xref: /openbmc/linux/scripts/recordmcount.c (revision 565d76cb)
1 /*
2  * recordmcount.c: construct a table of the locations of calls to 'mcount'
3  * so that ftrace can find them quickly.
4  * Copyright 2009 John F. Reiser <jreiser@BitWagon.com>.  All rights reserved.
5  * Licensed under the GNU General Public License, version 2 (GPLv2).
6  *
7  * Restructured to fit Linux format, as well as other updates:
8  *  Copyright 2010 Steven Rostedt <srostedt@redhat.com>, Red Hat Inc.
9  */
10 
11 /*
12  * Strategy: alter the .o file in-place.
13  *
14  * Append a new STRTAB that has the new section names, followed by a new array
15  * ElfXX_Shdr[] that has the new section headers, followed by the section
16  * contents for __mcount_loc and its relocations.  The old shstrtab strings,
17  * and the old ElfXX_Shdr[] array, remain as "garbage" (commonly, a couple
18  * kilobytes.)  Subsequent processing by /bin/ld (or the kernel module loader)
19  * will ignore the garbage regions, because they are not designated by the
20  * new .e_shoff nor the new ElfXX_Shdr[].  [In order to remove the garbage,
21  * then use "ld -r" to create a new file that omits the garbage.]
22  */
23 
24 #include <sys/types.h>
25 #include <sys/mman.h>
26 #include <sys/stat.h>
27 #include <elf.h>
28 #include <fcntl.h>
29 #include <setjmp.h>
30 #include <stdio.h>
31 #include <stdlib.h>
32 #include <string.h>
33 #include <unistd.h>
34 
35 static int fd_map;	/* File descriptor for file being modified. */
36 static int mmap_failed; /* Boolean flag. */
37 static void *ehdr_curr; /* current ElfXX_Ehdr *  for resource cleanup */
38 static char gpfx;	/* prefix for global symbol name (sometimes '_') */
39 static struct stat sb;	/* Remember .st_size, etc. */
40 static jmp_buf jmpenv;	/* setjmp/longjmp per-file error escape */
41 static const char *altmcount;	/* alternate mcount symbol name */
42 
43 /* setjmp() return values */
44 enum {
45 	SJ_SETJMP = 0,  /* hardwired first return */
46 	SJ_FAIL,
47 	SJ_SUCCEED
48 };
49 
50 /* Per-file resource cleanup when multiple files. */
51 static void
52 cleanup(void)
53 {
54 	if (!mmap_failed)
55 		munmap(ehdr_curr, sb.st_size);
56 	else
57 		free(ehdr_curr);
58 	close(fd_map);
59 }
60 
61 static void __attribute__((noreturn))
62 fail_file(void)
63 {
64 	cleanup();
65 	longjmp(jmpenv, SJ_FAIL);
66 }
67 
68 static void __attribute__((noreturn))
69 succeed_file(void)
70 {
71 	cleanup();
72 	longjmp(jmpenv, SJ_SUCCEED);
73 }
74 
75 /* ulseek, uread, ...:  Check return value for errors. */
76 
77 static off_t
78 ulseek(int const fd, off_t const offset, int const whence)
79 {
80 	off_t const w = lseek(fd, offset, whence);
81 	if ((off_t)-1 == w) {
82 		perror("lseek");
83 		fail_file();
84 	}
85 	return w;
86 }
87 
88 static size_t
89 uread(int const fd, void *const buf, size_t const count)
90 {
91 	size_t const n = read(fd, buf, count);
92 	if (n != count) {
93 		perror("read");
94 		fail_file();
95 	}
96 	return n;
97 }
98 
99 static size_t
100 uwrite(int const fd, void const *const buf, size_t const count)
101 {
102 	size_t const n = write(fd, buf, count);
103 	if (n != count) {
104 		perror("write");
105 		fail_file();
106 	}
107 	return n;
108 }
109 
110 static void *
111 umalloc(size_t size)
112 {
113 	void *const addr = malloc(size);
114 	if (0 == addr) {
115 		fprintf(stderr, "malloc failed: %zu bytes\n", size);
116 		fail_file();
117 	}
118 	return addr;
119 }
120 
121 /*
122  * Get the whole file as a programming convenience in order to avoid
123  * malloc+lseek+read+free of many pieces.  If successful, then mmap
124  * avoids copying unused pieces; else just read the whole file.
