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8feff1cacc
During tests and checks, I've discovered that there were failures to convert mcount callers into nops. Looking deeper into these failures, code that was attempted to be changed was not an mcount caller. The current code only updates if the code being changed is what it expects, but I still investigate any time there is a failure. What was happening is that a weak symbol was being used as a reference for other mcount callers. That weak symbol was also referenced elsewhere so the offsets were using the strong symbol and not the function symbol that it was referenced from. This patch changes the setting up of the mcount_loc section to search for a global function that is not weak. It will pick a local over a weak but if only a weak is found in a section, a warning is printed and the mcount location is not recorded (just to be safe). Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
360 lines
9.8 KiB
Perl
Executable file
360 lines
9.8 KiB
Perl
Executable file
#!/usr/bin/perl -w
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# (c) 2008, Steven Rostedt <srostedt@redhat.com>
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# Licensed under the terms of the GNU GPL License version 2
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#
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# recordmcount.pl - makes a section called __mcount_loc that holds
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# all the offsets to the calls to mcount.
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#
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#
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# What we want to end up with is a section in vmlinux called
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# __mcount_loc that contains a list of pointers to all the
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# call sites in the kernel that call mcount. Later on boot up, the kernel
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# will read this list, save the locations and turn them into nops.
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# When tracing or profiling is later enabled, these locations will then
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# be converted back to pointers to some function.
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#
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# This is no easy feat. This script is called just after the original
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# object is compiled and before it is linked.
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#
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# The references to the call sites are offsets from the section of text
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# that the call site is in. Hence, all functions in a section that
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# has a call site to mcount, will have the offset from the beginning of
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# the section and not the beginning of the function.
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#
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# The trick is to find a way to record the beginning of the section.
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# The way we do this is to look at the first function in the section
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# which will also be the location of that section after final link.
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# e.g.
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#
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# .section ".text.sched"
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# .globl my_func
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# my_func:
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# [...]
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# call mcount (offset: 0x5)
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# [...]
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# ret
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# other_func:
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# [...]
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# call mcount (offset: 0x1b)
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# [...]
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#
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# Both relocation offsets for the mcounts in the above example will be
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# offset from .text.sched. If we make another file called tmp.s with:
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#
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# .section __mcount_loc
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# .quad my_func + 0x5
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# .quad my_func + 0x1b
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#
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# We can then compile this tmp.s into tmp.o, and link it to the original
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# object.
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#
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# But this gets hard if my_func is not globl (a static function).
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# In such a case we have:
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#
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# .section ".text.sched"
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# my_func:
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# [...]
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# call mcount (offset: 0x5)
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# [...]
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# ret
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# .globl my_func
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# other_func:
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# [...]
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# call mcount (offset: 0x1b)
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# [...]
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#
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# If we make the tmp.s the same as above, when we link together with
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# the original object, we will end up with two symbols for my_func:
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# one local, one global. After final compile, we will end up with
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# an undefined reference to my_func.
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#
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# Since local objects can reference local variables, we need to find
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# a way to make tmp.o reference the local objects of the original object
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# file after it is linked together. To do this, we convert the my_func
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# into a global symbol before linking tmp.o. Then after we link tmp.o
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# we will only have a single symbol for my_func that is global.
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# We can convert my_func back into a local symbol and we are done.
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#
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# Here are the steps we take:
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#
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# 1) Record all the local symbols by using 'nm'
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# 2) Use objdump to find all the call site offsets and sections for
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# mcount.
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# 3) Compile the list into its own object.
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# 4) Do we have to deal with local functions? If not, go to step 8.
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# 5) Make an object that converts these local functions to global symbols
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# with objcopy.
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# 6) Link together this new object with the list object.
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# 7) Convert the local functions back to local symbols and rename
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# the result as the original object.
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# End.
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# 8) Link the object with the list object.
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# 9) Move the result back to the original object.
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# End.
