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 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	sym_vread_tick,
 67	sym_vread_tick_patch_start,
 68	sym_vread_tick_patch_end
 69};
 70
 71struct vdso_sym {
 72	const char *name;
 73	int export;
 74};
 75
 76struct vdso_sym required_syms[] = {
 77	[sym_vvar_start] = {"vvar_start", 1},
 78	[sym_VDSO_FAKE_SECTION_TABLE_START] = {
 79		"VDSO_FAKE_SECTION_TABLE_START", 0
 80	},
 81	[sym_VDSO_FAKE_SECTION_TABLE_END] = {
 82		"VDSO_FAKE_SECTION_TABLE_END", 0
 83	},
 84	[sym_vread_tick] = {"vread_tick", 1},
 85	[sym_vread_tick_patch_start] = {"vread_tick_patch_start", 1},
 86	[sym_vread_tick_patch_end] = {"vread_tick_patch_end", 1}
 87};
 88
 89__attribute__((format(printf, 1, 2))) __attribute__((noreturn))
 90static void fail(const char *format, ...)
 91{
 92	va_list ap;
 93
 94	va_start(ap, format);
 95	fprintf(stderr, "Error: ");
 96	vfprintf(stderr, format, ap);
 97	if (outfilename)
 98		unlink(outfilename);
 99	exit(1);
100	va_end(ap);
101}
102
103/*
104 * Evil macros for big-endian reads and writes
105 */
106#define GBE(x, bits, ifnot)						\
107	__builtin_choose_expr(						\
108		(sizeof(*(x)) == bits/8),				\
109		(__typeof__(*(x)))get_unaligned_be##bits(x), ifnot)
110
111#define LAST_GBE(x)							\
112	__builtin_choose_expr(sizeof(*(x)) == 1, *(x), (void)(0))
113
114#define GET_BE(x)							\
115	GBE(x, 64, GBE(x, 32, GBE(x, 16, LAST_GBE(x))))
116
117#define PBE(x, val, bits, ifnot)					\
118	__builtin_choose_expr(						\
119		(sizeof(*(x)) == bits/8),				\
120		put_unaligned_be##bits((val), (x)), ifnot)
121
122#define LAST_PBE(x, val)						\
123	__builtin_choose_expr(sizeof(*(x)) == 1, *(x) = (val), (void)(0))
124
125#define PUT_BE(x, val)					\
126	PBE(x, val, 64, PBE(x, val, 32, PBE(x, val, 16, LAST_PBE(x, val))))
127
128#define NSYMS ARRAY_SIZE(required_syms)
129
130#define BITSFUNC3(name, bits, suffix) name##bits##suffix
131#define BITSFUNC2(name, bits, suffix) BITSFUNC3(name, bits, suffix)
132#define BITSFUNC(name) BITSFUNC2(name, ELF_BITS, )
133
134#define INT_BITS BITSFUNC2(int, ELF_BITS, _t)
135
136#define ELF_BITS_XFORM2(bits, x) Elf##bits##_##x
137#define ELF_BITS_XFORM(bits, x) ELF_BITS_XFORM2(bits, x)
138#define ELF(x) ELF_BITS_XFORM(ELF_BITS, x)
139
140#define ELF_BITS 64
141#include "vdso2c.h"
142#undef ELF_BITS
143
144#define ELF_BITS 32
145#include "vdso2c.h"
146#undef ELF_BITS
147
148static void go(void *raw_addr, size_t raw_len,
149	       void *stripped_addr, size_t stripped_len,
150	       FILE *outfile, const char *name)
151{
152	Elf64_Ehdr *hdr = (Elf64_Ehdr *)raw_addr;
153
154	if (hdr->e_ident[EI_CLASS] == ELFCLASS64) {
155		go64(raw_addr, raw_len, stripped_addr, stripped_len,
156		     outfile, name);
157	} else if (hdr->e_ident[EI_CLASS] == ELFCLASS32) {
158		go32(raw_addr, raw_len, stripped_addr, stripped_len,
159		     outfile, name);
160	} else {
161		fail("unknown ELF class\n");
162	}
163}
164
165static void map_input(const char *name, void **addr, size_t *len, int prot)
166{
167	off_t tmp_len;
168
169	int fd = open(name, O_RDONLY);
170
171	if (fd == -1)
172		err(1, "%s", name);
173
174	tmp_len = lseek(fd, 0, SEEK_END);
175	if (tmp_len == (off_t)-1)
176		err(1, "lseek");
177	*len = (size_t)tmp_len;
178
179	*addr = mmap(NULL, tmp_len, prot, MAP_PRIVATE, fd, 0);
180	if (*addr == MAP_FAILED)
181		err(1, "mmap");
182
183	close(fd);
184}
185
186int main(int argc, char **argv)
187{
188	size_t raw_len, stripped_len;
189	void *raw_addr, *stripped_addr;
190	FILE *outfile;
191	char *name, *tmp;
192	int namelen;
193
194	if (argc != 4) {
195		printf("Usage: vdso2c RAW_INPUT STRIPPED_INPUT OUTPUT\n");
196		return 1;
197	}
198
199	/*
200	 * Figure out the struct name.  If we're writing to a .so file,
201	 * generate raw output insted.
202	 */
203	name = strdup(argv[3]);
204	namelen = strlen(name);
205	if (namelen >= 3 && !strcmp(name + namelen - 3, ".so")) {
206		name = NULL;
207	} else {
208		tmp = strrchr(name, '/');
209		if (tmp)
210			name = tmp + 1;
211		tmp = strchr(name, '.');
212		if (tmp)
213			*tmp = '\0';
214		for (tmp = name; *tmp; tmp++)
215			if (*tmp == '-')
216				*tmp = '_';
217	}
218
219	map_input(argv[1], &raw_addr, &raw_len, PROT_READ);
220	map_input(argv[2], &stripped_addr, &stripped_len, PROT_READ);
221
222	outfilename = argv[3];
223	outfile = fopen(outfilename, "w");
224	if (!outfile)
225		err(1, "%s", argv[2]);
226
227	go(raw_addr, raw_len, stripped_addr, stripped_len, outfile, name);
228
229	munmap(raw_addr, raw_len);
230	munmap(stripped_addr, stripped_len);
231	fclose(outfile);
232
233	return 0;
234}