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References: <20221115025527.13382-1-zhangqing@loongson.cn> <20221115025527.13382-2-zhangqing@loongson.cn>
In-Reply-To: <20221115025527.13382-2-zhangqing@loongson.cn>
From:   Huacai Chen <chenhuacai@kernel.org>
Date:   Tue, 15 Nov 2022 16:25:15 +0800
Message-ID: <CAAhV-H7JxZ9SAVXGLgY3sMo9jtuANxQqu4_o2FrBBfN-Kf=VFw@mail.gmail.com>
Subject: Re: [PATCH v6 1/9] LoongArch/ftrace: Add basic support
To:     Qing Zhang <zhangqing@loongson.cn>
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>
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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.

> +
> +/*
> + * 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
>
>