1#!/usr/bin/perl -w 2# (c) 2008, Steven Rostedt <[email protected]> 3# Licensed under the terms of the GNU GPL License version 2 4# 5# recordmcount.pl - makes a section called __mcount_loc that holds 6# all the offsets to the calls to mcount. 7# 8# 9# What we want to end up with is a section in vmlinux called 10# __mcount_loc that contains a list of pointers to all the 11# call sites in the kernel that call mcount. Later on boot up, the kernel 12# will read this list, save the locations and turn them into nops. 13# When tracing or profiling is later enabled, these locations will then 14# be converted back to pointers to some function. 15# 16# This is no easy feat. This script is called just after the original 17# object is compiled and before it is linked. 18# 19# The references to the call sites are offsets from the section of text 20# that the call site is in. Hence, all functions in a section that 21# has a call site to mcount, will have the offset from the beginning of 22# the section and not the beginning of the function. 23# 24# The trick is to find a way to record the beginning of the section. 25# The way we do this is to look at the first function in the section 26# which will also be the location of that section after final link. 27# e.g. 28# 29# .section ".sched.text", "ax" 30# .globl my_func 31# my_func: 32# [...] 33# call mcount (offset: 0x5) 34# [...] 35# ret 36# other_func: 37# [...] 38# call mcount (offset: 0x1b) 39# [...] 40# 41# Both relocation offsets for the mcounts in the above example will be 42# offset from .sched.text. If we make another file called tmp.s with: 43# 44# .section __mcount_loc 45# .quad my_func + 0x5 46# .quad my_func + 0x1b 47# 48# We can then compile this tmp.s into tmp.o, and link it to the original 49# object. 50# 51# But this gets hard if my_func is not globl (a static function). 52# In such a case we have: 53# 54# .section ".sched.text", "ax" 55# my_func: 56# [...] 57# call mcount (offset: 0x5) 58# [...] 59# ret 60# .globl my_func 61# other_func: 62# [...] 63# call mcount (offset: 0x1b) 64# [...] 65# 66# If we make the tmp.s the same as above, when we link together with 67# the original object, we will end up with two symbols for my_func: 68# one local, one global. After final compile, we will end up with 69# an undefined reference to my_func. 70# 71# Since local objects can reference local variables, we need to find 72# a way to make tmp.o reference the local objects of the original object 73# file after it is linked together. To do this, we convert the my_func 74# into a global symbol before linking tmp.o. Then after we link tmp.o 75# we will only have a single symbol for my_func that is global. 76# We can convert my_func back into a local symbol and we are done. 77# 78# Here are the steps we take: 79# 80# 1) Record all the local symbols by using 'nm' 81# 2) Use objdump to find all the call site offsets and sections for 82# mcount. 83# 3) Compile the list into its own object. 84# 4) Do we have to deal with local functions? If not, go to step 8. 85# 5) Make an object that converts these local functions to global symbols 86# with objcopy. 87# 6) Link together this new object with the list object. 88# 7) Convert the local functions back to local symbols and rename 89# the result as the original object. 90# End. 91# 8) Link the object with the list object. 92# 9) Move the result back to the original object. 93# End. 94# 95 96use strict; 97 98my $P = $0; 99$P =~ s@.