Root/scripts/recordmcount.c

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 <getopt.h>
28#include <elf.h>
29#include <fcntl.h>
30#include <setjmp.h>
31#include <stdio.h>
32#include <stdlib.h>
33#include <string.h>
34#include <unistd.h>
35
36static int fd_map; /* File descriptor for file being modified. */
37static int mmap_failed; /* Boolean flag. */
38static void *ehdr_curr; /* current ElfXX_Ehdr * for resource cleanup */
39static char gpfx; /* prefix for global symbol name (sometimes '_') */
40static struct stat sb; /* Remember .st_size, etc. */
41static jmp_buf jmpenv; /* setjmp/longjmp per-file error escape */
42static const char *altmcount; /* alternate mcount symbol name */
43static int warn_on_notrace_sect; /* warn when section has mcount not being recorded */
44
45/* setjmp() return values */
46enum {
47    SJ_SETJMP = 0, /* hardwired first return */
48    SJ_FAIL,
49    SJ_SUCCEED
50};
51
52/* Per-file resource cleanup when multiple files. */
53static void
54cleanup(void)
55{
56    if (!mmap_failed)
57        munmap(ehdr_curr, sb.st_size);
58    else
59        free(ehdr_curr);
60    close(fd_map);
61}
62
63static void __attribute__((noreturn))
64fail_file(void)
65{
66    cleanup();
67    longjmp(jmpenv, SJ_FAIL);
68}
69
70static void __attribute__((noreturn))
71succeed_file(void)
72{
73    cleanup();
74    longjmp(jmpenv, SJ_SUCCEED);
75}
76
77/* ulseek, uread, ...: Check return value for errors. */
78
79static off_t
80ulseek(int const fd, off_t const offset, int const whence)
81{
82    off_t const w = lseek(fd, offset, whence);
83    if (w == (off_t)-1) {
84        perror("lseek");
85        fail_file();
86    }
87    return w;
88}
89
90static size_t
91uread(int const fd, void *const buf, size_t const count)
92{
93    size_t const n = read(fd, buf, count);
94    if (n != count) {
95        perror("read");
96        fail_file();
97    }
98    return n;
99}
100
101static size_t
102uwrite(int const fd, void const *const buf, size_t const count)
103{
104    size_t const n = write(fd, buf, count);
105    if (n != count) {
106        perror("write");
107        fail_file();
108    }
109    return n;
110}
111
112static void *
113umalloc(size_t size)
114{
115    void *const addr = malloc(size);
116    if (addr == 0) {
117        fprintf(stderr, "malloc failed: %zu bytes\n", size);
118        fail_file();
119    }
120    return addr;
121}
122
123static unsigned char ideal_nop5_x86_64[5] = { 0x0f, 0x1f, 0x44, 0x00, 0x00 };
124static unsigned char ideal_nop5_x86_32[5] = { 0x3e, 0x8d, 0x74, 0x26, 0x00 };
125static unsigned char *ideal_nop;
126
127static char rel_type_nop;
128
129static int (*make_nop)(void *map, size_t const offset);
130
131static int make_nop_x86(void *map, size_t const offset)
132{
133    uint32_t *ptr;
134    unsigned char *op;
135
136    /* Confirm we have 0xe8 0x0 0x0 0x0 0x0 */
137    ptr = map + offset;
138    if (*ptr != 0)
139        return -1;
140
141    op = map + offset - 1;
142    if (*op != 0xe8)
143        return -1;
144
145    /* convert to nop */
146    ulseek(fd_map, offset - 1, SEEK_SET);
147    uwrite(fd_map, ideal_nop, 5);
148    return 0;
149}
150
151/*
152 * Get the whole file as a programming convenience in order to avoid
153 * malloc+lseek+read+free of many pieces. If successful, then mmap
154 * avoids copying unused pieces; else just read the whole file.
155 * Open for both read and write; new info will be appended to the file.
156 * Use MAP_PRIVATE so that a few changes to the in-memory ElfXX_Ehdr
157 * do not propagate to the file until an explicit overwrite at the last.
