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Subject: Re: [PATCH v6 1/9] LoongArch/ftrace: Add basic support
To:     Huacai Chen <chenhuacai@kernel.org>
Cc:     Steven Rostedt <rostedt@goodmis.org>,
        Ingo Molnar <mingo@redhat.com>, loongarch@lists.linux.dev,
        linux-kernel@vger.kernel.org, Jinyang He <hejinyang@loongson.cn>
References: <20221115025527.13382-1-zhangqing@loongson.cn>
 <20221115025527.13382-2-zhangqing@loongson.cn>
 <CAAhV-H7JxZ9SAVXGLgY3sMo9jtuANxQqu4_o2FrBBfN-Kf=VFw@mail.gmail.com>
From:   Qing Zhang <zhangqing@loongson.cn>
Message-ID: <0a32d7d6-b26f-87d7-49e3-31ad53218ec1@loongson.cn>
Date:   Tue, 15 Nov 2022 16:50:14 +0800
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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@loongson.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@loongson.cn>
>> Signed-off-by: Jinyang He <hejinyang@loongson.cn>
>> Signed-off-by: Qing Zhang <zhangqing@loongson.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).

  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(&current->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
>>
>>