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References: <20221115025527.13382-1-zhangqing@loongson.cn> <20221115025527.13382-2-zhangqing@loongson.cn>
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In-Reply-To: <0a32d7d6-b26f-87d7-49e3-31ad53218ec1@loongson.cn>
From:   Huacai Chen <chenhuacai@kernel.org>
Date:   Tue, 15 Nov 2022 17:04:51 +0800
Message-ID: <CAAhV-H7xwXks8gjOwdRtMXGvzXZo47KvoFoQ4z+FCuZZ1_iz9g@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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On Tue, Nov 15, 2022 at 4:51 PM Qing Zhang <zhangqing@loongson.cn> wrote:
>
> Hi, Huacai
>
> On 2022/11/15 =E4=B8=8B=E5=8D=884:25, Huacai Chen wrote:
> > Hi, Qing,
> >
> > On Tue, Nov 15, 2022 at 10:55 AM Qing Zhang <zhangqing@loongson.cn> wro=
te:
> >>
> >> 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 +=3D -DCC_USING_PATCHABLE_FUNCTION_ENTRY
> >> +CC_FLAGS_FTRACE :=3D -fpatchable-function-entry=3D2
> >> +endif
> >> +
> >>   ifdef CONFIG_64BIT
> >>   ld-emul                        =3D $(64bit-emul)
> >>   cflags-y               +=3D -mabi=3Dlp64s
> >> diff --git a/arch/loongarch/include/asm/ftrace.h b/arch/loongarch/incl=
ude/asm/ftrace.h
> >> new file mode 100644
> >> index 000000000000..6a3e76234618
> >> --- /dev/null
> >> +++ b/arch/loongarch/include/asm/ftrace.h
> >> @@ -0,0 +1,18 @@
> >> +/* SPDX-License-Identifier: GPL-2.0 */
> >> +/*
> >> + * Copyright (C) 2022 Loongson Technology Corporation Limited
> >> + */
> >> +
> >> +#ifndef _ASM_LOONGARCH_FTRACE_H
> >> +#define _ASM_LOONGARCH_FTRACE_H
> >> +
> >> +#ifdef CONFIG_FUNCTION_TRACER
> >> +#define MCOUNT_INSN_SIZE 4             /* sizeof mcount call */
> >> +
> >> +#ifndef __ASSEMBLY__
> >> +extern void _mcount(void);
> >> +#define mcount _mcount
> >> +
> >> +#endif /* __ASSEMBLY__ */
> >> +#endif /* CONFIG_FUNCTION_TRACER */
> >> +#endif /* _ASM_LOONGARCH_FTRACE_H */
> >> diff --git a/arch/loongarch/kernel/Makefile b/arch/loongarch/kernel/Ma=
kefile
> >> index 86744531b100..3f71bce1c7ce 100644
> >> --- a/arch/loongarch/kernel/Makefile
> >> +++ b/arch/loongarch/kernel/Makefile
> >> @@ -15,6 +15,14 @@ obj-$(CONFIG_EFI)            +=3D efi.o
> >>
> >>   obj-$(CONFIG_CPU_HAS_FPU)      +=3D fpu.o
> >>
> >> +ifdef CONFIG_FUNCTION_TRACER
> >> +obj-y +=3D mcount.o ftrace.o
> >> +CFLAGS_REMOVE_ftrace.o =3D $(CC_FLAGS_FTRACE)
> >> +CFLAGS_REMOVE_inst.o =3D $(CC_FLAGS_FTRACE)
> >> +CFLAGS_REMOVE_time.o =3D $(CC_FLAGS_FTRACE)
> >> +CFLAGS_REMOVE_perf_event.o =3D $(CC_FLAGS_FTRACE)
> >> +endif
> >> +
> >>   obj-$(CONFIG_MODULES)          +=3D module.o module-sections.o
> >>   obj-$(CONFIG_STACKTRACE)       +=3D stacktrace.o
> >>
> >> diff --git a/arch/loongarch/kernel/ftrace.c b/arch/loongarch/kernel/ft=
race.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.

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 =3D 32;
> >> +
> >> +       insn =3D (union loongarch_instruction *)insn_addr;
> >> +
> >> +       do {
> >> +               insn--;
> >> +               limit--;
> >> +
> >> +               if (is_ra_save_ins(insn))
> >> +                       *ra_off =3D -((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 =3D (unsigned long)&return_to_hand=
ler;
> >> +
> >> +       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) =3D return_ho=
oker;
> >> +
> >> +       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/mc=
ount.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 a=
ddress */
> >> +       move    a1, s0                          /* arg1: parent's retu=
rn address */
> >> +       jirl    ra, t2, 0                       /* (1) call *ftrace_tr=
ace_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: Calls=
ite self return addr */
> >> +       PTR_ADDI        a1, sp, MCOUNT_STACK_SIZE       /* arg1: Calls=
ite sp */
> >> +       move    a2, s0                                  /* arg2: Calls=
ite 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
> >>
> >>
>