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 < 6) { 104 print "usage: $P arch objdump objcopy cc ld nm rm mv inputfile\n"; 105 print "version: $V\n"; 106 exit(1); 107} 108 109my ($arch, $bits, $objdump, $objcopy, $cc, 110 $ld, $nm, $rm, $mv, $inputfile) = @ARGV; 111 112# Acceptable sections to record. 113my %text_sections = ( 114 ".text" => 1, 115); 116 117$objdump = "objdump" if ((length $objdump) == 0); 118$objcopy = "objcopy" if ((length $objcopy) == 0); 119$cc = "gcc" if ((length $cc) == 0); 120$ld = "ld" if ((length $ld) == 0); 121$nm = "nm" if ((length $nm) == 0); 122$rm = "rm" if ((length $rm) == 0); 123$mv = "mv" if ((length $mv) == 0); 124 125#print STDERR "running: $P '$arch' '$objdump' '$objcopy' '$cc' '$ld' " . 126# "'$nm' '$rm' '$mv' '$inputfile'\n"; 127 128my %locals; # List of local (static) functions 129my %weak; # List of weak functions 130my %convert; # List of local functions used that needs conversion 131 132my $type; 133my $section_regex; # Find the start of a section 134my $function_regex; # Find the name of a function 135 # (return offset and func name) 136my $mcount_regex; # Find the call site to mcount (return offset) 137 138if ($arch eq "x86") { 139 if ($bits == 64) { 140 $arch = "x86_64"; 141 } else { 142 $arch = "i386"; 143 } 144} 145 146if ($arch eq "x86_64") { 147 $section_regex = "Disassembly of section\\s+(\\S+):"; 148 $function_regex = "^([0-9a-fA-F]+)\\s+<(.*?)>:"; 149 $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\smcount([+-]0x[0-9a-zA-Z]+)?\$"; 150 $type = ".quad"; 151 152 # force flags for this arch 153 $ld .= " -m elf_x86_64"; 154 $objdump .= " -M x86-64"; 155 $objcopy .= " -O elf64-x86-64"; 156 $cc .= " -m64"; 157 158} elsif ($arch eq "i386") { 159 $section_regex = "Disassembly of section\\s+(\\S+):"; 160 $function_regex = "^([0-9a-fA-F]+)\\s+<(.*?)>:"; 161 $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\smcount\$"; 162 $type = ".long"; 163 164 # force flags for this arch 165 $ld .= " -m elf_i386"; 166 $objdump .= " -M i386"; 167 $objcopy .= " -O elf32-i386"; 168 $cc .= " -m32"; 169 170} else { 171 die "Arch $arch is not supported with CONFIG_FTRACE_MCOUNT_RECORD"; 172} 173 174my $text_found = 0; 175my $read_function = 0; 176my $opened = 0; 177my $mcount_section = "__mcount_loc"; 178 179my $dirname; 180my $filename; 181my $prefix; 182my $ext; 183 184if ($inputfile =~ m,^(.*)/([^/]*)$,) { 185 $dirname = $1; 186 $filename = $2; 187} else { 188 $dirname = "."; 189 $filename = $inputfile; 190} 191 192if ($filename =~ m,^(.*)(\.\S),) { 193 $prefix = $1; 194 $ext = $2; 195} else { 196 $prefix = $filename; 197 $ext = ""; 198} 199 200my $mcount_s = $dirname . "/.tmp_mc_" . $prefix . ".s"; 201my $mcount_o = $dirname . "/.tmp_mc_" . $prefix . ".o"; 202 203# 204# --globalize-symbols came out in 2.17, we must test the version 205# of objcopy, and if it is less than 2.17, then we can not 206# record local functions. 207my $use_locals = 01; 208my $local_warn_once = 0; 209my $found_version = 0; 210 211open (IN, "$objcopy --version |") || die "error running $objcopy"; 212while (<IN>) { 213 if (/objcopy.*\s(\d+)\.(\d+)/) { 214 my $major = $1; 215 my $minor = $2; 216 217 $found_version = 1; 218 if ($major < 2 || 219 ($major == 2 && $minor < 17)) { 220 $use_locals = 0; 221 } 222 last; 223 } 224} 225close (IN); 226 227if (!$found_version) { 228 print STDERR "WARNING: could not find objcopy version.\n" . 229 "\tDisabling local function references.\n"; 230} 231 232 233# 234# Step 1: find all the local (static functions) and weak symbols. 235# 't' is local, 'w/W' is weak (we never use a weak function) 236# 237open (IN, "$nm $inputfile|") || die "error running $nm"; 238while (<IN>) { 239 if (/^[0-9a-fA-F]+\s+t\s+(\S+)/) { 240 $locals{$1} = 1; 241 } elsif (/^[0-9a-fA-F]+\s+([wW])\s+(\S+)/) { 242 $weak{$2} = $1; 243 } 244} 245close(IN); 246 247my @offsets; # Array of offsets of mcount callers 248my $ref_func; # reference function to use for offsets 249my $offset = 0; # offset of ref_func to section beginning 250 251## 252# update_funcs - print out the current mcount callers 253# 254# Go through the list of offsets to callers and write them to 255# the output file in a format that can be read by an assembler. 