scripts/recordmcount.pl

   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
  96 use strict;
  97
  98 my $P = $0;
  99 $P =~ s@.*/@@g;
 100
 101 my $V = '0.1';
 102
 103 if ($#ARGV < 6) {
 104         print "usage: $P arch objdump objcopy cc ld nm rm mv inputfile\n";
 105         print "version: $V\n";
 106         exit(1);
 107 }
 108
 109 my ($arch, $objdump, $objcopy, $cc, $ld, $nm, $rm, $mv, $inputfile) = @ARGV;
 110
 111 if ($arch eq "i386") {
 112   $ld = "ld -m elf_i386";
 113   $objdump = "objdump -M i386";
 114   $objcopy = "objcopy -O elf32-i386";
 115   $cc = "gcc -m32";
 116 }
 117
 118 if ($arch eq "x86_64") {
 119   $ld = "ld -m elf_x86_64";
 120   $objdump = "objdump -M x86-64";
 121   $objcopy = "objcopy -O elf64-x86-64";
 122   $cc = "gcc -m64";
 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
 136 my %locals;
 137 my %convert;
 138
 139 my $type;
 140 my $section_regex;      # Find the start of a section
 141 my $function_regex;     # Find the name of a function (return func name)
 142 my $mcount_regex;       # Find the call site to mcount (return offset)
 143
 144 if ($arch eq "x86_64") {
 145     $section_regex = "Disassembly of section";
 146     $function_regex = "<(.*?)>:";
 147     $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\smcount([+-]0x[0-9a-zA-Z]+)?\$";
 148     $type = ".quad";
 149 } elsif ($arch eq "i386") {
 150     $section_regex = "Disassembly of section";
 151     $function_regex = "<(.*?)>:";
 152     $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\smcount\$";
 153     $type = ".long";
 154 } else {
 155     die "Arch $arch is not supported with CONFIG_FTRACE_MCOUNT_RECORD";
 156 }
 157
 158 my $text_found = 0;
 159 my $read_function = 0;
 160 my $opened = 0;
 161 my $text = "";
 162 my $mcount_section = "__mcount_loc";
 163
 164 my $dirname;
 165 my $filename;
 166 my $prefix;
 167 my $ext;
 168
 169 if ($inputfile =~ m,^(.*)/([^/]*)$,) {
 170     $dirname = $1;
 171     $filename = $2;
 172 } else {
 173     $dirname = ".";
 174     $filename = $inputfile;
 175 }
 176
 177 if ($filename =~ m,^(.*)(\.\S),) {
 178     $prefix = $1;
 179     $ext = $2;
 180 } else {
 181     $prefix = $filename;
 182     $ext = "";
 183 }
 184
 185 my $mcount_s = $dirname . "/.tmp_mc_" . $prefix . ".s";
 186 my $mcount_o = $dirname . "/.tmp_mc_" . $prefix . ".o";
 187
 188 #
 189 # Step 1: find all the local symbols (static functions).
 190 #
 191 open (IN, "$nm $inputfile|") || die "error running $nm";
 192 while (<IN>) {
 193     if (/^[0-9a-fA-F]+\s+t\s+(\S+)/) {
 194         $locals{$1} = 1;
 195     }
 196 }
 197 close(IN);
 198
 199 #
 200 # Step 2: find the sections and mcount call sites
 201 #
 202 open(IN, "$objdump -dr $inputfile|") || die "error running $objdump";
 203
 204 while (<IN>) {
 205     # is it a section?
 206     if (/$section_regex/) {
 207         $read_function = 1;
 208         $text_found = 0;
 209     # section found, now is this a start of a function?
 210     } elsif ($read_function && /$function_regex/) {
 211         $read_function = 0;
 212         $text_found = 1;
 213         $text = $1;
 214         # is this function static? If so, note this fact.
 215         if (defined $locals{$text}) {
 216             $convert{$text} = 1;
 217         }
 218     # is this a call site to mcount? If so, print the offset from the section
 219     } elsif ($text_found && /$mcount_regex/) {
 220         if (!$opened) {
 221             open(FILE, ">$mcount_s") || die "can't create $mcount_s\n";
 222             $opened = 1;
 223             print FILE "\t.section $mcount_section,\"a\",\@progbits\n";
 224         }
 225         print FILE "\t$type $text + 0x$1\n";
 226     }
 227 }
 228
 229 # If we did not find any mcount callers, we are done (do nothing).
 230 if (!$opened) {
 231     exit(0);
 232 }
 233
 234 close(FILE);
 235
 236 #
 237 # Step 3: Compile the file that holds the list of call sites to mcount.
 238 #
 239 `$cc -o $mcount_o -c $mcount_s`;
 240
 241 my @converts = keys %convert;
 242
 243 #
 244 # Step 4: Do we have sections that started with local functions?
 245 #
 246 if ($#converts >= 0) {
 247     my $globallist = "";
 248     my $locallist = "";
 249
 250     foreach my $con (@converts) {
 251         $globallist .= " --globalize-symbol $con";
 252         $locallist .= " --localize-symbol $con";
 253     }
 254
 255     my $globalobj = $dirname . "/.tmp_gl_" . $filename;
 256     my $globalmix = $dirname . "/.tmp_mx_" . $filename;
 257
 258     #
 259     # Step 5: set up each local function as a global
 260     #
 261     `$objcopy $globallist $inputfile $globalobj`;
 262
 263     #
 264     # Step 6: Link the global version to our list.
 265     #
 266     `$ld -r $globalobj $mcount_o -o $globalmix`;
 267
 268     #
 269     # Step 7: Convert the local functions back into local symbols
 270     #
 271     `$objcopy $locallist $globalmix $inputfile`;
 272
 273     # Remove the temp files
 274     `$rm $globalobj $globalmix`;
 275
 276 } else {
 277
 278     my $mix = $dirname . "/.tmp_mx_" . $filename;
 279
 280     #
 281     # Step 8: Link the object with our list of call sites object.
 282     #
 283     `$ld -r $inputfile $mcount_o -o $mix`;
 284
 285     #
 286     # Step 9: Move the result back to the original object.
 287     #
 288     `$mv $mix $inputfile`;
 289 }
 290
 291 # Clean up the temp files
 292 `$rm $mcount_o $mcount_s`;
 293
 294 exit(0);