Re: [PATCH] riscv/ftrace: Add basic support

From: Steven Rostedt
Date: Thu Nov 30 2017 - 15:24:31 EST

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On Thu, 30 Nov 2017 16:53:35 +0800
Alan Kao <nonerkao@xxxxxxxxx> wrote:

> This patch contains basic ftrace support for RV64I platform.
> Specifically, function tracer (HAVE_FUNCTION_TRACER), function graph
> tracer (HAVE_FUNCTION_GRAPH_TRACER), and a frame pointer test
> (HAVE_FUNCTION_GRAPH_FP_TEST) are implemented following the
> instructions in Documentation/trace/ftrace-design.txt.

Hmm, that document is somewhat out of date. Hopefully it was good
enough. I'm going to need some time to update it.

>
> Note that the functions in both ftrace.c and setup.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.

I'm curious to what is in setup.c that ftrace uses.

>
> Signed-off-by: Alan Kao <alankao@xxxxxxxxxxxxx>
> ---
> arch/riscv/Kconfig | 8 +++
> arch/riscv/include/asm/Kbuild | 1 -
> arch/riscv/include/asm/ftrace.h | 23 +++++++
> arch/riscv/kernel/Makefile | 7 ++
> arch/riscv/kernel/ftrace.c | 56 ++++++++++++++++
> arch/riscv/kernel/mcount.S | 139 ++++++++++++++++++++++++++++++++++++++++
> 6 files changed, 233 insertions(+), 1 deletion(-)
> create mode 100644 arch/riscv/include/asm/ftrace.h
> create mode 100644 arch/riscv/kernel/ftrace.c
> create mode 100644 arch/riscv/kernel/mcount.S
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 2e15e85c8f7e..07c3df0919b7 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -60,6 +60,12 @@ config PAGE_OFFSET
> config STACKTRACE_SUPPORT
> def_bool y
>
> +config TRACE_IRQFLAGS_SUPPORT
> + def_bool y
> +
> +config LOCKDEP_SUPPORT
> + def_bool y

Hmm, not sure the above is needed for function tracing.

> +
> config RWSEM_GENERIC_SPINLOCK
> def_bool y
>
> @@ -112,6 +118,8 @@ config ARCH_RV64I
> bool "RV64I"
> select CPU_SUPPORTS_64BIT_KERNEL
> select 64BIT
> + select HAVE_FUNCTION_TRACER
> + select HAVE_FUNCTION_GRAPH_TRACER
>
> endchoice
>
> diff --git a/arch/riscv/include/asm/Kbuild b/arch/riscv/include/asm/Kbuild
> index 18158be62a2b..680301bfbc4b 100644
> --- a/arch/riscv/include/asm/Kbuild
> +++ b/arch/riscv/include/asm/Kbuild
> @@ -12,7 +12,6 @@ generic-y += errno.h
> generic-y += exec.h
> generic-y += fb.h
> generic-y += fcntl.h
> -generic-y += ftrace.h
> generic-y += futex.h
> generic-y += hardirq.h
> generic-y += hash.h
> diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.h
> new file mode 100644
> index 000000000000..38beadb07ad5
> --- /dev/null
> +++ b/arch/riscv/include/asm/ftrace.h
> @@ -0,0 +1,23 @@
> +/*
> + * Copyright (C) 2017 Andes Technology Corporation
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program. If not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +/*
> + * The graph frame test is not possible if CONFIG_FRAME_POINTER is not enabled.
> + * Check arch/riscv/kernel/mcount.S for detail.
> + */
> +#if defined(CONFIG_FUNCTION_GRAPH_TRACER) && defined(CONFIG_FRAME_POINTER)
> +#define HAVE_FUNCTION_GRAPH_FP_TEST
> +#endif
> diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
> index ab8baf7bd142..15941f3b8363 100644
> --- a/arch/riscv/kernel/Makefile
> +++ b/arch/riscv/kernel/Makefile
> @@ -2,6 +2,11 @@
> # Makefile for the RISC-V Linux kernel
> #
>
> +#ifdef CONFIG_FTRACE
> +CFLAGS_REMOVE_ftrace.o = -pg
> +CFLAGS_REMOVE_setup.o = -pg
> +#endif
> +
> extra-y += head.o
> extra-y += vmlinux.lds
>
> @@ -29,5 +34,7 @@ CFLAGS_setup.o := -mcmodel=medany
> obj-$(CONFIG_SMP) += smpboot.o
> obj-$(CONFIG_SMP) += smp.o
> obj-$(CONFIG_MODULES) += module.o
> +obj-$(CONFIG_FUNCTION_TRACER) += mcount.o
> +obj-$(CONFIG_FUNCTION_GRAPH_TRACER) += ftrace.o
>
> clean:
> diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c
> new file mode 100644
> index 000000000000..e425c8f3f1cd
> --- /dev/null
> +++ b/arch/riscv/kernel/ftrace.c
> @@ -0,0 +1,56 @@
> +/*
> + * arch/riscv/kernel/ftrace.c
> + *
> + * Copyright (C) 2013 Linaro Limited
> + * Author: AKASHI Takahiro <takahiro.akashi@xxxxxxxxxx>
> + * Copyright (C) 2017 Andes Technology Corporation
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program. If not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +#include <linux/ftrace.h>
> +
> +#ifdef CONFIG_FUNCTION_GRAPH_TRACER

