#!/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, $bits, $objdump, $objcopy, $cc, $ld, $nm, $rm, $mv, $inputfile) = @ARGV; # Acceptable sections to record. my %text_sections = ( ".text" => 1, ); $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") { if ($bits == 64) { $arch = "x86_64"; } else { $arch = "i386"; } } if ($arch eq "x86_64") { $section_regex = "Disassembly of section\\s+(\\S+):"; $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\\s+(\\S+):"; $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/) { # Only record text sections that we know are safe if (defined($text_sections{$1})) { $read_function = 1; } else { $read_function = 0; } # print out any recorded offsets update_funcs() if ($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);