158 * This preserves most aspects of consistency (all except .st_size)
159 * for simultaneous readers of the file while we are appending to it.
160 * However, multiple writers still are bad. We choose not to use
161 * locking because it is expensive and the use case of kernel build
162 * makes multiple writers unlikely.
163 */
164static void *mmap_file(char const *fname)
165{
166    void *addr;
167
168    fd_map = open(fname, O_RDWR);
169    if (fd_map < 0 || fstat(fd_map, &sb) < 0) {
170        perror(fname);
171        fail_file();
172    }
173    if (!S_ISREG(sb.st_mode)) {
174        fprintf(stderr, "not a regular file: %s\n", fname);
175        fail_file();
176    }
177    addr = mmap(0, sb.st_size, PROT_READ|PROT_WRITE, MAP_PRIVATE,
178            fd_map, 0);
179    mmap_failed = 0;
180    if (addr == MAP_FAILED) {
181        mmap_failed = 1;
182        addr = umalloc(sb.st_size);
183        uread(fd_map, addr, sb.st_size);
184    }
185    return addr;
186}
187
188/* w8rev, w8nat, ...: Handle endianness. */
189
190static uint64_t w8rev(uint64_t const x)
191{
192    return ((0xff & (x >> (0 * 8))) << (7 * 8))
193           | ((0xff & (x >> (1 * 8))) << (6 * 8))
194           | ((0xff & (x >> (2 * 8))) << (5 * 8))
195           | ((0xff & (x >> (3 * 8))) << (4 * 8))
196           | ((0xff & (x >> (4 * 8))) << (3 * 8))
197           | ((0xff & (x >> (5 * 8))) << (2 * 8))
198           | ((0xff & (x >> (6 * 8))) << (1 * 8))
199           | ((0xff & (x >> (7 * 8))) << (0 * 8));
200}
201
202static uint32_t w4rev(uint32_t const x)
203{
204    return ((0xff & (x >> (0 * 8))) << (3 * 8))
205           | ((0xff & (x >> (1 * 8))) << (2 * 8))
206           | ((0xff & (x >> (2 * 8))) << (1 * 8))
207           | ((0xff & (x >> (3 * 8))) << (0 * 8));
208}
209
210static uint32_t w2rev(uint16_t const x)
211{
212    return ((0xff & (x >> (0 * 8))) << (1 * 8))
213           | ((0xff & (x >> (1 * 8))) << (0 * 8));
214}
215
216static uint64_t w8nat(uint64_t const x)
217{
218    return x;
219}
220
221static uint32_t w4nat(uint32_t const x)
222{
223    return x;
224}
225
226static uint32_t w2nat(uint16_t const x)
227{
228    return x;
229}
230
231static uint64_t (*w8)(uint64_t);
232static uint32_t (*w)(uint32_t);
233static uint32_t (*w2)(uint16_t);
234
235/* Names of the sections that could contain calls to mcount. */
236static int
237is_mcounted_section_name(char const *const txtname)
238{
239    return strcmp(".text", txtname) == 0 ||
240        strcmp(".ref.text", txtname) == 0 ||
241        strcmp(".sched.text", txtname) == 0 ||
242        strcmp(".spinlock.text", txtname) == 0 ||
243        strcmp(".irqentry.text", txtname) == 0 ||
244        strcmp(".kprobes.text", txtname) == 0 ||
245        strcmp(".text.unlikely", txtname) == 0;
246}
247
248/* 32 bit and 64 bit are very similar */
249#include "recordmcount.h"
250#define RECORD_MCOUNT_64
251#include "recordmcount.h"
252
253/* 64-bit EM_MIPS has weird ELF64_Rela.r_info.
254 * http://techpubs.sgi.com/library/manuals/4000/007-4658-001/pdf/007-4658-001.pdf
255 * We interpret Table 29 Relocation Operation (Elf64_Rel, Elf64_Rela) [p.40]
256 * to imply the order of the members; the spec does not say so.
