manual/probes.texi

   1 @node Internal Probes
   2 @c @node Internal Probes, , POSIX Threads, Top
   3 @c %MENU% Probes to monitor libc internal behavior
   4 @chapter Internal probes
   5
   6 In order to aid in debugging and monitoring internal behavior,
   7 @theglibc{} exposes nearly-zero-overhead SystemTap probes marked with
   8 the @code{libc} provider.
   9
  10 These probes are not part of the @glibcadj{} stable ABI, and they are
  11 subject to change or removal across releases.  Our only promise with
  12 regard to them is that, if we find a need to remove or modify the
  13 arguments of a probe, the modified probe will have a different name, so
  14 that program monitors relying on the old probe will not get unexpected
  15 arguments.
  16
  17 @menu
  18 * Memory Allocation Probes::  Probes in the memory allocation subsystem
  19 * Mathematical Function Probes::  Probes in mathematical functions
  20 * Non-local Goto Probes::  Probes in setjmp and longjmp
  21 @end menu
  22
  23 @node Memory Allocation Probes
  24 @section Memory Allocation Probes
  25
  26 These probes are designed to signal relatively unusual situations within
  27 the virtual memory subsystem of @theglibc{}.
  28
  29 @deftp Probe memory_sbrk_more (void *@var{$arg1}, size_t @var{$arg2})
  30 This probe is triggered after the main arena is extended by calling
  31 @code{sbrk}.  Argument @var{$arg1} is the additional size requested to
  32 @code{sbrk}, and @var{$arg2} is the pointer that marks the end of the
  33 @code{sbrk} area, returned in response to the request.
  34 @end deftp
  35
  36 @deftp Probe memory_sbrk_less (void *@var{$arg1}, size_t @var{$arg2})
  37 This probe is triggered after the size of the main arena is decreased by
  38 calling @code{sbrk}.  Argument @var{$arg1} is the size released by
  39 @code{sbrk} (the positive value, rather than the negative value passed
  40 to @code{sbrk}), and @var{$arg2} is the pointer that marks the end of
  41 the @code{sbrk} area, returned in response to the request.
  42 @end deftp
  43
  44 @deftp Probe memory_heap_new (void *@var{$arg1}, size_t @var{$arg2})
  45 This probe is triggered after a new heap is @code{mmap}ed.  Argument
  46 @var{$arg1} is a pointer to the base of the memory area, where the
  47 @code{heap_info} data structure is held, and @var{$arg2} is the size of
  48 the heap.
  49 @end deftp
  50
  51 @deftp Probe memory_heap_free (void *@var{$arg1}, size_t @var{$arg2})
  52 This probe is triggered @emph{before} (unlike the other sbrk and heap
  53 probes) a heap is completely removed via @code{munmap}.  Argument
  54 @var{$arg1} is a pointer to the heap, and @var{$arg2} is the size of the
  55 heap.
  56 @end deftp
  57
  58 @deftp Probe memory_heap_more (void *@var{$arg1}, size_t @var{$arg2})
  59 This probe is triggered after a trailing portion of an @code{mmap}ed
  60 heap is extended.  Argument @var{$arg1} is a pointer to the heap, and
  61 @var{$arg2} is the new size of the heap.
  62 @end deftp
  63
  64 @deftp Probe memory_heap_less (void *@var{$arg1}, size_t @var{$arg2})
  65 This probe is triggered after a trailing portion of an @code{mmap}ed
  66 heap is released.  Argument @var{$arg1} is a pointer to the heap, and
  67 @var{$arg2} is the new size of the heap.
