linux-kernel - Re: [PATCH V4 6/7] riscv: ftrace: Add DYNAMIC_FTRACE_WITH_DIRECT

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Date:   Thu, 1 Dec 2022 20:15:46 +0000
From:   Conor Dooley <conor@...nel.org>
To:     Palmer Dabbelt <palmer@...belt.com>
Cc:     guoren@...nel.org, anup@...infault.org,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Conor Dooley <conor.dooley@...rochip.com>, heiko@...ech.de,
        rostedt@...dmis.org, mhiramat@...nel.org, jolsa@...hat.com,
        bp@...e.de, jpoimboe@...nel.org, suagrfillet@...il.com,
        andy.chiu@...ive.com, mark.rutland@....com,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V4 6/7] riscv: ftrace: Add
 DYNAMIC_FTRACE_WITH_DIRECT_CALLS support

On Thu, Dec 01, 2022 at 12:06:39PM -0800, Palmer Dabbelt wrote:
> On Thu, 01 Dec 2022 12:02:56 PST (-0800), Conor Dooley wrote:
> > On Mon, Nov 28, 2022 at 10:32:29PM -0500, guoren@...nel.org wrote:
> > > From: Song Shuai <suagrfillet@...il.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@...il.com>
> > > Tested-by: Guo Ren <guoren@...nel.org>
> > > Signed-off-by: Guo Ren <guoren@...nel.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)
> > >  	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
> > 
> > Please sort new entries here in alphabetical order, so move the new
> > entry up by one line :)
> 
> IIRC whomever sorted these entrties orignially posted a script that does
> that.  Maybe that should be integrated into either checkpatch or one of the
> patchwork robots so we don't have to manually remember the alphabet?

If it actually does *sorting* I am not sure it's a suitable inclusion
as-is that'd seem better as a pre-commit hook. But maybe it can be
co-opted somehow. I'll try to dig it up off of lore tomorrow.

Thanks,
Conor.