257 * typedef unsigned char Elf64_Byte;
258 * fails on MIPS64 because their <elf.h> already has it!
259 */
260
261typedef uint8_t myElf64_Byte; /* Type for a 8-bit quantity. */
262
263union mips_r_info {
264    Elf64_Xword r_info;
265    struct {
266        Elf64_Word r_sym; /* Symbol index. */
267        myElf64_Byte r_ssym; /* Special symbol. */
268        myElf64_Byte r_type3; /* Third relocation. */
269        myElf64_Byte r_type2; /* Second relocation. */
270        myElf64_Byte r_type; /* First relocation. */
271    } r_mips;
272};
273
274static uint64_t MIPS64_r_sym(Elf64_Rel const *rp)
275{
276    return w(((union mips_r_info){ .r_info = rp->r_info }).r_mips.r_sym);
277}
278
279static void MIPS64_r_info(Elf64_Rel *const rp, unsigned sym, unsigned type)
280{
281    rp->r_info = ((union mips_r_info){
282        .r_mips = { .r_sym = w(sym), .r_type = type }
283    }).r_info;
284}
285
286static void
287do_file(char const *const fname)
288{
289    Elf32_Ehdr *const ehdr = mmap_file(fname);
290    unsigned int reltype = 0;
291
292    ehdr_curr = ehdr;
293    w = w4nat;
294    w2 = w2nat;
295    w8 = w8nat;
296    switch (ehdr->e_ident[EI_DATA]) {
297        static unsigned int const endian = 1;
298    default:
299        fprintf(stderr, "unrecognized ELF data encoding %d: %s\n",
300            ehdr->e_ident[EI_DATA], fname);
301        fail_file();
302        break;
303    case ELFDATA2LSB:
304        if (*(unsigned char const *)&endian != 1) {
305            /* main() is big endian, file.o is little endian. */
306            w = w4rev;
307            w2 = w2rev;
308            w8 = w8rev;
309        }
310        break;
311    case ELFDATA2MSB:
312        if (*(unsigned char const *)&endian != 0) {
313            /* main() is little endian, file.o is big endian. */
314            w = w4rev;
315            w2 = w2rev;
316            w8 = w8rev;
317        }
318        break;
319    } /* end switch */
320    if (memcmp(ELFMAG, ehdr->e_ident, SELFMAG) != 0
321    || w2(ehdr->e_type) != ET_REL
322    || ehdr->e_ident[EI_VERSION] != EV_CURRENT) {
323        fprintf(stderr, "unrecognized ET_REL file %s\n", fname);
324        fail_file();
325    }
326
327    gpfx = 0;
328    switch (w2(ehdr->e_machine)) {
329    default:
330        fprintf(stderr, "unrecognized e_machine %d %s\n",
331            w2(ehdr->e_machine), fname);
332        fail_file();
333        break;
334    case EM_386:
335        reltype = R_386_32;
336        make_nop = make_nop_x86;
337        ideal_nop = ideal_nop5_x86_32;
338        mcount_adjust_32 = -1;
339        break;
340    case EM_ARM: reltype = R_ARM_ABS32;
341             altmcount = "__gnu_mcount_nc";
342             break;
343    case EM_IA_64: reltype = R_IA64_IMM64; gpfx = '_'; break;
344    case EM_MIPS: /* reltype: e_class */ gpfx = '_'; break;
345    case EM_PPC: reltype = R_PPC_ADDR32; gpfx = '_'; break;
346    case EM_PPC64: reltype = R_PPC64_ADDR64; gpfx = '_'; break;
347    case EM_S390: /* reltype: e_class */ gpfx = '_'; break;
348    case EM_SH: reltype = R_SH_DIR32; break;
349    case EM_SPARCV9: reltype = R_SPARC_64; gpfx = '_'; break;
350    case EM_X86_64:
351        make_nop = make_nop_x86;
352        ideal_nop = ideal_nop5_x86_64;
353        reltype = R_X86_64_64;
354        mcount_adjust_64 = -1;
355        break;
356    } /* end switch */
357
358    switch (ehdr->e_ident[EI_CLASS]) {
359    default:
360        fprintf(stderr, "unrecognized ELF class %d %s\n",
361            ehdr->e_ident[EI_CLASS], fname);