125  * Open for both read and write; new info will be appended to the file.
126  * Use MAP_PRIVATE so that a few changes to the in-memory ElfXX_Ehdr
127  * do not propagate to the file until an explicit overwrite at the last.
128  * This preserves most aspects of consistency (all except .st_size)
129  * for simultaneous readers of the file while we are appending to it.
130  * However, multiple writers still are bad.  We choose not to use
131  * locking because it is expensive and the use case of kernel build
132  * makes multiple writers unlikely.
133  */
134 static void *mmap_file(char const *fname)
135 {
136 	void *addr;
137 
138 	fd_map = open(fname, O_RDWR);
139 	if (0 > fd_map || 0 > fstat(fd_map, &sb)) {
140 		perror(fname);
141 		fail_file();
142 	}
143 	if (!S_ISREG(sb.st_mode)) {
144 		fprintf(stderr, "not a regular file: %s\n", fname);
145 		fail_file();
146 	}
147 	addr = mmap(0, sb.st_size, PROT_READ|PROT_WRITE, MAP_PRIVATE,
148 		    fd_map, 0);
149 	mmap_failed = 0;
150 	if (MAP_FAILED == addr) {
151 		mmap_failed = 1;
152 		addr = umalloc(sb.st_size);
153 		uread(fd_map, addr, sb.st_size);
154 	}
155 	return addr;
156 }
157 
158 /* w8rev, w8nat, ...: Handle endianness. */
159 
160 static uint64_t w8rev(uint64_t const x)
161 {
162 	return   ((0xff & (x >> (0 * 8))) << (7 * 8))
163 	       | ((0xff & (x >> (1 * 8))) << (6 * 8))
164 	       | ((0xff & (x >> (2 * 8))) << (5 * 8))
165 	       | ((0xff & (x >> (3 * 8))) << (4 * 8))
166 	       | ((0xff & (x >> (4 * 8))) << (3 * 8))
167 	       | ((0xff & (x >> (5 * 8))) << (2 * 8))
168 	       | ((0xff & (x >> (6 * 8))) << (1 * 8))
169 	       | ((0xff & (x >> (7 * 8))) << (0 * 8));
170 }
171 
172 static uint32_t w4rev(uint32_t const x)
173 {
174 	return   ((0xff & (x >> (0 * 8))) << (3 * 8))
175 	       | ((0xff & (x >> (1 * 8))) << (2 * 8))
176 	       | ((0xff & (x >> (2 * 8))) << (1 * 8))
177 	       | ((0xff & (x >> (3 * 8))) << (0 * 8));
178 }
179 
180 static uint32_t w2rev(uint16_t const x)
181 {
182 	return   ((0xff & (x >> (0 * 8))) << (1 * 8))
183 	       | ((0xff & (x >> (1 * 8))) << (0 * 8));
184 }
185 
186 static uint64_t w8nat(uint64_t const x)
187 {
188 	return x;
189 }
190 
191 static uint32_t w4nat(uint32_t const x)
192 {
193 	return x;
194 }
195 
196 static uint32_t w2nat(uint16_t const x)
197 {
198 	return x;
199 }
200 
201 static uint64_t (*w8)(uint64_t);
202 static uint32_t (*w)(uint32_t);
203 static uint32_t (*w2)(uint16_t);
204 
205 /* Names of the sections that could contain calls to mcount. */
206 static int
207 is_mcounted_section_name(char const *const txtname)
208 {
209 	return 0 == strcmp(".text",           txtname) ||
210 		0 == strcmp(".ref.text",      txtname) ||
211 		0 == strcmp(".sched.text",    txtname) ||
212 		0 == strcmp(".spinlock.text", txtname) ||
213 		0 == strcmp(".irqentry.text", txtname) ||
214 		0 == strcmp(".text.unlikely", txtname);
215 }
216 
217 /* 32 bit and 64 bit are very similar */
218 #include "recordmcount.h"
219 #define RECORD_MCOUNT_64
220 #include "recordmcount.h"
221 
222 /* 64-bit EM_MIPS has weird ELF64_Rela.r_info.