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#
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use strict;
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my $P = $0;
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$P =~ s@.*/@@g;
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my $V = '0.1';
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if ($#ARGV < 6) {
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print "usage: $P arch objdump objcopy cc ld nm rm mv inputfile\n";
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print "version: $V\n";
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exit(1);
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}
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my ($arch, $objdump, $objcopy, $cc, $ld, $nm, $rm, $mv, $inputfile) = @ARGV;
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$objdump = "objdump" if ((length $objdump) == 0);
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$objcopy = "objcopy" if ((length $objcopy) == 0);
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$cc = "gcc" if ((length $cc) == 0);
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$ld = "ld" if ((length $ld) == 0);
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$nm = "nm" if ((length $nm) == 0);
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$rm = "rm" if ((length $rm) == 0);
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$mv = "mv" if ((length $mv) == 0);
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#print STDERR "running: $P '$arch' '$objdump' '$objcopy' '$cc' '$ld' " .
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# "'$nm' '$rm' '$mv' '$inputfile'\n";
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my %locals; # List of local (static) functions
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my %weak; # List of weak functions
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my %convert; # List of local functions used that needs conversion
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my $type;
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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
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# (return offset and func name)
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my $mcount_regex; # Find the call site to mcount (return offset)
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if ($arch eq "x86_64") {
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$section_regex = "Disassembly of section";
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$function_regex = "^([0-9a-fA-F]+)\\s+<(.*?)>:";
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$mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\smcount([+-]0x[0-9a-zA-Z]+)?\$";
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$type = ".quad";
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# force flags for this arch
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$ld .= " -m elf_x86_64";
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$objdump .= " -M x86-64";
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$objcopy .= " -O elf64-x86-64";
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$cc .= " -m64";
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} elsif ($arch eq "i386") {
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$section_regex = "Disassembly of section";
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$function_regex = "^([0-9a-fA-F]+)\\s+<(.*?)>:";
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$mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\smcount\$";
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$type = ".long";
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# force flags for this arch
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$ld .= " -m elf_i386";
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$objdump .= " -M i386";
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$objcopy .= " -O elf32-i386";
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$cc .= " -m32";
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} else {
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die "Arch $arch is not supported with CONFIG_FTRACE_MCOUNT_RECORD";
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}
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my $text_found = 0;
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my $read_function = 0;
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my $opened = 0;
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my $mcount_section = "__mcount_loc";
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my $dirname;
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my $filename;
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my $prefix;
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my $ext;
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if ($inputfile =~ m,^(.*)/([^/]*)$,) {
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$dirname = $1;
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$filename = $2;
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} else {
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$dirname = ".";
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$filename = $inputfile;
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}
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if ($filename =~ m,^(.*)(\.\S),) {
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$prefix = $1;
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$ext = $2;
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} else {
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$prefix = $filename;
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$ext = "";
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}
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my $mcount_s = $dirname . "/.tmp_mc_" . $prefix . ".s";
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my $mcount_o = $dirname . "/.tmp_mc_" . $prefix . ".o";
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#
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# Step 1: find all the local (static functions) and weak symbols.
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# 't' is local, 'w/W' is weak (we never use a weak function)
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#
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open (IN, "$nm $inputfile|") || die "error running $nm";
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while (<IN>) {
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if (/^[0-9a-fA-F]+\s+t\s+(\S+)/) {
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$locals{$1} = 1;
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} elsif (/^[0-9a-fA-F]+\s+([wW])\s+(\S+)/) {
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$weak{$2} = $1;
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}
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}
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close(IN);
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my @offsets; # Array of offsets of mcount callers
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my $ref_func; # reference function to use for offsets
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my $offset = 0; # offset of ref_func to section beginning
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##
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# update_funcs - print out the current mcount callers
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#
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# Go through the list of offsets to callers and write them to
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# the output file in a format that can be read by an assembler.