  68 @end deftp
  69
  70 @deftp Probe memory_malloc_retry (size_t @var{$arg1})
  71 @deftpx Probe memory_realloc_retry (size_t @var{$arg1}, void *@var{$arg2})
  72 @deftpx Probe memory_memalign_retry (size_t @var{$arg1}, size_t @var{$arg2})
  73 @deftpx Probe memory_calloc_retry (size_t @var{$arg1})
  74 These probes are triggered when the corresponding functions fail to
  75 obtain the requested amount of memory from the arena in use, before they
  76 call @code{arena_get_retry} to select an alternate arena in which to
  77 retry the allocation.  Argument @var{$arg1} is the amount of memory
  78 requested by the user; in the @code{calloc} case, that is the total size
  79 computed from both function arguments.  In the @code{realloc} case,
  80 @var{$arg2} is the pointer to the memory area being resized.  In the
  81 @code{memalign} case, @var{$arg2} is the alignment to be used for the
  82 request, which may be stricter than the value passed to the
  83 @code{memalign} function.  A @code{memalign} probe is also used by functions
  84 @code{posix_memalign, valloc} and @code{pvalloc}.
  85
  86 Note that the argument order does @emph{not} match that of the
  87 corresponding two-argument functions, so that in all of these probes the
  88 user-requested allocation size is in @var{$arg1}.
  89 @end deftp
  90
  91 @deftp Probe memory_arena_retry (size_t @var{$arg1}, void *@var{$arg2})
  92 This probe is triggered within @code{arena_get_retry} (the function
  93 called to select the alternate arena in which to retry an allocation
  94 that failed on the first attempt), before the selection of an alternate
  95 arena.  This probe is redundant, but much easier to use when it's not
  96 important to determine which of the various memory allocation functions
  97 is failing to allocate on the first try.  Argument @var{$arg1} is the
  98 same as in the function-specific probes, except for extra room for
  99 padding introduced by functions that have to ensure stricter alignment.
 100 Argument @var{$arg2} is the arena in which allocation failed.
 101 @end deftp
 102
 103 @deftp Probe memory_arena_new (void *@var{$arg1}, size_t @var{$arg2})
 104 This probe is triggered when @code{malloc} allocates and initializes an
 105 additional arena (not the main arena), but before the arena is assigned
 106 to the running thread or inserted into the internal linked list of
 107 arenas.  The arena's @code{malloc_state} internal data structure is
 108 located at @var{$arg1}, within a newly-allocated heap big enough to hold
 109 at least @var{$arg2} bytes.
 110 @end deftp
 111
 112 @deftp Probe memory_arena_reuse (void *@var{$arg1}, void *@var{$arg2})
 113 This probe is triggered when @code{malloc} has just selected an existing
 114 arena to reuse, and (temporarily) reserved it for exclusive use.
 115 Argument @var{$arg1} is a pointer to the newly-selected arena, and
 116 @var{$arg2} is a pointer to the arena previously used by that thread.
 117
 118 This occurs within
 119 @code{reused_arena}, right after the mutex mentioned in probe
 120 @code{memory_arena_reuse_wait} is acquired; argument @var{$arg1} will
 121 point to the same arena.  In this configuration, this will usually only
 122 occur once per thread.  The exception is when a thread first selected
 123 the main arena, but a subsequent allocation from it fails: then, and
 124 only then, may we switch to another arena to retry that allocations, and
 125 for further allocations within that thread.
 126 @end deftp
 127
 128 @deftp Probe memory_arena_reuse_wait (void *@var{$arg1}, void *@var{$arg2}, void *@var{$arg3})
 129 This probe is triggered when @code{malloc} is about to wait for an arena
 130 to become available for reuse.  Argument @var{$arg1} holds a pointer to
 131 the mutex the thread is going to wait on, @var{$arg2} is a pointer to a
 132 newly-chosen arena to be reused, and @var{$arg3} is a pointer to the
 133 arena previously used by that thread.
 134
 135 This occurs within
 136 @code{reused_arena}, when a thread first tries to allocate memory or
 137 needs a retry after a failure to allocate from the main arena, there
 138 isn't any free arena, the maximum number of arenas has been reached, and
 139 an existing arena was chosen for reuse, but its mutex could not be
 140 immediately acquired.  The mutex in @var{$arg1} is the mutex of the
 141 selected arena.
