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+#!/usr/bin/perl -w
+# (c) 2008, Steven Rostedt <srostedt@redhat.com>
+# Licensed under the terms of the GNU GPL License version 2
+#
+# recordmcount.pl - makes a section called __mcount_loc that holds
+# all the offsets to the calls to mcount.
+#
+#
+# What we want to end up with is a section in vmlinux called
+# __mcount_loc that contains a list of pointers to all the
+# call sites in the kernel that call mcount. Later on boot up, the kernel
+# will read this list, save the locations and turn them into nops.
+# When tracing or profiling is later enabled, these locations will then
+# be converted back to pointers to some function.
+#
+# This is no easy feat. This script is called just after the original
+# object is compiled and before it is linked.
+#
+# The references to the call sites are offsets from the section of text
+# that the call site is in. Hence, all functions in a section that
+# has a call site to mcount, will have the offset from the beginning of
+# the section and not the beginning of the function.
+#
+# The trick is to find a way to record the beginning of the section.
+# The way we do this is to look at the first function in the section
+# which will also be the location of that section after final link.
+# e.g.
+#
+# .section ".text.sched"
+# .globl my_func
+# my_func:
+# [...]
+# call mcount (offset: 0x5)
+# [...]
+# ret
+# other_func:
+# [...]
+# call mcount (offset: 0x1b)
+# [...]
+#
+# Both relocation offsets for the mcounts in the above example will be
+# offset from .text.sched. If we make another file called tmp.s with:
+#
+# .section __mcount_loc
+# .quad my_func + 0x5
+# .quad my_func + 0x1b
+#
+# We can then compile this tmp.s into tmp.o, and link it to the original
+# object.
+#
+# But this gets hard if my_func is not globl (a static function).
+# In such a case we have:
+#
+# .section ".text.sched"
+# my_func:
+# [...]
+# call mcount (offset: 0x5)
+# [...]
+# ret
+# .globl my_func
+# other_func:
+# [...]
+# call mcount (offset: 0x1b)
+# [...]
+#
+# If we make the tmp.s the same as above, when we link together with
+# the original object, we will end up with two symbols for my_func:
+# one local, one global. After final compile, we will end up with
+# an undefined reference to my_func.
+#
+# Since local objects can reference local variables, we need to find
+# a way to make tmp.o reference the local objects of the original object
+# file after it is linked together. To do this, we convert the my_func
+# into a global symbol before linking tmp.o. Then after we link tmp.o
+# we will only have a single symbol for my_func that is global.
+# We can convert my_func back into a local symbol and we are done.
+#
+# Here are the steps we take:
+#
+# 1) Record all the local symbols by using 'nm'
+# 2) Use objdump to find all the call site offsets and sections for
+# mcount.
+# 3) Compile the list into its own object.
+# 4) Do we have to deal with local functions? If not, go to step 8.
+# 5) Make an object that converts these local functions to global symbols
+# with objcopy.
+# 6) Link together this new object with the list object.
+# 7) Convert the local functions back to local symbols and rename
+# the result as the original object.
+# End.
+# 8) Link the object with the list object.
+# 9) Move the result back to the original object.
+# End.
+#
+
+use strict;
+
+my $P = $0;
+$P =~ s@.*/@@g;
+
+my $V = '0.1';
+
+if ($#ARGV < 6) {
+ print "usage: $P arch objdump objcopy cc ld nm rm mv inputfile\n";
+ print "version: $V\n";
+ exit(1);
+}
+
+my ($arch, $objdump, $objcopy, $cc, $ld, $nm, $rm, $mv, $inputfile) = @ARGV;
+
+$objdump = "objdump" if ((length $objdump) == 0);
+$objcopy = "objcopy" if ((length $objcopy) == 0);
+$cc = "gcc" if ((length $cc) == 0);
+$ld = "ld" if ((length $ld) == 0);
+$nm = "nm" if ((length $nm) == 0);
+$rm = "rm" if ((length $rm) == 0);
+$mv = "mv" if ((length $mv) == 0);
+
+#print STDERR "running: $P '$arch' '$objdump' '$objcopy' '$cc' '$ld' " .
