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 this is that each object file will have a
10 # section called __mcount_loc that will hold the list of pointers to mcount
11 # callers. After final linking, the vmlinux will have within .init.data the
12 # list of all callers to mcount between __start_mcount_loc and __stop_mcount_loc.
13 # Later on boot up, the kernel will read this list, save the locations and turn
14 # them into nops. When tracing or profiling is later enabled, these locations
15 # will then be converted back to pointers to some function.
17 # This is no easy feat. This script is called just after the original
18 # object is compiled and before it is linked.
20 # When parse this object file using 'objdump', the references to the call
21 # sites are offsets from the section that the call site is in. Hence, all
22 # functions in a section that has a call site to mcount, will have the
23 # offset from the beginning of the section and not the beginning of the
26 # But where this section will reside finally in vmlinx is undetermined at
27 # this point. So we can't use this kind of offsets to record the final
28 # address of this call site.
30 # The trick is to change the call offset referring the start of a section to
31 # referring a function symbol in this section. During the link step, 'ld' will
32 # compute the final address according to the information we record.
36 # .section ".sched.text", "ax"
40 # call mcount (offset: 0x10)
44 # func2: (offset: 0x20)
50 # call mcount (offset: 0x30)
53 # Both relocation offsets for the mcounts in the above example will be
54 # offset from .sched.text. If we choose global symbol func2 as a reference and
55 # make another file called tmp.s with the new offsets:
57 # .section __mcount_loc
61 # We can then compile this tmp.s into tmp.o, and link it back to the original
64 # In our algorithm, we will choose the first global function we meet in this
65 # section as the reference. But this gets hard if there is no global functions
66 # in this section. In such a case we have to select a local one. E.g. func1:
68 # .section ".sched.text", "ax"
71 # call mcount (offset: 0x10)
76 # call mcount (offset: 0x20)
78 # .section "other.section"
80 # If we make the tmp.s the same as above, when we link together with
81 # the original object, we will end up with two symbols for func1:
82 # one local, one global. After final compile, we will end up with
83 # an undefined reference to func1 or a wrong reference to another global
84 # func1 in other files.
86 # Since local objects can reference local variables, we need to find
87 # a way to make tmp.o reference the local objects of the original object
88 # file after it is linked together. To do this, we convert func1
89 # into a global symbol before linking tmp.o. Then after we link tmp.o
90 # we will only have a single symbol for func1 that is global.
91 # We can convert func1 back into a local symbol and we are done.
93 # Here are the steps we take:
95 # 1) Record all the local symbols by using 'nm'
96 # 2) Use objdump to find all the call site offsets and sections for
98 # 3) Compile the list into its own object.
99 # 4) Do we have to deal with local functions? If not, go to step 8.
100 # 5) Make an object that converts these local functions to global symbols
102 # 6) Link together this new object with the list object.
103 # 7) Convert the local functions back to local symbols and rename
104 # the result as the original object.
105 # 8) Link the object with the list object.
106 # 9) Move the result back to the original object.
117 print "usage: $P arch bits objdump objcopy cc ld nm rm mv is_module inputfile\n";
118 print "version: $V\n";
122 my ($arch, $bits, $objdump, $objcopy, $cc,
123 $ld, $nm, $rm, $mv, $is_module, $inputfile) = @ARGV;
125 # This file refers to mcount and shouldn't be ftraced, so lets' ignore it
126 if ($inputfile =~ m,kernel/trace/ftrace\.o$,) {
130 # Acceptable sections to record.
131 my %text_sections = (
134 ".spinlock.text" => 1,
135 ".irqentry.text" => 1,
136 ".text.unlikely" => 1,
139 $objdump = "objdump" if ((length $objdump) == 0);
140 $objcopy = "objcopy" if ((length $objcopy) == 0);
141 $cc = "gcc" if ((length $cc) == 0);
142 $ld = "ld" if ((length $ld) == 0);
143 $nm = "nm" if ((length $nm) == 0);
144 $rm = "rm" if ((length $rm) == 0);
145 $mv = "mv" if ((length $mv) == 0);
147 #print STDERR "running: $P '$arch' '$objdump' '$objcopy' '$cc' '$ld' " .
148 # "'$nm' '$rm' '$mv' '$inputfile'\n";
150 my %locals; # List of local (static) functions
151 my %weak; # List of weak functions
152 my %convert; # List of local functions used that needs conversion
155 my $nm_regex; # Find the local functions (return function)
156 my $section_regex; # Find the start of a section
157 my $function_regex; # Find the name of a function
158 # (return offset and func name)
159 my $mcount_regex; # Find the call site to mcount (return offset)
160 my $alignment; # The .align value to use for $mcount_section
161 my $section_type; # Section header plus possible alignment command
162 my $can_use_local = 0; # If we can use local function references
165 # check_objcopy - whether objcopy supports --globalize-symbols
167 # --globalize-symbols came out in 2.17, we must test the version
168 # of objcopy, and if it is less than 2.17, then we can not
169 # record local functions.
