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";
126 my $section_regex; # Find the start of a section
127 my $function_regex; # Find the name of a function (return func name)
128 my $mcount_regex; # Find the call site to mcount (return offset)
130 if ($arch eq "x86_64") {
131 $section_regex = "Disassembly of section";
132 $function_regex = "<(.*?)>:";
133 $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\smcount([+-]0x[0-9a-zA-Z]+)?\$";
135 } elsif ($arch eq "i386") {
136 $section_regex = "Disassembly of section";
137 $function_regex = "<(.*?)>:";
138 $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\smcount\$";
141 die "Arch $arch is not supported with CONFIG_FTRACE_MCOUNT_RECORD";
145 my $read_function = 0;
148 my $mcount_section = "__mcount_loc";
155 if ($inputfile =~ m,^(.*)/([^/]*)$,) {
160 $filename = $inputfile;
163 if ($filename =~ m,^(.*)(\.\S),) {
171 my $mcount_s = $dirname . "/.tmp_mc_" . $prefix . ".s";
172 my $mcount_o = $dirname . "/.tmp_mc_" . $prefix . ".o";
175 # Step 1: find all the local symbols (static functions).
177 open (IN, "$nm $inputfile|") || die "error running $nm";
179 if (/^[0-9a-fA-F]+\s+t\s+(\S+)/) {
186 # Step 2: find the sections and mcount call sites
188 open(IN, "$objdump -dr $inputfile|") || die "error running $objdump";
192 if (/$section_regex/) {
195 # section found, now is this a start of a function?
196 } elsif ($read_function && /$function_regex/) {
200 # is this function static? If so, note this fact.
201 if (defined $locals{$text}) {
204 # is this a call site to mcount? If so, print the offset from the section
205 } elsif ($text_found && /$mcount_regex/) {
207 open(FILE, ">$mcount_s") || die "can't create $mcount_s\n";
209 print FILE "\t.section $mcount_section,\"a\",\@progbits\n";
211 print FILE "\t$type $text + 0x$1\n";
215 # If we did not find any mcount callers, we are done (do nothing).
223 # Step 3: Compile the file that holds the list of call sites to mcount.
225 `$cc -o $mcount_o -c $mcount_s`;
227 my @converts = keys %convert;
230 # Step 4: Do we have sections that started with local functions?
232 if ($#converts >= 0) {
236 foreach my $con (@converts) {
237 $globallist .= " --globalize-symbol $con";
238 $locallist .= " --localize-symbol $con";
241 my $globalobj = $dirname . "/.tmp_gl_" . $filename;
242 my $globalmix = $dirname . "/.tmp_mx_" . $filename;
245 # Step 5: set up each local function as a global
247 `$objcopy $globallist $inputfile $globalobj`;
250 # Step 6: Link the global version to our list.
252 `$ld -r $globalobj $mcount_o -o $globalmix`;
255 # Step 7: Convert the local functions back into local symbols
257 `$objcopy $locallist $globalmix $inputfile`;
259 # Remove the temp files
260 `$rm $globalobj $globalmix`;
264 my $mix = $dirname . "/.tmp_mx_" . $filename;
267 # Step 8: Link the object with our list of call sites object.
269 `$ld -r $inputfile $mcount_o -o $mix`;
272 # Step 9: Move the result back to the original object.
274 `$mv $mix $inputfile`;
277 # Clean up the temp files
278 `$rm $mcount_o $mcount_s`;