Re: [PATCH v4 10/12] riscv: Implement HAVE_DYNAMIC_FTRACE_WITH_CALL_OPS

[Conor Dooley <conor@kernel.org>]

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On Mon, Feb 23, 2026 at 03:41:26PM +0000, Puranjay Mohan wrote:
> On Mon, Feb 23, 2026 at 3:28 PM Conor Dooley <conor.dooley@microchip.com> wrote:
> >
> > On Mon, Feb 23, 2026 at 03:18:17PM +0000, Puranjay Mohan wrote:
> > > On Sat, Feb 21, 2026 at 12:15 PM Conor Dooley <conor@kernel.org> wrote:
> > > >
> > > > Hey,
> > > >
> > > > On Tue, Apr 08, 2025 at 02:08:34AM +0800, Andy Chiu wrote:
> > > > > From: Puranjay Mohan <puranjay12@gmail.com>
> > > > >
> > > > > This patch enables support for DYNAMIC_FTRACE_WITH_CALL_OPS on RISC-V.
> > > > > This allows each ftrace callsite to provide an ftrace_ops to the common
> > > > > ftrace trampoline, allowing each callsite to invoke distinct tracer
> > > > > functions without the need to fall back to list processing or to
> > > > > allocate custom trampolines for each callsite. This significantly speeds
> > > > > up cases where multiple distinct trace functions are used and callsites
> > > > > are mostly traced by a single tracer.

> > > > >
> > > > > Signed-off-by: Puranjay Mohan <puranjay12@gmail.com>
> > > > >
> > > > > [update kconfig, asm, refactor]
> > > > >
> > > > > Signed-off-by: Andy Chiu <andybnac@gmail.com>
> > > > > Tested-by: Björn Töpel <bjorn@rivosinc.com>
> > > >
> > > > I bisected a boot failure to this commit [c217157bcd1df ("riscv:
> > > > Implement HAVE_DYNAMIC_FTRACE_WITH_CALL_OPS")] yesterday, that appears
> > > > to be affecting all LLVM versions that I currently have installed. From
> > > > some initial testing of Kconfig options, it looks like the issue is
> > > > CFI_CLANG related because when I disable CFI_CLANG things work once
> > > > more. Since this option depends on !CFI_CLANG, but is def_bool y, I
> > > > modified Kconfig to force disable it at all times and tested
> > > > !DYNAMIC_FTRACE_WITH_CALL_OPS && !CFG_CLANG, which did boot.
> > > >
> > > > I dunno anything about what's going on in this patch, but so little in
> > > > it relates to having DYNAMIC_FTRACE_WITH_CALL_OPS, that I was able to
> > > > figure out that the problem is -fpatchable-function-entry=8,4
> > > >
> > >
> > > DYNAMIC_FTRACE_WITH_CALL_OPS can't work together with CFI_CLANG.
> > >
> > > arm64 has:
> > >
> > > select HAVE_DYNAMIC_FTRACE_WITH_CALL_OPS \
> > > if (DYNAMIC_FTRACE_WITH_ARGS && !CFI && \
> > >    (CC_IS_CLANG || !CC_OPTIMIZE_FOR_SIZE))
> > >
> > > would need something similar for riscv if not already done.
> >
> >
> > I think you've misunderstood my email. We already have:
> >
> >         select HAVE_DYNAMIC_FTRACE_WITH_CALL_OPS if (DYNAMIC_FTRACE_WITH_ARGS && !CFI)
> >
> > The problem is that the patch broke using CFI_CLANG, due to the
> > fpatchable-function-entry change.
> 
> 
> Yeah, sorry I did not see the patch,
> the original one I sent had:
> 
> +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
> 
> 
> The basic Idea is that we can't put nops before the function entry
> when using CFI_CLANG, because they both interfere with each other.
> 
> the fix should be something like:

Ye, this is what Nathan and I both did locally, give or take. I just
wasn't sure if this was actually correct to do or if it was just
papering over an issue with our CFI support. Do you want to send this as
a patch?

> 
> -- >8 --
> 
> diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
> index 371da75a47f9..94100810a6a4 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)
> 
> -- 8< --
> 
> 
> Thanks,
> Puranjay

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