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 {"__kernel_vsyscall", true}, 79 {"__kernel_sigreturn", true}, 80 {"__kernel_rt_sigreturn", true}, 81 {"int80_landing_pad", true}, 82 {"vdso32_rt_sigreturn_landing_pad", true}, 83 {"vdso32_sigreturn_landing_pad", true}, 84 {"__futex_list64_try_unlock_cs_start", true}, 85 {"__futex_list64_try_unlock_cs_end", true}, 86 {"__futex_list32_try_unlock_cs_start", true}, 87 {"__futex_list32_try_unlock_cs_end", true}, 88 }; 89 90 __attribute__((format(printf, 1, 2))) __attribute__((noreturn)) 91 static void fail(const char *format, ...) 92 { 93 va_list ap; 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 little-endian reads and writes 105 */ 106 #define GLE(x, bits, ifnot) \ 107 __builtin_choose_expr( \ 108 (sizeof(*(x)) == bits/8), \ 109 (__typeof__(*(x)))get_unaligned_le##bits(x), ifnot) 110 111 extern void bad_get_le(void); 112 #define LAST_GLE(x) \ 113 __builtin_choose_expr(sizeof(*(x)) == 1, *(x), bad_get_le()) 114 115 #define GET_LE(x) \ 116 GLE(x, 64, GLE(x, 32, GLE(x, 16, LAST_GLE(x)))) 117 118 #define PLE(x, val, bits, ifnot) \ 119 __builtin_choose_expr( \ 120 (sizeof(*(x)) == bits/8), \ 121 put_unaligned_le##bits((val), (x)), ifnot) 122 123 extern void bad_put_le(void); 124 #define LAST_PLE(x, val) \ 125 __builtin_choose_expr(sizeof(*(x)) == 1, *(x) = (val), bad_put_le()) 126 127 #define PUT_LE(x, val) \ 128 PLE(x, val, 64, PLE(x, val, 32, PLE(x, val, 16, LAST_PLE(x, val)))) 129 130 131 #define NSYMS ARRAY_SIZE(required_syms) 132 133 #define BITSFUNC3(name, bits, suffix) name##bits##suffix 134 #define BITSFUNC2(name, bits, suffix) BITSFUNC3(name, bits, suffix) 135 #define BITSFUNC(name) BITSFUNC2(name, ELF_BITS, ) 136 137 #define INT_BITS BITSFUNC2(int, ELF_BITS, _t) 138 139 #define ELF_BITS_XFORM2(bits, x) Elf##bits##_##x 140 #define ELF_BITS_XFORM(bits, x) ELF_BITS_XFORM2(bits, x) 141 #define ELF(x) ELF_BITS_XFORM(ELF_BITS, x) 142 143 #define ELF_BITS 64 144 #include "vdso2c.h" 145 #undef ELF_BITS 146 147 #define ELF_BITS 32 148 #include "vdso2c.h" 149 #undef ELF_BITS 150 151 static void go(void *raw_addr, size_t raw_len, 152 void *stripped_addr, size_t stripped_len, 153 FILE *outfile, const char *name) 154 { 155 Elf64_Ehdr *hdr = (Elf64_Ehdr *)raw_addr; 156 157 if (hdr->e_ident[EI_CLASS] == ELFCLASS64) { 158 go64(raw_addr, raw_len, stripped_addr, stripped_len, 159 outfile, name); 160 } else if (hdr->e_ident[EI_CLASS] == ELFCLASS32) { 161 go32(raw_addr, raw_len, stripped_addr, stripped_len, 162 outfile, name); 163 } else { 164 fail("unknown ELF class\n"); 165 } 166 } 167 168 static void map_input(const char *name, void **addr, size_t *len, int prot) 169 { 170 off_t tmp_len; 171 172 int fd = open(name, O_RDONLY); 173 if (fd == -1) 174 err(1, "open(%s)", name); 175 176 tmp_len = lseek(fd, 0, SEEK_END); 177 if (tmp_len == (off_t)-1) 178 err(1, "lseek"); 179 *len = (size_t)tmp_len; 180 181 *addr = mmap(NULL, tmp_len, prot, MAP_PRIVATE, fd, 0); 182 if (*addr == MAP_FAILED) 183 err(1, "mmap"); 184 185 close(fd); 186 } 187 188 int main(int argc, char **argv) 189 { 190 size_t raw_len, stripped_len; 191 void *raw_addr, *stripped_addr; 192 FILE *outfile; 193 char *name, *tmp; 194 int namelen; 195 196 if (argc != 4) { 197 printf("Usage: vdso2c RAW_INPUT STRIPPED_INPUT OUTPUT\n"); 198 return 1; 199 } 200 201 /* 202 * Figure out the struct name. If we're writing to a .so file, 203 * generate raw output instead. 204 */ 205 name = strdup(argv[3]); 206 namelen = strlen(name); 207 if (namelen >= 3 && !strcmp(name + namelen - 3, ".so")) { 208 name = NULL; 209 } else { 210 tmp = strrchr(name, '/'); 211 if (tmp) 212 name = tmp + 1; 213 tmp = strchr(name, '.'); 214 if (tmp) 215 *tmp = '\0'; 216 for (tmp = name; *tmp; tmp++) 217 if (*tmp == '-') 218 *tmp = '_'; 219 } 220 221 map_input(argv[1], &raw_addr, &raw_len, PROT_READ); 222 map_input(argv[2], &stripped_addr, &stripped_len, PROT_READ); 223 224 outfilename = argv[3]; 225 outfile = fopen(outfilename, "w"); 226 if (!outfile) 227 err(1, "fopen(%s)", outfilename); 228 229 go(raw_addr, raw_len, stripped_addr, stripped_len, outfile, name); 230 231 munmap(raw_addr, raw_len); 232 munmap(stripped_addr, stripped_len); 233 fclose(outfile); 234 235 return 0; 236 } 237