 142 @end deftp
 143
 144 @deftp Probe memory_arena_reuse_free_list (void *@var{$arg1})
 145 This probe is triggered when @code{malloc} has chosen an arena that is
 146 in the free list for use by a thread, within the @code{get_free_list}
 147 function.  The argument @var{$arg1} holds a pointer to the selected arena.
 148 @end deftp
 149
 150 @deftp Probe memory_mallopt (int @var{$arg1}, int @var{$arg2})
 151 This probe is triggered when function @code{mallopt} is called to change
 152 @code{malloc} internal configuration parameters, before any change to
 153 the parameters is made.  The arguments @var{$arg1} and @var{$arg2} are
 154 the ones passed to the @code{mallopt} function.
 155 @end deftp
 156
 157 @deftp Probe memory_mallopt_mxfast (int @var{$arg1}, int @var{$arg2})
 158 This probe is triggered shortly after the @code{memory_mallopt} probe,
 159 when the parameter to be changed is @code{M_MXFAST}, and the requested
 160 value is in an acceptable range.  Argument @var{$arg1} is the requested
 161 value, and @var{$arg2} is the previous value of this @code{malloc}
 162 parameter.
 163 @end deftp
 164
 165 @deftp Probe memory_mallopt_trim_threshold (int @var{$arg1}, int @var{$arg2}, int @var{$arg3})
 166 This probe is triggere shortly after the @code{memory_mallopt} probe,
 167 when the parameter to be changed is @code{M_TRIM_THRESHOLD}.  Argument
 168 @var{$arg1} is the requested value, @var{$arg2} is the previous value of
 169 this @code{malloc} parameter, and @var{$arg3} is nonzero if dynamic
 170 threshold adjustment was already disabled.
 171 @end deftp
 172
 173 @deftp Probe memory_mallopt_top_pad (int @var{$arg1}, int @var{$arg2}, int @var{$arg3})
 174 This probe is triggered shortly after the @code{memory_mallopt} probe,
 175 when the parameter to be changed is @code{M_TOP_PAD}.  Argument
 176 @var{$arg1} is the requested value, @var{$arg2} is the previous value of
 177 this @code{malloc} parameter, and @var{$arg3} is nonzero if dynamic
 178 threshold adjustment was already disabled.
 179 @end deftp
 180
 181 @deftp Probe memory_mallopt_mmap_threshold (int @var{$arg1}, int @var{$arg2}, int @var{$arg3})
 182 This probe is triggered shortly after the @code{memory_mallopt} probe,
 183 when the parameter to be changed is @code{M_MMAP_THRESHOLD}, and the
 184 requested value is in an acceptable range.  Argument @var{$arg1} is the
 185 requested value, @var{$arg2} is the previous value of this @code{malloc}
 186 parameter, and @var{$arg3} is nonzero if dynamic threshold adjustment
 187 was already disabled.
 188 @end deftp
 189
 190 @deftp Probe memory_mallopt_mmap_max (int @var{$arg1}, int @var{$arg2}, int @var{$arg3})
 191 This probe is triggered shortly after the @code{memory_mallopt} probe,
 192 when the parameter to be changed is @code{M_MMAP_MAX}.  Argument
 193 @var{$arg1} is the requested value, @var{$arg2} is the previous value of
 194 this @code{malloc} parameter, and @var{$arg3} is nonzero if dynamic
 195 threshold adjustment was already disabled.
 196 @end deftp
 197
 198 @deftp Probe memory_mallopt_check_action (int @var{$arg1}, int @var{$arg2})
 199 This probe is triggered shortly after the @code{memory_mallopt} probe,
 200 when the parameter to be changed is @code{M_CHECK_ACTION}.  Argument
 201 @var{$arg1} is the requested value, and @var{$arg2} is the previous
 202 value of this @code{malloc} parameter.
