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Date: Tue, 15 Nov 2022 17:04:51 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Qing Zhang <zhangqing@...ngson.cn>
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
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.
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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