#!/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 this is that each object file will have a # section called __mcount_loc that will hold the list of pointers to mcount # callers. After final linking, the vmlinux will have within .init.data the # list of all callers to mcount between __start_mcount_loc and __stop_mcount_loc. # 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. # # When parse this object file using 'objdump', the references to the call # sites are offsets from the section 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. # # But where this section will reside finally in vmlinx is undetermined at # this point. So we can't use this kind of offsets to record the final # address of this call site. # # The trick is to change the call offset referring the start of a section to # referring a function symbol in this section. During the link step, 'ld' will # compute the final address according to the information we record. # # e.g. # # .section ".sched.text", "ax" # [...] # func1: # [...] # call mcount (offset: 0x10) # [...] # ret # .globl fun2 # func2: (offset: 0x20) # [...] # [...] # ret # func3: # [...] # call mcount (offset: 0x30) # [...] # # Both relocation offsets for the mcounts in the above example will be # offset from .sched.text. If we choose global symbol func2 as a reference and # make another file called tmp.s with the new offsets: # # .section __mcount_loc # .quad func2 - 0x10 # .quad func2 + 0x10 # # We can then compile this tmp.s into tmp.o, and link it back to the original # object. # # In our algorithm, we will choose the first global function we meet in this # section as the reference. But this gets hard if there is no global functions # in this section. In such a case we have to select a local one. E.g. func1: # # .section ".sched.text", "ax" # func1: # [...] # call mcount (offset: 0x10) # [...] # ret # func2: # [...] # call mcount (offset: 0x20) # [...] # .section "other.section" # # 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 func1: # one local, one global. After final compile, we will end up with # an undefined reference to func1 or a wrong reference to another global # func1 in other files. # # 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 func1 # into a global symbol before linking tmp.o. Then after we link tmp.o # we will only have a single symbol for func1 that is global. # We can convert func1 back into a local symbol and we are done. # # Here are the steps we take: # # 1) Record all the local and weak 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. # 8) Link the object with the list object. # 9) Move the result back to the original object. # use strict; my $P = $0; $P =~ s@.*/@@g; my $V = '0.1'; if ($#ARGV != 10) { print "usage: $P arch bits objdump objcopy cc ld nm rm mv is_module inputfile\n"; print "version: $V\n"; exit(1); } my ($arch, $bits, $objdump, $objcopy, $cc, $ld, $nm, $rm, $mv, $is_module, $inputfile) = @ARGV; # This file refers to mcount and shouldn't be ftraced, so lets' ignore it if ($inputfile =~ m,kernel/trace/ftrace\.o$,) { exit(0); } # Acceptable sections to record. my %text_sections = ( ".text" => 1, ".sched.text" => 1, ".spinlock.text" => 1, ".irqentry.text" => 1, ".text.unlikely" => 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 $local_regex; # Match a local function (return function) my $weak_regex; # Match a weak function (return function) 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) my $alignment; # The .align value to use for $mcount_section my $section_type; # Section header plus possible alignment command my $can_use_local = 0; # If we can use local function references # Shut up recordmcount if user has older objcopy my $quiet_recordmcount = ".tmp_quiet_recordmcount"; my $print_warning = 1; $print_warning = 0 if ( -f $quiet_recordmcount); ## # check_objcopy - whether objcopy supports --globalize-symbols # # --globalize-symbols came out in 2.17, we must test the version # of objcopy, and if it is less than 2.17, then we can not # record local functions. sub check_objcopy { open (IN, "$objcopy --version |") or die "error running $objcopy"; while (<IN>) { if (/objcopy.*\s(\d+)\.(\d+)/) { $can_use_local = 1 if ($1 > 2 || ($1 == 2 && $2 >= 17)); last; } } close (IN); if (!$can_use_local && $print_warning) { print STDERR "WARNING: could not find objcopy version or version " . "is less than 2.17.\n" . "\tLocal function references are disabled.\n"; open (QUIET, ">$quiet_recordmcount"); printf QUIET "Disables the warning from recordmcount.pl\n"; close QUIET; } } if ($arch eq "x86") { if ($bits == 64) { $arch = "x86_64"; } else { $arch = "i386"; } } # # We base the defaults off of i386, the other archs may # feel free to change them in the below if statements. # $local_regex = "^[0-9a-fA-F]+\\s+t\\s+(\\S+)"; $weak_regex = "^[0-9a-fA-F]+\\s+([wW])\\s+(\\S+)"; $section_regex = "Disassembly of section\\s+(\\S+):"; $function_regex = "^([0-9a-fA-F]+)\\s+<(.*?)>:"; $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\smcount\$"; $section_type = '@progbits'; $type = ".long"; if ($arch eq "x86_64") { $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\smcount([+-]0x[0-9a-zA-Z]+)?