This file only gets compiled when that config is set. This #ifdef is
somewhat redundant.

> +/*
> + * Most of this file is copied from arm64.
> + */
> +void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
> + unsigned long frame_pointer)
> +{
> + unsigned long return_hooker = (unsigned long)&return_to_handler;
> + unsigned long old;
> + struct ftrace_graph_ent trace;
> + int err;
> +
> + if (unlikely(atomic_read(&current->tracing_graph_pause)))
> + return;
> +
> + /*
> + * We don't suffer access faults, so no extra fault-recovery assembly
> + * is needed here.
> + */
> + old = *parent;
> +
> + trace.func = self_addr;
> + trace.depth = current->curr_ret_stack + 1;
> +
> + if (!ftrace_graph_entry(&trace))
> + return;
> +
> + err = ftrace_push_return_trace(old, self_addr, &trace.depth,
> + frame_pointer, NULL);
> + if (err == -EBUSY)
> + return;
> + *parent = return_hooker;
> +}
> +#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
> diff --git a/arch/riscv/kernel/mcount.S b/arch/riscv/kernel/mcount.S
> new file mode 100644
> index 000000000000..5307358219bf
> --- /dev/null
> +++ b/arch/riscv/kernel/mcount.S
> @@ -0,0 +1,139 @@
> +/*
> + * Copyright (C) 2017 Andes Technology Corporation
> + * Author: Alan Kao <alankao@xxxxxxxxxxxxx>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program. If not, see <http://www.gnu.org/licenses/>.
> + */
> +#include <linux/init.h>
> +#include <linux/linkage.h>
> +#include <asm/asm.h>
> +#include <asm/csr.h>
> +#include <asm/unistd.h>
> +#include <asm/thread_info.h>
> +#include <asm/asm-offsets.h>
> +#include <asm-generic/export.h>
> +#include <asm/ftrace.h>
> +
> + .text
> +
> + .macro SAVE_ABI_STATE
> + addi sp, sp, -16
> + sd s0, 0(sp)
> + sd ra, 8(sp)
> + addi s0, sp, 16
> + .endm
> +
> + /*
> + * The call to ftrace_return_to_handler would overwrite the return
> + * register if a0 was not saved.
> + */
> + .macro SAVE_RET_ABI_STATE
> + addi sp, sp, -32
> + sd s0, 16(sp)
> + sd ra, 24(sp)
> + sd a0, 8(sp)
> + addi s0, sp, 32
> + .endm
> +
> + .macro STORE_ABI_STATE
> + ld ra, 8(sp)
> + ld s0, 0(sp)
> + addi sp, sp, 16
> + .endm
> +
> + .macro STORE_RET_ABI_STATE
> + ld ra, 24(sp)
> + ld s0, 16(sp)
> + ld a0, 8(sp)
> + addi sp, sp, 32
> + .endm
> +
> +ENTRY(ftrace_stub)
> + ret
> +ENDPROC(ftrace_stub)
> +
> +#ifdef CONFIG_FUNCTION_GRAPH_TRACER
> +ENTRY(return_to_handler)
> +/*
> + * On implementing the frame point test, the ideal way is to compare the
> + * s0 (frame pointer, if enabled) on entry and the sp (stack pointer) on return.
> + * However, the psABI of variable-length-argument functions does not allow this.
> + *
> + * So alternatively we check the *old* frame pointer position, that is, the
> + * value stored in -16(s0) on entry, and the s0 on return.
> + */
> +#ifdef HAVE_FUNCTION_GRAPH_FP_TEST
> + mv t6, s0
> +#endif
> + SAVE_RET_ABI_STATE
> +#ifdef HAVE_FUNCTION_GRAPH_FP_TEST
> + mv a0, t6
> +#endif
> + la t0, ftrace_return_to_handler
> + jalr t0
> + mv a1, a0
> + STORE_RET_ABI_STATE
> + jr a1
> +ENDPROC(return_to_handler)
> +EXPORT_SYMBOL(return_to_handler)
> +#endif
> +
> +ENTRY(_mcount)
> + la t4, ftrace_stub
> +#ifdef CONFIG_FUNCTION_GRAPH_TRACER
> + la t0, ftrace_graph_return
> + ld t1, 0(t0)
> + bne t1, t4, do_ftrace_graph_caller

