2 # (c) 2008, Steven Rostedt <srostedt@redhat.com>
3 # Licensed under the terms of the GNU GPL License version 2
5 # recordmcount.pl - makes a section called __mcount_loc that holds
6 # all the offsets to the calls to mcount.
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.
16 # This is no easy feat. This script is called just after the original
17 # object is compiled and before it is linked.
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.
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.
29 # .section ".sched.text", "ax"
33 # call mcount (offset: 0x5)
38 # call mcount (offset: 0x1b)
41 # Both relocation offsets for the mcounts in the above example will be
42 # offset from .sched.text. If we make another file called tmp.s with:
44 # .section __mcount_loc
46 # .quad my_func + 0x1b
48 # We can then compile this tmp.s into tmp.o, and link it to the original
51 # But this gets hard if my_func is not globl (a static function).
52 # In such a case we have:
54 # .section ".sched.text", "ax"
57 # call mcount (offset: 0x5)
63 # call mcount (offset: 0x1b)
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.
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.
78 # Here are the steps we take:
80 # 1) Record all the local symbols by using 'nm'
81 # 2) Use objdump to find all the call site offsets and sections for
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
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.
91 # 8) Link the object with the list object.
92 # 9) Move the result back to the original object.
104 print "usage: $P arch bits objdump objcopy cc ld nm rm mv is_module inputfile\n";
105 print "version: $V\n";
109 my ($arch, $bits, $objdump, $objcopy, $cc,
110 $ld, $nm, $rm, $mv, $is_module, $inputfile) = @ARGV;
112 # This file refers to mcount and shouldn't be ftraced, so lets' ignore it
113 if ($inputfile eq "kernel/trace/ftrace.o") {
117 # Acceptable sections to record.
118 my %text_sections = (
121 ".spinlock.text" => 1,
122 ".irqentry.text" => 1,
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);
133 #print STDERR "running: $P '$arch' '$objdump' '$objcopy' '$cc' '$ld' " .
134 # "'$nm' '$rm' '$mv' '$inputfile'\n";
136 my %locals; # List of local (static) functions
137 my %weak; # List of weak functions
138 my %convert; # List of local functions used that needs conversion
141 my $nm_regex; # Find the local functions (return function)
142 my $section_regex; # Find the start of a section
143 my $function_regex; # Find the name of a function
144 # (return offset and func name)
145 my $mcount_regex; # Find the call site to mcount (return offset)
146 my $alignment; # The .align value to use for $mcount_section
147 my $section_type; # Section header plus possible alignment command
149 if ($arch eq "x86") {
158 # We base the defaults off of i386, the other archs may
159 # feel free to change them in the below if statements.
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 $section_type = '@progbits';
168 if ($arch eq "x86_64") {
169 $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\smcount([+-]0x[0-9a-zA-Z]+)?\$";
173 # force flags for this arch
174 $ld .= " -m elf_x86_64";
175 $objdump .= " -M x86-64";
176 $objcopy .= " -O elf64-x86-64";
179 } elsif ($arch eq "i386") {
182 # force flags for this arch
183 $ld .= " -m elf_i386";
184 $objdump .= " -M i386";
185 $objcopy .= " -O elf32-i386";
188 } elsif ($arch eq "s390" && $bits == 32) {
189 $mcount_regex = "^\\s*([0-9a-fA-F]+):\\s*R_390_32\\s+_mcount\$";
191 $ld .= " -m elf_s390";
194 } elsif ($arch eq "s390" && $bits == 64) {
195 $mcount_regex = "^\\s*([0-9a-fA-F]+):\\s*R_390_(PC|PLT)32DBL\\s+_mcount\\+0x2\$";
198 $ld .= " -m elf64_s390";
201 } elsif ($arch eq "sh") {
204 # force flags for this arch
205 $ld .= " -m shlelf_linux";
206 $objcopy .= " -O elf32-sh-linux";
209 } elsif ($arch eq "powerpc") {
210 $nm_regex = "^[0-9a-fA-F]+\\s+t\\s+(\\.?\\S+)";
211 $function_regex = "^([0-9a-fA-F]+)\\s+<(\\.?.*?)>:";
212 $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s\\.?_mcount\$";
218 } elsif ($arch eq "arm") {
220 $section_type = '%progbits';
222 } elsif ($arch eq "ia64") {
223 $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s_mcount\$";
226 if ($is_module eq "0") {
227 $cc .= " -mconstant-gp";
230 die "Arch $arch is not supported with CONFIG_FTRACE_MCOUNT_RECORD";
234 my $read_function = 0;
236 my $mcount_section = "__mcount_loc";
243 if ($inputfile =~ m,^(.*)/([^/]*)$,) {
248 $filename = $inputfile;
251 if ($filename =~ m,^(.*)(\.\S),) {
259 my $mcount_s = $dirname . "/.tmp_mc_" . $prefix . ".s";
260 my $mcount_o = $dirname . "/.tmp_mc_" . $prefix . ".o";
263 # --globalize-symbols came out in 2.17, we must test the version
264 # of objcopy, and if it is less than 2.17, then we can not
265 # record local functions.
