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+#!/usr/bin/perl -w
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+# (c) 2008, Steven Rostedt <srostedt@redhat.com>
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+# Licensed under the terms of the GNU GPL License version 2
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+#
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+# recordmcount.pl - makes a section called __mcount_loc that holds
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+# all the offsets to the calls to mcount.
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+#
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+#
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+# What we want to end up with is a section in vmlinux called
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+# __mcount_loc that contains a list of pointers to all the
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+# call sites in the kernel that call mcount. Later on boot up, the kernel
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+# will read this list, save the locations and turn them into nops.
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+# When tracing or profiling is later enabled, these locations will then
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+# be converted back to pointers to some function.
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+#
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+# This is no easy feat. This script is called just after the original
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+# object is compiled and before it is linked.
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+#
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+# The references to the call sites are offsets from the section of text
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+# that the call site is in. Hence, all functions in a section that
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+# has a call site to mcount, will have the offset from the beginning of
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+# the section and not the beginning of the function.
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+#
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+# The trick is to find a way to record the beginning of the section.
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+# The way we do this is to look at the first function in the section
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+# which will also be the location of that section after final link.
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+# e.g.
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+#
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+# .section ".text.sched"
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+# .globl my_func
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+# my_func:
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+# [...]
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+# call mcount (offset: 0x5)
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+# [...]
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+# ret
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+# other_func:
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+# [...]
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+# call mcount (offset: 0x1b)
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+# [...]
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+#
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+# Both relocation offsets for the mcounts in the above example will be
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+# offset from .text.sched. If we make another file called tmp.s with:
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+#
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+# .section __mcount_loc
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+# .quad my_func + 0x5
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+# .quad my_func + 0x1b
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+#
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+# We can then compile this tmp.s into tmp.o, and link it to the original
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+# object.
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+#
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+# But this gets hard if my_func is not globl (a static function).
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+# In such a case we have:
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+#
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+# .section ".text.sched"
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+# my_func:
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+# [...]
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+# call mcount (offset: 0x5)
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+# [...]
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+# ret
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+# .globl my_func
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+# other_func:
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+# [...]
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+# call mcount (offset: 0x1b)
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+# [...]
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+#
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+# If we make the tmp.s the same as above, when we link together with
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+# the original object, we will end up with two symbols for my_func:
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+# one local, one global. After final compile, we will end up with
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+# an undefined reference to my_func.
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+#
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+# Since local objects can reference local variables, we need to find
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+# a way to make tmp.o reference the local objects of the original object
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+# file after it is linked together. To do this, we convert the my_func
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+# into a global symbol before linking tmp.o. Then after we link tmp.o
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+# we will only have a single symbol for my_func that is global.
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+# We can convert my_func back into a local symbol and we are done.
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+#
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+# Here are the steps we take:
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+#
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+# 1) Record all the local symbols by using 'nm'
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+# 2) Use objdump to find all the call site offsets and sections for
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+# mcount.
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+# 3) Compile the list into its own object.
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+# 4) Do we have to deal with local functions? If not, go to step 8.
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+# 5) Make an object that converts these local functions to global symbols
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+# with objcopy.
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+# 6) Link together this new object with the list object.
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+# 7) Convert the local functions back to local symbols and rename
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+# the result as the original object.
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+# End.
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+# 8) Link the object with the list object.
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+# 9) Move the result back to the original object.
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+# End.
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+#
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+
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+use strict;
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+
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+my $P = $0;
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+$P =~ s@.*/@@g;
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+
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+my $V = '0.1';
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+
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+if ($#ARGV < 6) {
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+ print "usage: $P arch objdump objcopy cc ld nm rm mv inputfile\n";
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+ print "version: $V\n";
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+ exit(1);
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+}
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+
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+my ($arch, $objdump, $objcopy, $cc, $ld, $nm, $rm, $mv, $inputfile) = @ARGV;
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+
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+$objdump = "objdump" if ((length $objdump) == 0);
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+$objcopy = "objcopy" if ((length $objcopy) == 0);
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+$cc = "gcc" if ((length $cc) == 0);
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+$ld = "ld" if ((length $ld) == 0);
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+$nm = "nm" if ((length $nm) == 0);
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+$rm = "rm" if ((length $rm) == 0);
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+$mv = "mv" if ((length $mv) == 0);
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+
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+#print STDERR "running: $P '$arch' '$objdump' '$objcopy' '$cc' '$ld' " .
