linux-kernel - Re: [PATCH] tracing: Use _text and the kernel offset in last_boot

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Message-Id: <20250328063848.8d4a71fbb8e2a969c46bb27d@kernel.org>
Date: Fri, 28 Mar 2025 06:38:48 +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>
Subject: Re: [PATCH] tracing: Use _text and the kernel offset in
 last_boot_info

On Wed, 26 Mar 2025 22:03:04 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> From: Steven Rostedt <rostedt@...dmis.org>
> 
> Instead of using kaslr_offset() just record the location of "_text". This
> makes it possible for user space to use either the System.map or
> /proc/kallsyms as what to map all addresses to functions with.
> 

Looks good to me.

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

Thank you,


> Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
> ---
>  kernel/trace/trace.c | 18 ++++++------------
>  1 file changed, 6 insertions(+), 12 deletions(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 85128ef96246..3b8f5e3313e0 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -51,7 +51,7 @@
>  #include <linux/workqueue.h>
>  #include <linux/sort.h>
>  
> -#include <asm/setup.h> /* COMMAND_LINE_SIZE and kaslr_offset() */
> +#include <asm/setup.h> /* COMMAND_LINE_SIZE */
>  
>  #include "trace.h"
>  #include "trace_output.h"
> @@ -5995,7 +5995,7 @@ struct trace_mod_entry {
>  };
>  
>  struct trace_scratch {
> -	unsigned long		kaslr_addr;
> +	unsigned long		text_addr;
>  	unsigned long		nr_entries;
>  	struct trace_mod_entry	entries[];
>  };
> @@ -6137,11 +6137,7 @@ static void update_last_data(struct trace_array *tr)
>  	kfree_rcu(module_delta, rcu);
>  
>  	/* Set the persistent ring buffer meta data to this address */
> -#ifdef CONFIG_RANDOMIZE_BASE
> -	tscratch->kaslr_addr = kaslr_offset();
> -#else
> -	tscratch->kaslr_addr = 0;
> -#endif
> +	tscratch->text_addr = (unsigned long)_text;
>  }
>  
>  /**
> @@ -7000,7 +6996,7 @@ static void show_last_boot_header(struct seq_file *m, struct trace_array *tr)
>  	 * should not be the same as the current boot.
>  	 */
>  	if (tscratch && (tr->flags & TRACE_ARRAY_FL_LAST_BOOT))
> -		seq_printf(m, "%lx\t[kernel]\n", tscratch->kaslr_addr);
> +		seq_printf(m, "%lx\t[kernel]\n", tscratch->text_addr);
>  	else
>  		seq_puts(m, "# Current\n");
>  }
> @@ -9465,10 +9461,8 @@ static void setup_trace_scratch(struct trace_array *tr,
>  	tr->scratch = tscratch;
>  	tr->scratch_size = size;
>  
> -#ifdef CONFIG_RANDOMIZE_BASE
> -	if (tscratch->kaslr_addr)
> -		tr->text_delta = kaslr_offset() - tscratch->kaslr_addr;
> -#endif
> +	if (tscratch->text_addr)
> +		tr->text_delta = (unsigned long)_text - tscratch->text_addr;
>  
>  	if (struct_size(tscratch, entries, tscratch->nr_entries) > size)
>  		goto reset;
> -- 
> 2.47.2
> 


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