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Date: Thu, 24 Nov 2022 10:08:10 +0800 From: Guo Ren <guoren@...nel.org> To: Song Shuai <suagrfillet@...il.com> Cc: paul.walmsley@...ive.com, palmer@...belt.com, aou@...s.berkeley.edu, rostedt@...dmis.org, mhiramat@...nel.org, mark.rutland@....com, peterz@...radead.org, jolsa@...hat.com, bp@...e.de, jpoimboe@...nel.org, linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH 1/2] riscv/ftrace: add DYNAMIC_FTRACE_WITH_DIRECT_CALLS support On Thu, Nov 24, 2022 at 1:27 AM Song Shuai <suagrfillet@...il.com> wrote: > > Guo Ren <guoren@...nel.org> 于2022年11月23日周三 23:02写道: > > > > Cool job, thx. > > > > On Wed, Nov 23, 2022 at 10:20 PM Song Shuai <suagrfillet@...il.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@...il.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. > > > The direct_caller has the same program layout as the ftrace_caller, which means > the reg t0 will never be changed when direct_caller returns. > > If regs->t0 changes here and ftrace_regs_caller executes `jr t0`, > direct_caller will enter the dead loop. ? ftrace_regs_caller->call_direct_funcs-> arch_ftrace_set_direct_caller-> ftrace_regs_caller jr t0. Only call_direct_funcs call arch_ftrace_set_direct_caller ! static void call_direct_funcs(unsigned long ip, unsigned long pip, struct ftrace_ops *ops, struct ftrace_regs *fregs) { struct pt_regs *regs = ftrace_get_regs(fregs); unsigned long addr; addr = ftrace_find_rec_direct(ip); if (!addr) return; arch_ftrace_set_direct_caller(regs, addr); } > > Actually the reg t0 always saves the address of function entry with 8B > offset, it should only > changed by the IPMODIFY ops instead of the direct_ops. > >> > >> +} > >> + > >> #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 -- Best Regards Guo Ren
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