xref: /openbmc/linux/scripts/recordmcount.c (revision 4800cd83)
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(".sched.text",    txtname) ||
211 		0 == strcmp(".spinlock.text", txtname) ||
212 		0 == strcmp(".irqentry.text", txtname) ||
213 		0 == strcmp(".text.unlikely", txtname);
214 }
215 
216 /* 32 bit and 64 bit are very similar */
217 #include "recordmcount.h"
218 #define RECORD_MCOUNT_64
219 #include "recordmcount.h"
220 
221 /* 64-bit EM_MIPS has weird ELF64_Rela.r_info.
222  * http://techpubs.sgi.com/library/manuals/4000/007-4658-001/pdf/007-4658-001.pdf
223  * We interpret Table 29 Relocation Operation (Elf64_Rel, Elf64_Rela) [p.40]
224  * to imply the order of the members; the spec does not say so.
225  *	typedef unsigned char Elf64_Byte;
226  * fails on MIPS64 because their <elf.h> already has it!
227  */
228 
229 typedef uint8_t myElf64_Byte;		/* Type for a 8-bit quantity.  */
230 
231 union mips_r_info {
232 	Elf64_Xword r_info;
233 	struct {
234 		Elf64_Word r_sym;		/* Symbol index.  */
235 		myElf64_Byte r_ssym;		/* Special symbol.  */
236 		myElf64_Byte r_type3;		/* Third relocation.  */
237 		myElf64_Byte r_type2;		/* Second relocation.  */
238 		myElf64_Byte r_type;		/* First relocation.  */
239 	} r_mips;
240 };
241 
242 static uint64_t MIPS64_r_sym(Elf64_Rel const *rp)
243 {
244 	return w(((union mips_r_info){ .r_info = rp->r_info }).r_mips.r_sym);
245 }
246 
247 static void MIPS64_r_info(Elf64_Rel *const rp, unsigned sym, unsigned type)
248 {
249 	rp->r_info = ((union mips_r_info){
250 		.r_mips = { .r_sym = w(sym), .r_type = type }
251 	}).r_info;
252 }
253 
254 static void
255 do_file(char const *const fname)
256 {
257 	Elf32_Ehdr *const ehdr = mmap_file(fname);
258 	unsigned int reltype = 0;
259 
260 	ehdr_curr = ehdr;
261 	w = w4nat;
262 	w2 = w2nat;
263 	w8 = w8nat;
264 	switch (ehdr->e_ident[EI_DATA]) {
265 		static unsigned int const endian = 1;
266 	default: {
267 		fprintf(stderr, "unrecognized ELF data encoding %d: %s\n",
268 			ehdr->e_ident[EI_DATA], fname);
269 		fail_file();
270 	} break;
271 	case ELFDATA2LSB: {
272 		if (1 != *(unsigned char const *)&endian) {
273 			/* main() is big endian, file.o is little endian. */
274 			w = w4rev;
275 			w2 = w2rev;
276 			w8 = w8rev;
277 		}
278 	} break;
279 	case ELFDATA2MSB: {
280 		if (0 != *(unsigned char const *)&endian) {
281 			/* main() is little endian, file.o is big endian. */
282 			w = w4rev;
283 			w2 = w2rev;
284 			w8 = w8rev;
285 		}
286 	} break;
287 	}  /* end switch */
288 	if (0 != memcmp(ELFMAG, ehdr->e_ident, SELFMAG)
289 	||  ET_REL != w2(ehdr->e_type)
290 	||  EV_CURRENT != ehdr->e_ident[EI_VERSION]) {
291 		fprintf(stderr, "unrecognized ET_REL file %s\n", fname);
292 		fail_file();
293 	}
294 
295 	gpfx = 0;
296 	switch (w2(ehdr->e_machine)) {
297 	default: {
298 		fprintf(stderr, "unrecognized e_machine %d %s\n",
299 			w2(ehdr->e_machine), fname);
300 		fail_file();
301 	} break;
302 	case EM_386:	 reltype = R_386_32;                   break;
303 	case EM_ARM:	 reltype = R_ARM_ABS32;
304 			 altmcount = "__gnu_mcount_nc";
305 			 break;
306 	case EM_IA_64:	 reltype = R_IA64_IMM64;   gpfx = '_'; break;