362        fail_file();
363        break;
364    case ELFCLASS32:
365        if (w2(ehdr->e_ehsize) != sizeof(Elf32_Ehdr)
366        || w2(ehdr->e_shentsize) != sizeof(Elf32_Shdr)) {
367            fprintf(stderr,
368                "unrecognized ET_REL file: %s\n", fname);
369            fail_file();
370        }
371        if (w2(ehdr->e_machine) == EM_S390) {
372            reltype = R_390_32;
373            mcount_adjust_32 = -4;
374        }
375        if (w2(ehdr->e_machine) == EM_MIPS) {
376            reltype = R_MIPS_32;
377            is_fake_mcount32 = MIPS32_is_fake_mcount;
378        }
379        do32(ehdr, fname, reltype);
380        break;
381    case ELFCLASS64: {
382        Elf64_Ehdr *const ghdr = (Elf64_Ehdr *)ehdr;
383        if (w2(ghdr->e_ehsize) != sizeof(Elf64_Ehdr)
384        || w2(ghdr->e_shentsize) != sizeof(Elf64_Shdr)) {
385            fprintf(stderr,
386                "unrecognized ET_REL file: %s\n", fname);
387            fail_file();
388        }
389        if (w2(ghdr->e_machine) == EM_S390) {
390            reltype = R_390_64;
391            mcount_adjust_64 = -8;
392        }
393        if (w2(ghdr->e_machine) == EM_MIPS) {
394            reltype = R_MIPS_64;
395            Elf64_r_sym = MIPS64_r_sym;
396            Elf64_r_info = MIPS64_r_info;
397            is_fake_mcount64 = MIPS64_is_fake_mcount;
398        }
399        do64(ghdr, fname, reltype);
400        break;
401    }
402    } /* end switch */
403
404    cleanup();
405}
406
407int
408main(int argc, char *argv[])
409{
410    const char ftrace[] = "/ftrace.o";
411    int ftrace_size = sizeof(ftrace) - 1;
412    int n_error = 0; /* gcc-4.3.0 false positive complaint */
413    int c;
414    int i;
415
416    while ((c = getopt(argc, argv, "w")) >= 0) {
417        switch (c) {
418        case 'w':
419            warn_on_notrace_sect = 1;
420            break;
421        default:
422            fprintf(stderr, "usage: recordmcount [-w] file.o...\n");
423            return 0;
424        }
425    }
426
427    if ((argc - optind) < 1) {
428        fprintf(stderr, "usage: recordmcount [-w] file.o...\n");
429        return 0;
430    }
431
432    /* Process each file in turn, allowing deep failure. */
433    for (i = optind; i < argc; i++) {
434        char *file = argv[i];
435        int const sjval = setjmp(jmpenv);
436        int len;
437
438        /*
439         * The file kernel/trace/ftrace.o references the mcount
440         * function but does not call it. Since ftrace.o should
441         * not be traced anyway, we just skip it.
442         */
443        len = strlen(file);
444        if (len >= ftrace_size &&
445            strcmp(file + (len - ftrace_size), ftrace) == 0)
446            continue;
447
448        switch (sjval) {
449        default:
450            fprintf(stderr, "internal error: %s\n", file);
451            exit(1);
452            break;
453        case SJ_SETJMP: /* normal sequence */
454            /* Avoid problems if early cleanup() */
455            fd_map = -1;
456            ehdr_curr = NULL;
457            mmap_failed = 1;
458            do_file(file);
459            break;
460        case SJ_FAIL: /* error in do_file or below */
461            ++n_error;
462            break;
463        case SJ_SUCCEED: /* premature success */
464            /* do nothing */
465            break;
466        } /* end switch */
467    }
468    return !!n_error;
469}
470
471
472

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