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Message-ID: <577c4455-24fa-9a49-d993-9a7bc5f63ac6@loongson.cn>
Date: Tue, 15 Nov 2022 19:06:49 +0800
From: Qing Zhang <zhangqing@...ngson.cn>
To: Huacai Chen <chenhuacai@...nel.org>
Cc: Steven Rostedt <rostedt@...dmis.org>,
Ingo Molnar <mingo@...hat.com>, loongarch@...ts.linux.dev,
linux-kernel@...r.kernel.org, Jinyang He <hejinyang@...ngson.cn>
Subject: Re: [PATCH v6 1/9] LoongArch/ftrace: Add basic support
Hi, huacai
On 2022/11/15 下午5:04, Huacai Chen wrote:
> On Tue, Nov 15, 2022 at 4:51 PM Qing Zhang <zhangqing@...ngson.cn> wrote:
>>
>> Hi, Huacai
>>
>> On 2022/11/15 下午4:25, Huacai Chen wrote:
>>> Hi, Qing,
>>>
>>> On Tue, Nov 15, 2022 at 10:55 AM Qing Zhang <zhangqing@...ngson.cn> wrote:
>>>>
>>>> This patch contains basic ftrace support for LoongArch.
>>>> Specifically, function tracer (HAVE_FUNCTION_TRACER), function graph
>>>> tracer (HAVE_FUNCTION_GRAPH_TRACER) are implemented following the
>>>> instructions in Documentation/trace/ftrace-design.txt.
>>>>
>>>> Use `-pg` makes stub like a child function `void _mcount(void *ra)`.
>>>> Thus, it can be seen store RA and open stack before `call _mcount`.
>>>> Find `open stack` at first, and then find `store RA`
>>>>
>>>> Note that the functions in both inst.c and time.c should not be
>>>> hooked with the compiler's -pg option: to prevent infinite self-
>>>> referencing for the former, and to ignore early setup stuff for the
>>>> latter.
>>>>
>>>> Co-developed-by: Jinyang He <hejinyang@...ngson.cn>
>>>> Signed-off-by: Jinyang He <hejinyang@...ngson.cn>
>>>> Signed-off-by: Qing Zhang <zhangqing@...ngson.cn>
>>>> ---
>>>> arch/loongarch/Kconfig | 2 +
>>>> arch/loongarch/Makefile | 5 ++
>>>> arch/loongarch/include/asm/ftrace.h | 18 ++++++
>>>> arch/loongarch/kernel/Makefile | 8 +++
>>>> arch/loongarch/kernel/ftrace.c | 74 +++++++++++++++++++++++
>>>> arch/loongarch/kernel/mcount.S | 94 +++++++++++++++++++++++++++++
>>>> 6 files changed, 201 insertions(+)
>>>> create mode 100644 arch/loongarch/include/asm/ftrace.h
>>>> create mode 100644 arch/loongarch/kernel/ftrace.c
>>>> create mode 100644 arch/loongarch/kernel/mcount.S
>>>>
>>>> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
>>>> index 1943f840e494..92c4ec8c8527 100644
>>>> --- a/arch/loongarch/Kconfig
>>>> +++ b/arch/loongarch/Kconfig
>>>> @@ -91,6 +91,8 @@ config LOONGARCH
>>>> select HAVE_EBPF_JIT
>>>> select HAVE_EXIT_THREAD
>>>> select HAVE_FAST_GUP
>>>> + select HAVE_FUNCTION_GRAPH_TRACER
>>> This line should be moved to another patch.
