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SubjectFunctions with Large Stack Usage

After having read of the stack overflow "issues" awhile back, a couple
of ideas gelled, with this script as a result. The script finds
functions that use a large (changeable) amount of stack space. Note:
it's heuristic, it's static, it only looks at compiled-in functions, and
says nothing about the dynamic system. It DOES point out functions that
may (MAY) need to be examined closer.

The functions and their sizes are:

check huft_build (stack 1436)
check inflate_fixed (stack 1168)
check inflate_dynamic (stack 1308)
check pci_sanity_check (stack 804)
check pcibios_fixup_peer_bridges (stack 804)
check elf_core_dump (stack 592)
check xfs_ioctl (stack 752)
check semctl_main (stack 588)
check extract_entropy (stack 708)
check vt_ioctl (stack 756)
check ide_unregister (stack 880)
check cdrom_buffer_sectors (stack 516)
check cdrom_read_intr (stack 532)
check cdrom_slot_status (stack 1040)
check cdrom_number_of_slots (stack 1040)
check cdrom_select_disc (stack 1040)
check cdrom_ioctl (stack 1084)
check pci_do_scan_bus (stack 680)

This is from kernel 2.4.19-xfs (yes, I'm an XFS weenie ;-).

How it works: With Keith Owens' KDB patch, one may compile the kernel
with frame pointers. With the Disassemble::X86 Perl module from CPAN
it's easy. It requires the vmlinux and files, and for each
function looks at the first 10 instructions for the 'sub esp,N'. The N
is the number of bytes of stack used.

I'm not subscribed to this list. I tried once, but it's much too busy
for me to keep up with, and actually get any work done ;-). So, please
CC: me if you wish me to be included.

I apologize in advance for 1) the C-like Perl code, and 2) for
attaching it. I've tried an in-line paste before, but it wraps, and
makes it even uglier than before.

Comments, bugs, and enhancements are encouraged. Thanks!

Please return to your regularly scheduled discussions.

kernel, n.: A part of an operating system that preserves the
medieval traditions of sorcery and black art.

# check_stack --- check for too deep stack depths; it most likely only
# only works for the linux kernel....

use 5.006;
use strict;
use warnings;
use Getopt::Std;
use lib "blib/lib";
use Disassemble::X86;

use vars qw ( $opt_d );
getopts ("d") and $#ARGV == 1 or die <<END_USAGE;
usage: $0 [-d] vmlinux
-d debug ON

# slurp up the whole object file
open OBJ, "<$ARGV[0]" or die "$0: can't read $ARGV[0]: $!\n";
my $slash_save = $/;
undef $/;
my $file = <OBJ>;
close OBJ;
$/ = $slash_save;

# init the disassembler
my $dis = Disassemble::X86->new (
start => 0xc0100000 - 0x1000, # text addr - file offset
pos => 0,
size => 32,
text => $file,

# you may change these as you see fit

# max_check is the maximum number of instructions to scan for the 'sub esp,...'
# before giving up
my $max_check = 10;

# stack_limit is the size that we'll consider worthy of reporting
my $stack_limit = 512;

# end of changables

# max_stack is the maximum stack size we saw
my $max_stack = 0;

# open It contains the address, type, and names of each function
# (among other things)
open MAP, "<$ARGV[1]" or die "$0: can't read $ARGV[1]: $!\n";

while (<MAP>) {
my ($addr, $type, $name) = split (' ', $_);
next if $name =~ /^\./; # we don't want names like '.yadda'
if ($type =~ /^[Tt]$/) { # we only want text symbols
print "looking at $name ($addr)\n" if $opt_d;

$dis->pos (hex ($addr));
for (my $i = 0; $i < $max_check && !$dis->at_end; $i++) {
my $op = $dis->disasm ();
printf "%04x %s\n", $dis->op_start (), $op if $opt_d;
next if (!defined $op);
if ($op =~ /sub esp,(0x[[:xdigit:]]+)/) {
my $stack = hex ($1);
$max_stack = $stack if $stack > $max_stack;
printf "check $name (stack %d)\n", $stack
if $stack >= $stack_limit;

close MAP;

print "max single stack used is $max_stack\n";

exit 0;

# end check_stack
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