[PATCH] riscv: tracing: Fix __write_overflow_field in ftrace_partial_regs()

[Alexandre Ghiti]

Hi Charlie,

On 25/02/2025 03:42, Charlie Jenkins wrote:
> The size of &regs->a0 is unknown, causing the error:
>
> ../include/linux/fortify-string.h:571:25: warning: call to
> '__write_overflow_field' declared with attribute warning: detected write
> beyond size of field (1st parameter); maybe use struct_group()?
> [-Wattribute-warning]


I can't reproduce this warning with gcc and llvm, even when setting by 
hand -Wattribute-warning when compiling bpf_trace.c (which is the user 
of ftrace_partial_regs()).

Which toolchain did you use?

Thanks,

Alex


>
> Fix this by wrapping the required registers in pt_regs with
> struct_group() and reference the group when doing the offending
> memcpy().
>
> Signed-off-by: Charlie Jenkins <charlie at rivosinc.com>
> ---
>   arch/riscv/include/asm/ftrace.h |  2 +-
>   arch/riscv/include/asm/ptrace.h | 18 ++++++++++--------
>   2 files changed, 11 insertions(+), 9 deletions(-)
>
> diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.h
> index c4721ce44ca474654b37b3d51bc0a63d46bc1eff..ec6db1162021fbf4fa48fc87e7984266040aa7d9 100644
> --- a/arch/riscv/include/asm/ftrace.h
> +++ b/arch/riscv/include/asm/ftrace.h
> @@ -207,7 +207,7 @@ ftrace_partial_regs(const struct ftrace_regs *fregs, struct pt_regs *regs)
>   {
>   	struct __arch_ftrace_regs *afregs = arch_ftrace_regs(fregs);
>   
> -	memcpy(&regs->a0, afregs->args, sizeof(afregs->args));
> +	memcpy(&regs->a_regs, afregs->args, sizeof(afregs->args));
>   	regs->epc = afregs->epc;
>   	regs->ra = afregs->ra;
>   	regs->sp = afregs->sp;
> diff --git a/arch/riscv/include/asm/ptrace.h b/arch/riscv/include/asm/ptrace.h
> index b5b0adcc85c18e15c156de11172a5d7f03ada037..2910231977cb71dac3cc42f2dc32590284204057 100644
> --- a/arch/riscv/include/asm/ptrace.h
> +++ b/arch/riscv/include/asm/ptrace.h
> @@ -23,14 +23,16 @@ struct pt_regs {
>   	unsigned long t2;
>   	unsigned long s0;
>   	unsigned long s1;
> -	unsigned long a0;
> -	unsigned long a1;
> -	unsigned long a2;
> -	unsigned long a3;
> -	unsigned long a4;
> -	unsigned long a5;
> -	unsigned long a6;
> -	unsigned long a7;
> +	struct_group(a_regs,
> +		unsigned long a0;
> +		unsigned long a1;
> +		unsigned long a2;
> +		unsigned long a3;
> +		unsigned long a4;
> +		unsigned long a5;
> +		unsigned long a6;
> +		unsigned long a7;
> +	);
>   	unsigned long s2;
>   	unsigned long s3;
>   	unsigned long s4;
>
> ---
> base-commit: d082ecbc71e9e0bf49883ee4afd435a77a5101b6
> change-id: 20250224-fix_ftrace_partial_regs-eddaf4a7e5ed