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 keep a section table for a few reasons:
15 *
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
21 *
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.
24 *
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.
28 *
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
34 * that.
35 */
36
37/*
38 * Copyright (c) 2017 Oracle and/or its affiliates. All rights reserved.
39 */
40
41#include <inttypes.h>
42#include <stdint.h>
43#include <unistd.h>
44#include <stdarg.h>
45#include <stdlib.h>
46#include <stdio.h>
47#include <string.h>
48#include <fcntl.h>
49#include <err.h>
50
51#include <sys/mman.h>
52#include <sys/types.h>
53#include <tools/be_byteshift.h>
54
55#include <linux/elf.h>
56#include <linux/types.h>
57#include <linux/kernel.h>
58
59const char *outfilename;
60
61/* Symbols that we need in vdso2c. */
62enum {
63	sym_vvar_start,
64	sym_VDSO_FAKE_SECTION_TABLE_START,
65	sym_VDSO_FAKE_SECTION_TABLE_END,
66};
67
68struct vdso_sym {
69	const char *name;
70	int export;
71};
72
73struct 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
77	},
78	[sym_VDSO_FAKE_SECTION_TABLE_END] = {
79		"VDSO_FAKE_SECTION_TABLE_END", 0
80	},
81};
82
83__attribute__((format(printf, 1, 2))) __attribute__((noreturn))
84static void fail(const char *format, ...)
85{
86	va_list ap;
87
88	va_start(ap, format);
89	fprintf(stderr, "Error: ");
90	vfprintf(stderr, format, ap);
91	if (outfilename)
92		unlink(outfilename);
93	exit(1);
94	va_end(ap);
95}
96
97/*
98 * Evil macros for big-endian reads and writes
99 */
100#define GBE(x, bits, ifnot)						\
101	__builtin_choose_expr(						\
102		(sizeof(*(x)) == bits/8),				\
103		(__typeof__(*(x)))get_unaligned_be##bits(x), ifnot)
104
105#define LAST_GBE(x)							\
106	__builtin_choose_expr(sizeof(*(x)) == 1, *(x), (void)(0))
107
108#define GET_BE(x)							\
109	GBE(x, 64, GBE(x, 32, GBE(x, 16, LAST_GBE(x))))
110
111#define PBE(x, val, bits, ifnot)					\
112	__builtin_choose_expr(						\
113		(sizeof(*(x)) == bits/8),				\
114		put_unaligned_be##bits((val), (x)), ifnot)
115
116#define LAST_PBE(x, val)						\
117	__builtin_choose_expr(sizeof(*(x)) == 1, *(x) = (val), (void)(0))
118
119#define PUT_BE(x, val)					\
120	PBE(x, val, 64, PBE(x, val, 32, PBE(x, val, 16, LAST_PBE(x, val))))
121
122#define NSYMS ARRAY_SIZE(required_syms)
123
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, )
127
128#define INT_BITS BITSFUNC2(int, ELF_BITS, _t)
129
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)
133
134#define ELF_BITS 64
135#include "vdso2c.h"
136#undef ELF_BITS
137
138#define ELF_BITS 32
139#include "vdso2c.h"
140#undef ELF_BITS
141
142static void go(void *raw_addr, size_t raw_len,
143	       void *stripped_addr, size_t stripped_len,
144	       FILE *outfile, const char *name)
145{
146	Elf64_Ehdr *hdr = (Elf64_Ehdr *)raw_addr;
147
148	if (hdr->e_ident[EI_CLASS] == ELFCLASS64) {
149		go64(raw_addr, raw_len, stripped_addr, stripped_len,
150		     outfile, name);
151	} else if (hdr->e_ident[EI_CLASS] == ELFCLASS32) {
152		go32(raw_addr, raw_len, stripped_addr, stripped_len,
153		     outfile, name);
154	} else {
155		fail("unknown ELF class\n");
156	}
157}
158
159static void map_input(const char *name, void **addr, size_t *len, int prot)
160{
161	off_t tmp_len;
162
163	int fd = open(name, O_RDONLY);
164
165	if (fd == -1)
166		err(1, "%s", name);
167
168	tmp_len = lseek(fd, 0, SEEK_END);
169	if (tmp_len == (off_t)-1)
170		err(1, "lseek");
171	*len = (size_t)tmp_len;
172
173	*addr = mmap(NULL, tmp_len, prot, MAP_PRIVATE, fd, 0);
174	if (*addr == MAP_FAILED)
175		err(1, "mmap");
176
177	close(fd);
178}
179
180int main(int argc, char **argv)
181{
182	size_t raw_len, stripped_len;
183	void *raw_addr, *stripped_addr;
184	FILE *outfile;
185	char *name, *tmp;
186	int namelen;
187
188	if (argc != 4) {
189		printf("Usage: vdso2c RAW_INPUT STRIPPED_INPUT OUTPUT\n");
190		return 1;
191	}
192
193	/*
194	 * Figure out the struct name.  If we're writing to a .so file,
195	 * generate raw output insted.
196	 */
197	name = strdup(argv[3]);
198	namelen = strlen(name);
199	if (namelen >= 3 && !strcmp(name + namelen - 3, ".so")) {
200		name = NULL;
201	} else {
202		tmp = strrchr(name, '/');
203		if (tmp)
204			name = tmp + 1;
205		tmp = strchr(name, '.');
206		if (tmp)
207			*tmp = '\0';
208		for (tmp = name; *tmp; tmp++)
209			if (*tmp == '-')
210				*tmp = '_';
211	}
212
213	map_input(argv[1], &raw_addr, &raw_len, PROT_READ);
214	map_input(argv[2], &stripped_addr, &stripped_len, PROT_READ);
215
216	outfilename = argv[3];
217	outfile = fopen(outfilename, "w");
218	if (!outfile)
219		err(1, "%s", argv[2]);
220
221	go(raw_addr, raw_len, stripped_addr, stripped_len, outfile, name);
222
223	munmap(raw_addr, raw_len);
224	munmap(stripped_addr, stripped_len);
225	fclose(outfile);
226
227	return 0;
228}
229