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
69const char *outfilename;
70
71/* Symbols that we need in vdso2c. */
72enum {
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
80const int special_pages[] = {
81	sym_vvar_page,
82	sym_hpet_page,
83};
84
85struct vdso_sym {
86	const char *name;
87	bool export;
88};
89
90struct 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))
108static 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
128extern 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
140extern 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
168static 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
185static 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
205int 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}
254