elf/dl-profile.c

   1 /* Profiling of shared libraries.
   2    Copyright (C) 1997, 1998, 1999, 2000 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.
   5    Based on the BSD mcount implementation.
   6
   7    The GNU C Library is free software; you can redistribute it and/or
   8    modify it under the terms of the GNU Library General Public License as
   9    published by the Free Software Foundation; either version 2 of the
  10    License, or (at your option) any later version.
  11
  12    The GNU C Library is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15    Library General Public License for more details.
  16
  17    You should have received a copy of the GNU Library General Public
  18    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  19    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  20    Boston, MA 02111-1307, USA.  */
  21
  22 #include <errno.h>
  23 #include <fcntl.h>
  24 #include <inttypes.h>
  25 #include <limits.h>
  26 #include <stdio.h>
  27 #include <stdlib.h>
  28 #include <string.h>
  29 #include <unistd.h>
  30 #include <ldsodefs.h>
  31 #include <sys/gmon.h>
  32 #include <sys/gmon_out.h>
  33 #include <sys/mman.h>
  34 #include <sys/param.h>
  35 #include <sys/stat.h>
  36 #include <atomicity.h>
  37
  38 /* The LD_PROFILE feature has to be implemented different to the
  39    normal profiling using the gmon/ functions.  The problem is that an
  40    arbitrary amount of processes simulataneously can be run using
  41    profiling and all write the results in the same file.  To provide
  42    this mechanism one could implement a complicated mechanism to merge
  43    the content of two profiling runs or one could extend the file
  44    format to allow more than one data set.  For the second solution we
  45    would have the problem that the file can grow in size beyond any
  46    limit and both solutions have the problem that the concurrency of
  47    writing the results is a big problem.
  48
  49    Another much simpler method is to use mmap to map the same file in
  50    all using programs and modify the data in the mmap'ed area and so
  51    also automatically on the disk.  Using the MAP_SHARED option of
  52    mmap(2) this can be done without big problems in more than one
  53    file.
  54
  55    This approach is very different from the normal profiling.  We have
  56    to use the profiling data in exactly the way they are expected to
  57    be written to disk.  But the normal format used by gprof is not usable
  58    to do this.  It is optimized for size.  It writes the tags as single
  59    bytes but this means that the following 32/64 bit values are
  60    unaligned.
  61
  62    Therefore we use a new format.  This will look like this
  63
  64                                         0  1  2  3      <- byte is 32 bit word
  65         0000                            g  m  o  n
  66         0004                            *version*       <- GMON_SHOBJ_VERSION
  67         0008                            00 00 00 00
  68         000c                            00 00 00 00
  69         0010                            00 00 00 00
  70
  71         0014                            *tag*           <- GMON_TAG_TIME_HIST
  72         0018                            ?? ?? ?? ??
  73                                         ?? ?? ?? ??     <- 32/64 bit LowPC
  74         0018+A                          ?? ?? ?? ??
  75                                         ?? ?? ?? ??     <- 32/64 bit HighPC
  76         0018+2*A                        *histsize*
  77         001c+2*A                        *profrate*
  78         0020+2*A                        s  e  c  o
  79         0024+2*A                        n  d  s  \0
  80         0028+2*A                        \0 \0 \0 \0
  81         002c+2*A                        \0 \0 \0
  82         002f+2*A                        s
  83
  84         0030+2*A                        ?? ?? ?? ??     <- Count data
  85         ...                             ...
  86         0030+2*A+K                      ?? ?? ?? ??
  87
  88         0030+2*A+K                      *tag*           <- GMON_TAG_CG_ARC
  89         0034+2*A+K                      *lastused*
  90         0038+2*A+K                      ?? ?? ?? ??
  91                                         ?? ?? ?? ??     <- FromPC#1
  92         0038+3*A+K                      ?? ?? ?? ??
  93                                         ?? ?? ?? ??     <- ToPC#1
  94         0038+4*A+K                      ?? ?? ?? ??     <- Count#1
  95         ...                             ...                ...
  96         0038+(2*(CN-1)+2)*A+(CN-1)*4+K  ?? ?? ?? ??
  97                                         ?? ?? ?? ??     <- FromPC#CGN
  98         0038+(2*(CN-1)+3)*A+(CN-1)*4+K  ?? ?? ?? ??
  99                                         ?? ?? ?? ??     <- ToPC#CGN
 100         0038+(2*CN+2)*A+(CN-1)*4+K      ?? ?? ?? ??     <- Count#CGN
 101
 102    We put (for now?) no basic block information in the file since this would
 103    introduce rase conditions among all the processes who want to write them.
