linux-kernel - Re: [PATCH 1/1] kallsyms: enhance %pS/s/b printing when KALLSYSMS is disabled

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Date:   Mon, 28 Feb 2022 14:03:30 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Maninder Singh <maninder1.s@...sung.com>
Cc:     mcgrof@...nel.org, pmladek@...e.com, rostedt@...dmis.org,
        senozhatsky@...omium.org, linux@...musvillemoes.dk,
        akpm@...ux-foundation.org, wangkefeng.wang@...wei.com,
        v.narang@...sung.com, swboyd@...omium.org, ojeda@...nel.or,
        linux-kernel@...r.kernel.org, linux-modules@...r.kernel.org,
        avimalin@...il.com, atomlin@...hat.com
Subject: Re: [PATCH 1/1] kallsyms: enhance %pS/s/b printing when KALLSYSMS is
 disabled

On Mon, Feb 28, 2022 at 11:04:47AM +0530, Maninder Singh wrote:
> with commit '82b37e632513 ("kallsyms: print module name in %ps/S
> case when KALLSYMS is disabled"), module name printing was enhanced.
> 
> As per suggestion from Petr Mladek <pmladek@...e.com>, covering
> other flavours also to print build id also.
> 
> for %pB no change as it needs to know symbol name to adjust address
> value which can't be done without KALLSYMS.
> 
> original output with KALLSYMS:
> [8.842129] ps function_1 [crash]
> [8.842735] pS function_1+0x4/0x2c [crash]
> [8.842890] pSb function_1+0x4/0x2c [crash b367e79021b9f3b0172f9a36d4261c1f528ca1b3]
> [8.843175] pB function_1+0x4/0x2c [crash]
> [8.843362] pBb function_1+0x4/0x2c [crash b367e79021b9f3b0172f9a36d4261c1f528ca1b3]
> 
> original output without KALLSYMS:
> [12.487424] ps 0xffff800000eb008c
> [12.487598] pS 0xffff800000eb008c
> [12.487723] pSb 0xffff800000eb008c
> [12.487850] pB 0xffff800000eb008c
> [12.487967] pBb 0xffff800000eb008c
> 
> With patched kernel without KALLSYMS:
> [9.205207] ps 0xffff800000eb008c [crash]
> [9.205564] pS 0xffff800000eb0000+0x8c [crash]
> [9.205757] pSb 0xffff800000eb0000+0x8c [crash b367e79021b9f3b0172f9a36d4261c1f528ca1b3]
> [9.206066] pB 0xffff800000eb0000+0x8c [crash]
> [9.206257] pBb 0xffff800000eb0000+0x8c [crash b367e79021b9f3b0172f9a36d4261c1f528ca1b3]

...

> +static int sprint_module_info(char *buf, char *end, unsigned long value,
> +			     const char *fmt)
> +{
> +	struct module *mod;
> +	unsigned long offset = 1;
> +	unsigned long base;

> +	int ret = 0;

This is hard to find if it's not close to the first use.
Since you are using positive numbers...

> +	const char *modname;
> +	int modbuildid = 0;
> +	int len;
> +#if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID)
> +	const unsigned char *buildid = NULL;
> +#endif
> +
> +	if (is_ksym_addr(value))
> +		return 0;

> +	if (*fmt == 'B' && fmt[1] == 'b')
> +		modbuildid = 1;
> +	else if (*fmt == 'S' && (fmt[1] == 'b' || (fmt[1] == 'R' && fmt[2] == 'b')))

Why not to split to two conditionals? Would be easier to get,

> +		modbuildid = 1;
> +	else if (*fmt != 's') {

These all are inconsistent, please switch to fmt[0].

> +		/*
> +		 * do nothing.
> +		 */
> +	} else
> +		offset = 0;
> +
> +	preempt_disable();
> +	mod = __module_address(value);
> +	if (mod) {
> +		ret = 1;
> +		modname = mod->name;
> +#if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID)
> +		if (modbuildid)
> +			buildid = mod->build_id;
> +#endif
> +		if (offset) {
> +			base = (unsigned long)mod->core_layout.base;
> +			offset = value - base;
> +		}
> +	}
> +
> +	preempt_enable();

> +	if (!ret)

This looks a bit strange, but okay, I'm not familiar with the function of this
code.

> +		return 0;
> +
> +	/* address belongs to module */
> +	if (offset)
> +		len = sprintf(buf, "0x%lx+0x%lx", base, offset);
> +	else
> +		len = sprintf(buf, "0x%lx", value);
> +
> +	len += sprintf(buf + len, " [%s", modname);
> +#if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID)
> +	if (modbuildid && buildid) {
> +		/* build ID should match length of sprintf */
> +		static_assert(sizeof(typeof_member(struct module, build_id)) == 20);
> +		len += sprintf(buf + len, " %20phN", buildid);
> +	}
> +#endif
> +	len += sprintf(buf + len, "]");
> +
> +	return len;
> +}

-- 
With Best Regards,
Andy Shevchenko