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Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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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 warnings;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, $inputfile) = @ARGV;
# This file refers to mcount and shouldn't be ftraced, so lets' ignore itif ($inputfile =~ m,kernel/trace/ftrace\.o$,) { exit(0);}
# Acceptable sections to record.my %text_sections = ( ".text" => 1, ".init.text" => 1, ".ref.text" => 1, ".sched.text" => 1, ".spinlock.text" => 1, ".irqentry.text" => 1, ".softirqentry.text" => 1, ".kprobes.text" => 1, ".cpuidle.text" => 1, ".text.unlikely" => 1,);
# Acceptable section-prefixes to record.my %text_section_prefixes = ( ".text." => 1,);
# Note: we are nice to C-programmers here, thus we skip the '||='-idiom.$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) functionsmy %weak; # List of weak functionsmy %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 sectionmy $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 offsetmy $alignment; # The .align value to use for $mcount_sectionmy $section_type; # Section header plus possible alignment command
if ($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]+):.*\\s(mcount|__fentry__)\$";$section_type = '@progbits';$mcount_adjust = 0;$type = ".long";
if ($arch eq "x86_64") { $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s(mcount|__fentry__)([+-]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" && $bits == 64) { if ($cc =~ /-DCC_USING_HOTPATCH/) { $mcount_regex = "^\\s*([0-9a-fA-F]+):\\s*c0 04 00 00 00 00\\s*(brcl\\s*0,|jgnop\\s*)[0-9a-f]+ <([^\+]*)>\$"; $mcount_adjust = 0; } $alignment = 8; $type = ".quad"; $ld .= " -m elf64_s390"; $cc .= " -m64";
} elsif ($arch eq "sh") { $alignment = 2;
# force flags for this arch $ld .= " -m shlelf_linux"; if ($endian eq "big") { $objcopy .= " -O elf32-shbig-linux"; } else { $objcopy .= " -O elf32-sh-linux"; }
} elsif ($arch eq "powerpc") { my $ldemulation;
$local_regex = "^[0-9a-fA-F]+\\s+t\\s+(\\.?\\S+)"; # See comment in the sparc64 section for why we use '\w'. $function_regex = "^([0-9a-fA-F]+)\\s+<(\\.?\\w*?)>:"; $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s\\.?_mcount\$";
if ($endian eq "big") { $cc .= " -mbig-endian "; $ld .= " -EB "; $ldemulation = "ppc" } else { $cc .= " -mlittle-endian "; $ld .= " -EL "; $ldemulation = "lppc" } if ($bits == 64) { $type = ".quad"; $cc .= " -m64 "; $ld .= " -m elf64".$ldemulation." "; } else { $cc .= " -m32 "; $ld .= " -m elf32".$ldemulation." "; }
} 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 "arm64") { $alignment = 3; $section_type = '%progbits'; $mcount_regex = "^\\s*([0-9a-fA-F]+):\\s*R_AARCH64_CALL26\\s+_mcount\$"; $type = ".quad";} elsif ($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 switch 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 "riscv") { $function_regex = "^([0-9a-fA-F]+)\\s+<([^.0-9][0-9a-zA-Z_\\.]+)>:"; $mcount_regex = "^\\s*([0-9a-fA-F]+):\\sR_RISCV_CALL(_PLT)?\\s_mcount\$"; $type = ".quad"; $alignment = 2;} elsif ($arch eq "csky") { $mcount_regex = "^\\s*([0-9a-fA-F]+):\\s*R_CKCORE_PCREL_JSR_IMM26BY2\\s+_mcount\$"; $alignment = 2;} else { die "Arch $arch is not supported with CONFIG_DYNAMIC_FTRACE";}
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_" . $prefix . ".o";
## Step 1: find all the local (static functions) and weak symbols.# 't' is local, 'w/W' is weak#open (IN, "$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 callersmy $ref_func; # reference function to use for offsetsmy $offset = 0; # offset of ref_func to section beginning
### update_funcs - print out the current mcount callers## Go through the list of offsets to callers and write them to# the output file in a format that can be read by an assembler.#sub update_funcs{ return unless ($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}) { $convert{$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, "LC_ALL=C $objdump -hdr $inputfile|") || die "error running $objdump";
my $text;
# read headers firstmy $read_headers = 1;
while (<IN>) {
if ($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{$1}); if (!$read_function) { foreach my $prefix (keys %text_section_prefixes) { if (substr($1, 0, length $prefix) eq $prefix) { $read_function = 1; last; } } } # 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) + $mcount_adjust); }}
# dump out anymore offsets that may have been foundupdate_funcs();
# If we did not find any mcount callers, we are done (do nothing).if (!$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);
# vim: softtabstop=4