+# "'$nm' '$rm' '$mv' '$inputfile'\n";
+
+my %locals; # List of local (static) functions
+my %weak; # List of weak functions
+my %convert; # List of local functions used that needs conversion
+
+my $type;
+my $section_regex; # Find the start of a section
+my $function_regex; # Find the name of a function
+ # (return offset and func name)
+my $mcount_regex; # Find the call site to mcount (return offset)
+
+if ($arch eq "x86_64") {
+ $section_regex = "Disassembly of section";
+ $function_regex = "^([0-9a-fA-F]+)\\s+<(.*?)>:";
+ $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\smcount([+-]0x[0-9a-zA-Z]+)?\$";
+ $type = ".quad";
+
+ # force flags for this arch
+ $ld .= " -m elf_x86_64";
+ $objdump .= " -M x86-64";
+ $objcopy .= " -O elf64-x86-64";
+ $cc .= " -m64";
+
+} elsif ($arch eq "i386") {
+ $section_regex = "Disassembly of section";
+ $function_regex = "^([0-9a-fA-F]+)\\s+<(.*?)>:";
+ $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\smcount\$";
+ $type = ".long";
+
+ # force flags for this arch
+ $ld .= " -m elf_i386";
+ $objdump .= " -M i386";
+ $objcopy .= " -O elf32-i386";
+ $cc .= " -m32";
+
+} else {
+ die "Arch $arch is not supported with CONFIG_FTRACE_MCOUNT_RECORD";
+}
+
+my $text_found = 0;
+my $read_function = 0;
+my $opened = 0;
+my $mcount_section = "__mcount_loc";
+
+my $dirname;
+my $filename;
+my $prefix;
+my $ext;
+
+if ($inputfile =~ m,^(.*)/([^/]*)$,) {
+ $dirname = $1;
+ $filename = $2;
+} else {
+ $dirname = ".";
+ $filename = $inputfile;
+}
+
+if ($filename =~ m,^(.*)(\.\S),) {
+ $prefix = $1;
+ $ext = $2;
+} else {
+ $prefix = $filename;
+ $ext = "";
+}
+
+my $mcount_s = $dirname . "/.tmp_mc_" . $prefix . ".s";
+my $mcount_o = $dirname . "/.tmp_mc_" . $prefix . ".o";
+
+#
+# --globalize-symbols came out in 2.17, we must test the version
+# of objcopy, and if it is less than 2.17, then we can not
+# record local functions.
+my $use_locals = 01;
+my $local_warn_once = 0;
+my $found_version = 0;
+
+open (IN, "$objcopy --version |") || die "error running $objcopy";
+while (<IN>) {
+ if (/objcopy.*\s(\d+)\.(\d+)/) {
+ my $major = $1;
+ my $minor = $2;
+
+ $found_version = 1;
+ if ($major < 2 ||
+ ($major == 2 && $minor < 17)) {
+ $use_locals = 0;
+ }
+ last;
+ }
+}
+close (IN);
+
+if (!$found_version) {
+ print STDERR "WARNING: could not find objcopy version.\n" .
+ "\tDisabling local function references.\n";
+}
+
+
+#
+# Step 1: find all the local (static functions) and weak symbols.
+# 't' is local, 'w/W' is weak (we never use a weak function)
+#
+open (IN, "$nm $inputfile|") || die "error running $nm";
+while (<IN>) {
+ if (/^[0-9a-fA-F]+\s+t\s+(\S+)/) {
+ $locals{$1} = 1;
+ } elsif (/^[0-9a-fA-F]+\s+([wW])\s+(\S+)/) {
+ $weak{$2} = $1;
+ }
+}
+close(IN);
+
+my @offsets; # Array of offsets of mcount callers
+my $ref_func; # reference function to use for offsets
+my $offset = 0; # offset of ref_func to section beginning
+
+##
+# update_funcs - print out the current mcount callers
+#
+# Go through the list of offsets to callers and write them to
+# the output file in a format that can be read by an assembler.
+#
+sub update_funcs
+{
+ return if ($#offsets < 0);
+
+ defined($ref_func) || die "No function to reference";
+
+ # A section only had a weak function, to represent it.
+ # Unfortunately, a weak function may be overwritten by another
+ # function of the same name, making all these offsets incorrect.