 104
 105    `K' is the number of count entries which is computed as
 106
 107                 textsize / HISTFRACTION
 108
 109    `CG' in the above table is the number of call graph arcs.  Normally,
 110    the table is sparse and the profiling code writes out only the those
 111    entries which are really used in the program run.  But since we must
 112    not extend this table (the profiling file) we'll keep them all here.
 113    So CN can be executed in advance as
 114
 115                 MINARCS <= textsize*(ARCDENSITY/100) <= MAXARCS
 116
 117    Now the remaining question is: how to build the data structures we can
 118    work with from this data.  We need the from set and must associate the
 119    froms with all the associated tos.  We will do this by constructing this
 120    data structures at the program start.  To do this we'll simply visit all
 121    entries in the call graph table and add it to the appropriate list.  */
 122
 123 extern int __profile_frequency (void);
 124
 125 /* We define a special type to address the elements of the arc table.
 126    This is basically the `gmon_cg_arc_record' format but it includes
 127    the room for the tag and it uses real types.  */
 128 struct here_cg_arc_record
 129   {
 130     uintptr_t from_pc;
 131     uintptr_t self_pc;
 132     uint32_t count;
 133   } __attribute__ ((packed));
 134
 135 static struct here_cg_arc_record *data;
 136
 137 /* This is the number of entry which have been incorporated in the toset.  */
 138 static uint32_t narcs;
 139 /* This is a pointer to the object representing the number of entries
 140    currently in the mmaped file.  At no point of time this has to be the
 141    same as NARCS.  If it is equal all entries from the file are in our
 142    lists.  */
 143 static volatile uint32_t *narcsp;
 144
 145 /* Description of the currently profiled object.  */
 146 static long int state = GMON_PROF_OFF;
 147
 148 static volatile uint16_t *kcount;
 149 static size_t kcountsize;
 150
 151 struct here_fromstruct
 152   {
 153     struct here_cg_arc_record volatile *here;
 154     uint16_t link;
 155   };
 156
 157 static uint16_t *tos;
 158 static size_t tossize;
 159
 160 static struct here_fromstruct *froms;
 161 static size_t fromssize;
 162 static size_t fromlimit;
 163 static size_t fromidx;
 164
 165 static uintptr_t lowpc;
 166 static uintptr_t highpc;
 167 static size_t textsize;
 168 static unsigned int hashfraction;
 169 static unsigned int log_hashfraction;
 170
 171 /* This is the information about the mmaped memory.  */
 172 static struct gmon_hdr *addr;
 173 static off_t expected_size;
 174
 175 /* See profil(2) where this is described.  */
 176 static int s_scale;
 177 #define SCALE_1_TO_1    0x10000L
 178
 179
 180 \f
 181 /* Set up profiling data to profile object desribed by MAP.  The output
 182    file is found (or created) in OUTPUT_DIR.  */
 183 void
 184 internal_function
 185 _dl_start_profile (struct link_map *map, const char *output_dir)
 186 {
 187   char *filename;
 188   int fd;
 189   struct stat st;
 190   const ElfW(Phdr) *ph;
 191   ElfW(Addr) mapstart = ~((ElfW(Addr)) 0);
 192   ElfW(Addr) mapend = 0;
 193   struct gmon_hdr gmon_hdr;
 194   struct gmon_hist_hdr hist_hdr;
 195   char *hist, *cp;
 196   size_t idx;
 197
 198   /* Compute the size of the sections which contain program code.  */
 199   for (ph = map->l_phdr; ph < &map->l_phdr[map->l_phnum]; ++ph)
 200     if (ph->p_type == PT_LOAD && (ph->p_flags & PF_X))
 201       {
 202         ElfW(Addr) start = (ph->p_vaddr & ~(_dl_pagesize - 1));
 203         ElfW(Addr) end = ((ph->p_vaddr + ph->p_memsz + _dl_pagesize - 1)
 204                           & ~(_dl_pagesize - 1));
