summaryrefslogtreecommitdiff
path: root/arch/x86/vdso/vdso2c.c
blob: 8627db24a7f6a25993bc3cb5a53157cab7c7df1a (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
/*
 * vdso2c - A vdso image preparation tool
 * Copyright (c) 2014 Andy Lutomirski and others
 * Licensed under the GPL v2
 *
 * vdso2c requires stripped and unstripped input.  It would be trivial
 * to fully strip the input in here, but, for reasons described below,
 * we need to write a section table.  Doing this is more or less
 * equivalent to dropping all non-allocatable sections, but it's
 * easier to let objcopy handle that instead of doing it ourselves.
 * If we ever need to do something fancier than what objcopy provides,
 * it would be straightforward to add here.
 *
 * We're keep a section table for a few reasons:
 *
 * The Go runtime had a couple of bugs: it would read the section
 * table to try to figure out how many dynamic symbols there were (it
 * shouldn't have looked at the section table at all) and, if there
 * were no SHT_SYNDYM section table entry, it would use an
 * uninitialized value for the number of symbols.  An empty DYNSYM
 * table would work, but I see no reason not to write a valid one (and
 * keep full performance for old Go programs).  This hack is only
 * needed on x86_64.
 *
 * The bug was introduced on 2012-08-31 by:
 * https://code.google.com/p/go/source/detail?r=56ea40aac72b
 * and was fixed on 2014-06-13 by:
 * https://code.google.com/p/go/source/detail?r=fc1cd5e12595
 *
 * Binutils has issues debugging the vDSO: it reads the section table to
 * find SHT_NOTE; it won't look at PT_NOTE for the in-memory vDSO, which
 * would break build-id if we removed the section table.  Binutils
 * also requires that shstrndx != 0.  See:
 * https://sourceware.org/bugzilla/show_bug.cgi?id=17064
 *
 * elfutils might not look for PT_NOTE if there is a section table at
 * all.  I don't know whether this matters for any practical purpose.
 *
 * For simplicity, rather than hacking up a partial section table, we
 * just write a mostly complete one.  We omit non-dynamic symbols,
 * though, since they're rather large.
 *
 * Once binutils gets fixed, we might be able to drop this for all but
 * the 64-bit vdso, since build-id only works in kernel RPMs, and
 * systems that update to new enough kernel RPMs will likely update
 * binutils in sync.  build-id has never worked for home-built kernel
 * RPMs without manual symlinking, and I suspect that no one ever does
 * that.
 */

#include <inttypes.h>
#include <stdint.h>
#include <unistd.h>
#include <stdarg.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <fcntl.h>
#include <err.h>

#include <sys/mman.h>
#include <sys/types.h>

#include <tools/le_byteshift.h>

#include <linux/elf.h>
#include <linux/types.h>

const char *outfilename;

/* Symbols that we need in vdso2c. */
enum {
	sym_vvar_start,
	sym_vvar_page,
	sym_hpet_page,
	sym_VDSO_FAKE_SECTION_TABLE_START,
	sym_VDSO_FAKE_SECTION_TABLE_END,
};

const int special_pages[] = {
	sym_vvar_page,
	sym_hpet_page,
};

struct vdso_sym {
	const char *name;
	bool export;
};

struct vdso_sym required_syms[] = {
	[sym_vvar_start] = {"vvar_start", true},
	[sym_vvar_page] = {"vvar_page", true},
	[sym_hpet_page] = {"hpet_page", true},
	[sym_VDSO_FAKE_SECTION_TABLE_START] = {
		"VDSO_FAKE_SECTION_TABLE_START", false
	},
	[sym_VDSO_FAKE_SECTION_TABLE_END] = {
		"VDSO_FAKE_SECTION_TABLE_END", false
	},
	{"VDSO32_NOTE_MASK", true},
	{"VDSO32_SYSENTER_RETURN", true},
	{"__kernel_vsyscall", true},
	{"__kernel_sigreturn", true},
	{"__kernel_rt_sigreturn", true},
};

__attribute__((format(printf, 1, 2))) __attribute__((noreturn))
static void fail(const char *format, ...)
{
	va_list ap;
	va_start(ap, format);
	fprintf(stderr, "Error: ");
	vfprintf(stderr, format, ap);
	if (outfilename)
		unlink(outfilename);
	exit(1);
	va_end(ap);
}

