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recordmcount.h
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1 /*
2  * recordmcount.h
3  *
4  * This code was taken out of recordmcount.c written by
5  * Copyright 2009 John F. Reiser <[email protected]>. All rights reserved.
6  *
7  * The original code had the same algorithms for both 32bit
8  * and 64bit ELF files, but the code was duplicated to support
9  * the difference in structures that were used. This
10  * file creates a macro of everything that is different between
11  * the 64 and 32 bit code, such that by including this header
12  * twice we can create both sets of functions by including this
13  * header once with RECORD_MCOUNT_64 undefined, and again with
14  * it defined.
15  *
16  * This conversion to macros was done by:
17  * Copyright 2010 Steven Rostedt <[email protected]>, Red Hat Inc.
18  *
19  * Licensed under the GNU General Public License, version 2 (GPLv2).
20  */
21 #undef append_func
22 #undef is_fake_mcount
23 #undef fn_is_fake_mcount
24 #undef MIPS_is_fake_mcount
25 #undef mcount_adjust
26 #undef sift_rel_mcount
27 #undef nop_mcount
28 #undef find_secsym_ndx
29 #undef __has_rel_mcount
30 #undef has_rel_mcount
31 #undef tot_relsize
32 #undef get_mcountsym
33 #undef get_sym_str_and_relp
34 #undef do_func
35 #undef Elf_Addr
36 #undef Elf_Ehdr
37 #undef Elf_Shdr
38 #undef Elf_Rel
39 #undef Elf_Rela
40 #undef Elf_Sym
41 #undef ELF_R_SYM
42 #undef Elf_r_sym
43 #undef ELF_R_INFO
44 #undef Elf_r_info
45 #undef ELF_ST_BIND
46 #undef ELF_ST_TYPE
47 #undef fn_ELF_R_SYM
48 #undef fn_ELF_R_INFO
49 #undef uint_t
50 #undef _w
51 #undef _align
52 #undef _size
53 
54 #ifdef RECORD_MCOUNT_64
55 # define append_func append64
56 # define sift_rel_mcount sift64_rel_mcount
57 # define nop_mcount nop_mcount_64
58 # define find_secsym_ndx find64_secsym_ndx
59 # define __has_rel_mcount __has64_rel_mcount
60 # define has_rel_mcount has64_rel_mcount
61 # define tot_relsize tot64_relsize
62 # define get_sym_str_and_relp get_sym_str_and_relp_64
63 # define do_func do64
64 # define get_mcountsym get_mcountsym_64
65 # define is_fake_mcount is_fake_mcount64
66 # define fn_is_fake_mcount fn_is_fake_mcount64
67 # define MIPS_is_fake_mcount MIPS64_is_fake_mcount
68 # define mcount_adjust mcount_adjust_64
69 # define Elf_Addr Elf64_Addr
70 # define Elf_Ehdr Elf64_Ehdr
71 # define Elf_Shdr Elf64_Shdr
72 # define Elf_Rel Elf64_Rel
73 # define Elf_Rela Elf64_Rela
74 # define Elf_Sym Elf64_Sym
75 # define ELF_R_SYM ELF64_R_SYM
76 # define Elf_r_sym Elf64_r_sym
77 # define ELF_R_INFO ELF64_R_INFO
78 # define Elf_r_info Elf64_r_info
79 # define ELF_ST_BIND ELF64_ST_BIND
80 # define ELF_ST_TYPE ELF64_ST_TYPE
81 # define fn_ELF_R_SYM fn_ELF64_R_SYM
82 # define fn_ELF_R_INFO fn_ELF64_R_INFO
83 # define uint_t uint64_t
84 # define _w w8
85 # define _align 7u
86 # define _size 8
87 #else
88 # define append_func append32
89 # define sift_rel_mcount sift32_rel_mcount
90 # define nop_mcount nop_mcount_32
91 # define find_secsym_ndx find32_secsym_ndx