 205
 206         if (start < mapstart)
 207           mapstart = start;
 208         if (end > mapend)
 209           mapend = end;
 210       }
 211
 212   /* Now we can compute the size of the profiling data.  This is done
 213      with the same formulars as in `monstartup' (see gmon.c).  */
 214   state = GMON_PROF_OFF;
 215   lowpc = ROUNDDOWN (mapstart + map->l_addr,
 216                      HISTFRACTION * sizeof (HISTCOUNTER));
 217   highpc = ROUNDUP (mapend + map->l_addr,
 218                     HISTFRACTION * sizeof (HISTCOUNTER));
 219   textsize = highpc - lowpc;
 220   kcountsize = textsize / HISTFRACTION;
 221   hashfraction = HASHFRACTION;
 222   if ((HASHFRACTION & (HASHFRACTION - 1)) == 0)
 223     /* If HASHFRACTION is a power of two, mcount can use shifting
 224        instead of integer division.  Precompute shift amount.  */
 225     log_hashfraction = __ffs (hashfraction * sizeof (*froms)) - 1;
 226   else
 227     log_hashfraction = -1;
 228   tossize = textsize / HASHFRACTION;
 229   fromlimit = textsize * ARCDENSITY / 100;
 230   if (fromlimit < MINARCS)
 231     fromlimit = MINARCS;
 232   if (fromlimit > MAXARCS)
 233     fromlimit = MAXARCS;
 234   fromssize = fromlimit * sizeof (struct here_fromstruct);
 235
 236   expected_size = (sizeof (struct gmon_hdr)
 237                    + 4 + sizeof (struct gmon_hist_hdr) + kcountsize
 238                    + 4 + 4 + fromssize * sizeof (struct here_cg_arc_record));
 239
 240   /* Create the gmon_hdr we expect or write.  */
 241   memset (&gmon_hdr, '\0', sizeof (struct gmon_hdr));
 242   memcpy (&gmon_hdr.cookie[0], GMON_MAGIC, sizeof (gmon_hdr.cookie));
 243   *(int32_t *) gmon_hdr.version = GMON_SHOBJ_VERSION;
 244
 245   /* Create the hist_hdr we expect or write.  */
 246   *(char **) hist_hdr.low_pc = (char *) mapstart;
 247   *(char **) hist_hdr.high_pc = (char *) mapend;
 248   *(int32_t *) hist_hdr.hist_size = kcountsize / sizeof (HISTCOUNTER);
 249   *(int32_t *) hist_hdr.prof_rate = __profile_frequency ();
 250   strncpy (hist_hdr.dimen, "seconds", sizeof (hist_hdr.dimen));
 251   hist_hdr.dimen_abbrev = 's';
 252
 253   /* First determine the output name.  We write in the directory
 254      OUTPUT_DIR and the name is composed from the shared objects
 255      soname (or the file name) and the ending ".profile".  */
 256   filename = (char *) alloca (strlen (output_dir) + 1 + strlen (_dl_profile)
 257                               + sizeof ".profile");
 258   cp = __stpcpy (filename, output_dir);
 259   *cp++ = '/';
 260   __stpcpy (__stpcpy (cp, _dl_profile), ".profile");
 261
 262   fd = __open (filename, O_RDWR | O_CREAT, 0666);
 263   if (fd == -1)
 264     {
 265       /* We cannot write the profiling data so don't do anything.  */
 266       char buf[400];
 267       _dl_sysdep_message (filename, ": cannot open file: ",
 268                           __strerror_r (errno, buf, sizeof buf),
 269                           "\n", NULL);
 270       return;
 271     }
 272
 273   if (fstat (fd, &st) < 0 || !S_ISREG (st.st_mode))
 274     {
 275       /* Not stat'able or not a regular file => don't use it.  */
 276       char buf[400];
 277       int errnum = errno;
 278       __close (fd);
 279       _dl_sysdep_message (filename, ": cannot stat file: ",
 280                           __strerror_r (errnum, buf, sizeof buf),
 281                           "\n", NULL);
 282       return;
 283     }
 284
 285   /* Test the size.  If it does not match what we expect from the size
 286      values in the map MAP we don't use it and warn the user.  */
 287   if (st.st_size == 0)
 288     {
 289       /* We have to create the file.  */
 290       char buf[_dl_pagesize];
 291
