Re: [PATCH 3/3] riscv: Select HAVE_DYNAMIC_FTRACE when -fpatchable-function-entry is available

[Fangrui Song]

On 2021-03-25, Nathan Chancellor wrote:
> clang prior to 13.0.0 does not support -fpatchable-function-entry for
> RISC-V.
>
> clang: error: unsupported option '-fpatchable-function-entry=8' for target 'riscv64-unknown-linux-gnu'
>
> To avoid this error, only select HAVE_DYNAMIC_FTRACE when this option is
> not available.

If clang -fpatchable-function-entry=8 does not error "unsupported
option" for one target, it means the backend feature is supported on
this target.

Reviewed-by: Fangrui Song <maskray@xxxxxxxxxx>

> Fixes: afc76b8b8011 ("riscv: Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT")
> Link: https://github.com/ClangBuiltLinux/linux/issues/1268
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
> Signed-off-by: Nathan Chancellor <nathan@xxxxxxxxxx>
> ---
> arch/riscv/Kconfig | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 87d7b52f278f..ba1d07640b66 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -227,7 +227,7 @@ config ARCH_RV64I
> 	bool "RV64I"
> 	select 64BIT
> 	select ARCH_SUPPORTS_INT128 if CC_HAS_INT128 && GCC_VERSION >= 50000
> -	select HAVE_DYNAMIC_FTRACE if MMU
> +	select HAVE_DYNAMIC_FTRACE if MMU && $(cc-option,-fpatchable-function-entry=8)
> 	select HAVE_DYNAMIC_FTRACE_WITH_REGS if HAVE_DYNAMIC_FTRACE
> 	select HAVE_FTRACE_MCOUNT_RECORD
> 	select HAVE_FUNCTION_GRAPH_TRACER
> --
> 2.31.0
>
> --
> You received this message because you are subscribed to the Google Groups "Clang Built Linux" group.
> To unsubscribe from this group and stop receiving emails from it, send an email to clang-built-linux+unsubscribe@xxxxxxxxxxxxxxxx.
> To view this discussion on the web visit https://groups.google.com/d/msgid/clang-built-linux/20210325223807.2423265-4-nathan%40kernel.org.