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    SubjectRe: [PATCH 1/2] riscv/ftrace: add DYNAMIC_FTRACE_WITH_DIRECT_CALLS support
    Hi Song,

    On Wed, Nov 23, 2022 at 10:20 PM Song Shuai <suagrfillet@gmail.com> wrote:
    >
    > This patch adds DYNAMIC_FTRACE_WITH_DIRECT_CALLS support for RISC-V.
    >
    > select the DYNAMIC_FTRACE_WITH_DIRECT_CALLS to provide the
    > register_ftrace_direct[_multi] interfaces allowing users to register
    > the customed trampoline (direct_caller) as the mcount for one or
    > more target functions. And modify_ftrace_direct[_multi] are also
    > provided for modifying direct_caller.
    >
    > To make the direct_caller and the other ftrace hooks (eg. function/fgraph
    > tracer, k[ret]probes) co-exist, a temporary register is nominated to
    > store the address of direct_caller in ftrace_regs_caller. After the
    > setting of the address direct_caller by direct_ops->func and the
    > RESTORE_REGS in ftrace_regs_caller, direct_caller will be jumped to
    > by the `jr` inst.
    >
    > Signed-off-by: Song Shuai <suagrfillet@gmail.com>
    > ---
    > arch/riscv/Kconfig | 1 +
    > arch/riscv/include/asm/ftrace.h | 6 ++++++
    > arch/riscv/kernel/mcount-dyn.S | 4 ++++
    > 3 files changed, 11 insertions(+)
    >
    > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
    > index 39ec8d628cf6..d083ec08d0b6 100644
    > --- a/arch/riscv/Kconfig
    > +++ b/arch/riscv/Kconfig
    > @@ -278,6 +278,7 @@ config ARCH_RV64I
    > select ARCH_SUPPORTS_INT128 if CC_HAS_INT128
    > select HAVE_DYNAMIC_FTRACE if !XIP_KERNEL && MMU && $(cc-option,-fpatchable-function-entry=8)
    > select HAVE_DYNAMIC_FTRACE_WITH_REGS if HAVE_DYNAMIC_FTRACE
    > + select HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
    > select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL
    > select HAVE_FUNCTION_GRAPH_TRACER
    > select HAVE_FUNCTION_TRACER if !XIP_KERNEL && !PREEMPTION
    > diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.h
    > index 01bebb28eabe..be4d57566139 100644
    > --- a/arch/riscv/include/asm/ftrace.h
    > +++ b/arch/riscv/include/asm/ftrace.h
    > @@ -114,6 +114,12 @@ struct ftrace_regs;
    > void ftrace_graph_func(unsigned long ip, unsigned long parent_ip,
    > struct ftrace_ops *op, struct ftrace_regs *fregs);
    > #define ftrace_graph_func ftrace_graph_func
    > +
    > +static inline void arch_ftrace_set_direct_caller(struct pt_regs *regs, unsigned long addr)
    > +{
    > + regs->t1 = addr;
    How about regs->t0 = addr; ?
    And delete all mcount-dyn.S modification.
    > +}
    > +
    > #endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
    >
    > #endif /* __ASSEMBLY__ */
    > diff --git a/arch/riscv/kernel/mcount-dyn.S b/arch/riscv/kernel/mcount-dyn.S
    > index 466c6ef217b1..b89c85a58569 100644
    > --- a/arch/riscv/kernel/mcount-dyn.S
    > +++ b/arch/riscv/kernel/mcount-dyn.S
    > @@ -233,6 +233,7 @@ ENDPROC(ftrace_caller)
    > #else /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
    > ENTRY(ftrace_regs_caller)
    > SAVE_ABI_REGS 1
    > + REG_S x0, PT_T1(sp)
    > PREPARE_ARGS
    >
    > ftrace_regs_call:
    > @@ -241,7 +242,10 @@ ftrace_regs_call:
    >
    >
    > RESTORE_ABI_REGS 1
    > + bnez t1,.Ldirect
    > jr t0
    > +.Ldirect:
    > + jr t1
    > ENDPROC(ftrace_regs_caller)
    >
    > ENTRY(ftrace_caller)
    > --
    > 2.20.1
    >


    --
    Best Regards
    Guo Ren

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