arch/x86/entry/vdso/vdso2c.c

   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_VDSO_FAKE_SECTION_TABLE_START,
  77         sym_VDSO_FAKE_SECTION_TABLE_END,
  78 };
  79
  80 const int special_pages[] = {
  81         sym_vvar_page,
  82         sym_hpet_page,
  83 };
  84
  85 struct vdso_sym {
  86         const char *name;
  87         bool export;
  88 };
  89
  90 struct vdso_sym required_syms[] = {
  91         [sym_vvar_start] = {"vvar_start", true},
  92         [sym_vvar_page] = {"vvar_page", true},
  93         [sym_hpet_page] = {"hpet_page", true},
  94         [sym_VDSO_FAKE_SECTION_TABLE_START] = {
  95                 "VDSO_FAKE_SECTION_TABLE_START", false
  96         },
  97         [sym_VDSO_FAKE_SECTION_TABLE_END] = {
  98                 "VDSO_FAKE_SECTION_TABLE_END", false
  99         },
 100         {"VDSO32_NOTE_MASK", true},
 101         {"VDSO32_SYSENTER_RETURN", true},
 102         {"__kernel_vsyscall", true},
 103         {"__kernel_sigreturn", true},
 104         {"__kernel_rt_sigreturn", true},
 105 };
 106
 107 __attribute__((format(printf, 1, 2))) __attribute__((noreturn))
 108 static void fail(const char *format, ...)
 109 {
 110         va_list ap;
 111         va_start(ap, format);
 112         fprintf(stderr, "Error: ");
 113         vfprintf(stderr, format, ap);
 114         if (outfilename)
 115                 unlink(outfilename);
 116         exit(1);
 117         va_end(ap);
 118 }
 119
 120 /*
 121  * Evil macros for little-endian reads and writes
 122  */
 123 #define GLE(x, bits, ifnot)                                             \
 124         __builtin_choose_expr(                                          \
 125                 (sizeof(*(x)) == bits/8),                               \
 126                 (__typeof__(*(x)))get_unaligned_le##bits(x), ifnot)
 127
 128 extern void bad_get_le(void);
 129 #define LAST_GLE(x)                                                     \
 130         __builtin_choose_expr(sizeof(*(x)) == 1, *(x), bad_get_le())
 131
 132 #define GET_LE(x)                                                       \
 133         GLE(x, 64, GLE(x, 32, GLE(x, 16, LAST_GLE(x))))
 134
 135 #define PLE(x, val, bits, ifnot)                                        \
 136         __builtin_choose_expr(                                          \
 137                 (sizeof(*(x)) == bits/8),                               \
 138                 put_unaligned_le##bits((val), (x)), ifnot)
 139
 140 extern void bad_put_le(void);
 141 #define LAST_PLE(x, val)                                                \
 142         __builtin_choose_expr(sizeof(*(x)) == 1, *(x) = (val), bad_put_le())
 143
 144 #define PUT_LE(x, val)                                  \
 145         PLE(x, val, 64, PLE(x, val, 32, PLE(x, val, 16, LAST_PLE(x, val))))
 146
 147
 148 #define NSYMS (sizeof(required_syms) / sizeof(required_syms[0]))
 149
 150 #define BITSFUNC3(name, bits, suffix) name##bits##suffix
 151 #define BITSFUNC2(name, bits, suffix) BITSFUNC3(name, bits, suffix)
 152 #define BITSFUNC(name) BITSFUNC2(name, ELF_BITS, )
 153
 154 #define INT_BITS BITSFUNC2(int, ELF_BITS, _t)
 155
 156 #define ELF_BITS_XFORM2(bits, x) Elf##bits##_##x
 157 #define ELF_BITS_XFORM(bits, x) ELF_BITS_XFORM2(bits, x)
 158 #define ELF(x) ELF_BITS_XFORM(ELF_BITS, x)
 159
 160 #define ELF_BITS 64
 161 #include "vdso2c.h"
 162 #undef ELF_BITS
 163
 164 #define ELF_BITS 32
 165 #include "vdso2c.h"
 166 #undef ELF_BITS
 167
 168 static void go(void *raw_addr, size_t raw_len,
 169                void *stripped_addr, size_t stripped_len,
 170                FILE *outfile, const char *name)
 171 {
 172         Elf64_Ehdr *hdr = (Elf64_Ehdr *)raw_addr;
 173
 174         if (hdr->e_ident[EI_CLASS] == ELFCLASS64) {
 175                 go64(raw_addr, raw_len, stripped_addr, stripped_len,
 176                      outfile, name);
 177         } else if (hdr->e_ident[EI_CLASS] == ELFCLASS32) {
 178                 go32(raw_addr, raw_len, stripped_addr, stripped_len,
 179                      outfile, name);
 180         } else {
 181                 fail("unknown ELF class\n");
 182         }
 183 }
 184
 185 static void map_input(const char *name, void **addr, size_t *len, int prot)
 186 {
 187         off_t tmp_len;
 188
 189         int fd = open(name, O_RDONLY);
 190         if (fd == -1)
 191                 err(1, "%s", name);
 192
 193         tmp_len = lseek(fd, 0, SEEK_END);
 194         if (tmp_len == (off_t)-1)
 195                 err(1, "lseek");
 196         *len = (size_t)tmp_len;
 197
 198         *addr = mmap(NULL, tmp_len, prot, MAP_PRIVATE, fd, 0);
 199         if (*addr == MAP_FAILED)
 200                 err(1, "mmap");
 201
 202         close(fd);
 203 }
 204
 205 int main(int argc, char **argv)
 206 {
 207         size_t raw_len, stripped_len;
 208         void *raw_addr, *stripped_addr;
 209         FILE *outfile;
 210         char *name, *tmp;
 211         int namelen;
 212
 213         if (argc != 4) {
 214                 printf("Usage: vdso2c RAW_INPUT STRIPPED_INPUT OUTPUT\n");
 215                 return 1;
 216         }
 217
 218         /*
 219          * Figure out the struct name.  If we're writing to a .so file,
 220          * generate raw output insted.
 221          */
 222         name = strdup(argv[3]);
 223         namelen = strlen(name);
 224         if (namelen >= 3 && !strcmp(name + namelen - 3, ".so")) {
 225                 name = NULL;
 226         } else {
 227                 tmp = strrchr(name, '/');
 228                 if (tmp)
 229                         name = tmp + 1;
 230                 tmp = strchr(name, '.');
 231                 if (tmp)
 232                         *tmp = '\0';
 233                 for (tmp = name; *tmp; tmp++)
 234                         if (*tmp == '-')
 235                                 *tmp = '_';
 236         }
 237
 238         map_input(argv[1], &raw_addr, &raw_len, PROT_READ);
 239         map_input(argv[2], &stripped_addr, &stripped_len, PROT_READ);
 240
 241         outfilename = argv[3];
 242         outfile = fopen(outfilename, "w");
 243         if (!outfile)
 244                 err(1, "%s", argv[2]);
 245
 246         go(raw_addr, raw_len, stripped_addr, stripped_len, outfile, name);
 247
 248         munmap(raw_addr, raw_len);
 249         munmap(stripped_addr, stripped_len);
 250         fclose(outfile);
 251
 252         return 0;
 253 }