\$"; $type = ".quad"; $alignment = 8; # 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") { $alignment = 4; # force flags for this arch $ld .= " -m elf_i386"; $objdump .= " -M i386"; $objcopy .= " -O elf32-i386"; $cc .= " -m32"; } elsif ($arch eq "s390" && $bits == 32) { $mcount_regex = "^\\s*([0-9a-fA-F]+):\\s*R_390_32\\s+_mcount\$"; $alignment = 4; $ld .= " -m elf_s390"; $cc .= " -m31"; } elsif ($arch eq "s390" && $bits == 64) { $mcount_regex = "^\\s*([0-9a-fA-F]+):\\s*R_390_(PC|PLT)32DBL\\s+_mcount\\+0x2\$"; $alignment = 8; $type = ".quad"; $ld .= " -m elf64_s390"; $cc .= " -m64"; } elsif ($arch eq "sh") { $alignment = 2; # force flags for this arch $ld .= " -m shlelf_linux"; $objcopy .= " -O elf32-sh-linux"; $cc .= " -m32"; } elsif ($arch eq "powerpc") { $local_regex = "^[0-9a-fA-F]+\\s+t\\s+(\\.?\\S+)"; $function_regex = "^([0-9a-fA-F]+)\\s+<(\\.?.*?)>:"; $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s\\.?_mcount\$"; if ($bits == 64) { $type = ".quad"; } } elsif ($arch eq "arm") { $alignment = 2; $section_type = '%progbits'; } elsif ($arch eq "ia64") { $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s_mcount\$"; $type = "data8"; if ($is_module eq "0") { $cc .= " -mconstant-gp"; } } elsif ($arch eq "sparc64") { # In the objdump output there are giblets like: # 0000000000000000 <igmp_net_exit-0x18>: # As there's some data blobs that get emitted into the # text section before the first instructions and the first # real symbols. We don't want to match that, so to combat # this we use '\w' so we'll match just plain symbol names, # and not those that also include hex offsets inside of the # '<>' brackets. Actually the generic function_regex setting # could safely use this too. $function_regex = "^([0-9a-fA-F]+)\\s+<(\\w*?)>:"; # Sparc64 calls '_mcount' instead of plain 'mcount'. $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s_mcount\$"; $alignment = 8; $type = ".xword"; $ld .= " -m elf64_sparc"; $cc .= " -m64"; $objcopy .= " -O elf64-sparc"; } 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_" . $prefix . ".o"; check_objcopy(); # # Step 1: find all the local (static functions) and weak symbols. # 't' is local, 'w/W' is weak # open (IN, "$nm $inputfile|") || die "error running $nm"; while (<IN>) { if (/$local_regex/) { $locals{$1} = 1; } elsif (/$weak_regex/) { $weak{$2} = $1; } } close(IN); my @offsets; # Array of offsets of mcount callers my $ref_func; # reference function to use for offsets my $offset = 0; # offset of ref_func to section beginning ## # update_funcs - print out the current mcount callers # # Go through the list of offsets to callers and write them to # the output file in a format that can be read by an assembler. # sub update_funcs { return unless ($ref_func and @offsets); # Sanity check on weak function. A weak function may be overwritten by # another function of the same name, making all these offsets incorrect. if (defined $weak{$ref_func}) { die "$inputfile: ERROR: referencing weak function" . " $ref_func for mcount\n"; } # is this function static? If so, note this fact. if (defined $locals{$ref_func}) { # only use locals if objcopy supports globalize-symbols if (!$can_use_local) { 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 $mcount_section,\"a\",$section_type\n"; print FILE "\t.align $alignment\n" if (defined($alignment)); } 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 -hdr $inputfile|") || die "error running $objdump"; my $text; # read headers first my $read_headers = 1; while (<IN>) { if ($read_headers && /$mcount_section/) { # # Somehow the make process can execute this script on an # object twice. If it does, we would duplicate the mcount # section and it will cause the function tracer self test # to fail. Check if the mcount section exists, and if it does, # warn and exit. # print STDERR "ERROR: $mcount_section already in $inputfile\n" . "\tThis may be an indication that your build is corrupted.\n" . "\tDelete $inputfile and try again. If the same object file\n" . "\tstill causes an issue, then disable CONFIG_DYNAMIC_FTRACE.\n"; exit(-1); } # is it a section? if (/$section_regex/) { $read_headers = 0; # Only record text sections that we know are safe if (defined($text_sections{$1})) { $read_function = 1; } else { $read_function = 0; } # print out any recorded offsets update_funcs(); # 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; $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; $offset = hex $1; } else { # if we already have a function, and this is weak, skip it if (!defined($ref_func) && !defined($weak{$text}) && # PPC64 can have symbols that start with .L and # gcc considers these special. Don't use them! $text !~ /^\.L/) { $ref_func = $text; $offset = hex $1; } } } # is this a call site to mcount? If so, record it to print later if ($text_found && /$mcount_regex/) { $offsets[$#offsets + 1] = hex $1; } } # dump out anymore offsets that may have been found update_funcs(); # If we did not find any mcount callers, we are done (do nothing). if (!$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);