 292       memset (buf, '\0', _dl_pagesize);
 293
 294       if (__lseek (fd, expected_size & ~(_dl_pagesize - 1), SEEK_SET) == -1)
 295         {
 296           char buf[400];
 297           int errnum;
 298         cannot_create:
 299           errnum = errno;
 300           __close (fd);
 301           _dl_sysdep_message (filename, ": cannot create file: ",
 302                               __strerror_r (errnum, buf, sizeof buf),
 303                               "\n", NULL);
 304           return;
 305         }
 306
 307       if (TEMP_FAILURE_RETRY (__libc_write (fd, buf, (expected_size
 308                                                       & (_dl_pagesize - 1))))
 309           < 0)
 310         goto cannot_create;
 311     }
 312   else if (st.st_size != expected_size)
 313     {
 314       __close (fd);
 315     wrong_format:
 316
 317       if (addr != NULL)
 318         __munmap ((void *) addr, expected_size);
 319
 320       _dl_sysdep_message (filename,
 321                           ": file is no correct profile data file for `",
 322                           _dl_profile, "'\n", NULL);
 323       return;
 324     }
 325
 326   addr = (struct gmon_hdr *) __mmap (NULL, expected_size, PROT_READ|PROT_WRITE,
 327                                      MAP_SHARED|MAP_FILE, fd, 0);
 328   if (addr == (struct gmon_hdr *) MAP_FAILED)
 329     {
 330       char buf[400];
 331       int errnum = errno;
 332       __close (fd);
 333       _dl_sysdep_message (filename, ": cannot map file: ",
 334                           __strerror_r (errnum, buf, sizeof buf),
 335                           "\n", NULL);
 336       return;
 337     }
 338
 339   /* We don't need the file desriptor anymore.  */
 340   __close (fd);
 341
 342   /* Pointer to data after the header.  */
 343   hist = (char *) (addr + 1);
 344   kcount = (uint16_t *) ((char *) hist + sizeof (uint32_t)
 345                          + sizeof (struct gmon_hist_hdr));
 346
 347   /* Compute pointer to array of the arc information.  */
 348   narcsp = (uint32_t *) ((char *) kcount + kcountsize + sizeof (uint32_t));
 349   data = (struct here_cg_arc_record *) ((char *) narcsp + sizeof (uint32_t));
 350
 351   if (st.st_size == 0)
 352     {
 353       /* Create the signature.  */
 354       memcpy (addr, &gmon_hdr, sizeof (struct gmon_hdr));
 355
 356       *(uint32_t *) hist = GMON_TAG_TIME_HIST;
 357       memcpy (hist + sizeof (uint32_t), &hist_hdr,
 358               sizeof (struct gmon_hist_hdr));
 359
 360       narcsp[-1] = GMON_TAG_CG_ARC;
 361     }
 362   else
 363     {
 364       /* Test the signature in the file.  */
 365       if (memcmp (addr, &gmon_hdr, sizeof (struct gmon_hdr)) != 0
 366           || *(uint32_t *) hist != GMON_TAG_TIME_HIST
 367           || memcmp (hist + sizeof (uint32_t), &hist_hdr,
 368                      sizeof (struct gmon_hist_hdr)) != 0
 369           || narcsp[-1] != GMON_TAG_CG_ARC)
 370         goto wrong_format;
 371     }
 372
 373   /* Allocate memory for the froms data and the pointer to the tos records.  */
 374   tos = (uint16_t *) calloc (tossize + fromssize, 1);
 375   if (tos == NULL)
 376     {
 377       __munmap ((void *) addr, expected_size);
 378       _dl_sysdep_fatal ("Out of memory while initializing profiler\n", NULL);
 379       /* NOTREACHED */
 380     }
 381
 382   froms = (struct here_fromstruct *) ((char *) tos + tossize);
 383   fromidx = 0;
 384
 385   /* Now we have to process all the arc count entries.  BTW: it is
 386      not critical whether the *NARCSP value changes meanwhile.  Before
 387      we enter a new entry in to toset we will check that everything is
 388      available in TOS.  This happens in _dl_mcount.