>>>
>>>> + select HAVE_FUNCTION_TRACER
>>>> select HAVE_GENERIC_VDSO
>>>> select HAVE_IOREMAP_PROT
>>>> select HAVE_IRQ_EXIT_ON_IRQ_STACK
>>>> diff --git a/arch/loongarch/Makefile b/arch/loongarch/Makefile
>>>> index a0fc1f9980e3..6832a8f891fd 100644
>>>> --- a/arch/loongarch/Makefile
>>>> +++ b/arch/loongarch/Makefile
>>>> @@ -36,6 +36,11 @@ ifneq ($(SUBARCH),$(ARCH))
>>>> endif
>>>> endif
>>>>
>>>> +ifdef CONFIG_DYNAMIC_FTRACE
>>>> +KBUILD_CPPFLAGS += -DCC_USING_PATCHABLE_FUNCTION_ENTRY
>>>> +CC_FLAGS_FTRACE := -fpatchable-function-entry=2
>>>> +endif
>>>> +
>>>> ifdef CONFIG_64BIT
>>>> ld-emul = $(64bit-emul)
>>>> cflags-y += -mabi=lp64s
>>>> diff --git a/arch/loongarch/include/asm/ftrace.h b/arch/loongarch/include/asm/ftrace.h
>>>> new file mode 100644
>>>> index 000000000000..6a3e76234618
>>>> --- /dev/null
>>>> +++ b/arch/loongarch/include/asm/ftrace.h
>>>> @@ -0,0 +1,18 @@
>>>> +/* SPDX-License-Identifier: GPL-2.0 */
>>>> +/*
>>>> + * Copyright (C) 2022 Loongson Technology Corporation Limited
>>>> + */
>>>> +
>>>> +#ifndef _ASM_LOONGARCH_FTRACE_H
>>>> +#define _ASM_LOONGARCH_FTRACE_H
>>>> +
>>>> +#ifdef CONFIG_FUNCTION_TRACER
>>>> +#define MCOUNT_INSN_SIZE 4 /* sizeof mcount call */
>>>> +
>>>> +#ifndef __ASSEMBLY__
>>>> +extern void _mcount(void);
>>>> +#define mcount _mcount
>>>> +
>>>> +#endif /* __ASSEMBLY__ */
>>>> +#endif /* CONFIG_FUNCTION_TRACER */
>>>> +#endif /* _ASM_LOONGARCH_FTRACE_H */
>>>> diff --git a/arch/loongarch/kernel/Makefile b/arch/loongarch/kernel/Makefile
>>>> index 86744531b100..3f71bce1c7ce 100644
>>>> --- a/arch/loongarch/kernel/Makefile
>>>> +++ b/arch/loongarch/kernel/Makefile
>>>> @@ -15,6 +15,14 @@ obj-$(CONFIG_EFI) += efi.o
>>>>
>>>> obj-$(CONFIG_CPU_HAS_FPU) += fpu.o
>>>>
>>>> +ifdef CONFIG_FUNCTION_TRACER
>>>> +obj-y += mcount.o ftrace.o
>>>> +CFLAGS_REMOVE_ftrace.o = $(CC_FLAGS_FTRACE)
>>>> +CFLAGS_REMOVE_inst.o = $(CC_FLAGS_FTRACE)
>>>> +CFLAGS_REMOVE_time.o = $(CC_FLAGS_FTRACE)
>>>> +CFLAGS_REMOVE_perf_event.o = $(CC_FLAGS_FTRACE)
>>>> +endif
>>>> +
>>>> obj-$(CONFIG_MODULES) += module.o module-sections.o
>>>> obj-$(CONFIG_STACKTRACE) += stacktrace.o
>>>>
>>>> diff --git a/arch/loongarch/kernel/ftrace.c b/arch/loongarch/kernel/ftrace.c
>>>> new file mode 100644
>>>> index 000000000000..c8ddc5f11f32
>>>> --- /dev/null
>>>> +++ b/arch/loongarch/kernel/ftrace.c
>>>> @@ -0,0 +1,74 @@
>>>> +// SPDX-License-Identifier: GPL-2.0
>>>> +/*
>>>> + * Copyright (C) 2022 Loongson Technology Corporation Limited
>>>> + */
>>>> +
>>>> +#include <linux/uaccess.h>
>>>> +#include <linux/init.h>
>>>> +#include <linux/ftrace.h>
>>>> +#include <linux/syscalls.h>
>>>> +
>>>> +#include <asm/asm.h>
>>>> +#include <asm/asm-offsets.h>
>>>> +#include <asm/cacheflush.h>
>>>> +#include <asm/inst.h>
>>>> +#include <asm/loongarch.h>
>>>> +#include <asm/syscall.h>
>>>> +#include <asm/unistd.h>
>>>> +
>>>> +#include <asm-generic/sections.h>
>>>> +
>>>> +#ifdef CONFIG_FUNCTION_GRAPH_TRACER
>>> This should also be moved to another patch.
