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

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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: Naveen N Rao <naveen@kernel.org>
Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://patch.msgid.link/20241030070850.1361304-11-hbathini@linux.ibm.com
This commit is contained in:
Naveen N Rao 2024-10-30 12:38:43 +05:30 committed by Michael Ellerman
parent 9670f6d209
commit 782f46cbce
3 changed files with 59 additions and 1 deletions
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2
arch/powerpc/Kconfig
View File

@ -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

8
arch/powerpc/Makefile.postlink
View File

@ -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

50
arch/powerpc/tools/ftrace_check.sh Executable file
View File

@ -0,0 +1,50 @@
#!/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