92 # define __has_rel_mcount __has32_rel_mcount
93 # define has_rel_mcount has32_rel_mcount
94 # define tot_relsize tot32_relsize
95 # define get_sym_str_and_relp get_sym_str_and_relp_32
96 # define do_func do32
97 # define get_mcountsym get_mcountsym_32
98 # define is_fake_mcount is_fake_mcount32
99 # define fn_is_fake_mcount fn_is_fake_mcount32
100 # define MIPS_is_fake_mcount MIPS32_is_fake_mcount
101 # define mcount_adjust mcount_adjust_32
102 # define Elf_Addr Elf32_Addr
103 # define Elf_Ehdr Elf32_Ehdr
104 # define Elf_Shdr Elf32_Shdr
105 # define Elf_Rel Elf32_Rel
106 # define Elf_Rela Elf32_Rela
107 # define Elf_Sym Elf32_Sym
108 # define ELF_R_SYM ELF32_R_SYM
109 # define Elf_r_sym Elf32_r_sym
110 # define ELF_R_INFO ELF32_R_INFO
111 # define Elf_r_info Elf32_r_info
112 # define ELF_ST_BIND ELF32_ST_BIND
113 # define ELF_ST_TYPE ELF32_ST_TYPE
114 # define fn_ELF_R_SYM fn_ELF32_R_SYM
115 # define fn_ELF_R_INFO fn_ELF32_R_INFO
116 # define uint_t uint32_t
117 # define _w w
118 # define _align 3u
119 # define _size 4
120 #endif
121 
122 /* Functions and pointers that do_file() may override for specific e_machine. */
123 static int fn_is_fake_mcount(Elf_Rel const *rp)
124 {
125  return 0;
126 }
127 static int (*is_fake_mcount)(Elf_Rel const *rp) = fn_is_fake_mcount;
128 
129 static uint_t fn_ELF_R_SYM(Elf_Rel const *rp)
130 {
131  return ELF_R_SYM(_w(rp->r_info));
132 }
133 static uint_t (*Elf_r_sym)(Elf_Rel const *rp) = fn_ELF_R_SYM;
134 
135 static void fn_ELF_R_INFO(Elf_Rel *const rp, unsigned sym, unsigned type)
136 {
137  rp->r_info = _w(ELF_R_INFO(sym, type));
138 }
139 static void (*Elf_r_info)(Elf_Rel *const rp, unsigned sym, unsigned type) = fn_ELF_R_INFO;
140 
141 static int mcount_adjust = 0;
142 
143 /*
144  * MIPS mcount long call has 2 _mcount symbols, only the position of the 1st
145  * _mcount symbol is needed for dynamic function tracer, with it, to disable
146  * tracing(ftrace_make_nop), the instruction in the position is replaced with
147  * the "b label" instruction, to enable tracing(ftrace_make_call), replace the
148  * instruction back. So, here, we set the 2nd one as fake and filter it.
149  *
150  * c: 3c030000 lui v1,0x0 <--> b label
151  * c: R_MIPS_HI16 _mcount
152  * c: R_MIPS_NONE *ABS*
153  * c: R_MIPS_NONE *ABS*
154  * 10: 64630000 daddiu v1,v1,0
155  * 10: R_MIPS_LO16 _mcount
156  * 10: R_MIPS_NONE *ABS*
157  * 10: R_MIPS_NONE *ABS*
158  * 14: 03e0082d move at,ra
159  * 18: 0060f809 jalr v1
160  * label:
161  */
162 #define MIPS_FAKEMCOUNT_OFFSET 4
163 
164 static int MIPS_is_fake_mcount(Elf_Rel const *rp)
165 {
166  static Elf_Addr old_r_offset;
167  Elf_Addr current_r_offset = _w(rp->r_offset);
168  int is_fake;
169 
170  is_fake = old_r_offset &&
171  (current_r_offset - old_r_offset == MIPS_FAKEMCOUNT_OFFSET);
172  old_r_offset = current_r_offset;
173 
174  return is_fake;
175 }
176 
177 /* Append the new shstrtab, Elf_Shdr[], __mcount_loc and its relocations. */
178 static void append_func(Elf_Ehdr *const ehdr,
179  Elf_Shdr *const shstr,
