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powerpc/ftrace: Add support for -fpatchable-function-entry

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GCC v13.1 updated support for -fpatchable-function-entry on ppc64le to
emit nops after the local entry point, rather than before it. This
allows us to use this in the kernel for ftrace purposes. A new script is
added under arch/powerpc/tools/ to help detect if nops are emitted after
the function local entry point, or before the global entry point.

With -fpatchable-function-entry, we no longer have the profiling
instructions generated at function entry, so we only need to validate
the presence of two nops at the ftrace location in ftrace_init_nop(). We
patch the preceding instruction with 'mflr r0' to match the
-mprofile-kernel ABI for subsequent ftrace use.

This changes the profiling instructions used on ppc32. The default -pg
option emits an additional 'stw' instruction after 'mflr r0' and before
the branch to _mcount 'bl _mcount'. This is very similar to the original
-mprofile-kernel implementation on ppc64le, where an additional 'std'
instruction was used to save LR to its save location in the caller's
stackframe. Subsequently, this additional store was removed in later
compiler versions for performance reasons. The same reasons apply for
ppc32 so we only patch in a 'mflr r0'.

Signed-off-by: Naveen N Rao <naveen@kernel.org>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/68586d22981a2c3bb45f27a2b621173d10a7d092.1687166935.git.naveen@kernel.org
This commit is contained in:
Naveen N Rao 2023-06-19 15:17:34 +05:30 committed by Michael Ellerman
parent c91c5a8286
commit 0f71dcfb4a
8 changed files with 64 additions and 9 deletions
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14
arch/powerpc/Kconfig
View File

@ -186,6 +186,7 @@ config PPC
select DYNAMIC_FTRACE if FUNCTION_TRACER
select EDAC_ATOMIC_SCRUB
select EDAC_SUPPORT
select FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY if ARCH_USING_PATCHABLE_FUNCTION_ENTRY
select GENERIC_ATOMIC64 if PPC32
select GENERIC_CLOCKEVENTS_BROADCAST if SMP
select GENERIC_CMOS_UPDATE
@ -227,8 +228,8 @@ config PPC
select HAVE_DEBUG_KMEMLEAK
select HAVE_DEBUG_STACKOVERFLOW
select HAVE_DYNAMIC_FTRACE
select HAVE_DYNAMIC_FTRACE_WITH_ARGS if MPROFILE_KERNEL || PPC32
select HAVE_DYNAMIC_FTRACE_WITH_REGS if MPROFILE_KERNEL || PPC32
select HAVE_DYNAMIC_FTRACE_WITH_ARGS if ARCH_USING_PATCHABLE_FUNCTION_ENTRY || MPROFILE_KERNEL || PPC32
select HAVE_DYNAMIC_FTRACE_WITH_REGS if ARCH_USING_PATCHABLE_FUNCTION_ENTRY || MPROFILE_KERNEL || PPC32
select HAVE_EBPF_JIT
select HAVE_EFFICIENT_UNALIGNED_ACCESS
select HAVE_FAST_GUP
@ -256,7 +257,7 @@ config PPC
select HAVE_MOD_ARCH_SPECIFIC
select HAVE_NMI if PERF_EVENTS || (PPC64 && PPC_BOOK3S)
select HAVE_OPTPROBES
select HAVE_OBJTOOL if PPC32 || MPROFILE_KERNEL
select HAVE_OBJTOOL if ARCH_USING_PATCHABLE_FUNCTION_ENTRY || MPROFILE_KERNEL || PPC32
select HAVE_OBJTOOL_MCOUNT if HAVE_OBJTOOL
select HAVE_PERF_EVENTS
select HAVE_PERF_EVENTS_NMI if PPC64
@ -554,6 +555,13 @@ config MPROFILE_KERNEL
def_bool $(success,$(srctree)/arch/powerpc/tools/gcc-check-mprofile-kernel.sh $(CC) -mlittle-endian) if CPU_LITTLE_ENDIAN
def_bool $(success,$(srctree)/arch/powerpc/tools/gcc-check-mprofile-kernel.sh $(CC) -mbig-endian) if CPU_BIG_ENDIAN
config ARCH_USING_PATCHABLE_FUNCTION_ENTRY
depends on FUNCTION_TRACER && (PPC32 || PPC64_ELF_ABI_V2)
depends on $(cc-option,-fpatchable-function-entry=2)
def_bool y if PPC32
def_bool $(success,$(srctree)/arch/powerpc/tools/gcc-check-fpatchable-function-entry.sh $(CC) -mlittle-endian) if PPC64 && CPU_LITTLE_ENDIAN
def_bool $(success,$(srctree)/arch/powerpc/tools/gcc-check-fpatchable-function-entry.sh $(CC) -mbig-endian) if PPC64 && CPU_BIG_ENDIAN
config HOTPLUG_CPU
bool "Support for enabling/disabling CPUs"
depends on SMP && (PPC_PSERIES || \

