linux-kernel - Re: [PATCH] riscv: ftrace: Add parentheses in macro definitions of make_call_t0 and make_call

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Message-ID: <83830ab7-e15c-476f-b583-0df8d614f7cf@ghiti.fr>
Date: Wed, 26 Feb 2025 15:27:17 +0100
From: Alexandre Ghiti <alex@...ti.fr>
To: Juhan Jin <juhan.jin@...mail.com>, guoren@...nel.org,
 guoren@...ux.alibaba.com, rostedt@...dmis.org, mhiramat@...nel.org,
 mark.rutland@....com, paul.walmsley@...ive.com, palmer@...belt.com,
 aou@...s.berkeley.edu
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
 linux-riscv@...ts.infradead.org
Subject: Re: [PATCH] riscv: ftrace: Add parentheses in macro definitions of
 make_call_t0 and make_call_ra

Hi Juhan,

On 06/02/2025 20:28, Juhan Jin wrote:
> This patch adds parentheses to parameters caller and callee of macros
> make_call_t0 and make_call_ra. Every existing invocation of these two
> macros uses a single variable for each argument, so the absence of the
> parentheses seems okay. However, future invocations might use more
> complex expressions as arguments. For example, a future invocation might
> look like this: make_call_t0(a - b, c, call). Without parentheses in the
> macro definition, the macro invocation expands to:
>
> ...
> unsigned int offset = (unsigned long) c - (unsigned long) a - b;
> ...
>
> which is clearly wrong.
>
> The use of parentheses ensures arguments are correctly evaluated and
> potentially saves future users of make_call_t0 and make_call_ra debugging
> trouble.
>
> Fixes: 6724a76cff85 ("riscv: ftrace: Reduce the detour code size to half")
> Signed-off-by: Juhan Jin <juhan.jin@...mail.com>
> ---
>   arch/riscv/include/asm/ftrace.h | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.h
> index c4721ce44ca4..2636ee00ccf0 100644
> --- a/arch/riscv/include/asm/ftrace.h
> +++ b/arch/riscv/include/asm/ftrace.h
> @@ -92,7 +92,7 @@ struct dyn_arch_ftrace {
>   #define make_call_t0(caller, callee, call)				\
>   do {									\
>   	unsigned int offset =						\
> -		(unsigned long) callee - (unsigned long) caller;	\
> +		(unsigned long) (callee) - (unsigned long) (caller);	\
>   	call[0] = to_auipc_t0(offset);					\
>   	call[1] = to_jalr_t0(offset);					\
>   } while (0)
> @@ -108,7 +108,7 @@ do {									\
>   #define make_call_ra(caller, callee, call)				\
>   do {									\
>   	unsigned int offset =						\
> -		(unsigned long) callee - (unsigned long) caller;	\
> +		(unsigned long) (callee) - (unsigned long) (caller);	\
>   	call[0] = to_auipc_ra(offset);					\
>   	call[1] = to_jalr_ra(offset);					\
>   } while (0)
>
> base-commit: 2014c95afecee3e76ca4a56956a936e23283f05b


Probably not worth going into fixes since the problem is not around for 
now, but that's still a good catch:

Reviewed-by: Alexandre Ghiti <alexghiti@...osinc.com>

Thanks,

Alex