If function graph is enabled, you jump straight to the graph tracer,
but never return back to here?

> +
> + la t3, ftrace_graph_entry
> + ld t2, 0(t3)
> + la t6, ftrace_graph_entry_stub
> + bne t2, t6, do_ftrace_graph_caller
> +#endif
> + la t3, ftrace_trace_function
> + ld t5, 0(t3)
> + bne t5, t4, do_trace
> + ret
> +
> +#ifdef CONFIG_FUNCTION_GRAPH_TRACER
> +/*
> + * A pseudo representation for the function graph tracer:
> + * prepare_to_return(&ra_to_caller_of_caller, ra_to_caller)
> + */
> +do_ftrace_graph_caller:
> + addi a0, s0, -8
> + mv a1, ra
> +#ifdef HAVE_FUNCTION_GRAPH_FP_TEST
> + ld a2, -16(s0)
> +#endif
> + SAVE_ABI_STATE
> + la t0, prepare_ftrace_return
> + jalr t0
> + STORE_ABI_STATE

I'm guessing you don't support function tracer and function graph
tracer running at the same time?

-- Steve

> + ret
> +#endif
> +
> +/*
> + * A pseudo representation for the function tracer:
> + * (*ftrace_trace_function)(ra_to_caller, ra_to_caller_of_caller)
> + */
> +do_trace:
> + ld a1, -8(s0)
> + mv a0, ra
> +
> + SAVE_ABI_STATE
> + jalr t5
> + STORE_ABI_STATE
> + ret
> +ENDPROC(_mcount)
> +EXPORT_SYMBOL(_mcount)

Next message: Rob Herring: "Re: [PATCH] dt-bindings: pinctrl: uniphier: add UniPhier pinctrl binding"
Previous message: Olof Johansson: "Re: [patches] Re: [PATCH 08/10] RISC-V: Set __ARCH_WANT_RENAMEAT to pick up generic version"
In reply to: Palmer Dabbelt: "Re: [patches] Re: [PATCH] riscv/ftrace: Add basic support"
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