>>
>> No, CONFIG_FUNCTION_GRAPH_TRACER is the basic feature, as the first
>> patch for non-dynamic ftrace, unless it is a separate patch, which is
>> obviously not necessary (Refer to the first submission of riscv and
>> arm64 here).
> But FUNCTION_GRAPH_TRACER is added until Patch-4.
Separate non dynamic FUNCTION_ GRAPH_ TRACER and dynamic
FUNCTION_GRAPH_TRACER
can be placed in a patch, However, since the dynamic can completely
replace the
non dynamic, my idea is to put the non dynamic content in the first
patch, which
is more consistent with our idea of gradual evolution at the beginning,
How do you think?
Thanks,
- Qing
>
> Huacai
>>
>> Thanks,
>> - Qing
>>>
>>>> +
>>>> +/*
>>>> + * As `call _mcount` follows LoongArch psABI, ra-saved operation and
>>>> + * stack operation can be found before this insn.
>>>> + */
>>>> +
>>>> +static int ftrace_get_parent_ra_addr(unsigned long insn_addr, int *ra_off)
>>>> +{
>>>> + union loongarch_instruction *insn;
>>>> + int limit = 32;
>>>> +
>>>> + insn = (union loongarch_instruction *)insn_addr;
>>>> +
>>>> + do {
>>>> + insn--;
>>>> + limit--;
>>>> +
>>>> + if (is_ra_save_ins(insn))
>>>> + *ra_off = -((1 << 12) - insn->reg2i12_format.immediate);
>>>> +
>>>> + } while (!is_stack_alloc_ins(insn) && limit);
>>>> +
>>>> + if (!limit)
>>>> + return -EINVAL;
>>>> +
>>>> + return 0;
>>>> +}
>>>> +
>>>> +void prepare_ftrace_return(unsigned long self_addr,
>>>> + unsigned long callsite_sp, unsigned long old)
>>>> +{
>>>> + int ra_off;
>>>> + unsigned long return_hooker = (unsigned long)&return_to_handler;
>>>> +
>>>> + if (unlikely(ftrace_graph_is_dead()))
>>>> + return;
>>>> +
>>>> + if (unlikely(atomic_read(¤t->tracing_graph_pause)))
>>>> + return;
>>>> +
>>>> + if (ftrace_get_parent_ra_addr(self_addr, &ra_off))
>>>> + goto out;
>>>> +
>>>> + if (!function_graph_enter(old, self_addr, 0, NULL))
>>>> + *(unsigned long *)(callsite_sp + ra_off) = return_hooker;
>>>> +
>>>> + return;
>>>> +
>>>> +out:
>>>> + ftrace_graph_stop();
>>>> + WARN_ON(1);
>>>> +}
>>>> +#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
>>>> diff --git a/arch/loongarch/kernel/mcount.S b/arch/loongarch/kernel/mcount.S
>>>> new file mode 100644
>>>> index 000000000000..3de7c2d7fd12
>>>> --- /dev/null
>>>> +++ b/arch/loongarch/kernel/mcount.S
>>>> @@ -0,0 +1,94 @@
>>>> +/* SPDX-License-Identifier: GPL-2.0 */
>>>> +/*
>>>> + * LoongArch specific _mcount support
>>>> + *
>>>> + * Copyright (C) 2022 Loongson Technology Corporation Limited
>>>> + */
>>>> +
>>>> +#include <asm/export.h>
