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_" . $prefix . ".o"; 188 189# 190# Step 1: find all the local (static functions) and weak symbols. 191# 't' is local, 'w/W' is weak (we never use a weak function) 192# 193open (IN, "$nm $inputfile|") || die "error running $nm"; 194while (<IN>) { 195 if (/^[0-9a-fA-F]+\s+t\s+(\S+)/) { 196 $locals{$1} = 1; 197 } elsif (/^[0-9a-fA-F]+\s+([wW])\s+(\S+)/) { 198 $weak{$2} = $1; 199 } 200} 201close(IN); 202 203my @offsets; # Array of offsets of mcount callers 204my $ref_func; # reference function to use for offsets 205my $offset = 0; # offset of ref_func to section beginning 206 207## 208# update_funcs - print out the current mcount callers 209# 210# Go through the list of offsets to callers and write them to 211# the output file in a format that can be read by an assembler. 212# 213sub update_funcs 214{ 215 return if ($#offsets < 0); 216 217 defined($ref_func) || die "No function to reference"; 218 219 # A section only had a weak function, to represent it. 220 # Unfortunately, a weak function may be overwritten by another 221 # function of the same name, making all these offsets incorrect. 222 # To be safe, we simply print a warning and bail. 223 if (defined $weak{$ref_func}) { 224 print STDERR 225 "$inputfile: WARNING: referencing weak function" . 226 " $ref_func for mcount\n"; 227 return; 228 } 229 230 # is this function static? If so, note this fact. 231 if (defined $locals{$ref_func}) { 232 $convert{$ref_func} = 1; 233 } 234 235 # Loop through all the mcount caller offsets and print a reference 236 # to the caller based from the ref_func. 237 for (my $i=0; $i <= $#offsets; $i++) { 238 if (!$opened) { 239 open(FILE, ">$mcount_s") || die "can't create $mcount_s\n"; 240 $opened = 1; 241 print FILE "\t.section $mcount_section,\"a\",\@progbits\n"; 242 } 243 printf FILE "\t%s %s + %d\n", $type, $ref_func, $offsets[$i] - $offset; 244 } 245} 246 247# 248# Step 2: find the sections and mcount call sites 249# 250open(IN, "$objdump -dr $inputfile|") || die "error running $objdump"; 251 252my $text; 253 254while (<IN>) { 255 # is it a section? 256 if (/$section_regex/) { 257 $read_function = 1; 258 # print out any recorded offsets 259 update_funcs() if ($text_found); 260 261 # reset all markers and arrays 262 $text_found = 0; 263 undef($ref_func); 264 undef(@offsets); 265 266 # section found, now is this a start of a function? 267 } elsif ($read_function && /$function_regex/) { 268 $text_found = 1; 269 $offset = hex $1; 270 $text = $2; 271 272 # if this is either a local function or a weak function 273 # keep looking for functions that are global that 274 # we can use safely. 275 if (!defined($locals{$text}) && !defined($weak{$text})) { 276 $ref_func = $text; 277 $read_function = 0; 278 } else { 279 # if we already have a function, and this is weak, skip it 280 if (!defined($ref_func) || !defined($weak{$text})) { 281 $ref_func = $text; 282 } 283 } 284 } 285 286 # is this a call site to mcount? If so, record it to print later 287 if ($text_found && /$mcount_regex/) { 288 $offsets[$#offsets + 1] = hex $1; 289 } 290} 291 292# dump out anymore offsets that may have been found 293update_funcs() if ($text_found); 294 295# If we did not find any mcount callers, we are done (do nothing). 296if (!$opened) { 297 exit(0); 298} 299 300close(FILE); 301 302# 303# Step 3: Compile the file that holds the list of call sites to mcount. 304# 305`$cc -o $mcount_o -c $mcount_s`; 306 307my @converts = keys %convert; 308 309# 310# Step 4: Do we have sections that started with local functions? 311# 312if ($#converts >= 0) { 313 my $globallist = ""; 314 my $locallist = ""; 315 316 foreach my $con (@converts) { 317 $globallist .= " --globalize-symbol $con"; 318 $locallist .= " --localize-symbol $con"; 319 } 320 321 my $globalobj = $dirname . "/.tmp_gl_" . $filename; 322 my $globalmix = $dirname . "/.tmp_mx_" . $filename; 323 324 # 325 # Step 5: set up each local function as a global 326 # 327 `$objcopy $globallist $inputfile $globalobj`; 328 329 # 330 # Step 6: Link the global version to our list. 331 # 332 `$ld -r $globalobj $mcount_o -o $globalmix`; 333 334 # 335 # Step 7: Convert the local functions back into local symbols 336 # 337 `$objcopy $locallist $globalmix $inputfile`; 338 339 # Remove the temp files 340 `$rm $globalobj $globalmix`; 341 342} else { 343 344 my $mix = $dirname . "/.tmp_mx_" . $filename; 345 346 # 347 # Step 8: Link the object with our list of call sites object. 348 # 349 `$ld -r $inputfile $mcount_o -o $mix`; 350 351 # 352 # Step 9: Move the result back to the original object. 353 # 354 `$mv $mix $inputfile`; 355} 356 357# Clean up the temp files 358`$rm $mcount_o $mcount_s`; 359 360exit(0); 361