Re: [PATCH v16 04/18] function_graph: Replace fgraph_ret_regs with ftrace_regs

Heiko Carstens
2024-10-15T18:39:48Z

On Tue, Oct 15, 2024 at 10:29:17AM +0900, Masami Hiramatsu (Google) wrote:
> From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
>
> Use ftrace_regs instead of fgraph_ret_regs for tracing return value
> on function_graph tracer because of simplifying the callback interface.
>
> The CONFIG_HAVE_FUNCTION_GRAPH_RETVAL is also replaced by
> CONFIG_HAVE_FUNCTION_GRAPH_FREGS.
>
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

...

> diff --git a/arch/s390/kernel/mcount.S b/arch/s390/kernel/mcount.S
> index 7e267ef63a7f..a9ca56ea0858 100644
> --- a/arch/s390/kernel/mcount.S
> +++ b/arch/s390/kernel/mcount.S
> @@ -134,14 +134,15 @@ SYM_CODE_END(ftrace_common)
> SYM_FUNC_START(return_to_handler)
> stmg %r2,%r5,32(%r15)
> lgr %r1,%r15
> - aghi %r15,-(STACK_FRAME_OVERHEAD+__FGRAPH_RET_SIZE)
> + aghi %r15,-(STACK_FRAME_OVERHEAD+STACK_FRAME_SIZE_FREGS)
> stg %r1,__SF_BACKCHAIN(%r15)
> - la %r3,STACK_FRAME_OVERHEAD(%r15)
> - stg %r1,__FGRAPH_RET_FP(%r3)
> - stg %r2,__FGRAPH_RET_GPR2(%r3)
> - lgr %r2,%r3
> + la %r4,STACK_FRAME_OVERHEAD(%r15)
> + stg %r2,__PT_R2(%r4)
> + stg %r3,__PT_R3(%r4)
> + stg %r1,__PT_R15(%r4)
> + lgr %r2,%r4
> brasl %r14,ftrace_return_to_handler
> - aghi %r15,STACK_FRAME_OVERHEAD+__FGRAPH_RET_SIZE
> + aghi %r15,STACK_FRAME_SIZE_FREGS
> lgr %r14,%r2
> lmg %r2,%r5,32(%r15)
> BR_EX %r14

Why didn't you simply merge the addon patch which I provided, and
which I tested?
https://lore.kernel.org/all/20240916121656.20933-B-hca@linux.ibm.com

That would make things much simpler... e.g. your new patch is also
writing r3 to fregs, why? The stackframe allocation is also wrong.
I didn't try, but I guess the above code would crash instantly.