/*
 * Evil macros for little-endian reads and writes
 */
#define GLE(x, bits, ifnot)						\
	__builtin_choose_expr(						\
		(sizeof(*(x)) == bits/8),				\
		(__typeof__(*(x)))get_unaligned_le##bits(x), ifnot)

extern void bad_get_le(void);
#define LAST_GLE(x)							\
	__builtin_choose_expr(sizeof(*(x)) == 1, *(x), bad_get_le())

#define GET_LE(x)							\
	GLE(x, 64, GLE(x, 32, GLE(x, 16, LAST_GLE(x))))

#define PLE(x, val, bits, ifnot)					\
	__builtin_choose_expr(						\
		(sizeof(*(x)) == bits/8),				\
		put_unaligned_le##bits((val), (x)), ifnot)

extern void bad_put_le(void);
#define LAST_PLE(x, val)						\
	__builtin_choose_expr(sizeof(*(x)) == 1, *(x) = (val), bad_put_le())

#define PUT_LE(x, val)					\
	PLE(x, val, 64, PLE(x, val, 32, PLE(x, val, 16, LAST_PLE(x, val))))


#define NSYMS (sizeof(required_syms) / sizeof(required_syms[0]))

#define BITSFUNC3(name, bits, suffix) name##bits##suffix
#define BITSFUNC2(name, bits, suffix) BITSFUNC3(name, bits, suffix)
#define BITSFUNC(name) BITSFUNC2(name, ELF_BITS, )

#define INT_BITS BITSFUNC2(int, ELF_BITS, _t)

#define ELF_BITS_XFORM2(bits, x) Elf##bits##_##x
#define ELF_BITS_XFORM(bits, x) ELF_BITS_XFORM2(bits, x)
#define ELF(x) ELF_BITS_XFORM(ELF_BITS, x)

#define ELF_BITS 64
#include "vdso2c.h"
#undef ELF_BITS

#define ELF_BITS 32
#include "vdso2c.h"
#undef ELF_BITS

static void go(void *raw_addr, size_t raw_len,
	       void *stripped_addr, size_t stripped_len,
	       FILE *outfile, const char *name)
{
	Elf64_Ehdr *hdr = (Elf64_Ehdr *)raw_addr;

	if (hdr->e_ident[EI_CLASS] == ELFCLASS64) {
		go64(raw_addr, raw_len, stripped_addr, stripped_len,
		     outfile, name);
	} else if (hdr->e_ident[EI_CLASS] == ELFCLASS32) {
		go32(raw_addr, raw_len, stripped_addr, stripped_len,
		     outfile, name);
	} else {
		fail("unknown ELF class\n");
	}
}

static void map_input(const char *name, void **addr, size_t *len, int prot)
{
	off_t tmp_len;

	int fd = open(name, O_RDONLY);
	if (fd == -1)
		err(1, "%s", name);

	tmp_len = lseek(fd, 0, SEEK_END);
	if (tmp_len == (off_t)-1)
		err(1, "lseek");
	*len = (size_t)tmp_len;

	*addr = mmap(NULL, tmp_len, prot, MAP_PRIVATE, fd, 0);
	if (*addr == MAP_FAILED)
		err(1, "mmap");

	close(fd);
}

int main(int argc, char **argv)
{
	size_t raw_len, stripped_len;
	void *raw_addr, *stripped_addr;
	FILE *outfile;
	char *name, *tmp;
	int namelen;

	if (argc != 4) {
		printf("Usage: vdso2c RAW_INPUT STRIPPED_INPUT OUTPUT\n");
		return 1;
	}

	/*
	 * Figure out the struct name.  If we're writing to a .so file,
	 * generate raw output insted.
	 */
	name = strdup(argv[3]);
	namelen = strlen(name);
	if (namelen >= 3 && !strcmp(name + namelen - 3, ".so")) {
		name = NULL;
	} else {
		tmp = strrchr(name, '/');
		if (tmp)
			name = tmp + 1;
		tmp = strchr(name, '.');
		if (tmp)
			*tmp = '\0';
		for (tmp = name; *tmp; tmp++)
			if (*tmp == '-')
				*tmp = '_';
	}

	map_input(argv[1], &raw_addr, &raw_len, PROT_READ);
	map_input(argv[2], &stripped_addr, &stripped_len, PROT_READ);

	outfilename = argv[3];
	outfile = fopen(outfilename, "w");
	if (!outfile)
		err(1, "%s", argv[2]);

	go(raw_addr, raw_len, stripped_addr, stripped_len, outfile, name);

	munmap(raw_addr, raw_len);
	munmap(stripped_addr, stripped_len);
	fclose(outfile);

	return 0;
}