*/@@g; 100 101my $V = '0.1'; 102 103if ($#ARGV < 7) { 104 print "usage: $P arch bits objdump objcopy cc ld nm rm mv is_module inputfile\n"; 105 print "version: $V\n"; 106 exit(1); 107} 108 109my ($arch, $bits, $objdump, $objcopy, $cc, 110 $ld, $nm, $rm, $mv, $is_module, $inputfile) = @ARGV; 111 112# This file refers to mcount and shouldn't be ftraced, so lets' ignore it 113if ($inputfile eq "kernel/trace/ftrace.o") { 114 exit(0); 115} 116 117# Acceptable sections to record. 118my %text_sections = ( 119 ".text" => 1, 120 ".sched.text" => 1, 121 ".spinlock.text" => 1, 122 ".irqentry.text" => 1, 123); 124 125$objdump = "objdump" if ((length $objdump) == 0); 126$objcopy = "objcopy" if ((length $objcopy) == 0); 127$cc = "gcc" if ((length $cc) == 0); 128$ld = "ld" if ((length $ld) == 0); 129$nm = "nm" if ((length $nm) == 0); 130$rm = "rm" if ((length $rm) == 0); 131$mv = "mv" if ((length $mv) == 0); 132 133#print STDERR "running: $P '$arch' '$objdump' '$objcopy' '$cc' '$ld' " . 134# "'$nm' '$rm' '$mv' '$inputfile'\n"; 135 136my %locals; # List of local (static) functions 137my %weak; # List of weak functions 138my %convert; # List of local functions used that needs conversion 139 140my $type; 141my $nm_regex; # Find the local functions (return function) 142my $section_regex; # Find the start of a section 143my $function_regex; # Find the name of a function 144 # (return offset and func name) 145my $mcount_regex; # Find the call site to mcount (return offset) 146my $alignment; # The .align value to use for $mcount_section 147my $section_type; # Section header plus possible alignment command 148 149if ($arch eq "x86") { 150 if ($bits == 64) { 151 $arch = "x86_64"; 152 } else { 153 $arch = "i386"; 154 } 155} 156 157# 158# We base the defaults off of i386, the other archs may 159# feel free to change them in the below if statements. 160# 161$nm_regex = "^[0-9a-fA-F]+\\s+t\\s+(\\S+)"; 162$section_regex = "Disassembly of section\\s+(\\S+):"; 163$function_regex = "^([0-9a-fA-F]+)\\s+<(.*?)>:"; 164$mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\smcount\$"; 165$section_type = '@progbits'; 166$type = ".long"; 167 168if ($arch eq "x86_64") { 169 $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\smcount([+-]0x[0-9a-zA-Z]+)?\$"; 170 $type = ".quad"; 171 $alignment = 8; 172 173 # force flags for this arch 174 $ld .= " -m elf_x86_64"; 175 $objdump .= " -M x86-64"; 176 $objcopy .= " -O elf64-x86-64"; 177 $cc .= " -m64"; 178 179} elsif ($arch eq "i386") { 180 $alignment = 4; 181 182 # force flags for this arch 183 $ld .= " -m elf_i386"; 184 $objdump .= " -M i386"; 185 $objcopy .= " -O elf32-i386"; 186 $cc .= " -m32"; 187 188} elsif ($arch eq "s390" && $bits == 32) { 189 $mcount_regex = "^\\s*([0-9a-fA-F]+):\\s*R_390_32\\s+_mcount\$"; 190 $alignment = 4; 191 $ld .= " -m elf_s390"; 192 $cc .= " -m31"; 193 194} elsif ($arch eq "s390" && $bits == 64) { 195 $mcount_regex = "^\\s*([0-9a-fA-F]+):\\s*R_390_(PC|PLT)32DBL\\s+_mcount\\+0x2\$"; 196 $alignment = 8; 197 $type = ".quad"; 198 $ld .= " -m elf64_s390"; 199 $cc .= " -m64"; 200 201} elsif ($arch eq "sh") { 202 $alignment = 2; 203 204 # force flags for this arch 205 $ld .= " -m shlelf_linux"; 206 $objcopy .= " -O elf32-sh-linux"; 207 $cc .= " -m32"; 208 209} elsif ($arch eq "powerpc") { 210 $nm_regex = "^[0-9a-fA-F]+\\s+t\\s+(\\.?\\S+)"; 211 $function_regex = "^([0-9a-fA-F]+)\\s+<(\\.?.*?)>:"; 212 $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s\\.?_mcount\$"; 213 214 if ($bits == 64) { 215 $type = ".quad"; 216 } 217 218} elsif ($arch eq "arm") { 219 $alignment = 2; 220 $section_type = '%progbits'; 221 222} elsif ($arch eq "ia64") { 223 $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s_mcount\$"; 224 $type = "data8"; 225 226 if ($is_module eq "0") { 227 $cc .