stackdelta

#!/usr/bin/env perl
# SPDX-License-Identifier: GPL-2.0

# Read two files produced by the stackusage script, and show the
# delta between them.
#
# Currently, only shows changes for functions listed in both files. We
# could add an option to show also functions which have vanished or
# appeared (which would often be due to gcc making other inlining
# decisions).
#
# Another possible option would be a minimum absolute value for the
# delta.
#
# A third possibility is for sorting by delta, but that can be
# achieved by piping to sort -k5,5g.

sub read_stack_usage_file {
    my %su;
    my $f = shift;
    open(my $fh, '<', $f)
	or die "cannot open $f: $!";
    while (<$fh>) {
	chomp;
	my ($file, $func, $size, $type) = split;
	# Old versions of gcc (at least 4.7) have an annoying quirk in
	# that a (static) function whose name has been changed into
	# for example ext4_find_unwritten_pgoff.isra.11 will show up
	# in the .su file with a name of just "11". Since such a
	# numeric suffix is likely to change across different
	# commits/compilers/.configs or whatever else we're trying to
	# tweak, we can't really track those functions, so we just
	# silently skip them.
	#
	# Newer gcc (at least 5.0) report the full name, so again,
	# since the suffix is likely to change, we strip it.
	next if $func =~ m/^[0-9]+$/;
	$func =~ s/\..*$//;
	# Line numbers are likely to change; strip those.
	$file =~ s/:[0-9]+$//;
	$su{"${file}\t${func}"} = {size => $size, type => $type};
    }
    close($fh);
    return \%su;
}

@ARGV == 2
    or die "usage: $0 <old> <new>";

my $old = read_stack_usage_file($ARGV[0]);
my $new = read_stack_usage_file($ARGV[1]);
my @common = sort grep {exists $new->{$_}} keys %$old;
for (@common) {
    my $x = $old->{$_}{size};
    my $y = $new->{$_}{size};
    my $delta = $y - $x;
    if ($delta) {
	printf "%s\t%d\t%d\t%+d\n", $_, $x, $y, $delta;
    }
}