307 	case EM_MIPS:	 /* reltype: e_class    */ gpfx = '_'; break;
308 	case EM_PPC:	 reltype = R_PPC_ADDR32;   gpfx = '_'; break;
309 	case EM_PPC64:	 reltype = R_PPC64_ADDR64; gpfx = '_'; break;
310 	case EM_S390:    /* reltype: e_class    */ gpfx = '_'; break;
311 	case EM_SH:	 reltype = R_SH_DIR32;                 break;
312 	case EM_SPARCV9: reltype = R_SPARC_64;     gpfx = '_'; break;
313 	case EM_X86_64:	 reltype = R_X86_64_64;                break;
314 	}  /* end switch */
315 
316 	switch (ehdr->e_ident[EI_CLASS]) {
317 	default: {
318 		fprintf(stderr, "unrecognized ELF class %d %s\n",
319 			ehdr->e_ident[EI_CLASS], fname);
320 		fail_file();
321 	} break;
322 	case ELFCLASS32: {
323 		if (sizeof(Elf32_Ehdr) != w2(ehdr->e_ehsize)
324 		||  sizeof(Elf32_Shdr) != w2(ehdr->e_shentsize)) {
325 			fprintf(stderr,
326 				"unrecognized ET_REL file: %s\n", fname);
327 			fail_file();
328 		}
329 		if (EM_S390 == w2(ehdr->e_machine))
330 			reltype = R_390_32;
331 		if (EM_MIPS == w2(ehdr->e_machine)) {
332 			reltype = R_MIPS_32;
333 			is_fake_mcount32 = MIPS32_is_fake_mcount;
334 		}
335 		do32(ehdr, fname, reltype);
336 	} break;
337 	case ELFCLASS64: {
338 		Elf64_Ehdr *const ghdr = (Elf64_Ehdr *)ehdr;
339 		if (sizeof(Elf64_Ehdr) != w2(ghdr->e_ehsize)
340 		||  sizeof(Elf64_Shdr) != w2(ghdr->e_shentsize)) {
341 			fprintf(stderr,
342 				"unrecognized ET_REL file: %s\n", fname);
343 			fail_file();
344 		}
345 		if (EM_S390 == w2(ghdr->e_machine))
346 			reltype = R_390_64;
347 		if (EM_MIPS == w2(ghdr->e_machine)) {
348 			reltype = R_MIPS_64;
349 			Elf64_r_sym = MIPS64_r_sym;
350 			Elf64_r_info = MIPS64_r_info;
351 			is_fake_mcount64 = MIPS64_is_fake_mcount;
352 		}
353 		do64(ghdr, fname, reltype);
354 	} break;
355 	}  /* end switch */
356 
357 	cleanup();
358 }
359 
360 int
361 main(int argc, char const *argv[])
362 {
363 	const char ftrace[] = "/ftrace.o";
364 	int ftrace_size = sizeof(ftrace) - 1;
365 	int n_error = 0;  /* gcc-4.3.0 false positive complaint */
366 
367 	if (argc <= 1) {
368 		fprintf(stderr, "usage: recordmcount file.o...\n");
369 		return 0;
370 	}
371 
372 	/* Process each file in turn, allowing deep failure. */
373 	for (--argc, ++argv; 0 < argc; --argc, ++argv) {
374 		int const sjval = setjmp(jmpenv);
375 		int len;
376 
377 		/*
378 		 * The file kernel/trace/ftrace.o references the mcount
379 		 * function but does not call it. Since ftrace.o should
380 		 * not be traced anyway, we just skip it.
381 		 */
382 		len = strlen(argv[0]);
383 		if (len >= ftrace_size &&
384 		    strcmp(argv[0] + (len - ftrace_size), ftrace) == 0)
385 			continue;
386 
387 		switch (sjval) {
388 		default: {
389 			fprintf(stderr, "internal error: %s\n", argv[0]);
390 			exit(1);
391 		} break;
392 		case SJ_SETJMP: {  /* normal sequence */
393 			/* Avoid problems if early cleanup() */
394 			fd_map = -1;
395 			ehdr_curr = NULL;
396 			mmap_failed = 1;
397 			do_file(argv[0]);
398 		} break;
399 		case SJ_FAIL: {  /* error in do_file or below */
400 			++n_error;
401 		} break;
402 		case SJ_SUCCEED: {  /* premature success */
403 			/* do nothing */
404 		} break;
405 		}  /* end switch */
406 	}
407 	return !!n_error;
408 }
409 
410 
411