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 ".text.sched"
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 .text.sched. 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 ".text.sched"
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 objdump objcopy cc ld nm rm mv inputfile\n";
105 print "version: $V\n";
109 my ($arch, $bits, $objdump, $objcopy, $cc,
110 $ld, $nm, $rm, $mv, $inputfile) = @ARGV;
112 # Acceptable sections to record.
113 my %text_sections = (
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);
125 #print STDERR "running: $P '$arch' '$objdump' '$objcopy' '$cc' '$ld' " .
126 # "'$nm' '$rm' '$mv' '$inputfile'\n";
128 my %locals; # List of local (static) functions
129 my %weak; # List of weak functions
130 my %convert; # List of local functions used that needs conversion
133 my $section_regex; # Find the start of a section
134 my $function_regex; # Find the name of a function
135 # (return offset and func name)
136 my $mcount_regex; # Find the call site to mcount (return offset)
138 if ($arch eq "x86") {
146 if ($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]+)?\$";
152 # force flags for this arch
153 $ld .= " -m elf_x86_64";
154 $objdump .= " -M x86-64";
155 $objcopy .= " -O elf64-x86-64";
158 } elsif ($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\$";
164 # force flags for this arch
165 $ld .= " -m elf_i386";
166 $objdump .= " -M i386";
167 $objcopy .= " -O elf32-i386";
170 } elsif ($arch eq "sh") {
171 $section_regex = "Disassembly of section\\s+(\\S+):";
172 $function_regex = "^([0-9a-fA-F]+)\\s+<(.*?)>:";
173 $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\smcount\$";
176 # force flags for this arch
177 $ld .= " -m shlelf_linux";
178 $objcopy .= " -O elf32-sh-linux";
182 die "Arch $arch is not supported with CONFIG_FTRACE_MCOUNT_RECORD";
186 my $read_function = 0;
188 my $mcount_section = "__mcount_loc";
195 if ($inputfile =~ m,^(.*)/([^/]*)$,) {
200 $filename = $inputfile;
203 if ($filename =~ m,^(.*)(\.\S),) {
211 my $mcount_s = $dirname . "/.tmp_mc_" . $prefix . ".s";
212 my $mcount_o = $dirname . "/.tmp_mc_" . $prefix . ".o";
215 # --globalize-symbols came out in 2.17, we must test the version
216 # of objcopy, and if it is less than 2.17, then we can not
217 # record local functions.
219 my $local_warn_once = 0;
220 my $found_version = 0;
222 open (IN, "$objcopy --version |") || die "error running $objcopy";
224 if (/objcopy.*\s(\d+)\.(\d+)/) {
230 ($major == 2 && $minor < 17)) {
238 if (!$found_version) {
239 print STDERR "WARNING: could not find objcopy version.\n" .
240 "\tDisabling local function references.\n";
245 # Step 1: find all the local (static functions) and weak symbols.
246 # 't' is local, 'w/W' is weak (we never use a weak function)
248 open (IN, "$nm $inputfile|") || die "error running $nm";
250 if (/^[0-9a-fA-F]+\s+t\s+(\S+)/) {
252 } elsif (/^[0-9a-fA-F]+\s+([wW])\s+(\S+)/) {
258 my @offsets; # Array of offsets of mcount callers
259 my $ref_func; # reference function to use for offsets
260 my $offset = 0; # offset of ref_func to section beginning
263 # update_funcs - print out the current mcount callers
265 # Go through the list of offsets to callers and write them to
266 # the output file in a format that can be read by an assembler.
270 return if ($#offsets < 0);
272 defined($ref_func) || die "No function to reference";
274 # A section only had a weak function, to represent it.
275 # Unfortunately, a weak function may be overwritten by another
276 # function of the same name, making all these offsets incorrect.
277 # To be safe, we simply print a warning and bail.
278 if (defined $weak{$ref_func}) {
280 "$inputfile: WARNING: referencing weak function" .
281 " $ref_func for mcount\n";
285 # is this function static? If so, note this fact.
286 if (defined $locals{$ref_func}) {
288 # only use locals if objcopy supports globalize-symbols
292 $convert{$ref_func} = 1;
295 # Loop through all the mcount caller offsets and print a reference
296 # to the caller based from the ref_func.
297 for (my $i=0; $i <= $#offsets; $i++) {
299 open(FILE, ">$mcount_s") || die "can't create $mcount_s\n";
301 print FILE "\t.section $mcount_section,\"a\",\@progbits\n";
303 printf FILE "\t%s %s + %d\n", $type, $ref_func, $offsets[$i] - $offset;
308 # Step 2: find the sections and mcount call sites
310 open(IN, "$objdump -dr $inputfile|") || die "error running $objdump";
316 if (/$section_regex/) {
318 # Only record text sections that we know are safe
319 if (defined($text_sections{$1})) {
324 # print out any recorded offsets
325 update_funcs() if ($text_found);
327 # reset all markers and arrays
332 # section found, now is this a start of a function?
333 } elsif ($read_function && /$function_regex/) {
338 # if this is either a local function or a weak function
339 # keep looking for functions that are global that
341 if (!defined($locals{$text}) && !defined($weak{$text})) {
345 # if we already have a function, and this is weak, skip it
346 if (!defined($ref_func) || !defined($weak{$text})) {
352 # is this a call site to mcount? If so, record it to print later
353 if ($text_found && /$mcount_regex/) {
354 $offsets[$#offsets + 1] = hex $1;
358 # dump out anymore offsets that may have been found
359 update_funcs() if ($text_found);
361 # If we did not find any mcount callers, we are done (do nothing).
369 # Step 3: Compile the file that holds the list of call sites to mcount.
371 `$cc -o $mcount_o -c $mcount_s`;
373 my @converts = keys %convert;
376 # Step 4: Do we have sections that started with local functions?
378 if ($#converts >= 0) {
382 foreach my $con (@converts) {
383 $globallist .= " --globalize-symbol $con";
384 $locallist .= " --localize-symbol $con";
387 my $globalobj = $dirname . "/.tmp_gl_" . $filename;
388 my $globalmix = $dirname . "/.tmp_mx_" . $filename;
391 # Step 5: set up each local function as a global
393 `$objcopy $globallist $inputfile $globalobj`;
396 # Step 6: Link the global version to our list.
398 `$ld -r $globalobj $mcount_o -o $globalmix`;
401 # Step 7: Convert the local functions back into local symbols
403 `$objcopy $locallist $globalmix $inputfile`;
405 # Remove the temp files
406 `$rm $globalobj $globalmix`;
410 my $mix = $dirname . "/.tmp_mx_" . $filename;
413 # Step 8: Link the object with our list of call sites object.
415 `$ld -r $inputfile $mcount_o -o $mix`;
418 # Step 9: Move the result back to the original object.
420 `$mv $mix $inputfile`;
423 # Clean up the temp files
424 `$rm $mcount_o $mcount_s`;