Re: [PATCH] riscv: ftrace: only use pre-function NOPs with call ops

Re: [PATCH] riscv: ftrace: only use pre-function NOPs with call ops

[Rui Qi]

On 7/6/26 8:35 PM, Rui Qi wrote:
> Commit c217157bcd1d ("riscv: Implement
> HAVE_DYNAMIC_FTRACE_WITH_CALL_OPS") changed CC_FLAGS_FTRACE to use
> -fpatchable-function-entry=8,4 or -fpatchable-function-entry=4,2
> for all dynamic ftrace builds. That layout makes the compiler place an
> 8-byte area before the function entry, which is used as the per-callsite
> ftrace_ops literal when CONFIG_DYNAMIC_FTRACE_WITH_CALL_OPS is enabled.
> 
> RISC-V can still build with CONFIG_DYNAMIC_FTRACE=y and
> CONFIG_DYNAMIC_FTRACE_WITH_CALL_OPS=n, for example when
> CONFIG_CFI_CLANG is enabled because HAVE_DYNAMIC_FTRACE_WITH_CALL_OPS
> is selected only when !CFI_CLANG. In that configuration
> ftrace_call_adjust() does not skip the pre-function literal area and
> only returns addr + MCOUNT_AUIPC_SIZE. With the pre-function layout,
> that points into the pre-entry padding instead of the callsite jalr, so
> dynamic ftrace records the wrong patch address.
> 
> Use the pre-function literal layout only when call ops are enabled.
> Otherwise keep the previous patchable-function-entry counts so the
> recorded address matches ftrace_call_adjust() non-call-ops path.
> 
> Fixes: c217157bcd1d ("riscv: Implement HAVE_DYNAMIC_FTRACE_WITH_CALL_OPS")
> Cc: stable@vger.kernel.org
> Signed-off-by: Rui Qi <qirui.001@bytedance.com>
> ---
>  arch/riscv/Makefile | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
> index 3070c3874305..235730a243aa 100644
> --- a/arch/riscv/Makefile
> +++ b/arch/riscv/Makefile
> @@ -14,11 +14,19 @@ endif
>  ifeq ($(CONFIG_DYNAMIC_FTRACE),y)
>  	LDFLAGS_vmlinux += --no-relax
>  	KBUILD_CPPFLAGS += -DCC_USING_PATCHABLE_FUNCTION_ENTRY
> +ifeq ($(CONFIG_DYNAMIC_FTRACE_WITH_CALL_OPS),y)
>  ifeq ($(CONFIG_RISCV_ISA_C),y)
>  	CC_FLAGS_FTRACE := -fpatchable-function-entry=8,4
>  else
>  	CC_FLAGS_FTRACE := -fpatchable-function-entry=4,2
>  endif
> +else
> +ifeq ($(CONFIG_RISCV_ISA_C),y)
> +	CC_FLAGS_FTRACE := -fpatchable-function-entry=4
> +else
> +	CC_FLAGS_FTRACE := -fpatchable-function-entry=2
> +endif
> +endif
>  endif
>  
>  ifeq ($(CONFIG_CMODEL_MEDLOW),y)


Hi,

Gentle ping on this patch. It's been about two months since submission
without any review feedback.

The patch fixes a bug where ftrace_call_adjust() returns the wrong
patch address when CONFIG_DYNAMIC_FTRACE_WITH_CALL_OPS is disabled
(e.g., under CONFIG_CFI_CLANG), because the pre-function literal
layout is still used unconditionally.

Adding the ftrace maintainers and mailing list, which were missing
from the original submission — that likely explains the lack of
response.

Link:
https://lore.kernel.org/r/20260706123554.455065-1-qirui.001@bytedance.com

Thanks,
Rui