1#!/usr/bin/perl -w 2# (c) 2008, Steven Rostedt <srostedt@redhat.com> 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 ".text.sched" 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 .text.sched. 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 ".text.sched" 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 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, $inputfile) = @ARGV; 111 112# Acceptable sections to record. 113my %text_sections = ( 114 ".text" => 1, 115 ".sched.text" => 1, 116 ".spinlock.text" => 1, 117 ".irqentry.text" => 1, 118); 119 120$objdump = "objdump" if ((length $objdump) == 0); 121$objcopy = "objcopy" if ((length $objcopy) == 0); 122$cc = "gcc" if ((length $cc) == 0); 123$ld = "ld" if ((length $ld) == 0); 124$nm = "nm" if ((length $nm) == 0); 125$rm = "rm" if ((length $rm) == 0); 126$mv = "mv" if ((length $mv) == 0); 127 128#print STDERR "running: $P '$arch' '$objdump' '$objcopy' '$cc' '$ld' " . 129# "'$nm' '$rm' '$mv' '$inputfile'\n"; 130 131my %locals; # List of local (static) functions 132my %weak; # List of weak functions 133my %convert; # List of local functions used that needs conversion 134 135my $type; 136my $nm_regex; # Find the local functions (return function) 137my $section_regex; # Find the start of a section 138my $function_regex; # Find the name of a function 139 # (return offset and func name) 140my $mcount_regex; # Find the call site to mcount (return offset) 141my $alignment; # The .align value to use for $mcount_section 142my $section_type; # Section header plus possible alignment command 143 144if ($arch eq "x86") { 145 if ($bits == 64) { 146 $arch = "x86_64"; 147 } else { 148 $arch = "i386"; 149 } 150} 151 152# 153# We base the defaults off of i386, the other archs may 154# feel free to change them in the below if statements. 155# 156$nm_regex = "^[0-9a-fA-F]+\\s+t\\s+(\\S+)"; 157$section_regex = "Disassembly of section\\s+(\\S+):"; 158$function_regex = "^([0-9a-fA-F]+)\\s+<(.*?)>:"; 159$mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\smcount\$"; 160$section_type = '@progbits'; 161$type = ".long"; 162 163if ($arch eq "x86_64") { 164 $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\smcount([+-]0x[0-9a-zA-Z]+)?\$"; 165 $type = ".quad"; 166 $alignment = 8; 167 168 # force flags for this arch 169 $ld .= " -m elf_x86_64"; 170 $objdump .= " -M x86-64"; 171 $objcopy .= " -O elf64-x86-64"; 172 $cc .= " -m64"; 173 174} elsif ($arch eq "i386") { 175 $alignment = 4; 176 177 # force flags for this arch 178 $ld .= " -m elf_i386"; 179 $objdump .= " -M i386"; 180 $objcopy .= " -O elf32-i386"; 181 $cc .= " -m32"; 182 183} elsif ($arch eq "sh") { 184 $alignment = 2; 185 186 # force flags for this arch 187 $ld .= " -m shlelf_linux"; 188 $objcopy .= " -O elf32-sh-linux"; 189 $cc .= " -m32"; 190 191} elsif ($arch eq "powerpc") { 192 $nm_regex = "^[0-9a-fA-F]+\\s+t\\s+(\\.?\\S+)"; 193 $function_regex = "^([0-9a-fA-F]+)\\s+<(\\.?.*?)>:"; 194 $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s\\.?_mcount\$"; 195 196 if ($bits == 64) { 197 $type = ".quad"; 198 } 199 200} elsif ($arch eq "arm") { 201 $alignment = 2; 202 $section_type = '%progbits'; 203 204} else { 205 die "Arch $arch is not supported with CONFIG_FTRACE_MCOUNT_RECORD"; 206} 207 208my $text_found = 0; 209my $read_function = 0; 210my $opened = 0; 211my $mcount_section = "__mcount_loc"; 212 213my $dirname; 214my $filename; 215my $prefix; 216my $ext; 217 218if ($inputfile =~ m,^(.*)/([^/]*)$,) { 219 $dirname = $1; 220 $filename = $2; 221} else { 222 $dirname = "."; 223 $filename = $inputfile; 224} 225 226if ($filename =~ m,^(.*)(\.\S),) { 227 $prefix = $1; 228 $ext = $2; 229} else { 230 $prefix = $filename; 231 $ext = ""; 232} 233 234my $mcount_s = $dirname . "/.tmp_mc_" . $prefix . ".s"; 235my $mcount_o = $dirname . "/.tmp_mc_" . $prefix . ".o"; 236 237# 238# --globalize-symbols came out in 2.17, we must test the version 239# of objcopy, and if it is less than 2.17, then we can not 240# record local functions. 241my $use_locals = 01; 242my $local_warn_once = 0; 243my $found_version = 0; 244 245open (IN, "$objcopy --version |") || die "error running $objcopy"; 246while (<IN>) { 247 if (/objcopy.*\s(\d+)\.(\d+)/) { 248 my $major = $1; 249 my $minor = $2; 250 251 $found_version = 1; 252 if ($major < 2 || 253 ($major == 2 && $minor < 17)) { 254 $use_locals = 0; 255 } 256 last; 257 } 258} 259close (IN); 260 261if (!$found_version) { 262 print STDERR "WARNING: could not find objcopy version.\n" . 263 "\tDisabling local function references.\n"; 264} 265 266 267# 268# Step 1: find all the local (static functions) and weak symbols. 