223  * http://techpubs.sgi.com/library/manuals/4000/007-4658-001/pdf/007-4658-001.pdf
224  * We interpret Table 29 Relocation Operation (Elf64_Rel, Elf64_Rela) [p.40]
225  * to imply the order of the members; the spec does not say so.
226  *	typedef unsigned char Elf64_Byte;
227  * fails on MIPS64 because their <elf.h> already has it!
228  */
229 
230 typedef uint8_t myElf64_Byte;		/* Type for a 8-bit quantity.  */
231 
232 union mips_r_info {
233 	Elf64_Xword r_info;
234 	struct {
235 		Elf64_Word r_sym;		/* Symbol index.  */
236 		myElf64_Byte r_ssym;		/* Special symbol.  */
237 		myElf64_Byte r_type3;		/* Third relocation.  */
238 		myElf64_Byte r_type2;		/* Second relocation.  */
239 		myElf64_Byte r_type;		/* First relocation.  */
240 	} r_mips;
241 };
242 
243 static uint64_t MIPS64_r_sym(Elf64_Rel const *rp)
244 {
245 	return w(((union mips_r_info){ .r_info = rp->r_info }).r_mips.r_sym);
246 }
247 
248 static void MIPS64_r_info(Elf64_Rel *const rp, unsigned sym, unsigned type)
249 {
250 	rp->r_info = ((union mips_r_info){
251 		.r_mips = { .r_sym = w(sym), .r_type = type }
252 	}).r_info;
253 }
254 
255 static void
256 do_file(char const *const fname)
257 {
258 	Elf32_Ehdr *const ehdr = mmap_file(fname);
259 	unsigned int reltype = 0;
260 
261 	ehdr_curr = ehdr;
262 	w = w4nat;
263 	w2 = w2nat;
264 	w8 = w8nat;
265 	switch (ehdr->e_ident[EI_DATA]) {
266 		static unsigned int const endian = 1;
267 	default: {
268 		fprintf(stderr, "unrecognized ELF data encoding %d: %s\n",
269 			ehdr->e_ident[EI_DATA], fname);
270 		fail_file();
271 	} break;
272 	case ELFDATA2LSB: {
273 		if (1 != *(unsigned char const *)&endian) {
274 			/* main() is big endian, file.o is little endian. */
275 			w = w4rev;
276 			w2 = w2rev;
277 			w8 = w8rev;
278 		}
279 	} break;
280 	case ELFDATA2MSB: {
281 		if (0 != *(unsigned char const *)&endian) {
282 			/* main() is little endian, file.o is big endian. */
283 			w = w4rev;
284 			w2 = w2rev;
285 			w8 = w8rev;
286 		}
287 	} break;
288 	}  /* end switch */
289 	if (0 != memcmp(ELFMAG, ehdr->e_ident, SELFMAG)
290 	||  ET_REL != w2(ehdr->e_type)
291 	||  EV_CURRENT != ehdr->e_ident[EI_VERSION]) {
292 		fprintf(stderr, "unrecognized ET_REL file %s\n", fname);
293 		fail_file();
294 	}
295 
296 	gpfx = 0;
297 	switch (w2(ehdr->e_machine)) {
298 	default: {
299 		fprintf(stderr, "unrecognized e_machine %d %s\n",
300 			w2(ehdr->e_machine), fname);
301 		fail_file();
302 	} break;
303 	case EM_386:	 reltype = R_386_32;                   break;
304 	case EM_ARM:	 reltype = R_ARM_ABS32;
305 			 altmcount = "__gnu_mcount_nc";
306 			 break;
307 	case EM_IA_64:	 reltype = R_IA64_IMM64;   gpfx = '_'; break;
308 	case EM_MIPS:	 /* reltype: e_class    */ gpfx = '_'; break;
309 	case EM_PPC:	 reltype = R_PPC_ADDR32;   gpfx = '_'; break;
310 	case EM_PPC64:	 reltype = R_PPC64_ADDR64; gpfx = '_'; break;
311 	case EM_S390:    /* reltype: e_class    */ gpfx = '_'; break;
