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Steven Rostedt8da38212008-08-14 15:45:07 -04001#!/usr/bin/perl -w
2# (c) 2008, Steven Rostedt <srostedt@redhat.com>
3# Licensed under the terms of the GNU GPL License version 2
4#
5# recordmcount.pl - makes a section called __mcount_loc that holds
6# all the offsets to the calls to mcount.
7#
8#
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.
15#
16# This is no easy feat. This script is called just after the original
17# object is compiled and before it is linked.
18#
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.
23#
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.
27# e.g.
28#
29# .section ".text.sched"
30# .globl my_func
31# my_func:
32# [...]
33# call mcount (offset: 0x5)
34# [...]
35# ret
36# other_func:
37# [...]
38# call mcount (offset: 0x1b)
39# [...]
40#
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:
43#
44# .section __mcount_loc
45# .quad my_func + 0x5
46# .quad my_func + 0x1b
47#
48# We can then compile this tmp.s into tmp.o, and link it to the original
49# object.
50#
51# But this gets hard if my_func is not globl (a static function).
52# In such a case we have:
53#
54# .section ".text.sched"
55# my_func:
56# [...]
57# call mcount (offset: 0x5)
58# [...]
59# ret
60# .globl my_func
61# other_func:
62# [...]
63# call mcount (offset: 0x1b)
64# [...]
65#
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.
70#
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.
77#
78# Here are the steps we take:
79#
80# 1) Record all the local symbols by using 'nm'
81# 2) Use objdump to find all the call site offsets and sections for
82# mcount.
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
86# with objcopy.
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.
90# End.
91# 8) Link the object with the list object.
92# 9) Move the result back to the original object.
93# End.
94#
95
96use strict;
97
98my $P = $0;
99$P =~ s@.*/@@g;
100
101my $V = '0.1';
102
103if ($#ARGV < 6) {
104 print "usage: $P arch objdump objcopy cc ld nm rm mv inputfile\n";
105 print "version: $V\n";
106 exit(1);
107}
108
109my ($arch, $objdump, $objcopy, $cc, $ld, $nm, $rm, $mv, $inputfile) = @ARGV;
110
111$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);
118
119#print STDERR "running: $P '$arch' '$objdump' '$objcopy' '$cc' '$ld' " .
120# "'$nm' '$rm' '$mv' '$inputfile'\n";
121
122my %locals;
123my %convert;
124
125my $type;
126my $section_regex; # Find the start of a section
127my $function_regex; # Find the name of a function (return func name)
128my $mcount_regex; # Find the call site to mcount (return offset)
129
130if ($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]+)?\$";
134 $type = ".quad";
135} elsif ($arch eq "i386") {
136 $section_regex = "Disassembly of section";
137 $function_regex = "<(.*?)>:";
138 $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\smcount\$";
139 $type = ".long";
140} else {
141 die "Arch $arch is not supported with CONFIG_FTRACE_MCOUNT_RECORD";
142}
143
144my $text_found = 0;
145my $read_function = 0;
146my $opened = 0;
147my $text = "";
148my $mcount_section = "__mcount_loc";
149
150my $dirname;
151my $filename;
152my $prefix;
153my $ext;
154
155if ($inputfile =~ m,^(.*)/([^/]*)$,) {
156 $dirname = $1;
157 $filename = $2;
158} else {
159 $dirname = ".";
160 $filename = $inputfile;
161}
162
163if ($filename =~ m,^(.*)(\.\S),) {
164 $prefix = $1;
165 $ext = $2;
166} else {
167 $prefix = $filename;
168 $ext = "";
169}
170
171my $mcount_s = $dirname . "/.tmp_mc_" . $prefix . ".s";
172my $mcount_o = $dirname . "/.tmp_mc_" . $prefix . ".o";
173
174#
175# Step 1: find all the local symbols (static functions).
176#
177open (IN, "$nm $inputfile|") || die "error running $nm";
178while (<IN>) {
179 if (/^[0-9a-fA-F]+\s+t\s+(\S+)/) {
180 $locals{$1} = 1;
181 }
182}
183close(IN);
184
185#
186# Step 2: find the sections and mcount call sites
187#
188open(IN, "$objdump -dr $inputfile|") || die "error running $objdump";
189
190while (<IN>) {
191 # is it a section?
192 if (/$section_regex/) {
193 $read_function = 1;
194 $text_found = 0;
195 # section found, now is this a start of a function?
196 } elsif ($read_function && /$function_regex/) {
197 $read_function = 0;
198 $text_found = 1;
199 $text = $1;
200 # is this function static? If so, note this fact.
201 if (defined $locals{$text}) {
202 $convert{$text} = 1;
203 }
204 # is this a call site to mcount? If so, print the offset from the section
205 } elsif ($text_found && /$mcount_regex/) {
206 if (!$opened) {
207 open(FILE, ">$mcount_s") || die "can't create $mcount_s\n";
208 $opened = 1;
209 print FILE "\t.section $mcount_section,\"a\",\@progbits\n";
210 }
211 print FILE "\t$type $text + 0x$1\n";
212 }
213}
214
215# If we did not find any mcount callers, we are done (do nothing).
216if (!$opened) {
217 exit(0);
218}
219
220close(FILE);
221
222#
223# Step 3: Compile the file that holds the list of call sites to mcount.
224#
225`$cc -o $mcount_o -c $mcount_s`;
226
227my @converts = keys %convert;
228
229#
230# Step 4: Do we have sections that started with local functions?
231#
232if ($#converts >= 0) {
233 my $globallist = "";
234 my $locallist = "";
235
236 foreach my $con (@converts) {
237 $globallist .= " --globalize-symbol $con";
238 $locallist .= " --localize-symbol $con";
239 }
240
241 my $globalobj = $dirname . "/.tmp_gl_" . $filename;
242 my $globalmix = $dirname . "/.tmp_mx_" . $filename;
243
244 #
245 # Step 5: set up each local function as a global
246 #
247 `$objcopy $globallist $inputfile $globalobj`;
248
249 #
250 # Step 6: Link the global version to our list.
251 #
252 `$ld -r $globalobj $mcount_o -o $globalmix`;
253
254 #
255 # Step 7: Convert the local functions back into local symbols
256 #
257 `$objcopy $locallist $globalmix $inputfile`;
258
259 # Remove the temp files
260 `$rm $globalobj $globalmix`;
261
262} else {
263
264 my $mix = $dirname . "/.tmp_mx_" . $filename;
265
266 #
267 # Step 8: Link the object with our list of call sites object.
268 #
269 `$ld -r $inputfile $mcount_o -o $mix`;
270
271 #
272 # Step 9: Move the result back to the original object.
273 #
274 `$mv $mix $inputfile`;
275}
276
277# Clean up the temp files
278`$rm $mcount_o $mcount_s`;
279
280exit(0);