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Diffstat (limited to 'scripts/recordmcount.pl')
| -rwxr-xr-x | scripts/recordmcount.pl | 395 |
1 files changed, 395 insertions, 0 deletions
diff --git a/scripts/recordmcount.pl b/scripts/recordmcount.pl new file mode 100755 index 000000000000..f56d760bd589 --- /dev/null +++ b/scripts/recordmcount.pl @@ -0,0 +1,395 @@ +#!/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); |