linux-kernel - Re: [PATCH v3 04/12] module: Add printk format to add module build ID to stacktraces

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Message-ID: <YG3J03GY+QqtKMlu@alley>
Date:   Wed, 7 Apr 2021 17:03:47 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, Jiri Olsa <jolsa@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Jessica Yu <jeyu@...nel.org>,
        Evan Green <evgreen@...omium.org>,
        Hsin-Yi Wang <hsinyi@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        linux-doc@...r.kernel.org, Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH v3 04/12] module: Add printk format to add module build
 ID to stacktraces

On Tue 2021-03-30 20:05:12, Stephen Boyd wrote:
> Let's make kernel stacktraces easier to identify by including the build
> ID[1] of a module if the stacktrace is printing a symbol from a module.
> This makes it simpler for developers to locate a kernel module's full
> debuginfo for a particular stacktrace. Combined with
> scripts/decode_stracktrace.sh, a developer can download the matching
> debuginfo from a debuginfod[2] server and find the exact file and line
> number for the functions plus offsets in a stacktrace that match the
> module. This is especially useful for pstore crash debugging where the
> kernel crashes are recorded in something like console-ramoops and the
> recovery kernel/modules are different or the debuginfo doesn't exist on
> the device due to space concerns (the debuginfo can be too large for
> space limited devices).
> 
> @@ -359,15 +369,17 @@ int lookup_symbol_attrs(unsigned long addr, unsigned long *size,
>  
>  /* Look up a kernel symbol and return it in a text buffer. */
>  static int __sprint_symbol(char *buffer, unsigned long address,
> -			   int symbol_offset, int add_offset)
> +			   int symbol_offset, int add_offset, int add_buildid)
>  {
>  	char *modname;
> +	const unsigned char *buildid;
>  	const char *name;
>  	unsigned long offset, size;
>  	int len;
>  
>  	address += symbol_offset;
> -	name = kallsyms_lookup(address, &size, &offset, &modname, buffer);
> +	name = kallsyms_lookup_buildid(address, &size, &offset, &modname, &buildid,
> +				       buffer);
>  	if (!name)
>  		return sprintf(buffer, "0x%lx", address - symbol_offset);
>  
> @@ -379,8 +391,12 @@ static int __sprint_symbol(char *buffer, unsigned long address,
>  	if (add_offset)
>  		len += sprintf(buffer + len, "+%#lx/%#lx", offset, size);

Please add something like:

	/* Keep BUILD_ID_SIZE_MAX in sync with the below used %20phN */
	BUILD_BUG_ON(BUILD_ID_SIZE_MAX != 20)

to make sure the the hard

>  
> -	if (modname)
> -		len += sprintf(buffer + len, " [%s]", modname);
> +	if (modname) {
> +		len += sprintf(buffer + len, " [%s", modname);
> +		if (IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID) && add_buildid && buildid)
> +			len += sprintf(buffer + len, " %20phN", buildid);
> +		len += sprintf(buffer + len, "]");
> +	}
>  
>  	return len;
>  }

Otherwise the approach looks fine to me. The main problem is that it
does not work for me as described in the other reply ;-)

Best Regards,
Petr