 203 @end deftp
 204
 205 @deftp Probe memory_mallopt_perturb (int @var{$arg1}, int @var{$arg2})
 206 This probe is triggered shortly after the @code{memory_mallopt} probe,
 207 when the parameter to be changed is @code{M_PERTURB}.  Argument
 208 @var{$arg1} is the requested value, and @var{$arg2} is the previous
 209 value of this @code{malloc} parameter.
 210 @end deftp
 211
 212 @deftp Probe memory_mallopt_arena_test (int @var{$arg1}, int @var{$arg2})
 213 This probe is triggered shortly after the @code{memory_mallopt} probe,
 214 when the parameter to be changed is @code{M_ARENA_TEST}, and the
 215 requested value is in an acceptable range.  Argument @var{$arg1} is the
 216 requested value, and @var{$arg2} is the previous value of this
 217 @code{malloc} parameter.
 218 @end deftp
 219
 220 @deftp Probe memory_mallopt_arena_max (int @var{$arg1}, int @var{$arg2})
 221 This probe is triggered shortly after the @code{memory_mallopt} probe,
 222 when the parameter to be changed is @code{M_ARENA_MAX}, and the
 223 requested value is in an acceptable range.  Argument @var{$arg1} is the
 224 requested value, and @var{$arg2} is the previous value of this
 225 @code{malloc} parameter.
 226 @end deftp
 227
 228 @deftp Probe memory_mallopt_free_dyn_thresholds (int @var{$arg1}, int @var{$arg2})
 229 This probe is triggered when function @code{free} decides to adjust the
 230 dynamic brk/mmap thresholds.  Argument @var{$arg1} and @var{$arg2} are
 231 the adjusted mmap and trim thresholds, respectively.
 232 @end deftp
 233
 234 @node Mathematical Function Probes
 235 @section Mathematical Function Probes
 236
 237 Some mathematical functions fall back to multiple precision arithmetic for
 238 some inputs to get last bit precision for their return values.  This multiple
 239 precision fallback is much slower than the default algorithms and may have a
 240 significant impact on application performance.  The systemtap probe markers
 241 described in this section may help you determine if your application calls
 242 mathematical functions with inputs that may result in multiple-precision
 243 arithmetic.
 244
 245 Unless explicitly mentioned otherwise, a precision of 1 implies 24 bits of
 246 precision in the mantissa of the multiple precision number.  Hence, a precision
 247 level of 32 implies 768 bits of precision in the mantissa.
 248
 249 @deftp Probe slowexp_p6 (double @var{$arg1}, double @var{$arg2})
 250 This probe is hit when the @code{exp} function is called with an input that
 251 results in multiple precision computation with precision 6. Argument
 252 @var{$arg1} is the input value and @var{$arg2} is the computed output.
 253 @end deftp
 254
 255 @deftp Probe slowexp_p32 (double @var{$arg1}, double @var{$arg2})
 256 This probe is hit when the @code{exp} function is called with an input that
 257 results in multiple precision computation with precision 32. Argument
 258 @var{$arg1} is the input value and @var{$arg2} is the computed output.
 259 @end deftp
 260
 261 @deftp Probe slowpow_p10 (double @var{$arg1}, double @var{$arg2}, double @var{$arg3}, double @var{$arg4})
 262 This probe is hit when the @code{pow} function is called with inputs that
 263 result in multiple precision computation with precision 10. Arguments
 264 @var{$arg1} and @var{$arg2} are the input values, @code{$arg3} is the value
 265 computed in the fast phase of the algorithm and @code{$arg4} is the final
 266 accurate value.
 267 @end deftp
 268
 269 @deftp Probe slowpow_p32 (double @var{$arg1}, double @var{$arg2}, double @var{$arg3}, double @var{$arg4})
 270 This probe is hit when the @code{pow} function is called with an input that
 271 results in multiple precision computation with precision 32. Arguments
 272 @var{$arg1} and @var{$arg2} are the input values, @code{$arg3} is the value
 273 computed in the fast phase of the algorithm and @code{$arg4} is the final
 274 accurate value.