= " -mconstant-gp"; 228 } 229} else { 230 die "Arch $arch is not supported with CONFIG_FTRACE_MCOUNT_RECORD"; 231} 232 233my $text_found = 0; 234my $read_function = 0; 235my $opened = 0; 236my $mcount_section = "__mcount_loc"; 237 238my $dirname; 239my $filename; 240my $prefix; 241my $ext; 242 243if ($inputfile =~ m,^(.*)/([^/]*)$,) { 244 $dirname = $1; 245 $filename = $2; 246} else { 247 $dirname = "."; 248 $filename = $inputfile; 249} 250 251if ($filename =~ m,^(.*)(\.\S),) { 252 $prefix = $1; 253 $ext = $2; 254} else { 255 $prefix = $filename; 256 $ext = ""; 257} 258 259my $mcount_s = $dirname . "/.tmp_mc_" . $prefix . ".s"; 260my $mcount_o = $dirname . "/.tmp_mc_" . $prefix . ".o"; 261 262# 263# --globalize-symbols came out in 2.17, we must test the version 264# of objcopy, and if it is less than 2.17, then we can not 265# record local functions. 266my $use_locals = 01; 267my $local_warn_once = 0; 268my $found_version = 0; 269 270open (IN, "$objcopy --version |") || die "error running $objcopy"; 271while (<IN>) { 272 if (/objcopy.*\s(\d+)\.(\d+)/) { 273 my $major = $1; 274 my $minor = $2; 275 276 $found_version = 1; 277 if ($major < 2 || 278 ($major == 2 && $minor < 17)) { 279 $use_locals = 0; 280 } 281 last; 282 } 283} 284close (IN); 285 286if (!$found_version) { 287 print STDERR "WARNING: could not find objcopy version.\n" . 288 "\tDisabling local function references.\n"; 289} 290 291# 292# Step 1: find all the local (static functions) and weak symbols. 293# 't' is local, 'w/W' is weak (we never use a weak function) 294# 295open (IN, "$nm $inputfile|") || die "error running $nm"; 296while (<IN>) { 297 if (/$nm_regex/) { 298 $locals{$1} = 1; 299 } elsif (/^[0-9a-fA-F]+\s+([wW])\s+(\S+)/) { 300 $weak{$2} = $1; 301 } 302} 303close(IN); 304 305my @offsets; # Array of offsets of mcount callers 306my $ref_func; # reference function to use for offsets 307my $offset = 0; # offset of ref_func to section beginning 308 309## 310# update_funcs - print out the current mcount callers 311# 312# Go through the list of offsets to callers and write them to 313# the output file in a format that can be read by an assembler. 314# 315sub update_funcs 316{ 317 return if ($#offsets < 0); 318 319 defined($ref_func) || die "No function to reference"; 320 321 # A section only had a weak function, to represent it. 322 # Unfortunately, a weak function may be overwritten by another 323 # function of the same name, making all these offsets incorrect. 324 # To be safe, we simply print a warning and bail. 325 if (defined $weak{$ref_func}) { 326 print STDERR 327 "$inputfile: WARNING: referencing weak function" . 328 " $ref_func for mcount\n"; 329 return; 330 } 331 332 # is this function static? If so, note this fact. 333 if (defined $locals{$ref_func}) { 334 335 # only use locals if objcopy supports globalize-symbols 336 if (!$use_locals) { 337 return; 338 } 339 $convert{$ref_func} = 1; 340 } 341 342 # Loop through all the mcount caller offsets and print a reference 343 # to the caller based from the ref_func. 344 for (my $i=0; $i <= $#offsets; $i++) { 345 if (!$opened) { 346 open(FILE, ">$mcount_s") || die "can't create $mcount_s\n"; 347 $opened = 1; 348 print FILE "\t.section $mcount_section,\"a\",$section_type\n"; 349 print FILE "\t.align $alignment\n" if (defined($alignment)); 350 } 351 printf FILE "\t%s %s + %d\n", $type, $ref_func, $offsets[$i] - $offset; 352 } 353} 354 355# 356# Step 2: find the sections and mcount call sites 357# 358open(IN, "$objdump -hdr $inputfile|") || die "error running $objdump"; 359 360my $text; 361 362my $read_headers = 1; 363 364while (<IN>) { 365 # is it a section? 