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, $inputfile) = @ARGV; 111 112# This file refers to mcount and shouldn't be ftraced, so lets' ignore it 113if ($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 "sh") { 189 $alignment = 2; 190 191 # force flags for this arch 192 $ld .= " -m shlelf_linux"; 193 $objcopy .= " -O elf32-sh-linux"; 194 $cc .= " -m32"; 195 196} elsif ($arch eq "powerpc") { 197 $nm_regex = "^[0-9a-fA-F]+\\s+t\\s+(\\.?\\S+)"; 198 $function_regex = "^([0-9a-fA-F]+)\\s+<(\\.?.*?)>:"; 199 $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s\\.?_mcount\$"; 200 201 if ($bits == 64) { 202 $type = ".quad"; 203 } 204 205} elsif ($arch eq "arm") { 206 $alignment = 2; 207 $section_type = '%progbits'; 208 209} else { 210 die "Arch $arch is not supported with CONFIG_FTRACE_MCOUNT_RECORD"; 211} 212 213my $text_found = 0; 214my $read_function = 0; 215my $opened = 0; 216my $mcount_section = "__mcount_loc"; 217 218my $dirname; 219my $filename; 220my $prefix; 221my $ext; 222 223if ($inputfile =~ m,^(.*)/([^/]*)$,) { 224 $dirname = $1; 225 $filename = $2; 226} else { 227 $dirname = "."; 228 $filename = $inputfile; 229} 230 231if ($filename =~ m,^(.*)(\.\S),) { 232 $prefix = $1; 233 $ext = $2; 234} else { 235 $prefix = $filename; 236 $ext = ""; 237} 238 239my $mcount_s = $dirname . "/.tmp_mc_" . $prefix . ".s"; 240my $mcount_o = $dirname . "/.tmp_mc_" . $prefix . ".o"; 241 242# 243# --globalize-symbols came out in 2.17, we must test the version 244# of objcopy, and if it is less than 2.17, then we can not 245# record local functions. 246my $use_locals = 01; 247my $local_warn_once = 0; 248my $found_version = 0; 249 250open (IN, "$objcopy --version |") || die "error running $objcopy"; 251while (<IN>) { 252 if (/objcopy.*\s(\d+)\.(\d+)/) { 253 my $major = $1; 254 my $minor = $2; 255 256 $found_version = 1; 257 if ($major < 2 || 258 ($major == 2 && $minor < 17)) { 259 $use_locals = 0; 260 } 261 last; 262 } 263} 264close (IN); 265 266if (!$found_version) { 267 print STDERR "WARNING: could not find objcopy version.\n" . 268 "\tDisabling local function references.\n"; 269} 270 271 272# 273# Step 1: find all the local (static functions) and weak symbols. 274# 't' is local, 'w/W' is weak (we never use a weak function) 275# 276open (IN, "$nm $inputfile|") || die "error running $nm"; 277while (<IN>) { 278 if (/$nm_regex/) { 279 $locals{$1} = 1; 280 } elsif (/^[0-9a-fA-F]+\s+([wW])\s+(\S+)/) { 281 $weak{$2} = $1; 282 } 283} 284close(IN); 285 286my @offsets; # Array of offsets of mcount callers 287my $ref_func; # reference function to use for offsets 288my $offset = 0; # offset of ref_func to section beginning 289 290## 291# update_funcs - print out the current mcount callers 292# 293# Go through the list of offsets to callers and write them to 294# the output file in a format that can be read by an assembler. 295# 296sub update_funcs 297{ 298 return if ($#offsets < 0); 299 300 defined($ref_func) || die "No function to reference"; 301 302 # A section only had a weak function, to represent it. 303 # Unfortunately, a weak function may be overwritten by another 304 # function of the same name, making all these offsets incorrect. 305 # To be safe, we simply print a warning and bail. 306 if (defined $weak{$ref_func}) { 307 print STDERR 308 "$inputfile: WARNING: referencing weak function" . 309 " $ref_func for mcount\n"; 310 return; 311 } 312 313 # is this function static? If so, note this fact. 314 if (defined $locals{$ref_func}) { 315 316 # only use locals if objcopy supports globalize-symbols 317 if (!