180  uint_t const *const mloc0,
181  uint_t const *const mlocp,
182  Elf_Rel const *const mrel0,
183  Elf_Rel const *const mrelp,
184  unsigned int const rel_entsize,
185  unsigned int const symsec_sh_link)
186 {
187  /* Begin constructing output file */
188  Elf_Shdr mcsec;
189  char const *mc_name = (sizeof(Elf_Rela) == rel_entsize)
190  ? ".rela__mcount_loc"
191  : ".rel__mcount_loc";
192  unsigned const old_shnum = w2(ehdr->e_shnum);
193  uint_t const old_shoff = _w(ehdr->e_shoff);
194  uint_t const old_shstr_sh_size = _w(shstr->sh_size);
195  uint_t const old_shstr_sh_offset = _w(shstr->sh_offset);
196  uint_t t = 1 + strlen(mc_name) + _w(shstr->sh_size);
197  uint_t new_e_shoff;
198 
199  shstr->sh_size = _w(t);
200  shstr->sh_offset = _w(sb.st_size);
201  t += sb.st_size;
202  t += (_align & -t); /* word-byte align */
203  new_e_shoff = t;
204 
205  /* body for new shstrtab */
206  ulseek(fd_map, sb.st_size, SEEK_SET);
207  uwrite(fd_map, old_shstr_sh_offset + (void *)ehdr, old_shstr_sh_size);
208  uwrite(fd_map, mc_name, 1 + strlen(mc_name));
209 
210  /* old(modified) Elf_Shdr table, word-byte aligned */
211  ulseek(fd_map, t, SEEK_SET);
212  t += sizeof(Elf_Shdr) * old_shnum;
213  uwrite(fd_map, old_shoff + (void *)ehdr,
214  sizeof(Elf_Shdr) * old_shnum);
215 
216  /* new sections __mcount_loc and .rel__mcount_loc */
217  t += 2*sizeof(mcsec);
218  mcsec.sh_name = w((sizeof(Elf_Rela) == rel_entsize) + strlen(".rel")
219  + old_shstr_sh_size);
220  mcsec.sh_type = w(SHT_PROGBITS);
221  mcsec.sh_flags = _w(SHF_ALLOC);
222  mcsec.sh_addr = 0;
223  mcsec.sh_offset = _w(t);
224  mcsec.sh_size = _w((void *)mlocp - (void *)mloc0);
225  mcsec.sh_link = 0;
226  mcsec.sh_info = 0;
227  mcsec.sh_addralign = _w(_size);
228  mcsec.sh_entsize = _w(_size);
229  uwrite(fd_map, &mcsec, sizeof(mcsec));
230 
231  mcsec.sh_name = w(old_shstr_sh_size);
232  mcsec.sh_type = (sizeof(Elf_Rela) == rel_entsize)
233  ? w(SHT_RELA)
234  : w(SHT_REL);
235  mcsec.sh_flags = 0;
236  mcsec.sh_addr = 0;
237  mcsec.sh_offset = _w((void *)mlocp - (void *)mloc0 + t);
238  mcsec.sh_size = _w((void *)mrelp - (void *)mrel0);
239  mcsec.sh_link = w(symsec_sh_link);
240  mcsec.sh_info = w(old_shnum);
241  mcsec.sh_addralign = _w(_size);
242  mcsec.sh_entsize = _w(rel_entsize);
243  uwrite(fd_map, &mcsec, sizeof(mcsec));
244 
245  uwrite(fd_map, mloc0, (void *)mlocp - (void *)mloc0);
246  uwrite(fd_map, mrel0, (void *)mrelp - (void *)mrel0);
247 
248  ehdr->e_shoff = _w(new_e_shoff);
249  ehdr->e_shnum = w2(2 + w2(ehdr->e_shnum)); /* {.rel,}__mcount_loc */
250  ulseek(fd_map, 0, SEEK_SET);
251  uwrite(fd_map, ehdr, sizeof(*ehdr));
252 }
253 
254 static unsigned get_mcountsym(Elf_Sym const *const sym0,
255  Elf_Rel const *relp,
256  char const *const str0)
257 {
258  unsigned mcountsym = 0;
259 
260  Elf_Sym const *const symp =
261  &sym0[Elf_r_sym(relp)];
262  char const *symname = &str0[w(symp->st_name)];
263  char const *mcount = gpfx == '_' ? "_mcount" : "mcount";
264  char const *fentry = "__fentry__";
265 
266  if (symname[0] == '.')
