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, $objdump, $objcopy, $cc, $ld, $nm, $rm, $mv, $inputfile) = @ARGV;
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);
119 #print STDERR "running: $P '$arch' '$objdump' '$objcopy' '$cc' '$ld' " .
120 # "'$nm' '$rm' '$mv' '$inputfile'\n";
122 my %locals; # List of local (static) functions
123 my %weak; # List of weak functions
124 my %convert; # List of local functions used that needs conversion
127 my $section_regex; # Find the start of a section
128 my $function_regex; # Find the name of a function
129 # (return offset and func name)
130 my $mcount_regex; # Find the call site to mcount (return offset)
132 if ($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]+)?\$";
138 # force flags for this arch
139 $ld .= " -m elf_x86_64";
140 $objdump .= " -M x86-64";
141 $objcopy .= " -O elf64-x86-64";
144 } elsif ($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\$";
150 # force flags for this arch
151 $ld .= " -m elf_i386";
152 $objdump .= " -M i386";
153 $objcopy .= " -O elf32-i386";
157 die "Arch $arch is not supported with CONFIG_FTRACE_MCOUNT_RECORD";
161 my $read_function = 0;
163 my $mcount_section = "__mcount_loc";
170 if ($inputfile =~ m,^(.*)/([^/]*)$,) {
175 $filename = $inputfile;
178 if ($filename =~ m,^(.*)(\.\S),) {
186 my $mcount_s = $dirname . "/.tmp_mc_" . $prefix . ".s";
187 my $mcount_o = $dirname . "/.tmp_mc_" . $prefix . ".o";
190 # Step 1: find all the local (static functions) and weak symbols.
191 # 't' is local, 'w/W' is weak (we never use a weak function)
193 open (IN, "$nm $inputfile|") || die "error running $nm";
195 if (/^[0-9a-fA-F]+\s+t\s+(\S+)/) {
197 } elsif (/^[0-9a-fA-F]+\s+([wW])\s+(\S+)/) {
203 my @offsets; # Array of offsets of mcount callers
204 my $ref_func; # reference function to use for offsets
205 my $offset = 0; # offset of ref_func to section beginning
208 # update_funcs - print out the current mcount callers
210 # Go through the list of offsets to callers and write them to
211 # the output file in a format that can be read by an assembler.
215 return if ($#offsets < 0);
217 defined($ref_func) || die "No function to reference";
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}) {
225 "$inputfile: WARNING: referencing weak function" .
226 " $ref_func for mcount\n";
230 # is this function static? If so, note this fact.
231 if (defined $locals{$ref_func}) {
232 $convert{$ref_func} = 1;
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; $i++) {
239 open(FILE, ">$mcount_s") || die "can't create $mcount_s\n";
241 print FILE "\t.section $mcount_section,\"a\",\@progbits\n";
243 printf FILE "\t%s %s + %d\n", $type, $ref_func, $offsets[$i] - $offset;
248 # Step 2: find the sections and mcount call sites
250 open(IN, "$objdump -dr $inputfile|") || die "error running $objdump";
256 if (/$section_regex/) {
258 # print out any recorded offsets
259 update_funcs() if ($text_found);
261 # reset all markers and arrays
266 # section found, now is this a start of a function?
267 } elsif ($read_function && /$function_regex/) {
272 # if this is either a local function or a weak function
273 # keep looking for functions that are global that
275 if (!defined($locals{$text}) && !defined($weak{$text})) {
279 # if we already have a function, and this is weak, skip it
280 if (!defined($ref_func) || !defined($weak{$text})) {
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 $1;
292 # dump out anymore offsets that may have been found
293 update_funcs() if ($text_found);
295 # If we did not find any mcount callers, we are done (do nothing).
303 # Step 3: Compile the file that holds the list of call sites to mcount.
305 `$cc -o $mcount_o -c $mcount_s`;
307 my @converts = keys %convert;
310 # Step 4: Do we have sections that started with local functions?
312 if ($#converts >= 0) {
316 foreach my $con (@converts) {
317 $globallist .= " --globalize-symbol $con";
318 $locallist .= " --localize-symbol $con";
321 my $globalobj = $dirname . "/.tmp_gl_" . $filename;
322 my $globalmix = $dirname . "/.tmp_mx_" . $filename;
325 # Step 5: set up each local function as a global
327 `$objcopy $globallist $inputfile $globalobj`;
330 # Step 6: Link the global version to our list.
332 `$ld -r $globalobj $mcount_o -o $globalmix`;
335 # Step 7: Convert the local functions back into local symbols
337 `$objcopy $locallist $globalmix $inputfile`;
339 # Remove the temp files
340 `$rm $globalobj $globalmix`;
344 my $mix = $dirname . "/.tmp_mx_" . $filename;
347 # Step 8: Link the object with our list of call sites object.
349 `$ld -r $inputfile $mcount_o -o $mix`;
352 # Step 9: Move the result back to the original object.
354 `$mv $mix $inputfile`;
357 # Clean up the temp files
358 `$rm $mcount_o $mcount_s`;