$use_locals) { 318 return; 319 } 320 $convert{$ref_func} = 1; 321 } 322 323 # Loop through all the mcount caller offsets and print a reference 324 # to the caller based from the ref_func. 325 for (my $i=0; $i <= $#offsets; $i++) { 326 if (!$opened) { 327 open(FILE, ">$mcount_s") || die "can't create $mcount_s\n"; 328 $opened = 1; 329 print FILE "\t.section $mcount_section,\"a\",$section_type\n"; 330 print FILE "\t.align $alignment\n" if (defined($alignment)); 331 } 332 printf FILE "\t%s %s + %d\n", $type, $ref_func, $offsets[$i] - $offset; 333 } 334} 335 336# 337# Step 2: find the sections and mcount call sites 338# 339open(IN, "$objdump -dr $inputfile|") || die "error running $objdump"; 340 341my $text; 342 343while (<IN>) { 344 # is it a section? 345 if (/$section_regex/) { 346 347 # Only record text sections that we know are safe 348 if (defined($text_sections{$1})) { 349 $read_function = 1; 350 } else { 351 $read_function = 0; 352 } 353 # print out any recorded offsets 354 update_funcs() if ($text_found); 355 356 # reset all markers and arrays 357 $text_found = 0; 358 undef($ref_func); 359 undef(@offsets); 360 361 # section found, now is this a start of a function? 362 } elsif ($read_function && /$function_regex/) { 363 $text_found = 1; 364 $offset = hex $1; 365 $text = $2; 366 367 # if this is either a local function or a weak function 368 # keep looking for functions that are global that 369 # we can use safely. 370 if (!defined($locals{$text}) && !defined($weak{$text})) { 371 $ref_func = $text; 372 $read_function = 0; 373 } else { 374 # if we already have a function, and this is weak, skip it 375 if (!defined($ref_func) || !defined($weak{$text})) { 376 $ref_func = $text; 377 } 378 } 379 } 380 381 # is this a call site to mcount? If so, record it to print later 382 if ($text_found && /$mcount_regex/) { 383 $offsets[$#offsets + 1] = hex $1; 384 } 385} 386 387# dump out anymore offsets that may have been found 388update_funcs() if ($text_found); 389 390# If we did not find any mcount callers, we are done (do nothing). 391if (!$opened) { 392 exit(0); 393} 394 395close(FILE); 396 397# 398# Step 3: Compile the file that holds the list of call sites to mcount. 399# 400`$cc -o $mcount_o -c $mcount_s`; 401 402my @converts = keys %convert; 403 404# 405# Step 4: Do we have sections that started with local functions? 406# 407if ($#converts >= 0) { 408 my $globallist = ""; 409 my $locallist = ""; 410 411 foreach my $con (@converts) { 412 $globallist .= " --globalize-symbol $con"; 413 $locallist .= " --localize-symbol $con"; 414 } 415 416 my $globalobj = $dirname . "/.tmp_gl_" . $filename; 417 my $globalmix = $dirname . "/.tmp_mx_" . $filename; 418 419 # 420 # Step 5: set up each local function as a global 421 # 422 `$objcopy $globallist $inputfile $globalobj`; 423 424 # 425 # Step 6: Link the global version to our list. 426 # 427 `$ld -r $globalobj $mcount_o -o $globalmix`; 428 429 # 430 # Step 7: Convert the local functions back into local symbols 431 # 432 `$objcopy $locallist $globalmix $inputfile`; 433 434 # Remove the temp files 435 `$rm $globalobj $globalmix`; 436 437} else { 438 439 my $mix = $dirname . "/.tmp_mx_" . $filename; 440 441 # 442 # Step 8: Link the object with our list of call sites object. 443 # 444 `$ld -r $inputfile $mcount_o -o $mix`; 445 446 # 447 # Step 9: Move the result back to the original object. 448 # 449 `$mv $mix $inputfile`; 450} 451 452# Clean up the temp files 453`$rm $mcount_o $mcount_s`; 454 455exit(0); 456