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scripts/recordmcount.pl
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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. # |
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# .section ".sched.text", "ax" |
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# .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 |
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# offset from .sched.text. If we make another file called tmp.s with: |
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# # .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: # |
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# .section ".sched.text", "ax" |
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# 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 $V = '0.1'; |
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if ($#ARGV < 7) { |
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print "usage: $P arch bits objdump objcopy cc ld nm rm mv is_module inputfile "; |
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print "version: $V "; exit(1); } |
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my ($arch, $bits, $objdump, $objcopy, $cc, |
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$ld, $nm, $rm, $mv, $is_module, $inputfile) = @ARGV; |
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# This file refers to mcount and shouldn't be ftraced, so lets' ignore it if ($inputfile eq "kernel/trace/ftrace.o") { exit(0); } |
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# Acceptable sections to record. my %text_sections = ( ".text" => 1, |
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".sched.text" => 1, ".spinlock.text" => 1, |
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".irqentry.text" => 1, |
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); |
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$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' "; |
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my %locals; # List of local (static) functions my %weak; # List of weak functions my %convert; # List of local functions used that needs conversion |
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my $type; |
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my $nm_regex; # Find the local functions (return function) |
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my $section_regex; # Find the start of a section |
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my $function_regex; # Find the name of a function # (return offset and func name) |
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my $mcount_regex; # Find the call site to mcount (return offset) |
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my $alignment; # The .align value to use for $mcount_section |
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my $section_type; # Section header plus possible alignment command |
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if ($arch eq "x86") { if ($bits == 64) { $arch = "x86_64"; } else { $arch = "i386"; } } |
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# # We base the defaults off of i386, the other archs may # feel free to change them in the below if statements. # $nm_regex = "^[0-9a-fA-F]+\\s+t\\s+(\\S+)"; $section_regex = "Disassembly of section\\s+(\\S+):"; $function_regex = "^([0-9a-fA-F]+)\\s+<(.*?)>:"; $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\smcount\$"; |
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$section_type = '@progbits'; |
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$type = ".long"; |
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if ($arch eq "x86_64") { |
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$mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\smcount([+-]0x[0-9a-zA-Z]+)?\$"; $type = ".quad"; |
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$alignment = 8; |
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# force flags for this arch $ld .= " -m elf_x86_64"; $objdump .= " -M x86-64"; $objcopy .= " -O elf64-x86-64"; $cc .= " -m64"; |
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} elsif ($arch eq "i386") { |
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$alignment = 4; |
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# force flags for this arch $ld .= " -m elf_i386"; $objdump .= " -M i386"; $objcopy .= " -O elf32-i386"; $cc .= " -m32"; |
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} elsif ($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"; $cc .= " -m64"; |
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} elsif ($arch eq "sh") { |
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$alignment = 2; |
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# force flags for this arch $ld .= " -m shlelf_linux"; $objcopy .= " -O elf32-sh-linux"; $cc .= " -m32"; |
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} elsif ($arch eq "powerpc") { $nm_regex = "^[0-9a-fA-F]+\\s+t\\s+(\\.?\\S+)"; |
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$function_regex = "^([0-9a-fA-F]+)\\s+<(\\.?.*?)>:"; $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s\\.?_mcount\$"; |
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if ($bits == 64) { $type = ".quad"; |
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} |
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} elsif ($arch eq "arm") { $alignment = 2; $section_type = '%progbits'; |
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} elsif ($arch eq "ia64") { $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s_mcount\$"; $type = "data8"; if ($is_module eq "0") { $cc .= " -mconstant-gp"; } |
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} elsif ($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"; |
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} else { die "Arch $arch is not supported with CONFIG_FTRACE_MCOUNT_RECORD"; } my $text_found = 0; my $read_function = 0; my $opened = 0; |
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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"; # |
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# --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. " . "\tDisabling local function references. "; } |
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# |
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# Step 1: find all the local (static functions) and weak symbols. # 't' is local, 'w/W' is weak (we never use a weak function) |
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# open (IN, "$nm $inputfile|") || die "error running $nm"; while (<IN>) { |
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if (/$nm_regex/) { |
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$locals{$1} = 1; |
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} elsif (/^[0-9a-fA-F]+\s+([wW])\s+(\S+)/) { $weak{$2} = $1; |
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} } close(IN); |
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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 "; return; } # is this function static? If so, note this fact. if (defined $locals{$ref_func}) { |
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# only use locals if objcopy supports globalize-symbols if (!$use_locals) { |
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return; } |
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$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 "; $opened = 1; |
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print FILE "\t.section $mcount_section,\"a\",$section_type "; |
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print FILE "\t.align $alignment " if (defined($alignment)); |
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} printf FILE "\t%s %s + %d ", $type, $ref_func, $offsets[$i] - $offset; } } |
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# # Step 2: find the sections and mcount call sites # |
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open(IN, "$objdump -hdr $inputfile|") || die "error running $objdump"; |
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my $text; |
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my $read_headers = 1; |
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while (<IN>) { # is it a section? if (/$section_regex/) { |
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$read_headers = 0; |
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# Only record text sections that we know are safe if (defined($text_sections{$1})) { $read_function = 1; } else { $read_function = 0; } |
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# print out any recorded offsets update_funcs() if ($text_found); # reset all markers and arrays |
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$text_found = 0; |
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undef($ref_func); undef(@offsets); |
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# section found, now is this a start of a function? } elsif ($read_function && /$function_regex/) { |
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$text_found = 1; |
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$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 = $text; } |
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} |
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} elsif ($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 " . "\tThis may be an indication that your build is corrupted. " . "\tDelete $inputfile and try again. If the same object file " . "\tstill causes an issue, then disable CONFIG_DYNAMIC_FTRACE. "; exit(-1); |
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} # is this a call site to mcount? If so, record it to print later if ($text_found && /$mcount_regex/) { $offsets[$#offsets + 1] = hex $1; |
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} } |
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# dump out anymore offsets that may have been found update_funcs() if ($text_found); |
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# 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); |