 275 @end deftp
 276
 277 @deftp Probe slowlog (int @var{$arg1}, double @var{$arg2}, double @var{$arg3})
 278 This probe is hit when the @code{log} function is called with an input that
 279 results in multiple precision computation.  Argument @var{$arg1} is the
 280 precision with which the computation succeeded.  Argument @var{$arg2} is the
 281 input and @var{$arg3} is the computed output.
 282 @end deftp
 283
 284 @deftp Probe slowlog_inexact (int @var{$arg1}, double @var{$arg2}, double @var{$arg3})
 285 This probe is hit when the @code{log} function is called with an input that
 286 results in multiple precision computation and none of the multiple precision
 287 computations result in an accurate result.  Argument @var{$arg1} is the maximum
 288 precision  with which computations were performed.  Argument @var{$arg2} is the
 289 input and @var{$arg3} is the computed output.
 290 @end deftp
 291
 292 @deftp Probe slowatan2 (int @var{$arg1}, double @var{$arg2}, double @var{$arg3}, double @var{$arg4})
 293 This probe is hit when the @code{atan2} function is called with an input that
 294 results in multiple precision computation.  Argument @var{$arg1} is the
 295 precision with which computation succeeded.  Arguments @var{$arg2} and
 296 @var{$arg3} are inputs to the @code{atan2} function and @var{$arg4} is the
 297 computed result.
 298 @end deftp
 299
 300 @deftp Probe slowatan2_inexact (int @var{$arg1}, double @var{$arg2}, double @var{$arg3}, double @var{$arg4})
 301 This probe is hit when the @code{atan} function is called with an input that
 302 results in multiple precision computation and none of the multiple precision
 303 computations result in an accurate result.  Argument @var{$arg1} is the maximum
 304 precision  with which computations were performed.  Arguments @var{$arg2} and
 305 @var{$arg3} are inputs to the @code{atan2} function and @var{$arg4} is the
 306 computed result.
 307 @end deftp
 308
 309 @deftp Probe slowatan (int @var{$arg1}, double @var{$arg2}, double @var{$arg3})
 310 This probe is hit when the @code{atan} function is called with an input that
 311 results in multiple precision computation.  Argument @var{$arg1} is the
 312 precision with which computation succeeded.  Argument @var{$arg2} is the
 313 input to the @code{atan} function and @var{$arg3} is the computed result.
 314 @end deftp
 315
 316 @deftp Probe slowatan_inexact (int @var{$arg1}, double @var{$arg2}, double @var{$arg3})
 317 This probe is hit when the @code{atan} function is called with an input that
 318 results in multiple precision computation and none of the multiple precision
 319 computations result in an accurate result.  Argument @var{$arg1} is the maximum
 320 precision  with which computations were performed.  Argument @var{$arg2} is the
 321 input to the @code{atan} function and @var{$arg3} is the computed result.
 322 @end deftp
 323
 324 @deftp Probe slowtan (double @var{$arg1}, double @var{$arg2})
 325 This probe is hit when the @code{tan} function is called with an input that
 326 results in multiple precision computation with precision 32.  Argument
 327 @var{$arg1} is the input to the function and @var{$arg2} is the computed
 328 result.
 329 @end deftp
 330
 331 @deftp Probe slowasin (double @var{$arg1}, double @var{$arg2})
 332 This probe is hit when the @code{asin} function is called with an input that
 333 results in multiple precision computation with precision 32.  Argument
 334 @var{$arg1} is the input to the function and @var{$arg2} is the computed
 335 result.
 336 @end deftp
 337
 338 @deftp Probe slowacos (double @var{$arg1}, double @var{$arg2})
 339 This probe is hit when the @code{acos} function is called with an input that
 340 results in multiple precision computation with precision 32.  Argument
 341 @var{$arg1} is the input to the function and @var{$arg2} is the computed
 342 result.