267  ++symname; /* ppc64 hack */
268  if (strcmp(mcount, symname) == 0 ||
269  (altmcount && strcmp(altmcount, symname) == 0) ||
270  (strcmp(fentry, symname) == 0))
271  mcountsym = Elf_r_sym(relp);
272 
273  return mcountsym;
274 }
275 
276 static void get_sym_str_and_relp(Elf_Shdr const *const relhdr,
277  Elf_Ehdr const *const ehdr,
278  Elf_Sym const **sym0,
279  char const **str0,
280  Elf_Rel const **relp)
281 {
282  Elf_Shdr *const shdr0 = (Elf_Shdr *)(_w(ehdr->e_shoff)
283  + (void *)ehdr);
284  unsigned const symsec_sh_link = w(relhdr->sh_link);
285  Elf_Shdr const *const symsec = &shdr0[symsec_sh_link];
286  Elf_Shdr const *const strsec = &shdr0[w(symsec->sh_link)];
287  Elf_Rel const *const rel0 = (Elf_Rel const *)(_w(relhdr->sh_offset)
288  + (void *)ehdr);
289 
290  *sym0 = (Elf_Sym const *)(_w(symsec->sh_offset)
291  + (void *)ehdr);
292 
293  *str0 = (char const *)(_w(strsec->sh_offset)
294  + (void *)ehdr);
295 
296  *relp = rel0;
297 }
298 
299 /*
300  * Look at the relocations in order to find the calls to mcount.
301  * Accumulate the section offsets that are found, and their relocation info,
302  * onto the end of the existing arrays.
303  */
304 static uint_t *sift_rel_mcount(uint_t *mlocp,
305  unsigned const offbase,
306  Elf_Rel **const mrelpp,
307  Elf_Shdr const *const relhdr,
308  Elf_Ehdr const *const ehdr,
309  unsigned const recsym,
310  uint_t const recval,
311  unsigned const reltype)
312 {
313  uint_t *const mloc0 = mlocp;
314  Elf_Rel *mrelp = *mrelpp;
315  Elf_Sym const *sym0;
316  char const *str0;
317  Elf_Rel const *relp;
318  unsigned rel_entsize = _w(relhdr->sh_entsize);
319  unsigned const nrel = _w(relhdr->sh_size) / rel_entsize;
320  unsigned mcountsym = 0;
321  unsigned t;
322 
323  get_sym_str_and_relp(relhdr, ehdr, &sym0, &str0, &relp);
324 
325  for (t = nrel; t; --t) {
326  if (!mcountsym)
327  mcountsym = get_mcountsym(sym0, relp, str0);
328 
329  if (mcountsym == Elf_r_sym(relp) && !is_fake_mcount(relp)) {
330  uint_t const addend =
331  _w(_w(relp->r_offset) - recval + mcount_adjust);
332  mrelp->r_offset = _w(offbase
333  + ((void *)mlocp - (void *)mloc0));
334  Elf_r_info(mrelp, recsym, reltype);
335  if (rel_entsize == sizeof(Elf_Rela)) {
336  ((Elf_Rela *)mrelp)->r_addend = addend;
337  *mlocp++ = 0;
338  } else
339  *mlocp++ = addend;
340 
341  mrelp = (Elf_Rel *)(rel_entsize + (void *)mrelp);
342  }
343  relp = (Elf_Rel const *)(rel_entsize + (void *)relp);
344  }
345  *mrelpp = mrelp;
346  return mlocp;
347 }
348 
349 /*
350  * Read the relocation table again, but this time its called on sections
351  * that are not going to be traced. The mcount calls here will be converted
352  * into nops.
