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