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Message-ID: <20220322094100.73dc3ad0@gandalf.local.home>
Date: Tue, 22 Mar 2022 09:41:00 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Chengming Zhou <zhouchengming@...edance.com>
Cc: mark.rutland@....com, mingo@...hat.com, tglx@...utronix.de,
catalin.marinas@....com, will@...nel.org,
dave.hansen@...ux.intel.com, broonie@...nel.org, x86@...nel.org,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
songmuchun@...edance.com, qirui.001@...edance.com
Subject: Re: [PATCH v3 3/3] arm64/ftrace: Make function graph use ftrace
directly
On Tue, 22 Mar 2022 20:48:00 +0800
Chengming Zhou <zhouchengming@...edance.com> wrote:
> Hello,
>
> ping... have any comments?
Hi Chengming,
BTW, if you don't hear back for a week, it's OK to send a ping. You don't
need to wait a month. Usually, it's just that the maintainers have other
priorities and will try to look at it when they get a chance, but then
forget to do so :-/
>
> Thanks.
>
> On 2022/2/24 5:32 下午, Chengming Zhou wrote:
> > As we do in commit 0c0593b45c9b ("x86/ftrace: Make function graph
> > use ftrace directly"), we don't need special hook for graph tracer,
> > but instead we use graph_ops:func function to install return_hooker.
> >
> > Since commit 3b23e4991fb6 ("arm64: implement ftrace with regs") add
> > implementation for FTRACE_WITH_REGS on arm64, we can easily adopt
> > the same cleanup on arm64. And this cleanup only changes the
> > FTRACE_WITH_REGS implementation, so the mcount-based implementation
> > is unaffected.
> >
> > Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>
> > ---
> > Changes in v3:
> > - Add comments in ftrace_graph_func() as suggested by Steve.
> >
> > Changes in v2:
> > - Remove FTRACE_WITH_REGS ftrace_graph_caller asm as suggested by Mark.
> > ---
> > arch/arm64/include/asm/ftrace.h | 7 +++++++
> > arch/arm64/kernel/entry-ftrace.S | 17 -----------------
> > arch/arm64/kernel/ftrace.c | 17 +++++++++++++++++
> > 3 files changed, 24 insertions(+), 17 deletions(-)
> >
> > diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h
> > index 1494cfa8639b..dbc45a4157fa 100644
> > --- a/arch/arm64/include/asm/ftrace.h
> > +++ b/arch/arm64/include/asm/ftrace.h
> > @@ -80,8 +80,15 @@ static inline unsigned long ftrace_call_adjust(unsigned long addr)
> >
> > #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
> > struct dyn_ftrace;
> > +struct ftrace_ops;
> > +struct ftrace_regs;
> > +
> > int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec);
> > #define ftrace_init_nop ftrace_init_nop
> > +
> > +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
> > #endif
> >
> > #define ftrace_return_address(n) return_address(n)
> > diff --git a/arch/arm64/kernel/entry-ftrace.S b/arch/arm64/kernel/entry-ftrace.S
> > index e535480a4069..d42a205ef625 100644
> > --- a/arch/arm64/kernel/entry-ftrace.S
> > +++ b/arch/arm64/kernel/entry-ftrace.S
> > @@ -97,12 +97,6 @@ SYM_CODE_START(ftrace_common)
> > SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBAL)
> > bl ftrace_stub
> >
> > -#ifdef CONFIG_FUNCTION_GRAPH_TRACER
> > -SYM_INNER_LABEL(ftrace_graph_call, SYM_L_GLOBAL) // ftrace_graph_caller();
> > - nop // If enabled, this will be replaced
> > - // "b ftrace_graph_caller"
> > -#endif
> > -
> > /*
> > * At the callsite x0-x8 and x19-x30 were live. Any C code will have preserved
> > * x19-x29 per the AAPCS, and we created frame records upon entry, so we need
> > @@ -127,17 +121,6 @@ ftrace_common_return:
> > ret x9
> > SYM_CODE_END(ftrace_common)
> >
> > -#ifdef CONFIG_FUNCTION_GRAPH_TRACER
> > -SYM_CODE_START(ftrace_graph_caller)
> > - ldr x0, [sp, #S_PC]
> > - sub x0, x0, #AARCH64_INSN_SIZE // ip (callsite's BL insn)
> > - add x1, sp, #S_LR // parent_ip (callsite's LR)
> > - ldr x2, [sp, #PT_REGS_SIZE] // parent fp (callsite's FP)
> > - bl prepare_ftrace_return
> > - b ftrace_common_return
> > -SYM_CODE_END(ftrace_graph_caller)
> > -#endif
> > -
> > #else /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
> >
> > /*
> > diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c
> > index 4506c4a90ac1..35eb7c9b5e53 100644
> > --- a/arch/arm64/kernel/ftrace.c
> > +++ b/arch/arm64/kernel/ftrace.c
> > @@ -268,6 +268,22 @@ void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent,
> > }
> >
> > #ifdef CONFIG_DYNAMIC_FTRACE
> > +
> > +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
Is there a case were we have DYNAMIC_FTRACE but not
DYNAMIC_FTRACE_WITH_REGS?
> > +void ftrace_graph_func(unsigned long ip, unsigned long parent_ip,
> > + struct ftrace_ops *op, struct ftrace_regs *fregs)
> > +{
> > + /*
> > + * Athough graph_ops doesn't have FTRACE_OPS_FL_SAVE_REGS set in flags,
> > + * regs can't be NULL in DYNAMIC_FTRACE_WITH_REGS. By design, it should
> > + * be fixed when DYNAMIC_FTRACE_WITH_ARGS is implemented.
> > + */
> > + struct pt_regs *regs = arch_ftrace_get_regs(fregs);
> > + unsigned long *parent = (unsigned long *)&procedure_link_pointer(regs);
> > +
> > + prepare_ftrace_return(ip, parent, frame_pointer(regs));
> > +}
> > +#else
You deleted ftrace_graph_caller above from entry-ftrace.S, if we can get
here with some options, wouldn't that break the build?
-- Steve
> > /*
> > * Turn on/off the call to ftrace_graph_caller() in ftrace_caller()
> > * depending on @enable.
> > @@ -297,5 +313,6 @@ int ftrace_disable_ftrace_graph_caller(void)
> > {
> > return ftrace_modify_graph_caller(false);
> > }
> > +#endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
> > #endif /* CONFIG_DYNAMIC_FTRACE */
> > #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
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