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
70const char *outfilename;
71
72/* Symbols that we need in vdso2c. */
73enum {
74	sym_vvar_start,
75	sym_vvar_page,
76	sym_pvclock_page,
77	sym_hvclock_page,
78	sym_timens_page,
79};
80
81const int special_pages[] = {
82	sym_vvar_page,
83	sym_pvclock_page,
84	sym_hvclock_page,
85	sym_timens_page,
86};
87
88struct vdso_sym {
89	const char *name;
90	bool export;
91};
92
93struct vdso_sym required_syms[] = {
94	[sym_vvar_start] = {"vvar_start", true},
95	[sym_vvar_page] = {"vvar_page", true},
96	[sym_pvclock_page] = {"pvclock_page", true},
97	[sym_hvclock_page] = {"hvclock_page", true},
98	[sym_timens_page] = {"timens_page", true},
99	{"VDSO32_NOTE_MASK", true},
100	{"__kernel_vsyscall", true},
101	{"__kernel_sigreturn", true},
102	{"__kernel_rt_sigreturn", true},
103	{"int80_landing_pad", true},
104	{"vdso32_rt_sigreturn_landing_pad", true},
105	{"vdso32_sigreturn_landing_pad", true},
106};
107
108__attribute__((format(printf, 1, 2))) __attribute__((noreturn))
109static void fail(const char *format, ...)
110{
111	va_list ap;
112	va_start(ap, format);
113	fprintf(stderr, "Error: ");
114	vfprintf(stderr, format, ap);
115	if (outfilename)
116		unlink(outfilename);
117	exit(1);
118	va_end(ap);
119}
120
121/*
122 * Evil macros for little-endian reads and writes
123 */
124#define GLE(x, bits, ifnot)						\
125	__builtin_choose_expr(						\
126		(sizeof(*(x)) == bits/8),				\
127		(__typeof__(*(x)))get_unaligned_le##bits(x), ifnot)
128
129extern void bad_get_le(void);
130#define LAST_GLE(x)							\
131	__builtin_choose_expr(sizeof(*(x)) == 1, *(x), bad_get_le())
132
133#define GET_LE(x)							\
134	GLE(x, 64, GLE(x, 32, GLE(x, 16, LAST_GLE(x))))
135
136#define PLE(x, val, bits, ifnot)					\
137	__builtin_choose_expr(						\
138		(sizeof(*(x)) == bits/8),				\
139		put_unaligned_le##bits((val), (x)), ifnot)
140
141extern void bad_put_le(void);
142#define LAST_PLE(x, val)						\
143	__builtin_choose_expr(sizeof(*(x)) == 1, *(x) = (val), bad_put_le())
144
145#define PUT_LE(x, val)					\
146	PLE(x, val, 64, PLE(x, val, 32, PLE(x, val, 16, LAST_PLE(x, val))))
147
148
149#define NSYMS ARRAY_SIZE(required_syms)
150
151#define BITSFUNC3(name, bits, suffix) name##bits##suffix
152#define BITSFUNC2(name, bits, suffix) BITSFUNC3(name, bits, suffix)
153#define BITSFUNC(name) BITSFUNC2(name, ELF_BITS, )
154
155#define INT_BITS BITSFUNC2(int, ELF_BITS, _t)
156
157#define ELF_BITS_XFORM2(bits, x) Elf##bits##_##x
158#define ELF_BITS_XFORM(bits, x) ELF_BITS_XFORM2(bits, x)
159#define ELF(x) ELF_BITS_XFORM(ELF_BITS, x)
160
161#define ELF_BITS 64
162#include "vdso2c.h"
163#undef ELF_BITS
164
165#define ELF_BITS 32
166#include "vdso2c.h"
167#undef ELF_BITS
168
169static void go(void *raw_addr, size_t raw_len,
170	       void *stripped_addr, size_t stripped_len,
171	       FILE *outfile, const char *name)
172{
173	Elf64_Ehdr *hdr = (Elf64_Ehdr *)raw_addr;
174
175	if (hdr->e_ident[EI_CLASS] == ELFCLASS64) {
176		go64(raw_addr, raw_len, stripped_addr, stripped_len,
177		     outfile, name);
178	} else if (hdr->e_ident[EI_CLASS] == ELFCLASS32) {
179		go32(raw_addr, raw_len, stripped_addr, stripped_len,
180		     outfile, name);
181	} else {
182		fail("unknown ELF class\n");
183	}
184}
185
186static void map_input(const char *name, void **addr, size_t *len, int prot)
187{
188	off_t tmp_len;
189
190	int fd = open(name, O_RDONLY);
191	if (fd == -1)
192		err(1, "open(%s)", name);
193
194	tmp_len = lseek(fd, 0, SEEK_END);
195	if (tmp_len == (off_t)-1)
196		err(1, "lseek");
197	*len = (size_t)tmp_len;
198
199	*addr = mmap(NULL, tmp_len, prot, MAP_PRIVATE, fd, 0);
200	if (*addr == MAP_FAILED)
201		err(1, "mmap");
202
203	close(fd);
204}
205
206int main(int argc, char **argv)
207{
208	size_t raw_len, stripped_len;
209	void *raw_addr, *stripped_addr;
210	FILE *outfile;
211	char *name, *tmp;
212	int namelen;
213
214	if (argc != 4) {
215		printf("Usage: vdso2c RAW_INPUT STRIPPED_INPUT OUTPUT\n");
216		return 1;
217	}
218
219	/*
220	 * Figure out the struct name.  If we're writing to a .so file,
221	 * generate raw output instead.
222	 */
223	name = strdup(argv[3]);
224	namelen = strlen(name);
225	if (namelen >= 3 && !strcmp(name + namelen - 3, ".so")) {
226		name = NULL;
227	} else {
228		tmp = strrchr(name, '/');
229		if (tmp)
230			name = tmp + 1;
231		tmp = strchr(name, '.');
232		if (tmp)
233			*tmp = '\0';
234		for (tmp = name; *tmp; tmp++)
235			if (*tmp == '-')
236				*tmp = '_';
237	}
238
239	map_input(argv[1], &raw_addr, &raw_len, PROT_READ);
240	map_input(argv[2], &stripped_addr, &stripped_len, PROT_READ);
241
242	outfilename = argv[3];
243	outfile = fopen(outfilename, "w");
244	if (!outfile)
245		err(1, "fopen(%s)", outfilename);
246
247	go(raw_addr, raw_len, stripped_addr, stripped_len, outfile, name);
248
249	munmap(raw_addr, raw_len);
250	munmap(stripped_addr, stripped_len);
251	fclose(outfile);
252
253	return 0;
254}
255