2 files changed, 286 insertions, 0 deletions

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 277cfe0b7100..463ddcc583ed 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -198,10 +198,16 @@ cmd_modversions =							\
         fi;
 endif
 
+ifdef CONFIG_FTRACE_MCOUNT_RECORD
+cmd_record_mcount = scripts/recordmcount.pl "$(ARCH)" \
+        "$(OBJDUMP)" "$(OBJCOPY)" "$(CC)" "$(LD)" "$(NM)" "$(RM)" "$(MV)" "$(@)";
+endif
+
 define rule_cc_o_c
         $(call echo-cmd,checksrc) $(cmd_checksrc)                         \
         $(call echo-cmd,cc_o_c) $(cmd_cc_o_c);                            \
         $(cmd_modversions)                                                \
+        $(cmd_record_mcount)                                              \
         scripts/basic/fixdep $(depfile) $@ '$(call make-cmd,cc_o_c)' >    \
                                                       $(dot-target).tmp;  \
         rm -f $(depfile);                                                 \
diff --git a/scripts/recordmcount.pl b/scripts/recordmcount.pl
new file mode 100755
index 000000000000..44b4b23e91b2
--- /dev/null
+++ b/scripts/recordmcount.pl
@@ -0,0 +1,280 @@
+#!/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;
+my %convert;
+
+my $type;
+my $section_regex;      # Find the start of a section
+my $function_regex;     # Find the name of a function (return 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 = "<(.*?)>:";
+    $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\smcount([+-]0x[0-9a-zA-Z]+)?\$";
+    $type = ".quad";
+} elsif ($arch eq "i386") {
+    $section_regex = "Disassembly of section";
+    $function_regex = "<(.*?)>:";
+    $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\smcount\$";
+    $type = ".long";
+} else {
+    die "Arch $arch is not supported with CONFIG_FTRACE_MCOUNT_RECORD";
+}
+
+my $text_found = 0;
+my $read_function = 0;
+my $opened = 0;
+my $text = "";
+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_" . $prefix . ".o";
+
+#
+# Step 1: find all the local symbols (static functions).
+#
+open (IN, "$nm $inputfile|") || die "error running $nm";
+while (<IN>) {
+    if (/^[0-9a-fA-F]+\s+t\s+(\S+)/) {
+        $locals{$1} = 1;
+    }
+}
+close(IN);
+
+#
+# Step 2: find the sections and mcount call sites
+#
+open(IN, "$objdump -dr $inputfile|") || die "error running $objdump";
+
+while (<IN>) {
+    # is it a section?
+    if (/$section_regex/) {
+        $read_function = 1;
+        $text_found = 0;
+    # section found, now is this a start of a function?
+    } elsif ($read_function && /$function_regex/) {
+        $read_function = 0;
+        $text_found = 1;
+        $text = $1;
+        # is this function static? If so, note this fact.
+        if (defined $locals{$text}) {
+            $convert{$text} = 1;
+        }
+    # is this a call site to mcount? If so, print the offset from the section
+    } elsif ($text_found && /$mcount_regex/) {
+        if (!$opened) {
+            open(FILE, ">$mcount_s") || die "can't create $mcount_s\n";
+            $opened = 1;
+            print FILE "\t.section $mcount_section,\"a\",\@progbits\n";
+        }
+        print FILE "\t$type $text + 0x$1\n";
+    }
+}
+
+# If we did not find any mcount callers, we are done (do nothing).
+if (!$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);