#!/usr/bin/env perl # SPDX-License-Identifier: GPL-2.0-only # (c) 2008, Steven Rostedt <srostedt@redhat.com> # # 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. #
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
# # 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";
# 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*?)>:";
$mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s\\.?_mcount\$";
} elsif ($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*?)>:";
$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 ";
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 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}) {
$convert{$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 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{$1}); if (!$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) + $mcount_adjust);
}
}
# dump out anymore offsets that may have been found
update_funcs();
# If we did not find any mcount callers, we are done (do nothing). if (!$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 = "";
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