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+# "'$nm' '$rm' '$mv' '$inputfile'\n";
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+
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+my %locals;
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+my %convert;
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+
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+my $type;
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+my $section_regex; # Find the start of a section
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+my $function_regex; # Find the name of a function (return func name)
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+my $mcount_regex; # Find the call site to mcount (return offset)
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+
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+if ($arch eq "x86_64") {
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+ $section_regex = "Disassembly of section";
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+ $function_regex = "<(.*?)>:";
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+ $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\smcount([+-]0x[0-9a-zA-Z]+)?\$";
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+ $type = ".quad";
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+} elsif ($arch eq "i386") {
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+ $section_regex = "Disassembly of section";
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+ $function_regex = "<(.*?)>:";
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+ $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\smcount\$";
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+ $type = ".long";
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+} else {
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+ die "Arch $arch is not supported with CONFIG_FTRACE_MCOUNT_RECORD";
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+}
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+
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+my $text_found = 0;
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+my $read_function = 0;
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+my $opened = 0;
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+my $text = "";
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+my $mcount_section = "__mcount_loc";
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+
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+my $dirname;
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+my $filename;
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+my $prefix;
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+my $ext;
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+
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+if ($inputfile =~ m,^(.*)/([^/]*)$,) {
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+ $dirname = $1;
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+ $filename = $2;
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+} else {
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+ $dirname = ".";
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+ $filename = $inputfile;
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+}
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+
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+if ($filename =~ m,^(.*)(\.\S),) {
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+ $prefix = $1;
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+ $ext = $2;
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+} else {
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+ $prefix = $filename;
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+ $ext = "";
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+}
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+
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+my $mcount_s = $dirname . "/.tmp_mc_" . $prefix . ".s";
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+my $mcount_o = $dirname . "/.tmp_mc_" . $prefix . ".o";
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+
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+#
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+# Step 1: find all the local symbols (static functions).
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+#
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+open (IN, "$nm $inputfile|") || die "error running $nm";
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+while (<IN>) {
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+ if (/^[0-9a-fA-F]+\s+t\s+(\S+)/) {
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+ $locals{$1} = 1;
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+ }
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+}
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+close(IN);
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+
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+#
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+# Step 2: find the sections and mcount call sites
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+#
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+open(IN, "$objdump -dr $inputfile|") || die "error running $objdump";
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+
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+while (<IN>) {
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+ # is it a section?
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+ if (/$section_regex/) {
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+ $read_function = 1;
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+ $text_found = 0;
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+ # section found, now is this a start of a function?
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+ } elsif ($read_function && /$function_regex/) {
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+ $read_function = 0;
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+ $text_found = 1;
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+ $text = $1;
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+ # is this function static? If so, note this fact.
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+ if (defined $locals{$text}) {
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+ $convert{$text} = 1;
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+ }
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+ # is this a call site to mcount? If so, print the offset from the section
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+ } elsif ($text_found && /$mcount_regex/) {
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+ if (!$opened) {
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+ open(FILE, ">$mcount_s") || die "can't create $mcount_s\n";
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+ $opened = 1;
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+ print FILE "\t.section $mcount_section,\"a\",\@progbits\n";
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+ }
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+ print FILE "\t$type $text + 0x$1\n";
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+ }
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+}
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+
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+# If we did not find any mcount callers, we are done (do nothing).
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+if (!$opened) {
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+ exit(0);
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+}
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+
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+close(FILE);
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+
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+#
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+# Step 3: Compile the file that holds the list of call sites to mcount.
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+#
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+`$cc -o $mcount_o -c $mcount_s`;
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+
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+my @converts = keys %convert;
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+
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+#
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+# Step 4: Do we have sections that started with local functions?
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+#
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+if ($#converts >= 0) {
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+ my $globallist = "";
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+ my $locallist = "";
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+
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+ foreach my $con (@converts) {
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+ $globallist .= " --globalize-symbol $con";
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+ $locallist .= " --localize-symbol $con";
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+ }
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+
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+ my $globalobj = $dirname . "/.tmp_gl_" . $filename;
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+ my $globalmix = $dirname . "/.tmp_mx_" . $filename;
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+
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+ #
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+ # Step 5: set up each local function as a global
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+ #
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+ `$objcopy $globallist $inputfile $globalobj`;
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+
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+ #
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+ # Step 6: Link the global version to our list.
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+ #
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+ `$ld -r $globalobj $mcount_o -o $globalmix`;
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+
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+ #
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+ # Step 7: Convert the local functions back into local symbols
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+ #
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+ `$objcopy $locallist $globalmix $inputfile`;
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+
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+ # Remove the temp files
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+ `$rm $globalobj $globalmix`;
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+
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+} else {
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+
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+ my $mix = $dirname . "/.tmp_mx_" . $filename;
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+
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+ #
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+ # Step 8: Link the object with our list of call sites object.
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+ #
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+ `$ld -r $inputfile $mcount_o -o $mix`;
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+
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+ #
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+ # Step 9: Move the result back to the original object.
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+ #
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+ `$mv $mix $inputfile`;
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+}
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+
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+# Clean up the temp files
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+`$rm $mcount_o $mcount_s`;
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+
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+exit(0);
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Steven Rostedt