scripts: add stackdelta script

#!/usr/bin/perl

# 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;

    }

}