2 * vdso2c - A vdso image preparation tool
3 * Copyright (c) 2014 Andy Lutomirski and others
4 * Licensed under the GPL v2
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.
14 * We keep a section table for a few reasons:
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
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.
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.
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
38 * Copyright (c) 2017 Oracle and/or its affiliates. All rights reserved.
52 #include <sys/types.h>
53 #include <tools/be_byteshift.h>
55 #include <linux/elf.h>
56 #include <linux/types.h>
57 #include <linux/kernel.h>
59 const char *outfilename;
61 /* Symbols that we need in vdso2c. */
64 sym_VDSO_FAKE_SECTION_TABLE_START,
65 sym_VDSO_FAKE_SECTION_TABLE_END,
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
78 [sym_VDSO_FAKE_SECTION_TABLE_END] = {
79 "VDSO_FAKE_SECTION_TABLE_END", 0
83 __attribute__((format(printf, 1, 2))) __attribute__((noreturn))
84 static void fail(const char *format, ...)
89 fprintf(stderr, "Error: ");
90 vfprintf(stderr, format, ap);
98 * Evil macros for big-endian reads and writes
100 #define GBE(x, bits, ifnot) \
101 __builtin_choose_expr( \
102 (sizeof(*(x)) == bits/8), \
103 (__typeof__(*(x)))get_unaligned_be##bits(x), ifnot)
105 #define LAST_GBE(x) \
106 __builtin_choose_expr(sizeof(*(x)) == 1, *(x), (void)(0))
109 GBE(x, 64, GBE(x, 32, GBE(x, 16, LAST_GBE(x))))
111 #define PBE(x, val, bits, ifnot) \
112 __builtin_choose_expr( \
113 (sizeof(*(x)) == bits/8), \
114 put_unaligned_be##bits((val), (x)), ifnot)
116 #define LAST_PBE(x, val) \
117 __builtin_choose_expr(sizeof(*(x)) == 1, *(x) = (val), (void)(0))
119 #define PUT_BE(x, val) \
120 PBE(x, val, 64, PBE(x, val, 32, PBE(x, val, 16, LAST_PBE(x, val))))
122 #define NSYMS ARRAY_SIZE(required_syms)
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, )
128 #define INT_BITS BITSFUNC2(int, ELF_BITS, _t)
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)
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)
146 Elf64_Ehdr *hdr = (Elf64_Ehdr *)raw_addr;
148 if (hdr->e_ident[EI_CLASS] == ELFCLASS64) {
149 go64(raw_addr, raw_len, stripped_addr, stripped_len,
151 } else if (hdr->e_ident[EI_CLASS] == ELFCLASS32) {
152 go32(raw_addr, raw_len, stripped_addr, stripped_len,
155 fail("unknown ELF class\n");
159 static void map_input(const char *name, void **addr, size_t *len, int prot)
163 int fd = open(name, O_RDONLY);
168 tmp_len = lseek(fd, 0, SEEK_END);
169 if (tmp_len == (off_t)-1)
171 *len = (size_t)tmp_len;
173 *addr = mmap(NULL, tmp_len, prot, MAP_PRIVATE, fd, 0);
174 if (*addr == MAP_FAILED)
180 int main(int argc, char **argv)
182 size_t raw_len, stripped_len;
183 void *raw_addr, *stripped_addr;
189 printf("Usage: vdso2c RAW_INPUT STRIPPED_INPUT OUTPUT\n");
194 * Figure out the struct name. If we're writing to a .so file,
195 * generate raw output insted.
197 name = strdup(argv[3]);
198 namelen = strlen(name);
199 if (namelen >= 3 && !strcmp(name + namelen - 3, ".so")) {
202 tmp = strrchr(name, '/');
205 tmp = strchr(name, '.');
208 for (tmp = name; *tmp; tmp++)
213 map_input(argv[1], &raw_addr, &raw_len, PROT_READ);
214 map_input(argv[2], &stripped_addr, &stripped_len, PROT_READ);
216 outfilename = argv[3];
217 outfile = fopen(outfilename, "w");
219 err(1, "%s", argv[2]);
221 go(raw_addr, raw_len, stripped_addr, stripped_len, outfile, name);
223 munmap(raw_addr, raw_len);
224 munmap(stripped_addr, stripped_len);