linux-kernel - Re: [PATCHv2] remove recently added perl build requirement

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Date:	Mon, 12 Jan 2015 17:01:10 -0800
From:	Kees Cook <keescook@...omium.org>
To:	Rob Landley <rob@...dley.net>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Fengguang Wu <fengguang.wu@...el.com>,
	Junjie Mao <eternal.n08@...il.com>,
	"# 3.4.x" <stable@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCHv2] remove recently added perl build requirement

On Mon, Jan 12, 2015 at 8:54 AM, Rob Landley <rob@...dley.net> wrote:
> From: Rob Landley <rob@...dley.net>
>
> Commit e6023367d779 ("x86, kaslr: Prevent .bss from overlaping initrd")
> added perl back to the kernel build dependencies in -rc6.

Ah, yeah, good call on Perl as a build dep.

> Replace those 39 lines of perl with 4 lines of shell script.
>
> Signed-off-by: Rob Landley <rob@...dley.net>
> Acked-by: Anca Emanuel <anca.emanuel@...il.com>
> ---
>
>  arch/x86/boot/compressed/Makefile |    6 ++--
>  arch/x86/tools/calc_run_size.pl   |   39 ----------------------------
>  2 files changed, 4 insertions(+), 41 deletions(-)
>
> Note: checkpatch.pl isn't a build dependency, it's a development dependency
> (like bloat-o-meter being written in python or "make xconfig" needing QT).
> Those aren't things you need to add to your cross compile environment
> to produce a binary. Different category of dependency.
>
> For more history on the issue, see https://lkml.org/lkml/2013/2/27/18
>
> --- linux/arch/x86/boot/compressed/Makefile
> +++ linux/arch/x86/boot/compressed/Makefile
> @@ -89,8 +76,10 @@
>  suffix-$(CONFIG_KERNEL_LZO)    := lzo
>  suffix-$(CONFIG_KERNEL_LZ4)    := lz4
>
> -RUN_SIZE = $(shell $(OBJDUMP) -h vmlinux | \
> -            perl $(srctree)/arch/x86/tools/calc_run_size.pl)
> +RUN_SIZE = $(shell NUM='\([0-9a-fA-F]*[ \t]*\)'; $(OBJDUMP) -h vmlinux | \
> +sed -n 's/^[ \t0-9]*.b[sr][sk][ \t]*'"$$NUM$$NUM$$NUM$$NUM"'.*/\1\4/p' | \
> +xargs | while read a b c d; do [ "$$b" != "$$d" ] && exit 1; \
> +expr $$(printf "%d + %d + %d" 0x$$a 0x$$b 0x$$c); done)
>  quiet_cmd_mkpiggy = MKPIGGY $@
>        cmd_mkpiggy = $(obj)/mkpiggy $< $(RUN_SIZE) > $@ || ( rm -f $@ ; false )

I'd much prefer a full shell script as this is hard to read. It loses
all the comments and variable names, etc. Also, this reverts commit
70b61e362187 ("x86, kaslr: Handle Gold linker for finding bss/brk").

-Kees

>
> --- linux/arch/x86/tools/calc_run_size.pl
> +++ /dev/null
> @@ -1,39 +0,0 @@
> -#!/usr/bin/perl
> -#
> -# Calculate the amount of space needed to run the kernel, including room for
> -# the .bss and .brk sections.
> -#
> -# Usage:
> -# objdump -h a.out | perl calc_run_size.pl
> -use strict;
> -
> -my $mem_size = 0;
> -my $file_offset = 0;
> -
> -my $sections=" *[0-9]+ \.(?:bss|brk) +";
> -while (<>) {
> -       if (/^$sections([0-9a-f]+) +(?:[0-9a-f]+ +){2}([0-9a-f]+)/) {
> -               my $size = hex($1);
> -               my $offset = hex($2);
> -               $mem_size += $size;
> -               if ($file_offset == 0) {
> -                       $file_offset = $offset;
> -               } elsif ($file_offset != $offset) {
> -                       # BFD linker shows the same file offset in ELF.
> -                       # Gold linker shows them as consecutive.
> -                       next if ($file_offset + $mem_size == $offset + $size);
> -
> -                       printf STDERR "file_offset: 0x%lx\n", $file_offset;
> -                       printf STDERR "mem_size: 0x%lx\n", $mem_size;
> -                       printf STDERR "offset: 0x%lx\n", $offset;
> -                       printf STDERR "size: 0x%lx\n", $size;
> -
> -                       die ".bss and .brk are non-contiguous\n";
> -               }
> -       }
> -}
> -
> -if ($file_offset == 0) {
> -       die "Never found .bss or .brk file offset\n";
> -}
> -printf("%d\n", $mem_size + $file_offset);



-- 
Kees Cook
Chrome OS Security
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