# Re: \[PATCH 4/7\] powerpc/64: tool to check head sections location sanity

- From: Michael Ellerman \<mpe@ellerman.id.au\>
- Date: 2016-11-15 00:55:27 
- List: linuxppc-dev
- Page: https://ratatoskr.run/linuxppc-dev/2016/11/9493633
- Thread: https://ratatoskr.run/linuxppc-dev/2016/10/9493207/t.md

```text
Nicholas Piggin [ref] writes:

> diff --git a/arch/powerpc/Makefile.postlink b/arch/powerpc/Makefile.postl=
ink
> index 1725e64..b8fe12b 100644
> --- a/arch/powerpc/Makefile.postlink
> +++ b/arch/powerpc/Makefile.postlink
> @@ -24,6 +27,9 @@ endif
>=20=20
>  vmlinux: FORCE
>  	@true
> +ifeq ($(CONFIG_PPC64),y)

You can just use:

ifdef CONFIG_PPC64

> +	$(call cmd,head_check)
> +endif
>  ifeq ($(CONFIG_RELOCATABLE),y)
>  	$(call if_changed,relocs_check)
>  endif
> @@ -32,6 +38,7 @@ endif
>  	@true
>=20=20
>  clean:
> +	rm -f .tmp_symbols.txt
>  	@true

We shouldn't need the true anymore should we?

> diff --git a/arch/powerpc/tools/head_check.sh b/arch/powerpc/tools/head_c=
heck.sh
> new file mode 100755
> index 0000000..9635fe7
> --- /dev/null
> +++ b/arch/powerpc/tools/head_check.sh
> @@ -0,0 +1,69 @@
> +#!/bin/sh

We run this explicitly via $(CONFIG_SHELL), so having a shebang here is
redundant and also a little confusing. I added "-x" here, to turn on
tracing, but it doesn't take effect, so I think better to just drop the
line. If anyone wants to run it manually they can just pass it to sh.

> +# Copyright =C2=A9 2016 IBM Corporation
> +
> +# This program is free software; you can redistribute it and/or
> +# modify it under the terms of the GNU General Public License
> +# as published by the Free Software Foundation; either version
> +# 2 of the License, or (at your option) any later version.
> +
> +# This script checks the head of a vmlinux for linker stubs that
> +# break our placement of fixed-location code for 64-bit.
> +
> +# based on relocs_check.pl
> +# Copyright =C2=A9 2009 IBM Corporation
> +
> +# READ THIS
> +#
> +# If the build dies here, it's likely code in head_64.S or nearby is
> +# referencing labels it can't reach, which results in the linker inserti=
ng
> +# stubs without the assembler's knowledge. This can move code around in =
ways
> +# that break the fixed location placement stuff (head-64.h). To debug,
> +# disassemble the vmlinux and look for branch stubs (long_branch, plt_br=
anch
> +# etc) in the fixed section region (0 - 0x8000ish). Check what places are
> +# calling those stubs.
> +#
> +# Linker stubs use the TOC pointer, so even if fixed section code could
> +# tolerate them being inserted into head code, they can't be allowed in =
low
> +# level entry code (boot, interrupt vectors, etc) until r2 is set up. Th=
is
> +# could cause the kernel to die in early boot.

Can you add:

# Turn this on if you want more debug output:
# set -x

> +
> +if [ $# -lt 2 ]; then
> +	echo "$0 [path to nm] [path to vmlinux]" 1>&2
> +	exit 1
> +fi
> +
> +# Have Kbuild supply the path to nm so we handle cross compilation.
> +nm=3D"$1"
> +vmlinux=3D"$2"
> +
> +nm "$vmlinux" | grep -e " T _stext$" -e " t start_first_256B$" -e " a te=
xt_start$" -e " t start_text$" -m4 > .tmp_symbols.txt

You don't use $nm there.

> +
> +
> +vma=3D$(cat .tmp_symbols.txt | grep " T _stext$" | cut -d' ' -f1)
> +
> +expected_start_head_addr=3D$vma
> +
> +start_head_addr=3D$(cat .tmp_symbols.txt | grep " t start_first_256B$" |=
 cut -d' ' -f1)
> +
> +if [ "$start_head_addr" !=3D "$expected_start_head_addr" ]; then
> +	echo "ERROR: head code starts at $start_head_addr, should be 0"
> +	echo "ERROR: see comments in arch/powerpc/tools/head_check.sh"

This is blowing up for me with ppc64e_defconfig.

It says:

ERROR: start_text address is c000000000001100, should be c000000000000200


cheers
```