FreeBSD/Linux Kernel Cross Reference
sys/scripts/recordmcount.pl

     #!/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 != 11) {
           print "usage: $P arch endian bits objdump objcopy cc ld nm rm mv is_module inputfile\n";
           print "version: $V\n";
           exit(1);
   }
   
   my ($arch, $endian, $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,
        ".ref.text" => 1,
        ".sched.text" => 1,
        ".spinlock.text" => 1,
        ".irqentry.text" => 1,
        ".kprobes.text" => 1,
        ".text.unlikely" => 1,
   );
   
   # Note: we are nice to C-programmers here, thus we skip the '||='-idiom.
   $objdump = 'objdump' if (!$objdump);
   $objcopy = 'objcopy' if (!$objcopy);
   $cc = 'gcc' if (!$cc);
   $ld = 'ld' if (!$ld);
   $nm = 'nm' if (!$nm);
   $rm = 'rm' if (!$rm);
   $mv = 'mv' if (!$mv);
   
   #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 $mcount_adjust;      # Address adjustment to mcount 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 ($arch =~ /(x86(_64)?)|(i386)/) {
       if ($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';
   $mcount_adjust = 0;
   $type = ".long";
   
   if ($arch eq "x86_64") {
       $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\smcount([+-]0x[0-9a-zA-Z]+)?\$";
       $type = ".quad";
       $alignment = 8;
       $mcount_adjust = -1;
   
       # 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;
       $mcount_adjust = -1;
   
       # 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\$";
       $mcount_adjust = -4;
       $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\$";
       $mcount_adjust = -8;
       $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';
       $mcount_regex = "^\\s*([0-9a-fA-F]+):\\s*R_ARM_(CALL|PC24|THM_CALL)" .
                           "\\s+(__gnu_mcount_nc|mcount)\$";
   
   } 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";
       $objcopy .= " -O elf64-sparc";
   } elsif ($arch eq "mips") {
       # To enable module support, we need to enable the -mlong-calls option
       # of gcc for module, after using this option, we can not get the real
       # offset of the calling to _mcount, but the offset of the lui
       # instruction or the addiu one. herein, we record the address of the
       # first one, and then we can replace this instruction by a branch
       # instruction to jump over the profiling function to filter the
       # indicated functions, or swith back to the lui instruction to trace
       # them, which means dynamic tracing.
       #
       #       c:  3c030000        lui     v1,0x0
       #                   c: R_MIPS_HI16  _mcount
       #                   c: R_MIPS_NONE  *ABS*
       #                   c: R_MIPS_NONE  *ABS*
       #      10:  64630000        daddiu  v1,v1,0
       #                   10: R_MIPS_LO16 _mcount
       #                   10: R_MIPS_NONE *ABS*
       #                   10: R_MIPS_NONE *ABS*
       #      14:  03e0082d        move    at,ra
       #      18:  0060f809        jalr    v1
       #
       # for the kernel:
       #
       #     10:   03e0082d        move    at,ra
       #     14:   0c000000        jal     0 <loongson_halt>
       #                    14: R_MIPS_26   _mcount
       #                    14: R_MIPS_NONE *ABS*
       #                    14: R_MIPS_NONE *ABS*
       #    18:   00020021        nop
       if ($is_module eq "0") {
               $mcount_regex = "^\\s*([0-9a-fA-F]+): R_MIPS_26\\s+_mcount\$";
       } else {
               $mcount_regex = "^\\s*([0-9a-fA-F]+): R_MIPS_HI16\\s+_mcount\$";
       }
       $objdump .= " -Melf-trad".$endian."mips ";
   
       if ($endian eq "big") {
               $endian = " -EB ";
               $ld .= " -melf".$bits."btsmip";
       } else {
               $endian = " -EL ";
               $ld .= " -melf".$bits."ltsmip";
       }
   
       $cc .= " -mno-abicalls -fno-pic -mabi=" . $bits . $endian;
       $ld .= $endian;
   
       if ($bits == 64) {
               $function_regex =
                   "^([0-9a-fA-F]+)\\s+<(.|[^\$]L.*?|\$[^L].*?|[^\$][^L].*?)>:";
               $type = ".dword";
       }
   } elsif ($arch eq "microblaze") {
       # Microblaze calls '_mcount' instead of plain 'mcount'.
       $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s_mcount\$";
   } elsif ($arch eq "blackfin") {
       $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s__mcount\$";
       $mcount_adjust = -4;
   } 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.
       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));
       }
       foreach my $cur_offset (@offsets) {
           printf FILE "\t%s %s + %d\n", $type, $ref_func, $cur_offset - $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
           $read_function = defined($text_sections{$1});
           # 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/) {
           push(@offsets, (hex $1) + $mcount_adjust);
       }
   }
   
   # 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);

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