+ # To be safe, we simply print a warning and bail.
+ if (defined $weak{$ref_func}) {
+ print STDERR
+ "$inputfile: WARNING: referencing weak function" .
+ " $ref_func for mcount\n";
+ return;
+ }
+
+ # is this function static? If so, note this fact.
+ if (defined $locals{$ref_func}) {
+
+ # only use locals if objcopy supports globalize-symbols
+ if (!$use_locals) {
+ return;
+ }
+ $convert{$ref_func} = 1;
+ }
+
+ # Loop through all the mcount caller offsets and print a reference
+ # to the caller based from the ref_func.
+ for (my $i=0; $i <= $#offsets; $i++) {
+ if (!$opened) {
+ open(FILE, ">$mcount_s") || die "can't create $mcount_s\n";
+ $opened = 1;
+ print FILE "\t.section $mcount_section,\"a\",\@progbits\n";
+ }
+ printf FILE "\t%s %s + %d\n", $type, $ref_func, $offsets[$i] - $offset;
+ }
+}
+
+#
+# Step 2: find the sections and mcount call sites
+#
+open(IN, "$objdump -dr $inputfile|") || die "error running $objdump";
+
+my $text;
+
+while (<IN>) {
+ # is it a section?
+ if (/$section_regex/) {
+ $read_function = 1;
+ # print out any recorded offsets
+ update_funcs() if ($text_found);
+
+ # reset all markers and arrays
+ $text_found = 0;
+ undef($ref_func);
+ undef(@offsets);
+
+ # section found, now is this a start of a function?
+ } elsif ($read_function && /$function_regex/) {
+ $text_found = 1;
+ $offset = hex $1;
+ $text = $2;
+
+ # if this is either a local function or a weak function
+ # keep looking for functions that are global that
+ # we can use safely.
+ if (!defined($locals{$text}) && !defined($weak{$text})) {
+ $ref_func = $text;
+ $read_function = 0;
+ } else {
+ # if we already have a function, and this is weak, skip it
+ if (!defined($ref_func) || !defined($weak{$text})) {
+ $ref_func = $text;
+ }
+ }
+ }
+
+ # is this a call site to mcount? If so, record it to print later
+ if ($text_found && /$mcount_regex/) {
+ $offsets[$#offsets + 1] = hex $1;
+ }
+}
+
+# dump out anymore offsets that may have been found
+update_funcs() if ($text_found);
+
+# If we did not find any mcount callers, we are done (do nothing).
+if (!$opened) {
+ exit(0);
+}
+
+close(FILE);
+
+#
+# Step 3: Compile the file that holds the list of call sites to mcount.
+#
+`$cc -o $mcount_o -c $mcount_s`;
+
+my @converts = keys %convert;
+
+#
+# Step 4: Do we have sections that started with local functions?
+#
+if ($#converts >= 0) {
+ my $globallist = "";
+ my $locallist = "";
+
+ foreach my $con (@converts) {
+ $globallist .= " --globalize-symbol $con";
+ $locallist .= " --localize-symbol $con";
+ }
+
+ my $globalobj = $dirname . "/.tmp_gl_" . $filename;
+ my $globalmix = $dirname . "/.tmp_mx_" . $filename;
+
+ #
+ # Step 5: set up each local function as a global
+ #
+ `$objcopy $globallist $inputfile $globalobj`;
+
+ #
+ # Step 6: Link the global version to our list.
+ #
+ `$ld -r $globalobj $mcount_o -o $globalmix`;
+
+ #
+ # Step 7: Convert the local functions back into local symbols
+ #
+ `$objcopy $locallist $globalmix $inputfile`;
+
+ # Remove the temp files
+ `$rm $globalobj $globalmix`;
+
+} else {
+
+ my $mix = $dirname . "/.tmp_mx_" . $filename;
+
+ #
+ # Step 8: Link the object with our list of call sites object.
+ #
+ `$ld -r $inputfile $mcount_o -o $mix`;
+
+ #
+ # Step 9: Move the result back to the original object.
+ #
+ `$mv $mix $inputfile`;
+}
+
+# Clean up the temp files
+`$rm $mcount_o $mcount_s`;
+
+exit(0);