312 	case EM_SH:	 reltype = R_SH_DIR32;                 break;
313 	case EM_SPARCV9: reltype = R_SPARC_64;     gpfx = '_'; break;
314 	case EM_X86_64:	 reltype = R_X86_64_64;                break;
315 	}  /* end switch */
316 
317 	switch (ehdr->e_ident[EI_CLASS]) {
318 	default: {
319 		fprintf(stderr, "unrecognized ELF class %d %s\n",
320 			ehdr->e_ident[EI_CLASS], fname);
321 		fail_file();
322 	} break;
323 	case ELFCLASS32: {
324 		if (sizeof(Elf32_Ehdr) != w2(ehdr->e_ehsize)
325 		||  sizeof(Elf32_Shdr) != w2(ehdr->e_shentsize)) {
326 			fprintf(stderr,
327 				"unrecognized ET_REL file: %s\n", fname);
328 			fail_file();
329 		}
330 		if (EM_S390 == w2(ehdr->e_machine))
331 			reltype = R_390_32;
332 		if (EM_MIPS == w2(ehdr->e_machine)) {
333 			reltype = R_MIPS_32;
334 			is_fake_mcount32 = MIPS32_is_fake_mcount;
335 		}
336 		do32(ehdr, fname, reltype);
337 	} break;
338 	case ELFCLASS64: {
339 		Elf64_Ehdr *const ghdr = (Elf64_Ehdr *)ehdr;
340 		if (sizeof(Elf64_Ehdr) != w2(ghdr->e_ehsize)
341 		||  sizeof(Elf64_Shdr) != w2(ghdr->e_shentsize)) {
342 			fprintf(stderr,
343 				"unrecognized ET_REL file: %s\n", fname);
344 			fail_file();
345 		}
346 		if (EM_S390 == w2(ghdr->e_machine))
347 			reltype = R_390_64;
348 		if (EM_MIPS == w2(ghdr->e_machine)) {
349 			reltype = R_MIPS_64;
350 			Elf64_r_sym = MIPS64_r_sym;
351 			Elf64_r_info = MIPS64_r_info;
352 			is_fake_mcount64 = MIPS64_is_fake_mcount;
353 		}
354 		do64(ghdr, fname, reltype);
355 	} break;
356 	}  /* end switch */
357 
358 	cleanup();
359 }
360 
361 int
362 main(int argc, char const *argv[])
363 {
364 	const char ftrace[] = "/ftrace.o";
365 	int ftrace_size = sizeof(ftrace) - 1;
366 	int n_error = 0;  /* gcc-4.3.0 false positive complaint */
367 
368 	if (argc <= 1) {
369 		fprintf(stderr, "usage: recordmcount file.o...\n");
370 		return 0;
371 	}
372 
373 	/* Process each file in turn, allowing deep failure. */
374 	for (--argc, ++argv; 0 < argc; --argc, ++argv) {
375 		int const sjval = setjmp(jmpenv);
376 		int len;
377 
378 		/*
379 		 * The file kernel/trace/ftrace.o references the mcount
380 		 * function but does not call it. Since ftrace.o should
381 		 * not be traced anyway, we just skip it.
382 		 */
383 		len = strlen(argv[0]);
384 		if (len >= ftrace_size &&
385 		    strcmp(argv[0] + (len - ftrace_size), ftrace) == 0)
386 			continue;
387 
388 		switch (sjval) {
389 		default: {
390 			fprintf(stderr, "internal error: %s\n", argv[0]);
391 			exit(1);
392 		} break;
393 		case SJ_SETJMP: {  /* normal sequence */
394 			/* Avoid problems if early cleanup() */
395 			fd_map = -1;
396 			ehdr_curr = NULL;
397 			mmap_failed = 1;
398 			do_file(argv[0]);
399 		} break;
400 		case SJ_FAIL: {  /* error in do_file or below */
401 			++n_error;
402 		} break;
403 		case SJ_SUCCEED: {  /* premature success */
404 			/* do nothing */
405 		} break;
406 		}  /* end switch */
407 	}
408 	return !!n_error;
409 }
410 
411 
412