118 119 #define PUT_BE(x, val) \ 120 PBE(x, val, 64, PBE(x, val, 32, PBE(x, val, 16, LAST_PBE(x, val)))) 121 122 #define NSYMS ARRAY_SIZE(required_syms) 123 124 #define BITSFUNC3(name, bits, suffix) name##bits##suffix 125 #define BITSFUNC2(name, bits, suffix) BITSFUNC3(name, bits, suffix) 126 #define BITSFUNC(name) BITSFUNC2(name, ELF_BITS, ) 127 128 #define INT_BITS BITSFUNC2(int, ELF_BITS, _t) 129 130 #define ELF_BITS_XFORM2(bits, x) Elf##bits##_##x 131 #define ELF_BITS_XFORM(bits, x) ELF_BITS_XFORM2(bits, x) 132 #define ELF(x) ELF_BITS_XFORM(ELF_BITS, x) 133 134 #define ELF_BITS 64 135 #include "vdso2c.h" 136 #undef ELF_BITS 137 138 #define ELF_BITS 32 139 #include "vdso2c.h" 140 #undef ELF_BITS 141 142 static void go(void *raw_addr, size_t raw_len, 143 void *stripped_addr, size_t stripped_len, 144 FILE *outfile, const char *name) 145 { 146 Elf64_Ehdr *hdr = (Elf64_Ehdr *)raw_addr; 147 148 if (hdr->e_ident[EI_CLASS] == ELFCLASS64) { 149 go64(raw_addr, raw_len, stripped_addr, stripped_len, 150 outfile, name); 151 } else if (hdr->e_ident[EI_CLASS] == ELFCLASS32) { 152 go32(raw_addr, raw_len, stripped_addr, stripped_len, 153 outfile, name); 154 } else { 155 fail("unknown ELF class\n"); 156 } 157 } 158 159 static void map_input(const char *name, void **addr, size_t *len, int prot) 160 { 161 off_t tmp_len; 162 163 int fd = open(name, O_RDONLY); 164 165 if (fd == -1) 166 err(1, "%s", name); 167 168 tmp_len = lseek(fd, 0, SEEK_END); 169 if (tmp_len == (off_t)-1) 170 err(1, "lseek"); 171 *len = (size_t)tmp_len; 172 173 *addr = mmap(NULL, tmp_len, prot, MAP_PRIVATE, fd, 0); 174 if (*addr == MAP_FAILED) 175 err(1, "mmap"); 176 177 close(fd); 178 } 179 180 int main(int argc, char **argv) 181 { 182 size_t raw_len, stripped_len; 183 void *raw_addr, *stripped_addr; 184 FILE *outfile; 185 char *name, *tmp; 186 int namelen; 187 188 if (argc != 4) { 189 printf("Usage: vdso2c RAW_INPUT STRIPPED_INPUT OUTPUT\n"); 190 return 1; 191 } 192 193 /* 194 * Figure out the struct name. If we're writing to a .so file, 195 * generate raw output insted. 196 */ 197 name = strdup(argv[3]); 198 namelen = strlen(name); 199 if (namelen >= 3 && !strcmp(name + namelen - 3, ".so")) { 200 name = NULL; 201 } else { 202 tmp = strrchr(name, '/'); 203 if (tmp) 204 name = tmp + 1; 205 tmp = strchr(name, '.'); 206 if (tmp) 207 *tmp = '\0'; 208 for (tmp = name; *tmp; tmp++) 209 if (*tmp == '-') 210 *tmp = '_'; 211 } 212 213 map_input(argv[1], &raw_addr, &raw_len, PROT_READ); 214 map_input(argv[2], &stripped_addr, &stripped_len, PROT_READ); 215 216 outfilename = argv[3]; 217 outfile = fopen(outfilename, "w"); 218 if (!outfile) 219 err(1, "%s", argv[2]); 220 221 go(raw_addr, raw_len, stripped_addr, stripped_len, outfile, name); 222 223 munmap(raw_addr, raw_len); 224 munmap(stripped_addr, stripped_len); 225 fclose(outfile); 226 227 return 0; 228 } 229