Re: [PATCH 1/9] LoongArch/ftrace: Add basic support

[Qing Zhang]

On 2022/8/20 上午1:25, Steven Rostedt wrote:
> On Fri, 19 Aug 2022 16:13:55 +0800
> Qing Zhang <zhangqing@xxxxxxxxxxx> wrote:
>
> > +#define MCOUNT_STACK_SIZE	(2 * SZREG)
> > +#define MCOUNT_S0_OFFSET	(0)
> > +#define MCOUNT_RA_OFFSET	(SZREG)
> > +
> > +	.macro MCOUNT_SAVE_REGS
> > +	PTR_ADDI sp, sp, -MCOUNT_STACK_SIZE
> > +	PTR_S	s0, sp, MCOUNT_S0_OFFSET
> > +	PTR_S	ra, sp, MCOUNT_RA_OFFSET
> > +	move	s0, a0
> > +	.endm
> > +
> > +	.macro MCOUNT_RESTORE_REGS
> > +	move	a0, s0
> > +	PTR_L	ra, sp, MCOUNT_RA_OFFSET
> > +	PTR_L	s0, sp, MCOUNT_S0_OFFSET
> > +	PTR_ADDI sp, sp, MCOUNT_STACK_SIZE
> > +	.endm
> > +
> > +
> > +SYM_FUNC_START(_mcount)
> > +	la	t1, ftrace_stub
> > +	la	t2, ftrace_trace_function	/* Prepare t2 for (1) */
> > +	PTR_L	t2, t2, 0
> > +	beq	t1, t2, fgraph_trace
> > +
> > +	MCOUNT_SAVE_REGS
> > +
> > +	move	a0, ra				/* arg0: self return address */
> > +	move	a1, s0				/* arg1: parent's return address */
> > +	jirl	ra, t2, 0			/* (1) call *ftrace_trace_function */
> > +
> > +	MCOUNT_RESTORE_REGS
>
> You know, if you can implement CONFIG_FTRACE_WITH_ARGS, where the default
> function callback gets a ftrace_regs pointer (that only holds what is
> needed for the arguments of the function as well as the stack pointer),
> then you could also implement function graph on top of that, and remove the
> need for the below "fgraph_trace" trampoline.
>
> I'd really would like all architectures to go that way. Also, the
> CONFIG_FTRACE_WITH_ARGS is all you need for live kernel patching.
Hi, Steve
I will add the implementation of CONFIG_FTRACE_WITH_ARGS in v2.

Thanks,
- Qing
> -- Steve
>
>
> > +
> > +fgraph_trace:
> > +#ifdef	CONFIG_FUNCTION_GRAPH_TRACER
> > +	la	t1, ftrace_stub
> > +	la	t3, ftrace_graph_return
> > +	PTR_L	t3, t3, 0
> > +	bne	t1, t3, ftrace_graph_caller
> > +	la	t1, ftrace_graph_entry_stub
> > +	la	t3, ftrace_graph_entry
> > +	PTR_L	t3, t3, 0
> > +	bne	t1, t3, ftrace_graph_caller
> > +#endif
> > +
> > +	.globl ftrace_stub
> > +ftrace_stub:
> > +	jirl	zero, ra, 0
> > +SYM_FUNC_END(_mcount)
> > +EXPORT_SYMBOL(_mcount)
> > +
> > +#ifdef CONFIG_FUNCTION_GRAPH_TRACER
> > +SYM_FUNC_START(ftrace_graph_caller)
> > +	MCOUNT_SAVE_REGS
> > +
> > +	PTR_ADDI	a0, ra, -4			/* arg0: Callsite self return addr */
> > +	PTR_ADDI	a1, sp, MCOUNT_STACK_SIZE	/* arg1: Callsite sp */
> > +	move	a2, s0					/* arg2: Callsite parent ra */
> > +	bl	prepare_ftrace_return
> > +
> > +	MCOUNT_RESTORE_REGS
> > +	jirl	zero, ra, 0
> > +SYM_FUNC_END(ftrace_graph_caller)