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#
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sub update_funcs
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{
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return if ($#offsets < 0);
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defined($ref_func) || die "No function to reference";
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# A section only had a weak function, to represent it.
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# Unfortunately, a weak function may be overwritten by another
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# function of the same name, making all these offsets incorrect.
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# To be safe, we simply print a warning and bail.
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if (defined $weak{$ref_func}) {
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print STDERR
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"$inputfile: WARNING: referencing weak function" .
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" $ref_func for mcount\n";
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return;
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}
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# is this function static? If so, note this fact.
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if (defined $locals{$ref_func}) {
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$convert{$ref_func} = 1;
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}
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# Loop through all the mcount caller offsets and print a reference
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# to the caller based from the ref_func.
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for (my $i=0; $i <= $#offsets; $i++) {
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if (!$opened) {
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open(FILE, ">$mcount_s") || die "can't create $mcount_s\n";
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$opened = 1;
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print FILE "\t.section $mcount_section,\"a\",\@progbits\n";
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}
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printf FILE "\t%s %s + %d\n", $type, $ref_func, $offsets[$i] - $offset;
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}
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}
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#
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# Step 2: find the sections and mcount call sites
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#
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open(IN, "$objdump -dr $inputfile|") || die "error running $objdump";
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my $text;
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while (<IN>) {
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# is it a section?
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if (/$section_regex/) {
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$read_function = 1;
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# print out any recorded offsets
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update_funcs() if ($text_found);
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# reset all markers and arrays
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$text_found = 0;
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undef($ref_func);
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undef(@offsets);
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# section found, now is this a start of a function?
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} elsif ($read_function && /$function_regex/) {
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$text_found = 1;
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$offset = hex $1;
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$text = $2;
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# if this is either a local function or a weak function
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# keep looking for functions that are global that
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# we can use safely.
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if (!defined($locals{$text}) && !defined($weak{$text})) {
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$ref_func = $text;
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$read_function = 0;
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} else {
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# if we already have a function, and this is weak, skip it
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if (!defined($ref_func) || !defined($weak{$text})) {
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$ref_func = $text;
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}
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}
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}
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# is this a call site to mcount? If so, record it to print later
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if ($text_found && /$mcount_regex/) {
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$offsets[$#offsets + 1] = hex $1;
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}
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}
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# dump out anymore offsets that may have been found
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update_funcs() if ($text_found);
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# If we did not find any mcount callers, we are done (do nothing).
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if (!$opened) {
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exit(0);
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}
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close(FILE);
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#
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# Step 3: Compile the file that holds the list of call sites to mcount.
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#
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`$cc -o $mcount_o -c $mcount_s`;
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my @converts = keys %convert;
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#
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# Step 4: Do we have sections that started with local functions?
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#
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if ($#converts >= 0) {
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my $globallist = "";
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my $locallist = "";
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foreach my $con (@converts) {
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$globallist .= " --globalize-symbol $con";
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$locallist .= " --localize-symbol $con";
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}
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my $globalobj = $dirname . "/.tmp_gl_" . $filename;
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my $globalmix = $dirname . "/.tmp_mx_" . $filename;
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#
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# Step 5: set up each local function as a global
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#
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`$objcopy $globallist $inputfile $globalobj`;
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#
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# Step 6: Link the global version to our list.
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#
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`$ld -r $globalobj $mcount_o -o $globalmix`;
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#
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# Step 7: Convert the local functions back into local symbols
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#
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`$objcopy $locallist $globalmix $inputfile`;
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# Remove the temp files
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`$rm $globalobj $globalmix`;
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} else {
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my $mix = $dirname . "/.tmp_mx_" . $filename;
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#
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# Step 8: Link the object with our list of call sites object.
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#
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`$ld -r $inputfile $mcount_o -o $mix`;
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#
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# Step 9: Move the result back to the original object.
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#
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`$mv $mix $inputfile`;
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}
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# Clean up the temp files
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`$rm $mcount_o $mcount_s`;
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exit(0);
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