recordmcount.c

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    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 
   36 static int fd_map;      /* File descriptor for file being modified. */
   37 static int mmap_failed; /* Boolean flag. */
   38 static void *ehdr_curr; /* current ElfXX_Ehdr *  for resource cleanup */
   39 static char gpfx;       /* prefix for global symbol name (sometimes '_') */
   40 static struct stat sb;  /* Remember .st_size, etc. */
   41 static jmp_buf jmpenv;  /* setjmp/longjmp per-file error escape */
   42 static const char *altmcount;   /* alternate mcount symbol name */
   43 static int warn_on_notrace_sect; /* warn when section has mcount not being recorded */
   44 
   45 /* setjmp() return values */
   46 enum {
   47         SJ_SETJMP = 0,  /* hardwired first return */
   48         SJ_FAIL,
   49         SJ_SUCCEED
   50 };
   51 
   52 /* Per-file resource cleanup when multiple files. */
   53 static void
   54 cleanup(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 
   63 static void __attribute__((noreturn))
   64 fail_file(void)
   65 {
   66         cleanup();
   67         longjmp(jmpenv, SJ_FAIL);
   68 }
   69 
   70 static void __attribute__((noreturn))
   71 succeed_file(void)
   72 {
   73         cleanup();
   74         longjmp(jmpenv, SJ_SUCCEED);
   75 }
   76 
   77 /* ulseek, uread, ...:  Check return value for errors. */
   78 
   79 static off_t
   80 ulseek(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 
   90 static size_t
   91 uread(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 
  101 static size_t
  102 uwrite(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 
  112 static void *
  113 umalloc(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 
  123 static unsigned char ideal_nop5_x86_64[5] = { 0x0f, 0x1f, 0x44, 0x00, 0x00 };
  124 static unsigned char ideal_nop5_x86_32[5] = { 0x3e, 0x8d, 0x74, 0x26, 0x00 };
  125 static unsigned char *ideal_nop;
  126 
  127 static char rel_type_nop;
  128 
  129 static int (*make_nop)(void *map, size_t const offset);
  130 
  131 static 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  */
  164 static 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 
  190 static 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 
  202 static 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 
  210 static 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 
  216 static uint64_t w8nat(uint64_t const x)
  217 {
  218         return x;
  219 }
  220 
  221 static uint32_t w4nat(uint32_t const x)
  222 {
  223         return x;
  224 }
  225 
  226 static uint32_t w2nat(uint16_t const x)
  227 {
  228         return x;
  229 }
  230 
  231 static uint64_t (*w8)(uint64_t);
  232 static uint32_t (*w)(uint32_t);
  233 static uint32_t (*w2)(uint16_t);
  234 
  235 /* Names of the sections that could contain calls to mcount. */
  236 static int
  237 is_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 
  261 typedef uint8_t myElf64_Byte;           /* Type for a 8-bit quantity.  */
  262 
  263 union 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 
  274 static 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 
  279 static 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 
  286 static void
  287 do_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 
  407 int
  408 main(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
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FreeBSD/Linux Kernel Cross Reference sys/scripts/recordmcount.c

FreeBSD/Linux Kernel Cross Reference
sys/scripts/recordmcount.c
