Commit 782f46cb authored by Naveen N Rao's avatar Naveen N Rao Committed by Michael Ellerman
Browse files

powerpc/ftrace: Add a postlink script to validate function tracer 



Function tracer on powerpc can only work with vmlinux having a .text
size of up to ~64MB due to powerpc branch instruction having a limited
relative branch range of 32MB. Today, this is only detected on kernel
boot when ftrace is init'ed. Add a post-link script to check the size of
.text so that we can detect this at build time, and break the build if
necessary.

We add a dependency on !COMPILE_TEST for CONFIG_HAVE_FUNCTION_TRACER so
that allyesconfig and other test builds can continue to work without
enabling ftrace.

Signed-off-by: default avatarNaveen N Rao <naveen@kernel.org>
Signed-off-by: default avatarHari Bathini <hbathini@linux.ibm.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://patch.msgid.link/20241030070850.1361304-11-hbathini@linux.ibm.com
parent 9670f6d2

arch/powerpc/Kconfig

+1 −1
Original line number Diff line number Diff line
@@ -243,7 +243,7 @@ config PPC 
	select HAVE_FUNCTION_DESCRIPTORS	if PPC64_ELF_ABI_V1

	select HAVE_FUNCTION_ERROR_INJECTION

	select HAVE_FUNCTION_GRAPH_TRACER

	select HAVE_FUNCTION_TRACER		if PPC64 || (PPC32 && CC_IS_GCC)

	select HAVE_FUNCTION_TRACER		if !COMPILE_TEST && (PPC64 || (PPC32 && CC_IS_GCC))

	select HAVE_GCC_PLUGINS			if GCC_VERSION >= 50200   # plugin support on gcc <= 5.1 is buggy on PPC

	select HAVE_GENERIC_VDSO

	select HAVE_HARDLOCKUP_DETECTOR_ARCH	if PPC_BOOK3S_64 && SMP

arch/powerpc/Makefile.postlink

+8 −0
Original line number Diff line number Diff line
@@ -24,6 +24,9 @@ else 
	$(CONFIG_SHELL) $(srctree)/arch/powerpc/tools/relocs_check.sh "$(OBJDUMP)" "$(NM)" "$@"

endif



quiet_cmd_ftrace_check = CHKFTRC $@

      cmd_ftrace_check = $(CONFIG_SHELL) $(srctree)/arch/powerpc/tools/ftrace_check.sh "$(NM)" "$@"



# `@true` prevents complaint when there is nothing to be done



vmlinux: FORCE
@@ -34,6 +37,11 @@ endif 
ifdef CONFIG_RELOCATABLE

	$(call if_changed,relocs_check)

endif

ifdef CONFIG_FUNCTION_TRACER

ifndef CONFIG_PPC64_ELF_ABI_V1

	$(call cmd,ftrace_check)

endif

endif



clean:

	rm -f .tmp_symbols.txt

arch/powerpc/tools/ftrace_check.sh

0 → 100755
+50 −0
Original line number Diff line number Diff line 
#!/bin/bash

# SPDX-License-Identifier: GPL-2.0-or-later

#

# This script checks vmlinux to ensure that all functions can call ftrace_caller() either directly,

# or through the stub, ftrace_tramp_text, at the end of kernel text.



# Error out if any command fails

set -e



# Allow for verbose output

if [ "$V" = "1" ]; then

	set -x

fi



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"



stext_addr=$($nm "$vmlinux" | grep -e " [TA] _stext$" | \

	cut -d' ' -f1 | tr '[:lower:]' '[:upper:]')

ftrace_caller_addr=$($nm "$vmlinux" | grep -e " T ftrace_caller$" | \

	cut -d' ' -f1 | tr '[:lower:]' '[:upper:]')

ftrace_tramp_addr=$($nm "$vmlinux" | grep -e " T ftrace_tramp_text$" | \

	cut -d' ' -f1 | tr '[:lower:]' '[:upper:]')



ftrace_caller_offset=$(echo "ibase=16;$ftrace_caller_addr - $stext_addr" | bc)

ftrace_tramp_offset=$(echo "ibase=16;$ftrace_tramp_addr - $ftrace_caller_addr" | bc)

sz_32m=$(printf "%d" 0x2000000)

sz_64m=$(printf "%d" 0x4000000)



# ftrace_caller - _stext < 32M

if [ "$ftrace_caller_offset" -ge "$sz_32m" ]; then

	echo "ERROR: ftrace_caller (0x$ftrace_caller_addr) is beyond 32MiB of _stext" 1>&2

	echo "ERROR: consider disabling CONFIG_FUNCTION_TRACER, or reducing the size \

		of kernel text" 1>&2

	exit 1

fi



# ftrace_tramp_text - ftrace_caller < 64M

if [ "$ftrace_tramp_offset" -ge "$sz_64m" ]; then

	echo "ERROR: kernel text extends beyond 64MiB from ftrace_caller" 1>&2

	echo "ERROR: consider disabling CONFIG_FUNCTION_TRACER, or reducing the size \

		of kernel text" 1>&2

	exit 1

fi