256# 257sub update_funcs 258{ 259 return if ($#offsets < 0); 260 261 defined($ref_func) || die "No function to reference"; 262 263 # A section only had a weak function, to represent it. 264 # Unfortunately, a weak function may be overwritten by another 265 # function of the same name, making all these offsets incorrect. 266 # To be safe, we simply print a warning and bail. 267 if (defined $weak{$ref_func}) { 268 print STDERR 269 "$inputfile: WARNING: referencing weak function" . 270 " $ref_func for mcount\n"; 271 return; 272 } 273 274 # is this function static? If so, note this fact. 275 if (defined $locals{$ref_func}) { 276 277 # only use locals if objcopy supports globalize-symbols 278 if (!$use_locals) { 279 return; 280 } 281 $convert{$ref_func} = 1; 282 } 283 284 # Loop through all the mcount caller offsets and print a reference 285 # to the caller based from the ref_func. 286 for (my $i=0; $i <= $#offsets; $i++) { 287 if (!$opened) { 288 open(FILE, ">$mcount_s") || die "can't create $mcount_s\n"; 289 $opened = 1; 290 print FILE "\t.section $mcount_section,\"a\",\@progbits\n"; 291 } 292 printf FILE "\t%s %s + %d\n", $type, $ref_func, $offsets[$i] - $offset; 293 } 294} 295 296# 297# Step 2: find the sections and mcount call sites 298# 299open(IN, "$objdump -dr $inputfile|") || die "error running $objdump"; 300 301my $text; 302 303while (<IN>) { 304 # is it a section? 305 if (/$section_regex/) { 306 307 # Only record text sections that we know are safe 308 if (defined($text_sections{$1})) { 309 $read_function = 1; 310 } else { 311 $read_function = 0; 312 } 313 # print out any recorded offsets 314 update_funcs() if ($text_found); 315 316 # reset all markers and arrays 317 $text_found = 0; 318 undef($ref_func); 319 undef(@offsets); 320 321 # section found, now is this a start of a function? 322 } elsif ($read_function && /$function_regex/) { 323 $text_found = 1; 324 $offset = hex $1; 325 $text = $2; 326 327 # if this is either a local function or a weak function 328 # keep looking for functions that are global that 329 # we can use safely. 330 if (!defined($locals{$text}) && !defined($weak{$text})) { 331 $ref_func = $text; 332 $read_function = 0; 333 } else { 334 # if we already have a function, and this is weak, skip it 335 if (!defined($ref_func) || !defined($weak{$text})) { 336 $ref_func = $text; 337 } 338 } 339 } 340 341 # is this a call site to mcount? If so, record it to print later 342 if ($text_found && /$mcount_regex/) { 343 $offsets[$#offsets + 1] = hex $1; 344 } 345} 346 347# dump out anymore offsets that may have been found 348update_funcs() if ($text_found); 349 350# If we did not find any mcount callers, we are done (do nothing). 351if (!$opened) { 352 exit(0); 353} 354 355close(FILE); 356 357# 358# Step 3: Compile the file that holds the list of call sites to mcount. 359# 360`$cc -o $mcount_o -c $mcount_s`; 361 362my @converts = keys %convert; 363 364# 365# Step 4: Do we have sections that started with local functions? 366# 367if ($#converts >= 0) { 368 my $globallist = ""; 369 my $locallist = ""; 370 371 foreach my $con (@converts) { 372 $globallist .= " --globalize-symbol $con"; 373 $locallist .= " --localize-symbol $con"; 374 } 375 376 my $globalobj = $dirname . "/.tmp_gl_" . $filename; 377 my $globalmix = $dirname . "/.tmp_mx_" . $filename; 378 379 # 380 # Step 5: set up each local function as a global 381 # 382 `$objcopy $globallist $inputfile $globalobj`; 383 384 # 385 # Step 6: Link the global version to our list. 386 # 387 `$ld -r $globalobj $mcount_o -o $globalmix`; 388 389 # 390 # Step 7: Convert the local functions back into local symbols 391 # 392 `$objcopy $locallist $globalmix $inputfile`; 393 394 # Remove the temp files 395 `$rm $globalobj $globalmix`; 396 397} else { 398 399 my $mix = $dirname . "/.tmp_mx_" . $filename; 400 401 # 402 # Step 8: Link the object with our list of call sites object. 403 # 404 `$ld -r $inputfile $mcount_o -o $mix`; 405 406 # 407 # Step 9: Move the result back to the original object. 408 # 409 `$mv $mix $inputfile`; 410} 411 412# Clean up the temp files 413`$rm $mcount_o $mcount_s`; 414 415exit(0); 416