 389
 390      Loading the entries in reverse order should help to get the most
 391      frequently used entries at the front of the list.  */
 392   for (idx = narcs = MIN (*narcsp, fromlimit); idx > 0; )
 393     {
 394       size_t to_index;
 395       size_t newfromidx;
 396       --idx;
 397       to_index = (data[idx].self_pc / (hashfraction * sizeof (*tos)));
 398       newfromidx = fromidx++;
 399       froms[newfromidx].here = &data[idx];
 400       froms[newfromidx].link = tos[to_index];
 401       tos[to_index] = newfromidx;
 402     }
 403
 404   /* Setup counting data.  */
 405   if (kcountsize < highpc - lowpc)
 406     {
 407 #if 0
 408       s_scale = ((double) kcountsize / (highpc - lowpc)) * SCALE_1_TO_1;
 409 #else
 410       size_t range = highpc - lowpc;
 411       size_t quot = range / kcountsize;
 412
 413       if (quot >= SCALE_1_TO_1)
 414         s_scale = 1;
 415       else if (quot >= SCALE_1_TO_1 / 256)
 416         s_scale = SCALE_1_TO_1 / quot;
 417       else if (range > ULONG_MAX / 256)
 418         s_scale = (SCALE_1_TO_1 * 256) / (range / (kcountsize / 256));
 419       else
 420         s_scale = (SCALE_1_TO_1 * 256) / ((range * 256) / kcountsize);
 421 #endif
 422     }
 423   else
 424     s_scale = SCALE_1_TO_1;
 425
 426   /* Start the profiler.  */
 427   __profil ((void *) kcount, kcountsize, lowpc, s_scale);
 428
 429   /* Turn on profiling.  */
 430   state = GMON_PROF_ON;
 431 }
 432
 433
 434 void
 435 _dl_mcount (ElfW(Addr) frompc, ElfW(Addr) selfpc)
 436 {
 437   uint16_t *topcindex;
 438   size_t i, fromindex;
 439   struct here_fromstruct *fromp;
 440
 441   if (! compare_and_swap (&state, GMON_PROF_ON, GMON_PROF_BUSY))
 442     return;
 443
 444   /* Compute relative addresses.  The shared object can be loaded at
 445      any address.  The value of frompc could be anything.  We cannot
 446      restrict it in any way, just set to a fixed value (0) in case it
 447      is outside the allowed range.  These calls show up as calls from
 448      <external> in the gprof output.  */
 449   frompc -= lowpc;
 450   if (frompc >= textsize)
 451     frompc = 0;
 452   selfpc -= lowpc;
 453   if (selfpc >= textsize)
 454     goto done;
 455
 456   /* Getting here we now have to find out whether the location was
 457      already used.  If yes we are lucky and only have to increment a
 458      counter (this also has to be atomic).  If the entry is new things
 459      are getting complicated...  */
 460
 461   /* Avoid integer divide if possible.  */
 462   if ((HASHFRACTION & (HASHFRACTION - 1)) == 0)
 463     i = selfpc >> log_hashfraction;
 464   else
 465     i = selfpc / (hashfraction * sizeof (*tos));
 466
 467   topcindex = &tos[i];
 468   fromindex = *topcindex;
 469
 470   if (fromindex == 0)
 471     goto check_new_or_add;
 472
 473   fromp = &froms[fromindex];
 474
 475   /* We have to look through the chain of arcs whether there is already
 476      an entry for our arc.  */
 477   while (fromp->here->from_pc != frompc)
 478     {
 479       if (fromp->link != 0)
 480         do
 481           fromp = &froms[fromp->link];
 482         while (fromp->link != 0 && fromp->here->from_pc != frompc);
 483
 484       if (fromp->here->from_pc != frompc)
 485         {
 486           topcindex = &fromp->link;
 487
 488         check_new_or_add:
 489           /* Our entry is not among the entries we read so far from the
 490              data file.  Now see whether we have to update the list.  */
 491           while (narcs != *narcsp && narcs < fromlimit)
 492             {
 493               size_t to_index;
 494               size_t newfromidx;
 495               to_index = (data[narcs].self_pc
 496                           / (hashfraction * sizeof (*tos)));
 497               newfromidx = fromidx++;
 498               froms[newfromidx].here = &data[narcs];
 499               froms[newfromidx].link = tos[to_index];
 500               tos[to_index] = newfromidx;
 501               ++narcs;
 502             }
 503
 504           /* If we still have no entry stop searching and insert.  */
 505           if (*topcindex == 0)
 506             {
 507               size_t newarc = 1 + exchange_and_add (narcsp, 1);
 508
 509               /* In rare cases it could happen that all entries in FROMS are
 510                  occupied.  So we cannot count this anymore.  */
 511               if (newarc >= fromlimit)
 512                 goto done;
 513
 514               fromp = &froms[*topcindex = fromidx++];
 515
 516               fromp->here = &data[newarc];
 517               data[newarc].from_pc = frompc;
 518               data[newarc].self_pc = selfpc;
 519               data[newarc].count = 0;
 520               fromp->link = 0;
 521               ++narcs;
 522
 523               break;
 524             }
 525
 526           fromp = &froms[*topcindex];
 527         }
 528       else
 529         /* Found in.  */
 530         break;
 531     }
 532
 533   /* Increment the counter.  */
 534   atomic_add (&fromp->here->count, 1);
 535
 536  done:
 537   state = GMON_PROF_ON;
 538 }