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    SubjectRe: [PATCH v7 1/9] LoongArch/ftrace: Add basic support
    Hi, Qing,

    On Wed, Nov 16, 2022 at 10:53 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
    > + 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
    I think these lines should be moved to Patch-3.

    Huacai
    > +
    > 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
    > +
    > +/*
    > + * 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
    > + 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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