172 open (IN, "$objcopy --version |") or die "error running $objcopy";
174 if (/objcopy.*\s(\d+)\.(\d+)/) {
175 $can_use_local = 1 if ($1 > 2 || ($1 == 2 && $2 >= 17));
181 if (!$can_use_local) {
182 print STDERR "WARNING: could not find objcopy version or version " .
183 "is less than 2.17.\n" .
184 "\tLocal function references is disabled.\n";
188 if ($arch eq "x86") {
197 # We base the defaults off of i386, the other archs may
198 # feel free to change them in the below if statements.
200 $nm_regex = "^[0-9a-fA-F]+\\s+t\\s+(\\S+)";
201 $section_regex = "Disassembly of section\\s+(\\S+):";
202 $function_regex = "^([0-9a-fA-F]+)\\s+<(.*?)>:";
203 $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\smcount\$";
204 $section_type = '@progbits';
207 if ($arch eq "x86_64") {
208 $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\smcount([+-]0x[0-9a-zA-Z]+)?\$";
212 # force flags for this arch
213 $ld .= " -m elf_x86_64";
214 $objdump .= " -M x86-64";
215 $objcopy .= " -O elf64-x86-64";
218 } elsif ($arch eq "i386") {
221 # force flags for this arch
222 $ld .= " -m elf_i386";
223 $objdump .= " -M i386";
224 $objcopy .= " -O elf32-i386";
227 } elsif ($arch eq "s390" && $bits == 32) {
228 $mcount_regex = "^\\s*([0-9a-fA-F]+):\\s*R_390_32\\s+_mcount\$";
230 $ld .= " -m elf_s390";
233 } elsif ($arch eq "s390" && $bits == 64) {
234 $mcount_regex = "^\\s*([0-9a-fA-F]+):\\s*R_390_(PC|PLT)32DBL\\s+_mcount\\+0x2\$";
237 $ld .= " -m elf64_s390";
240 } elsif ($arch eq "sh") {
243 # force flags for this arch
244 $ld .= " -m shlelf_linux";
245 $objcopy .= " -O elf32-sh-linux";
248 } elsif ($arch eq "powerpc") {
249 $nm_regex = "^[0-9a-fA-F]+\\s+t\\s+(\\.?\\S+)";
250 $function_regex = "^([0-9a-fA-F]+)\\s+<(\\.?.*?)>:";
251 $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s\\.?_mcount\$";
257 } elsif ($arch eq "arm") {
259 $section_type = '%progbits';
261 } elsif ($arch eq "ia64") {
262 $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s_mcount\$";
265 if ($is_module eq "0") {
266 $cc .= " -mconstant-gp";
268 } elsif ($arch eq "sparc64") {
269 # In the objdump output there are giblets like:
270 # 0000000000000000 <igmp_net_exit-0x18>:
271 # As there's some data blobs that get emitted into the
272 # text section before the first instructions and the first
273 # real symbols. We don't want to match that, so to combat
274 # this we use '\w' so we'll match just plain symbol names,
275 # and not those that also include hex offsets inside of the
276 # '<>' brackets. Actually the generic function_regex setting
277 # could safely use this too.
278 $function_regex = "^([0-9a-fA-F]+)\\s+<(\\w*?)>:";
280 # Sparc64 calls '_mcount' instead of plain 'mcount'.
281 $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s_mcount\$";
285 $ld .= " -m elf64_sparc";
287 $objcopy .= " -O elf64-sparc";
289 die "Arch $arch is not supported with CONFIG_FTRACE_MCOUNT_RECORD";
293 my $read_function = 0;
295 my $mcount_section = "__mcount_loc";
302 if ($inputfile =~ m,^(.*)/([^/]*)$,) {
307 $filename = $inputfile;
310 if ($filename =~ m,^(.*)(\.\S),) {
318 my $mcount_s = $dirname . "/.tmp_mc_" . $prefix . ".s";
319 my $mcount_o = $dirname . "/.tmp_mc_" . $prefix . ".o";
324 # Step 1: find all the local (static functions) and weak symbols.
