linux-kernel - Re: [PATCH] tracing: Have unsigned int function args displayed as hexadecimal

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Message-Id: <20250804221958.501b5573a0ceb9f8d33c8a1a@kernel.org>
Date: Mon, 4 Aug 2025 22:19:58 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: LKML <linux-kernel@...r.kernel.org>, Linux Trace Kernel
 <linux-trace-kernel@...r.kernel.org>, Masami Hiramatsu
 <mhiramat@...nel.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 bpf@...r.kernel.org, Douglas Raillard <douglas.raillard@....com>
Subject: Re: [PATCH] tracing: Have unsigned int function args displayed as
 hexadecimal

On Thu, 31 Jul 2025 19:31:26 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> From: Steven Rostedt <rostedt@...dmis.org>
> 
> Most function arguments that are passed in as unsigned int or unsigned
> long are better displayed as hexadecimal than normal integer. For example,
> the functions:
> 
> static void __create_object(unsigned long ptr, size_t size,
> 				int min_count, gfp_t gfp, unsigned int objflags);
> 
> static bool stack_access_ok(struct unwind_state *state, unsigned long _addr,
> 			    size_t len);
> 
> void __local_bh_disable_ip(unsigned long ip, unsigned int cnt);
> 
> Show up in the trace as:
> 
>     __create_object(ptr=-131387050520576, size=4096, min_count=1, gfp=3264, objflags=0) <-kmem_cache_alloc_noprof
>     stack_access_ok(state=0xffffc9000233fc98, _addr=-60473102566256, len=8) <-unwind_next_frame
>     __local_bh_disable_ip(ip=-2127311112, cnt=256) <-handle_softirqs
> 
> Instead, by displaying unsigned as hexadecimal, they look more like this:
> 
>     __create_object(ptr=0xffff8881028d2080, size=0x280, min_count=1, gfp=0x82820, objflags=0x0) <-kmem_cache_alloc_node_noprof
>     stack_access_ok(state=0xffffc90000003938, _addr=0xffffc90000003930, len=0x8) <-unwind_next_frame
>     __local_bh_disable_ip(ip=0xffffffff8133cef8, cnt=0x100) <-handle_softirqs
> 
> Which is much easier to understand as most unsigned longs are usually just
> pointers. Even the "unsigned int cnt" in __local_bh_disable_ip() looks
> better as hexadecimal as a lot of flags are passed as unsigned.
> 

Looks good to me. Maybe this format is better for programers :)

Acked-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>

Thanks,

> Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
> ---
>  kernel/trace/trace_output.c | 17 ++++++++++++++++-
>  1 file changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
> index 0b3db02030a7..b18393d66a7f 100644
> --- a/kernel/trace/trace_output.c
> +++ b/kernel/trace/trace_output.c
> @@ -690,6 +690,12 @@ int trace_print_lat_context(struct trace_iterator *iter)
>  }
>  
>  #ifdef CONFIG_FUNCTION_TRACE_ARGS
> +
> +static u32 btf_type_int(const struct btf_type *t)
> +{
> +	return *(u32 *)(t + 1);
> +}
> +
>  void print_function_args(struct trace_seq *s, unsigned long *args,
>  			 unsigned long func)
>  {
> @@ -701,6 +707,8 @@ void print_function_args(struct trace_seq *s, unsigned long *args,
>  	struct btf *btf;
>  	s32 tid, nr = 0;
>  	int a, p, x;
> +	int int_data;
> +	u16 encode;
>  
>  	trace_seq_printf(s, "(");
>  
> @@ -744,7 +752,14 @@ void print_function_args(struct trace_seq *s, unsigned long *args,
>  			trace_seq_printf(s, "0x%lx", arg);
>  			break;
>  		case BTF_KIND_INT:
> -			trace_seq_printf(s, "%ld", arg);
> +			/* Get the INT encodoing */
> +			int_data = btf_type_int(t);
> +                        encode = BTF_INT_ENCODING(int_data);
> +                        /* Print unsigned ints as hex */
> +                        if (encode & BTF_INT_SIGNED)
> +				trace_seq_printf(s, "%ld", arg);
> +                        else
> +                                trace_seq_printf(s, "0x%lx", arg);
>  			break;
>  		case BTF_KIND_ENUM:
>  			trace_seq_printf(s, "%ld", arg);
> -- 
> 2.47.2
> 


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>