Re: [PATCH V4 6/7] riscv: ftrace: Add DYNAMIC_FTRACE_WITH_DIRECT_CALLS support

Guo Ren
2022-11-30T07:30:18Z

On Tue, Nov 29, 2022 at 8:03 PM Song Shuai <suagrfillet@gmail.com> wrote:
>
> <guoren@kernel.org> 于2022年11月29日周二 03:33写道：
> >
> > From: Song Shuai <suagrfillet@gmail.com>
> >
> > 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>
> > Tested-by: Guo Ren <guoren@kernel.org>
> > Signed-off-by: Guo Ren <guoren@kernel.org>
> > ---
> > 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 1d0e5838b11b..2828537abfcd 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 && $(cc-option,-fpatchable-function-entry=8)
> I noticed this cc-option uses the '-fpatchable-function-entry=8' to
> judge if the compiler supports this option.
> Should we keep up with the CC_FLAGS_FTRACE modified in ("riscv:
> ftrace: Reduce the detour code size to half"),
> or follow the parisc architecture to set the value as '1,1' in the
> case of the CC_FLAGS_FTRACE is not constant.
> ```
> ./arch/parisc/Makefile:75:CC_FLAGS_FTRACE :=
> -fpatchable-function-entry=$(NOP_COUNT),$(shell echo
> $$(($(NOP_COUNT)-1)))
> ./arch/parisc/Kconfig:70: select HAVE_DYNAMIC_FTRACE if
> $(cc-option,-fpatchable-function-entry=1,1)
The -fpatchable-function-entry=8 is still okay for riscv because it's
big enough. Your proposal could be another optimization patch, not a
fixup (No bug happens :).

> ```
> > 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 84f856a3286e..4539f10fea56 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;
> > +}
> > +
> > #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..fef7c460f991 100644
> > --- a/arch/riscv/kernel/mcount-dyn.S
> > +++ b/arch/riscv/kernel/mcount-dyn.S
> > @@ -232,6 +232,7 @@ ENDPROC(ftrace_caller)
> >
> > #else /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
> > ENTRY(ftrace_regs_caller)
> > + move t1, zero
> > SAVE_ABI_REGS 1
> > PREPARE_ARGS
> >
> > @@ -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)
> > --
> > 2.36.1
> >
>
>
> --
> Thanks,
> Song

--
Best Regards
Guo Ren