powerpc/64: Tool to check head sections location sanity

-include include/config/auto.conf

include scripts/Kbuild.include

quiet_cmd_head_check = CHKHEAD $@

      cmd_head_check = $(CONFIG_SHELL) $(srctree)/arch/powerpc/tools/head_check.sh "$(NM)" "$@"

quiet_cmd_relocs_check = CHKREL  $@

ifdef CONFIG_PPC_BOOK3S_64

      cmd_relocs_check =						\

vmlinux: FORCE

	@true

ifdef CONFIG_PPC64

	$(call cmd,head_check)

endif

ifdef CONFIG_RELOCATABLE

	$(call if_changed,relocs_check)

endif

	@true

clean:

	@true

	rm -f .tmp_symbols.txt

PHONY += FORCE clean

 *   CLOSE_FIXED_SECTION() or elsewhere, there may be something

 *   unexpected being added there. Remove the '. = x_len' line, rebuild, and

 *   check what is pushing the section down.

 * - If the build dies in linking, check arch/powerpc/kernel/vmlinux.lds.S

 *   for instructions.

 * - If the build dies in linking, check arch/powerpc/tools/head_check.sh

 *   comments.

 * - If the kernel crashes or hangs in very early boot, it could be linker

 *   stubs at the start of the main text.

 */

#ifdef CONFIG_PPC64

		KEEP(*(.head.text.first_256B));

#ifdef CONFIG_PPC_BOOK3E

# define END_FIXED	0x100

#else

		KEEP(*(.head.text.real_vectors));

		*(.head.text.real_trampolines);

		*(.head.text.virt_trampolines);

# if defined(CONFIG_PPC_PSERIES) || defined(CONFIG_PPC_POWERNV)

		KEEP(*(.head.data.fwnmi_page));

#  define END_FIXED	0x8000

# else

#  define END_FIXED	0x7000

# endif

#endif

		ASSERT((. == END_FIXED), "vmlinux.lds.S: fixed section overflow error");

#else /* !CONFIG_PPC64 */

		HEAD_TEXT

#endif

	__head_end = .;

	/*

	 * If the build dies here, it's likely code in head_64.S is referencing

	 * labels it can't reach, and the linker inserting stubs without the

	 * assembler's knowledge. To debug, remove the above assert and

	 * rebuild. Look for branch stubs in the fixed section region.

	 *

	 * Linker stub generation could be allowed in "trampoline"

	 * sections if absolutely necessary, but this would require

	 * some rework of the fixed sections. Before resorting to this,

	 * consider references that have sufficient addressing range,

	 * (e.g., hand coded trampolines) so the linker does not have

	 * to add stubs.

	 *

	 * Linker stubs at the top of the main text section are currently not

	 * detected, and will result in a crash at boot due to offsets being

	 * wrong.

	 */

#ifdef CONFIG_PPC64

	/*

	 * BLOCK(0) overrides the default output section alignment because

# Copyright © 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 © 2009 IBM Corporation

# NOTE!

#

# If the build dies here, it's likely code in head_64.S/exception-64*.S or

# nearby, is branching to labels it can't reach directly, which results in the

# linker inserting branch stubs. This can move code around in ways that break

# the fixed section calculations (head-64.h). To debug this, disassemble the

# vmlinux and look for branch stubs (long_branch, plt_branch, etc.) in the

# fixed section region (0 - 0x8000ish). Check what code is calling those stubs,

# and perhaps change so a direct branch can reach.

#

# A ".linker_stub_catch" section is used to catch some stubs generated by

# early .text code, which tend to get placed at the start of the section.

# If there are too many such stubs, they can overflow this section. Expanding

# it may help (or reducing the number of stub branches).

#

# 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. This

# could cause the kernel to die in early boot.

# 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="$1"

vmlinux="$2"

# gcc-4.6-era toolchain make _stext an A (absolute) symbol rather than T

$nm "$vmlinux" | grep -e " [TA] _stext$" -e " t start_first_256B$" -e " a text_start$" -e " t start_text$" -m4 > .tmp_symbols.txt

vma=$(cat .tmp_symbols.txt | grep -e " [TA] _stext$" | cut -d' ' -f1)

expected_start_head_addr=$vma

start_head_addr=$(cat .tmp_symbols.txt | grep " t start_first_256B$" | cut -d' ' -f1)

if [ "$start_head_addr" != "$expected_start_head_addr" ]; then

	echo "ERROR: head code starts at $start_head_addr, should be $expected_start_head_addr"

	echo "ERROR: try to enable LD_HEAD_STUB_CATCH config option"

	echo "ERROR: see comments in arch/powerpc/tools/head_check.sh"

	exit 1

fi

top_vma=$(echo $vma | cut -d'0' -f1)

expected_start_text_addr=$(cat .tmp_symbols.txt | grep " a text_start$" | cut -d' ' -f1 | sed "s/^0/$top_vma/")

start_text_addr=$(cat .tmp_symbols.txt | grep " t start_text$" | cut -d' ' -f1)

if [ "$start_text_addr" != "$expected_start_text_addr" ]; then

	echo "ERROR: start_text address is $start_text_addr, should be $expected_start_text_addr"

	echo "ERROR: try to enable LD_HEAD_STUB_CATCH config option"

	echo "ERROR: see comments in arch/powerpc/tools/head_check.sh"

	exit 1

fi

rm -f .tmp_symbols.txt