>>>> +#include <asm/regdef.h>
>>>> +#include <asm/stackframe.h>
>>>> +#include <asm/ftrace.h>
>>>> +
>>>> + .text
>>>> +
>>>> +#define MCOUNT_STACK_SIZE (2 * SZREG)
>>>> +#define MCOUNT_S0_OFFSET (0)
>>>> +#define MCOUNT_RA_OFFSET (SZREG)
>>>> +
>>>> + .macro MCOUNT_SAVE_REGS
>>>> + PTR_ADDI sp, sp, -MCOUNT_STACK_SIZE
>>>> + PTR_S s0, sp, MCOUNT_S0_OFFSET
>>>> + PTR_S ra, sp, MCOUNT_RA_OFFSET
>>>> + move s0, a0
>>>> + .endm
>>>> +
>>>> + .macro MCOUNT_RESTORE_REGS
>>>> + move a0, s0
>>>> + PTR_L ra, sp, MCOUNT_RA_OFFSET
>>>> + PTR_L s0, sp, MCOUNT_S0_OFFSET
>>>> + PTR_ADDI sp, sp, MCOUNT_STACK_SIZE
>>>> + .endm
>>>> +
>>>> +
>>>> +SYM_FUNC_START(_mcount)
>>>> + la.pcrel t1, ftrace_stub
>>>> + la.pcrel t2, ftrace_trace_function /* Prepare t2 for (1) */
>>>> + PTR_L t2, t2, 0
>>>> + beq t1, t2, fgraph_trace
>>>> +
>>>> + MCOUNT_SAVE_REGS
>>>> +
>>>> + move a0, ra /* arg0: self return address */
>>>> + move a1, s0 /* arg1: parent's return address */
>>>> + jirl ra, t2, 0 /* (1) call *ftrace_trace_function */
>>>> +
>>>> + MCOUNT_RESTORE_REGS
>>>> +
>>>> +fgraph_trace:
>>>> +#ifdef CONFIG_FUNCTION_GRAPH_TRACER
>>> The same as above.
>>>
>>> Huacai
>>>> + la.pcrel t1, ftrace_stub
>>>> + la.pcrel t3, ftrace_graph_return
>>>> + PTR_L t3, t3, 0
>>>> + bne t1, t3, ftrace_graph_caller
>>>> + la.pcrel t1, ftrace_graph_entry_stub
>>>> + la.pcrel t3, ftrace_graph_entry
>>>> + PTR_L t3, t3, 0
>>>> + bne t1, t3, ftrace_graph_caller
>>>> +#endif
>>>> +
>>>> + .globl ftrace_stub
>>>> +ftrace_stub:
>>>> + jr ra
>>>> +SYM_FUNC_END(_mcount)
>>>> +EXPORT_SYMBOL(_mcount)
>>>> +
>>>> +#ifdef CONFIG_FUNCTION_GRAPH_TRACER
>>>> +SYM_FUNC_START(ftrace_graph_caller)
>>>> + MCOUNT_SAVE_REGS
>>>> +
>>>> + PTR_ADDI a0, ra, -4 /* arg0: Callsite self return addr */
>>>> + PTR_ADDI a1, sp, MCOUNT_STACK_SIZE /* arg1: Callsite sp */
>>>> + move a2, s0 /* arg2: Callsite parent ra */
>>>> + bl prepare_ftrace_return
>>>> +
>>>> + MCOUNT_RESTORE_REGS
>>>> + jr ra
>>>> +SYM_FUNC_END(ftrace_graph_caller)
>>>> +
>>>> +SYM_FUNC_START(return_to_handler)
>>>> + PTR_ADDI sp, sp, -2 * SZREG
>>>> + PTR_S a0, sp, 0
>>>> + PTR_S a1, sp, SZREG
>>>> +
>>>> + bl ftrace_return_to_handler
>>>> +
>>>> + /* restore the real parent address: a0 -> ra */
>>>> + move ra, a0
>>>> +
>>>> + PTR_L a0, sp, 0
>>>> + PTR_L a1, sp, SZREG
>>>> + PTR_ADDI sp, sp, 2 * SZREG
>>>> + jr ra
>>>> +SYM_FUNC_END(return_to_handler)
>>>> +#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
>>>> --
>>>> 2.36.0
>>>>
>>>>
>>
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