Re: [PATCH] arm64: ftrace: Define ftrace_stub_graph only with FUNCTION_GRAPH_TRACER

From: Mark Rutland
Date: Fri Nov 11 2022 - 11:09:44 EST


On Wed, Nov 09, 2022 at 07:28:31PM +0000, Sami Tolvanen wrote:
> The 0-day bot reports that arm64 builds with CONFIG_CFI_CLANG +
> CONFIG_FTRACE are broken when CONFIG_FUNCTION_GRAPH_TRACER is not
> enabled:
>
> ld.lld: error: undefined symbol: __kcfi_typeid_ftrace_stub_graph
> >>> referenced by entry-ftrace.S:299 (arch/arm64/kernel/entry-ftrace.S:299)
> >>> arch/arm64/kernel/entry-ftrace.o:(.text+0x48) in archive vmlinux.a
>
> This is caused by ftrace_stub_graph using SYM_TYPE_FUNC_START when
> the address of the function is not taken in any C translation unit.
>
> Fix the build by only defining ftrace_stub_graph when it's actually
> needed, i.e. with CONFIG_FUNCTION_GRAPH_TRACER.
>
> Link: https://lore.kernel.org/lkml/202210251659.tRMs78RH-lkp@xxxxxxxxx/
> Fixes: 883bbbffa5a4 ("ftrace,kcfi: Separate ftrace_stub() and ftrace_stub_graph()")
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
> Signed-off-by: Sami Tolvanen <samitolvanen@xxxxxxxxxx>

Acked-by: Mark Rutland <mark.rutland@xxxxxxx>

Mark.

> ---
> arch/arm64/kernel/entry-ftrace.S | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/arm64/kernel/entry-ftrace.S b/arch/arm64/kernel/entry-ftrace.S
> index 795344ab4ec4..322a831f8ede 100644
> --- a/arch/arm64/kernel/entry-ftrace.S
> +++ b/arch/arm64/kernel/entry-ftrace.S
> @@ -299,11 +299,11 @@ SYM_TYPED_FUNC_START(ftrace_stub)
> ret
> SYM_FUNC_END(ftrace_stub)
>
> +#ifdef CONFIG_FUNCTION_GRAPH_TRACER
> SYM_TYPED_FUNC_START(ftrace_stub_graph)
> ret
> SYM_FUNC_END(ftrace_stub_graph)
>
> -#ifdef CONFIG_FUNCTION_GRAPH_TRACER
> /*
> * void return_to_handler(void)
> *
>
> base-commit: f141df371335645ce29a87d9683a3f79fba7fd67
> --
> 2.38.1.431.g37b22c650d-goog
>