5
arch/powerpc/Makefile
View File

@ -143,11 +143,16 @@ CFLAGS-$(CONFIG_PPC32) += $(call cc-option, $(MULTIPLEWORD))
CFLAGS-$(CONFIG_PPC32) += $(call cc-option,-mno-readonly-in-sdata)
ifdef CONFIG_FUNCTION_TRACER
ifdef CONFIG_ARCH_USING_PATCHABLE_FUNCTION_ENTRY
KBUILD_CPPFLAGS += -DCC_USING_PATCHABLE_FUNCTION_ENTRY
CC_FLAGS_FTRACE := -fpatchable-function-entry=2
else
CC_FLAGS_FTRACE := -pg
ifdef CONFIG_MPROFILE_KERNEL
CC_FLAGS_FTRACE += -mprofile-kernel
endif
endif
endif
CFLAGS-$(CONFIG_TARGET_CPU_BOOL) += -mcpu=$(CONFIG_TARGET_CPU)
AFLAGS-$(CONFIG_TARGET_CPU_BOOL) += -mcpu=$(CONFIG_TARGET_CPU)

6
arch/powerpc/include/asm/ftrace.h
View File

@ -11,7 +11,7 @@
#define HAVE_FUNCTION_GRAPH_RET_ADDR_PTR
/* Ignore unused weak functions which will have larger offsets */
#ifdef CONFIG_MPROFILE_KERNEL
#if defined(CONFIG_MPROFILE_KERNEL) || defined(CONFIG_ARCH_USING_PATCHABLE_FUNCTION_ENTRY)
#define FTRACE_MCOUNT_MAX_OFFSET 16
#elif defined(CONFIG_PPC32)
#define FTRACE_MCOUNT_MAX_OFFSET 8
@ -22,7 +22,9 @@ extern void _mcount(void);
static inline unsigned long ftrace_call_adjust(unsigned long addr)
{
/* relocation of mcount call site is the same as the address */
if (IS_ENABLED(CONFIG_ARCH_USING_PATCHABLE_FUNCTION_ENTRY))
addr += MCOUNT_INSN_SIZE;
return addr;
}

4
arch/powerpc/include/asm/vermagic.h
View File

@ -2,7 +2,9 @@
#ifndef _ASM_VERMAGIC_H
#define _ASM_VERMAGIC_H
#ifdef CONFIG_MPROFILE_KERNEL
#ifdef CONFIG_ARCH_USING_PATCHABLE_FUNCTION_ENTRY
#define MODULE_ARCH_VERMAGIC_FTRACE "patchable-function-entry "
#elif defined(CONFIG_MPROFILE_KERNEL)
#define MODULE_ARCH_VERMAGIC_FTRACE "mprofile-kernel "
#else
#define MODULE_ARCH_VERMAGIC_FTRACE ""