 343 @end deftp
 344
 345 @deftp Probe slowsin (double @var{$arg1}, double @var{$arg2})
 346 This probe is hit when the @code{sin} function is called with an input that
 347 results in multiple precision computation with precision 32.  Argument
 348 @var{$arg1} is the input to the function and @var{$arg2} is the computed
 349 result.
 350 @end deftp
 351
 352 @deftp Probe slowcos (double @var{$arg1}, double @var{$arg2})
 353 This probe is hit when the @code{cos} function is called with an input that
 354 results in multiple precision computation with precision 32.  Argument
 355 @var{$arg1} is the input to the function and @var{$arg2} is the computed
 356 result.
 357 @end deftp
 358
 359 @deftp Probe slowsin_dx (double @var{$arg1}, double @var{$arg2}, double @var{$arg3})
 360 This probe is hit when the @code{sin} function is called with an input that
 361 results in multiple precision computation with precision 32.  Argument
 362 @var{$arg1} is the input to the function, @var{$arg2} is the error bound of
 363 @var{$arg1} and @var{$arg3} is the computed result.
 364 @end deftp
 365
 366 @deftp Probe slowcos_dx (double @var{$arg1}, double @var{$arg2}, double @var{$arg3})
 367 This probe is hit when the @code{cos} function is called with an input that
 368 results in multiple precision computation with precision 32.  Argument
 369 @var{$arg1} is the input to the function, @var{$arg2} is the error bound of
 370 @var{$arg1} and @var{$arg3} is the computed result.
 371 @end deftp
 372
 373 @node Non-local Goto Probes
 374 @section Non-local Goto Probes
 375
 376 These probes are used to signal calls to @code{setjmp}, @code{sigsetjmp},
 377 @code{longjmp} or @code{siglongjmp}.
 378
 379 @deftp Probe setjmp (void *@var{$arg1}, int @var{$arg2}, void *@var{$arg3})
 380 This probe is triggered whenever @code{setjmp} or @code{sigsetjmp} is
 381 called.  Argument @var{$arg1} is a pointer to the @code{jmp_buf}
 382 passed as the first argument of @code{setjmp} or @code{sigsetjmp},
 383 @var{$arg2} is the second argument of @code{sigsetjmp} or zero if this
 384 is a call to @code{setjmp} and @var{$arg3} is a pointer to the return
 385 address that will be stored in the @code{jmp_buf}.
 386 @end deftp
 387
 388 @deftp Probe longjmp (void *@var{$arg1}, int @var{$arg2}, void *@var{$arg3})
 389 This probe is triggered whenever @code{longjmp} or @code{siglongjmp}
 390 is called. Argument @var{$arg1} is a pointer to the @code{jmp_buf}
 391 passed as the first argument of @code{longjmp} or @code{siglongjmp},
 392 @var{$arg2} is the return value passed as the second argument of
 393 @code{longjmp} or @code{siglongjmp} and @var{$arg3} is a pointer to
 394 the return address @code{longjmp} or @code{siglongjmp} will return to.
 395
 396 The @code{longjmp} probe is triggered at a point where the registers
 397 have not yet been restored to the values in the @code{jmp_buf} and
 398 unwinding will show a call stack including the caller of
 399 @code{longjmp} or @code{siglongjmp}.
 400 @end deftp
 401
 402 @deftp Probe longjmp_target (void *@var{$arg1}, int @var{$arg2}, void *@var{$arg3})
 403 This probe is triggered under the same conditions and with the same
 404 arguments as the @code{longjmp} probe.
 405
 406 The @code{longjmp_target} probe is triggered at a point where the
 407 registers have been restored to the values in the @code{jmp_buf} and
 408 unwinding will show a call stack including the caller of @code{setjmp}
 409 or @code{sigsetjmp}.
 410 @end deftp