325 # 't' is local, 'w/W' is weak (we never use a weak function)
327 open (IN, "$nm $inputfile|") || die "error running $nm";
331 } elsif (/^[0-9a-fA-F]+\s+([wW])\s+(\S+)/) {
337 my @offsets; # Array of offsets of mcount callers
338 my $ref_func; # reference function to use for offsets
339 my $offset = 0; # offset of ref_func to section beginning
342 # update_funcs - print out the current mcount callers
344 # Go through the list of offsets to callers and write them to
345 # the output file in a format that can be read by an assembler.
349 return if ($#offsets < 0);
351 defined($ref_func) || die "No function to reference";
353 # A section only had a weak function, to represent it.
354 # Unfortunately, a weak function may be overwritten by another
355 # function of the same name, making all these offsets incorrect.
356 # To be safe, we simply print a warning and bail.
357 if (defined $weak{$ref_func}) {
359 "$inputfile: WARNING: referencing weak function" .
360 " $ref_func for mcount\n";
364 # is this function static? If so, note this fact.
365 if (defined $locals{$ref_func}) {
367 # only use locals if objcopy supports globalize-symbols
368 if (!$can_use_local) {
371 $convert{$ref_func} = 1;
374 # Loop through all the mcount caller offsets and print a reference
375 # to the caller based from the ref_func.
376 for (my $i=0; $i <= $#offsets; $i++) {
378 open(FILE, ">$mcount_s") || die "can't create $mcount_s\n";
380 print FILE "\t.section $mcount_section,\"a\",$section_type\n";
381 print FILE "\t.align $alignment\n" if (defined($alignment));
383 printf FILE "\t%s %s + %d\n", $type, $ref_func, $offsets[$i] - $offset;
388 # Step 2: find the sections and mcount call sites
390 open(IN, "$objdump -hdr $inputfile|") || die "error running $objdump";
394 my $read_headers = 1;
398 if (/$section_regex/) {
401 # Only record text sections that we know are safe
402 if (defined($text_sections{$1})) {
407 # print out any recorded offsets
408 update_funcs() if (defined($ref_func));
410 # reset all markers and arrays
415 # section found, now is this a start of a function?
416 } elsif ($read_function && /$function_regex/) {
420 # if this is either a local function or a weak function
421 # keep looking for functions that are global that
423 if (!defined($locals{$text}) && !defined($weak{$text})) {
428 # if we already have a function, and this is weak, skip it
429 if (!defined($ref_func) && !defined($weak{$text}) &&
430 # PPC64 can have symbols that start with .L and
431 # gcc considers these special. Don't use them!
437 } elsif ($read_headers && /$mcount_section/) {
439 # Somehow the make process can execute this script on an
440 # object twice. If it does, we would duplicate the mcount
441 # section and it will cause the function tracer self test
442 # to fail. Check if the mcount section exists, and if it does,
445 print STDERR "ERROR: $mcount_section already in $inputfile\n" .
446 "\tThis may be an indication that your build is corrupted.\n" .
447 "\tDelete $inputfile and try again. If the same object file\n" .
448 "\tstill causes an issue, then disable CONFIG_DYNAMIC_FTRACE.\n";
452 # is this a call site to mcount? If so, record it to print later
453 if ($text_found && /$mcount_regex/) {
454 $offsets[$#offsets + 1] = hex $1;
458 # dump out anymore offsets that may have been found
459 update_funcs() if (defined($ref_func));
461 # If we did not find any mcount callers, we are done (do nothing).
469 # Step 3: Compile the file that holds the list of call sites to mcount.
471 `$cc -o $mcount_o -c $mcount_s`;
473 my @converts = keys %convert;
476 # Step 4: Do we have sections that started with local functions?
478 if ($#converts >= 0) {
482 foreach my $con (@converts) {
483 $globallist .= " --globalize-symbol $con";
484 $locallist .= " --localize-symbol $con";
487 my $globalobj = $dirname . "/.tmp_gl_" . $filename;
488 my $globalmix = $dirname . "/.tmp_mx_" . $filename;
491 # Step 5: set up each local function as a global
493 `$objcopy $globallist $inputfile $globalobj`;
496 # Step 6: Link the global version to our list.
498 `$ld -r $globalobj $mcount_o -o $globalmix`;
501 # Step 7: Convert the local functions back into local symbols
503 `$objcopy $locallist $globalmix $inputfile`;
505 # Remove the temp files
506 `$rm $globalobj $globalmix`;
510 my $mix = $dirname . "/.tmp_mx_" . $filename;
513 # Step 8: Link the object with our list of call sites object.
515 `$ld -r $inputfile $mcount_o -o $mix`;
518 # Step 9: Move the result back to the original object.
520 `$mv $mix $inputfile`;
523 # Clean up the temp files
524 `$rm $mcount_o $mcount_s`;