2
arch/powerpc/kernel/module_64.c
View File

@ -465,7 +465,7 @@ int module_frob_arch_sections(Elf64_Ehdr *hdr,
return 0;
}
#ifdef CONFIG_MPROFILE_KERNEL
#if defined(CONFIG_MPROFILE_KERNEL) || defined(CONFIG_ARCH_USING_PATCHABLE_FUNCTION_ENTRY)
static u32 stub_insns[] = {
#ifdef CONFIG_PPC_KERNEL_PCREL

14
arch/powerpc/kernel/trace/ftrace.c
View File

@ -220,7 +220,12 @@ int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
int ret = 0;
/* Verify instructions surrounding the ftrace location */
if (IS_ENABLED(CONFIG_PPC32)) {
if (IS_ENABLED(CONFIG_ARCH_USING_PATCHABLE_FUNCTION_ENTRY)) {
/* Expect nops */
ret = ftrace_validate_inst(ip - 4, ppc_inst(PPC_RAW_NOP()));
if (!ret)
ret = ftrace_validate_inst(ip, ppc_inst(PPC_RAW_NOP()));
} else if (IS_ENABLED(CONFIG_PPC32)) {
/* Expected sequence: 'mflr r0', 'stw r0,4(r1)', 'bl _mcount' */
ret = ftrace_validate_inst(ip - 8, ppc_inst(PPC_RAW_MFLR(_R0)));
if (!ret)
@ -250,7 +255,12 @@ int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
/* Nop-out the ftrace location */
new = ppc_inst(PPC_RAW_NOP());
addr = MCOUNT_ADDR;
if (is_offset_in_branch_range(addr - ip)) {
if (IS_ENABLED(CONFIG_ARCH_USING_PATCHABLE_FUNCTION_ENTRY)) {
/* we instead patch-in the 'mflr r0' */
old = ppc_inst(PPC_RAW_NOP());
new = ppc_inst(PPC_RAW_MFLR(_R0));
ret = ftrace_modify_code(ip - 4, old, new);
} else if (is_offset_in_branch_range(addr - ip)) {
/* Within range */
old = ftrace_create_branch_inst(ip, addr, 1);
ret = ftrace_modify_code(ip, old, new);

2
arch/powerpc/kernel/trace/ftrace_entry.S
View File

@ -250,6 +250,7 @@ livepatch_handler:
blr
#endif /* CONFIG_LIVEPATCH */
#ifndef CONFIG_ARCH_USING_PATCHABLE_FUNCTION_ENTRY
_GLOBAL(mcount)
_GLOBAL(_mcount)
EXPORT_SYMBOL(_mcount)
@ -257,6 +258,7 @@ EXPORT_SYMBOL(_mcount)
mtctr r12
mtlr r0
bctr
#endif
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
_GLOBAL(return_to_handler)

26
arch/powerpc/tools/gcc-check-fpatchable-function-entry.sh Executable file
View File

@ -0,0 +1,26 @@
#!/bin/bash
# SPDX-License-Identifier: GPL-2.0
set -e
set -o pipefail
# To debug, uncomment the following line
# set -x
# Output from -fpatchable-function-entry can only vary on ppc64 elfv2, so this
# should not be invoked for other targets. Therefore we can pass in -m64 and
# -mabi explicitly, to take care of toolchains defaulting to other targets.
# Test whether the compile option -fpatchable-function-entry exists and
# generates appropriate code
echo "int func() { return 0; }" | \
$* -m64 -mabi=elfv2 -S -x c -O2 -fpatchable-function-entry=2 - -o - 2> /dev/null | \
grep -q "__patchable_function_entries"
# Test whether nops are generated after the local entry point
echo "int x; int func() { return x; }" | \
$* -m64 -mabi=elfv2 -S -x c -O2 -fpatchable-function-entry=2 - -o - 2> /dev/null | \
awk 'BEGIN { RS = ";" } /\.localentry.*nop.*\n[[:space:]]*nop/ { print $0 }' | \
grep -q "func:"
exit 0