269# 't' is local, 'w/W' is weak (we never use a weak function) 270# 271open (IN, "$nm $inputfile|") || die "error running $nm"; 272while (<IN>) { 273 if (/$nm_regex/) { 274 $locals{$1} = 1; 275 } elsif (/^[0-9a-fA-F]+\s+([wW])\s+(\S+)/) { 276 $weak{$2} = $1; 277 } 278} 279close(IN); 280 281my @offsets; # Array of offsets of mcount callers 282my $ref_func; # reference function to use for offsets 283my $offset = 0; # offset of ref_func to section beginning 284 285## 286# update_funcs - print out the current mcount callers 287# 288# Go through the list of offsets to callers and write them to 289# the output file in a format that can be read by an assembler. 290# 291sub update_funcs 292{ 293 return if ($#offsets < 0); 294 295 defined($ref_func) || die "No function to reference"; 296 297 # A section only had a weak function, to represent it. 298 # Unfortunately, a weak function may be overwritten by another 299 # function of the same name, making all these offsets incorrect. 300 # To be safe, we simply print a warning and bail. 301 if (defined $weak{$ref_func}) { 302 print STDERR 303 "$inputfile: WARNING: referencing weak function" . 304 " $ref_func for mcount\n"; 305 return; 306 } 307 308 # is this function static? If so, note this fact. 309 if (defined $locals{$ref_func}) { 310 311 # only use locals if objcopy supports globalize-symbols 312 if (!$use_locals) { 313 return; 314 } 315 $convert{$ref_func} = 1; 316 } 317 318 # Loop through all the mcount caller offsets and print a reference 319 # to the caller based from the ref_func. 320 for (my $i=0; $i <= $#offsets; $i++) { 321 if (!$opened) { 322 open(FILE, ">$mcount_s") || die "can't create $mcount_s\n"; 323 $opened = 1; 324 print FILE "\t.section $mcount_section,\"a\",$section_type\n"; 325 print FILE "\t.align $alignment\n" if (defined($alignment)); 326 } 327 printf FILE "\t%s %s + %d\n", $type, $ref_func, $offsets[$i] - $offset; 328 } 329} 330 331# 332# Step 2: find the sections and mcount call sites 333# 334open(IN, "$objdump -dr $inputfile|") || die "error running $objdump"; 335 336my $text; 337 338while (<IN>) { 339 # is it a section? 340 if (/$section_regex/) { 341 342 # Only record text sections that we know are safe 343 if (defined($text_sections{$1})) { 344 $read_function = 1; 345 } else { 346 $read_function = 0; 347 } 348 # print out any recorded offsets 349 update_funcs() if ($text_found); 350 351 # reset all markers and arrays 352 $text_found = 0; 353 undef($ref_func); 354 undef(@offsets); 355 356 # section found, now is this a start of a function? 357 } elsif ($read_function && /$function_regex/) { 358 $text_found = 1; 359 $offset = hex $1; 360 $text = $2; 361 362 # if this is either a local function or a weak function 363 # keep looking for functions that are global that 364 # we can use safely. 365 if (!defined($locals{$text}) && !defined($weak{$text})) { 366 $ref_func = $text; 367 $read_function = 0; 368 } else { 369 # if we already have a function, and this is weak, skip it 370 if (!defined($ref_func) || !defined($weak{$text})) { 371 $ref_func = $text; 372 } 373 } 374 } 375 376 # is this a call site to mcount? If so, record it to print later 377 if ($text_found && /$mcount_regex/) { 378 $offsets[$#offsets + 1] = hex $1; 379 } 380} 381 382# dump out anymore offsets that may have been found 383update_funcs() if ($text_found); 384 385# If we did not find any mcount callers, we are done (do nothing). 386if (!$opened) { 387 exit(0); 388} 389 390close(FILE); 391 392# 393# Step 3: Compile the file that holds the list of call sites to mcount. 394# 395`$cc -o $mcount_o -c $mcount_s`; 396 397my @converts = keys %convert; 398 399# 400# Step 4: Do we have sections that started with local functions? 401# 402if ($#converts >= 0) { 403 my $globallist = ""; 404 my $locallist = ""; 405 406 foreach my $con (@converts) { 407 $globallist .= " --globalize-symbol $con"; 408 $locallist .= " --localize-symbol $con"; 409 } 410 411 my $globalobj = $dirname . "/.tmp_gl_" . $filename; 412 my $globalmix = $dirname . "/.tmp_mx_" . $filename; 413 414 # 415 # Step 5: set up each local function as a global 416 # 417 `$objcopy $globallist $inputfile $globalobj`; 418 419 # 420 # Step 6: Link the global version to our list. 421 # 422 `$ld -r $globalobj $mcount_o -o $globalmix`; 423 424 # 425 # Step 7: Convert the local functions back into local symbols 426 # 427 `$objcopy $locallist $globalmix $inputfile`; 428 429 # Remove the temp files 430 `$rm $globalobj $globalmix`; 431 432} else { 433 434 my $mix = $dirname . "/.tmp_mx_" . $filename; 435 436 # 437 # Step 8: Link the object with our list of call sites object. 438 # 439 `$ld -r $inputfile $mcount_o -o $mix`; 440 441 # 442 # Step 9: Move the result back to the original object. 443 # 444 `$mv $mix $inputfile`; 445} 446 447# Clean up the temp files 448`$rm $mcount_o $mcount_s`; 449 450exit(0); 451