353  */
354 static void nop_mcount(Elf_Shdr const *const relhdr,
355  Elf_Ehdr const *const ehdr,
356  const char *const txtname)
357 {
358  Elf_Shdr *const shdr0 = (Elf_Shdr *)(_w(ehdr->e_shoff)
359  + (void *)ehdr);
360  Elf_Sym const *sym0;
361  char const *str0;
362  Elf_Rel const *relp;
363  Elf_Shdr const *const shdr = &shdr0[w(relhdr->sh_info)];
364  unsigned rel_entsize = _w(relhdr->sh_entsize);
365  unsigned const nrel = _w(relhdr->sh_size) / rel_entsize;
366  unsigned mcountsym = 0;
367  unsigned t;
368  int once = 0;
369 
370  get_sym_str_and_relp(relhdr, ehdr, &sym0, &str0, &relp);
371 
372  for (t = nrel; t; --t) {
373  int ret = -1;
374 
375  if (!mcountsym)
376  mcountsym = get_mcountsym(sym0, relp, str0);
377 
378  if (mcountsym == Elf_r_sym(relp) && !is_fake_mcount(relp)) {
379  if (make_nop)
380  ret = make_nop((void *)ehdr, shdr->sh_offset + relp->r_offset);
381  if (warn_on_notrace_sect && !once) {
382  printf("Section %s has mcount callers being ignored\n",
383  txtname);
384  once = 1;
385  /* just warn? */
386  if (!make_nop)
387  return;
388  }
389  }
390 
391  /*
392  * If we successfully removed the mcount, mark the relocation
393  * as a nop (don't do anything with it).
394  */
395  if (!ret) {
396  Elf_Rel rel;
397  rel = *(Elf_Rel *)relp;
398  Elf_r_info(&rel, Elf_r_sym(relp), rel_type_nop);
399  ulseek(fd_map, (void *)relp - (void *)ehdr, SEEK_SET);
400  uwrite(fd_map, &rel, sizeof(rel));
401  }
402  relp = (Elf_Rel const *)(rel_entsize + (void *)relp);
403  }
404 }
405 
406 
407 /*
408  * Find a symbol in the given section, to be used as the base for relocating
409  * the table of offsets of calls to mcount. A local or global symbol suffices,
410  * but avoid a Weak symbol because it may be overridden; the change in value
411  * would invalidate the relocations of the offsets of the calls to mcount.
412  * Often the found symbol will be the unnamed local symbol generated by
413  * GNU 'as' for the start of each section. For example:
414  * Num: Value Size Type Bind Vis Ndx Name
415  * 2: 00000000 0 SECTION LOCAL DEFAULT 1
416  */
417 static unsigned find_secsym_ndx(unsigned const txtndx,
418  char const *const txtname,
419  uint_t *const recvalp,
420  Elf_Shdr const *const symhdr,
421  Elf_Ehdr const *const ehdr)
422 {
423  Elf_Sym const *const sym0 = (Elf_Sym const *)(_w(symhdr->sh_offset)
424  + (void *)ehdr);
425  unsigned const nsym = _w(symhdr->sh_size) / _w(symhdr->sh_entsize);
426  Elf_Sym const *symp;
427  unsigned t;
428 
429  for (symp = sym0, t = nsym; t; --t, ++symp) {
430  unsigned int const st_bind = ELF_ST_BIND(symp->st_info);
431 
432  if (txtndx == w2(symp->st_shndx)
433  /* avoid STB_WEAK */
434  && (STB_LOCAL == st_bind || STB_GLOBAL == st_bind)) {
435  /* function symbols on ARM have quirks, avoid them */
436  if (w2(ehdr->e_machine) == EM_ARM
437  && ELF_ST_TYPE(symp->st_info) == STT_FUNC)
438  continue;
439 
440  *recvalp = _w(symp->st_value);
441  return symp - sym0;
442  }
443  }
444  fprintf(stderr, "Cannot find symbol for section %d: %s.\n",
445  txtndx, txtname);
446  fail_file();
447 }
448 
449 
450 /* Evade ISO C restriction: no declaration after statement in has_rel_mcount. */
451 static char const *
452 __has_rel_mcount(Elf_Shdr const *const relhdr, /* is SHT_REL or SHT_RELA */
453  Elf_Shdr const *const shdr0,
