Re: [PATCH v8 3/8] ARM: ftrace: Enable HAVE_FUNCTION_GRAPH_RETVAL

[Donglin Peng]

On 2023/3/28 22:02, Russell King (Oracle) wrote:
> On Tue, Mar 28, 2023 at 06:43:14AM -0700, Donglin Peng wrote:
> > The commit d4815c5d1bbd ("function_graph: Support recording and printing
> > the return value of function") laid the groundwork for the for the
> > funcgraph-retval, and this modification makes it available on the
> > ARM platform.
> >
> > We introduce a new structure called fgraph_ret_regs for the ARM platform
> > to hold return registers and the frame pointer. We then fill its content
> > in the return_to_handler and pass its address to the function
> > ftrace_return_to_handler to record the return value.
> >
> > Signed-off-by: Donglin Peng <pengdonglin@xxxxxxxxxxxxxx>
> > ---
> > v8:
> >   - Modify the control range of CONFIG_HAVE_FUNCTION_GRAPH_RETVAL
> > ---
> >   arch/arm/Kconfig               |  1 +
> >   arch/arm/include/asm/ftrace.h  | 18 ++++++++++++++++++
> >   arch/arm/kernel/entry-ftrace.S |  6 +++++-
> >   3 files changed, 24 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> > index e24a9820e12f..73061379855a 100644
> > --- a/arch/arm/Kconfig
> > +++ b/arch/arm/Kconfig
> > @@ -98,6 +98,7 @@ config ARM
> >   	select HAVE_FAST_GUP if ARM_LPAE
> >   	select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL
> >   	select HAVE_FUNCTION_ERROR_INJECTION
> > +	select HAVE_FUNCTION_GRAPH_RETVAL if HAVE_FUNCTION_GRAPH_TRACER
> >   	select HAVE_FUNCTION_GRAPH_TRACER
> >   	select HAVE_FUNCTION_TRACER if !XIP_KERNEL
> >   	select HAVE_GCC_PLUGINS
> > diff --git a/arch/arm/include/asm/ftrace.h b/arch/arm/include/asm/ftrace.h
> > index 7e9251ca29fe..2ab4bee21d79 100644
> > --- a/arch/arm/include/asm/ftrace.h
> > +++ b/arch/arm/include/asm/ftrace.h
> > @@ -77,4 +77,22 @@ static inline bool arch_syscall_match_sym_name(const char *sym,
> >   
> >   #endif /* ifndef __ASSEMBLY__ */
> >   
> > +
> > +#ifndef __ASSEMBLY__
> > +struct fgraph_ret_regs {
> > +	unsigned long regs[4];
> > +	unsigned long fp;
> > +};
> > +
> > +static inline unsigned long fgraph_ret_regs_return_value(struct fgraph_ret_regs *ret_regs)
> > +{
> > +	return ret_regs->regs[0];
> > +}
> > +
> > +static inline unsigned long fgraph_ret_regs_frame_pointer(struct fgraph_ret_regs *ret_regs)
> > +{
> > +	return ret_regs->fp;
> > +}
> > +#endif
> > +
> >   #endif /* _ASM_ARM_FTRACE */
> > diff --git a/arch/arm/kernel/entry-ftrace.S b/arch/arm/kernel/entry-ftrace.S
> > index 3e7bcaca5e07..5f1e74555b25 100644
> > --- a/arch/arm/kernel/entry-ftrace.S
> > +++ b/arch/arm/kernel/entry-ftrace.S
> > @@ -257,11 +257,15 @@ ENDPROC(ftrace_graph_regs_caller)
> >   
> >   #ifdef CONFIG_FUNCTION_GRAPH_TRACER
> >   ENTRY(return_to_handler)
> > +	sub	sp, sp, #4
> >   	stmdb	sp!, {r0-r3}
> > -	add	r0, sp, #16		@ sp at exit of instrumented routine
> > +	add	r0, sp, #20		@ sp at exit of instrumented routine
> > +	str	r0, [sp, #16]
> > +	mov	r0, sp
>
> 1) EABI wants the stack to be aligned to 8 bytes.
> 2) We can do better than this.
>
> 	mov	ip, sp
> 	stmdb	sp!, {r0-r3, ip, lr}
> 	mov	r0, sp

Great, I will modify it.

> >   	bl	ftrace_return_to_handler
> >   	mov	lr, r0			@ r0 has real ret addr
> >   	ldmia	sp!, {r0-r3}
>
> 	ldmia	sp, {r0-r3}		@ since we need to manually adjust sp,

Thanks, I will modify it.

> > +	add	sp, sp, #4		@ skip fp
>
> 	add	sp, sp, #4 * 6		@ restore stack pointer here

Thanks, I will modify it.

> >   	ret	lr
> >   ENDPROC(return_to_handler)
> >   #endif
> > --
> > 2.25.1
> >
> >
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