267 my $local_warn_once = 0;
268 my $found_version = 0;
270 open (IN, "$objcopy --version |") || die "error running $objcopy";
272 if (/objcopy.*\s(\d+)\.(\d+)/) {
278 ($major == 2 && $minor < 17)) {
286 if (!$found_version) {
287 print STDERR "WARNING: could not find objcopy version.\n" .
288 "\tDisabling local function references.\n";
292 # Step 1: find all the local (static functions) and weak symbols.
293 # 't' is local, 'w/W' is weak (we never use a weak function)
295 open (IN, "$nm $inputfile|") || die "error running $nm";
299 } elsif (/^[0-9a-fA-F]+\s+([wW])\s+(\S+)/) {
305 my @offsets; # Array of offsets of mcount callers
306 my $ref_func; # reference function to use for offsets
307 my $offset = 0; # offset of ref_func to section beginning
310 # update_funcs - print out the current mcount callers
312 # Go through the list of offsets to callers and write them to
313 # the output file in a format that can be read by an assembler.
317 return if ($#offsets < 0);
319 defined($ref_func) || die "No function to reference";
321 # A section only had a weak function, to represent it.
322 # Unfortunately, a weak function may be overwritten by another
323 # function of the same name, making all these offsets incorrect.
324 # To be safe, we simply print a warning and bail.
325 if (defined $weak{$ref_func}) {
327 "$inputfile: WARNING: referencing weak function" .
328 " $ref_func for mcount\n";
332 # is this function static? If so, note this fact.
333 if (defined $locals{$ref_func}) {
335 # only use locals if objcopy supports globalize-symbols
339 $convert{$ref_func} = 1;
342 # Loop through all the mcount caller offsets and print a reference
343 # to the caller based from the ref_func.
344 for (my $i=0; $i <= $#offsets; $i++) {
346 open(FILE, ">$mcount_s") || die "can't create $mcount_s\n";
348 print FILE "\t.section $mcount_section,\"a\",$section_type\n";
349 print FILE "\t.align $alignment\n" if (defined($alignment));
351 printf FILE "\t%s %s + %d\n", $type, $ref_func, $offsets[$i] - $offset;
356 # Step 2: find the sections and mcount call sites
358 open(IN, "$objdump -hdr $inputfile|") || die "error running $objdump";
362 my $read_headers = 1;
366 if (/$section_regex/) {
369 # Only record text sections that we know are safe
370 if (defined($text_sections{$1})) {
375 # print out any recorded offsets
376 update_funcs() if ($text_found);
378 # reset all markers and arrays
383 # section found, now is this a start of a function?
384 } elsif ($read_function && /$function_regex/) {
389 # if this is either a local function or a weak function
390 # keep looking for functions that are global that
392 if (!defined($locals{$text}) && !defined($weak{$text})) {
396 # if we already have a function, and this is weak, skip it
397 if (!defined($ref_func) || !defined($weak{$text})) {
401 } elsif ($read_headers && /$mcount_section/) {
403 # Somehow the make process can execute this script on an
404 # object twice. If it does, we would duplicate the mcount
405 # section and it will cause the function tracer self test
406 # to fail. Check if the mcount section exists, and if it does,
409 print STDERR "ERROR: $mcount_section already in $inputfile\n" .
410 "\tThis may be an indication that your build is corrupted.\n" .
411 "\tDelete $inputfile and try again. If the same object file\n" .
412 "\tstill causes an issue, then disable CONFIG_DYNAMIC_FTRACE.\n";
416 # is this a call site to mcount? If so, record it to print later
417 if ($text_found && /$mcount_regex/) {
418 $offsets[$#offsets + 1] = hex $1;
422 # dump out anymore offsets that may have been found
423 update_funcs() if ($text_found);
425 # If we did not find any mcount callers, we are done (do nothing).
433 # Step 3: Compile the file that holds the list of call sites to mcount.
435 `$cc -o $mcount_o -c $mcount_s`;
437 my @converts = keys %convert;
440 # Step 4: Do we have sections that started with local functions?
442 if ($#converts >= 0) {
446 foreach my $con (@converts) {
447 $globallist .= " --globalize-symbol $con";
448 $locallist .= " --localize-symbol $con";
451 my $globalobj = $dirname . "/.tmp_gl_" . $filename;
452 my $globalmix = $dirname . "/.tmp_mx_" . $filename;
455 # Step 5: set up each local function as a global
457 `$objcopy $globallist $inputfile $globalobj`;
460 # Step 6: Link the global version to our list.
462 `$ld -r $globalobj $mcount_o -o $globalmix`;
465 # Step 7: Convert the local functions back into local symbols
467 `$objcopy $locallist $globalmix $inputfile`;
469 # Remove the temp files
470 `$rm $globalobj $globalmix`;
474 my $mix = $dirname . "/.tmp_mx_" . $filename;
477 # Step 8: Link the object with our list of call sites object.
479 `$ld -r $inputfile $mcount_o -o $mix`;
482 # Step 9: Move the result back to the original object.
484 `$mv $mix $inputfile`;
487 # Clean up the temp files
488 `$rm $mcount_o $mcount_s`;