366 if (/$section_regex/) { 367 $read_headers = 0; 368 369 # Only record text sections that we know are safe 370 if (defined($text_sections{$1})) { 371 $read_function = 1; 372 } else { 373 $read_function = 0; 374 } 375 # print out any recorded offsets 376 update_funcs() if ($text_found); 377 378 # reset all markers and arrays 379 $text_found = 0; 380 undef($ref_func); 381 undef(@offsets); 382 383 # section found, now is this a start of a function? 384 } elsif ($read_function && /$function_regex/) { 385 $text_found = 1; 386 $offset = hex $1; 387 $text = $2; 388 389 # if this is either a local function or a weak function 390 # keep looking for functions that are global that 391 # we can use safely. 392 if (!defined($locals{$text}) && !defined($weak{$text})) { 393 $ref_func = $text; 394 $read_function = 0; 395 } else { 396 # if we already have a function, and this is weak, skip it 397 if (!defined($ref_func) || !defined($weak{$text})) { 398 $ref_func = $text; 399 } 400 } 401 } elsif ($read_headers && /$mcount_section/) { 402 # 403 # Somehow the make process can execute this script on an 404 # object twice. If it does, we would duplicate the mcount 405 # section and it will cause the function tracer self test 406 # to fail. Check if the mcount section exists, and if it does, 407 # warn and exit. 408 # 409 print STDERR "ERROR: $mcount_section already in $inputfile\n" . 410 "\tThis may be an indication that your build is corrupted.\n" . 411 "\tDelete $inputfile and try again. If the same object file\n" . 412 "\tstill causes an issue, then disable CONFIG_DYNAMIC_FTRACE.\n"; 413 exit(-1); 414 } 415 416 # is this a call site to mcount? If so, record it to print later 417 if ($text_found && /$mcount_regex/) { 418 $offsets[$#offsets + 1] = hex $1; 419 } 420} 421 422# dump out anymore offsets that may have been found 423update_funcs() if ($text_found); 424 425# If we did not find any mcount callers, we are done (do nothing). 426if (!$opened) { 427 exit(0); 428} 429 430close(FILE); 431 432# 433# Step 3: Compile the file that holds the list of call sites to mcount. 434# 435`$cc -o $mcount_o -c $mcount_s`; 436 437my @converts = keys %convert; 438 439# 440# Step 4: Do we have sections that started with local functions? 441# 442if ($#converts >= 0) { 443 my $globallist = ""; 444 my $locallist = ""; 445 446 foreach my $con (@converts) { 447 $globallist .= " --globalize-symbol $con"; 448 $locallist .= " --localize-symbol $con"; 449 } 450 451 my $globalobj = $dirname . "/.tmp_gl_" . $filename; 452 my $globalmix = $dirname . "/.tmp_mx_" . $filename; 453 454 # 455 # Step 5: set up each local function as a global 456 # 457 `$objcopy $globallist $inputfile $globalobj`; 458 459 # 460 # Step 6: Link the global version to our list. 461 # 462 `$ld -r $globalobj $mcount_o -o $globalmix`; 463 464 # 465 # Step 7: Convert the local functions back into local symbols 466 # 467 `$objcopy $locallist $globalmix $inputfile`; 468 469 # Remove the temp files 470 `$rm $globalobj $globalmix`; 471 472} else { 473 474 my $mix = $dirname . "/.tmp_mx_" . $filename; 475 476 # 477 # Step 8: Link the object with our list of call sites object. 478 # 479 `$ld -r $inputfile $mcount_o -o $mix`; 480 481 # 482 # Step 9: Move the result back to the original object. 483 # 484 `$mv $mix $inputfile`; 485} 486 487# Clean up the temp files 488`$rm $mcount_o $mcount_s`; 489 490exit(0); 491