454  char const *const shstrtab,
455  char const *const fname)
456 {
457  /* .sh_info depends on .sh_type == SHT_REL[,A] */
458  Elf_Shdr const *const txthdr = &shdr0[w(relhdr->sh_info)];
459  char const *const txtname = &shstrtab[w(txthdr->sh_name)];
460 
461  if (strcmp("__mcount_loc", txtname) == 0) {
462  fprintf(stderr, "warning: __mcount_loc already exists: %s\n",
463  fname);
464  succeed_file();
465  }
466  if (w(txthdr->sh_type) != SHT_PROGBITS ||
467  !(_w(txthdr->sh_flags) & SHF_EXECINSTR))
468  return NULL;
469  return txtname;
470 }
471 
472 static char const *has_rel_mcount(Elf_Shdr const *const relhdr,
473  Elf_Shdr const *const shdr0,
474  char const *const shstrtab,
475  char const *const fname)
476 {
477  if (w(relhdr->sh_type) != SHT_REL && w(relhdr->sh_type) != SHT_RELA)
478  return NULL;
479  return __has_rel_mcount(relhdr, shdr0, shstrtab, fname);
480 }
481 
482 
483 static unsigned tot_relsize(Elf_Shdr const *const shdr0,
484  unsigned nhdr,
485  const char *const shstrtab,
486  const char *const fname)
487 {
488  unsigned totrelsz = 0;
489  Elf_Shdr const *shdrp = shdr0;
490  char const *txtname;
491 
492  for (; nhdr; --nhdr, ++shdrp) {
493  txtname = has_rel_mcount(shdrp, shdr0, shstrtab, fname);
494  if (txtname && is_mcounted_section_name(txtname))
495  totrelsz += _w(shdrp->sh_size);
496  }
497  return totrelsz;
498 }
499 
500 
501 /* Overall supervision for Elf32 ET_REL file. */
502 static void
503 do_func(Elf_Ehdr *const ehdr, char const *const fname, unsigned const reltype)
504 {
505  Elf_Shdr *const shdr0 = (Elf_Shdr *)(_w(ehdr->e_shoff)
506  + (void *)ehdr);
507  unsigned const nhdr = w2(ehdr->e_shnum);
508  Elf_Shdr *const shstr = &shdr0[w2(ehdr->e_shstrndx)];
509  char const *const shstrtab = (char const *)(_w(shstr->sh_offset)
510  + (void *)ehdr);
511 
512  Elf_Shdr const *relhdr;
513  unsigned k;
514 
515  /* Upper bound on space: assume all relevant relocs are for mcount. */
516  unsigned const totrelsz = tot_relsize(shdr0, nhdr, shstrtab, fname);
517  Elf_Rel *const mrel0 = umalloc(totrelsz);
518  Elf_Rel * mrelp = mrel0;
519 
520  /* 2*sizeof(address) <= sizeof(Elf_Rel) */
521  uint_t *const mloc0 = umalloc(totrelsz>>1);
522  uint_t * mlocp = mloc0;
523 
524  unsigned rel_entsize = 0;
525  unsigned symsec_sh_link = 0;
526 
527  for (relhdr = shdr0, k = nhdr; k; --k, ++relhdr) {
528  char const *const txtname = has_rel_mcount(relhdr, shdr0,
529  shstrtab, fname);
530  if (txtname && is_mcounted_section_name(txtname)) {
531  uint_t recval = 0;
532  unsigned const recsym = find_secsym_ndx(
533  w(relhdr->sh_info), txtname, &recval,
534  &shdr0[symsec_sh_link = w(relhdr->sh_link)],
535  ehdr);
536 
537  rel_entsize = _w(relhdr->sh_entsize);
538  mlocp = sift_rel_mcount(mlocp,
539  (void *)mlocp - (void *)mloc0, &mrelp,
540  relhdr, ehdr, recsym, recval, reltype);
541  } else if (txtname && (warn_on_notrace_sect || make_nop)) {
542  /*
543  * This section is ignored by ftrace, but still
544  * has mcount calls. Convert them to nops now.
545  */
546  nop_mcount(relhdr, ehdr, txtname);
547  }
548  }
549  if (mloc0 != mlocp) {
550  append_func(ehdr, shstr, mloc0, mlocp, mrel0, mrelp,
551  rel_entsize, symsec_sh_link);
552  }
553  free(mrel0);
554  free(mloc0);
555 }
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