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

[Andrew Morton <akpm@linux-foundation.org>]

On Wed, 23 Mar 2022 15:04:27 -0700 Luis Chamberlain <mcgrof@kernel.org> wrote:

> On Wed, Mar 23, 2022 at 10:17:42PM +0530, Maninder Singh wrote:
> > ---
> > module-next -> module-testing: Petr's review and test tag is picked from previous version,
> > current version has slight changes (module.c -> module/main.c). No functional change in patch,
> > only init_build_id() function is moved to module/main.c as it can be independent of
> > kallsyms.
> 
> Andrew,
> 
> I see this patch is merged on your tree, any chance we can yield until
> the next release and I can then take it under modules-next ? It would
> help given the slew of changes I now have queued up not for v5.18 but
> for v5.19. I'm delaying the modules changes for v5.19 given the timing,
> it is too soon to merge for v5.18 as I want tons of testing on this
> all on linux-next after v5.18-rc1 is out.
> 

I don't actually have this patch in -mm.  What I do have is the below,
which I shall now drop.  All yours to deal with as you see fit!



From: Maninder Singh <maninder1.s@samsung.com>
Subject: kallsyms: print module name in %ps/S case when KALLSYMS is disabled

original:
With KALLSYMS
                   %pS                               %ps
[16.4200]  hello_init+0x0/0x24 [crash]        hello_init [crash]

Without KALLSYMS:
[16.2200]      0xbe200040                         0xbe200040

With Patch (Without KALLSYMS:) load address + current offset [Module Name]

[13.5993]  0xbe200000+0x40 [crash]           0xbe200000+0x40 [crash]

It will help in better debugging and checking when KALLSYMS is disabled,
user will get information about module name and load address of module.

verified for arm64:
/ # insmod /crash.ko

[   19.263556] 0xffff800000ec0000+0x38 [crash]

..

[   19.276023] Call trace:
[   19.276277]  0xffff800000ec0000+0x28 [crash]
[   19.276567]  0xffff800000ec0000+0x58 [crash]
[   19.276727]  0xffff800000ec0000+0x74 [crash]
[   19.276866]  0xffff8000080127d0
[   19.276978]  0xffff80000812d95c
[   19.277085]  0xffff80000812f554

Link: https://lkml.kernel.org/r/20220201040044.1528568-1-maninder1.s@samsung.com
Signed-off-by: Vaneet Narang <v.narang@samsung.com>
Co-developed-by: Vaneet Narang <v.narang@samsung.com>
Signed-off-by: Maninder Singh <maninder1.s@samsung.com>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Steven Rostedt (Google) <rostedt@goodmis.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Miroslav Benes <mbenes@suse.cz>
Cc: Stephen Boyd <swboyd@chromium.org>
Cc: Miguel Ojeda <ojeda@kernel.org>
Cc: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/kallsyms.h |   27 +++++++++++++++++++++++++++
 lib/vsprintf.c           |    5 +++--
 2 files changed, 30 insertions(+), 2 deletions(-)

--- a/include/linux/kallsyms.h~kallsyms-print-module-name-in-%ps-s-case-when-kallsyms-is-disabled
+++ a/include/linux/kallsyms.h
@@ -163,6 +163,33 @@ static inline bool kallsyms_show_value(c
 	return false;
 }
 
+#ifdef CONFIG_MODULES
+static inline int fill_minimal_module_info(char *sym, int size, unsigned long value)
+{
+	struct module *mod;
+	unsigned long offset;
+	int ret = 0;
+
+	preempt_disable();
+	mod = __module_address(value);
+	if (mod) {
+		offset = value - (unsigned long)mod->core_layout.base;
+		snprintf(sym, size - 1, "0x%lx+0x%lx [%s]",
+				(unsigned long)mod->core_layout.base, offset, mod->name);
+
+		sym[size - 1] = '\0';
+		ret = 1;
+	}
+
+	preempt_enable();
+	return ret;
+}
+#else
+static inline int fill_minimal_module_info(char *sym, int size, unsigned long value)
+{
+	return 0;
+}
+#endif /*CONFIG_MODULES*/
 #endif /*CONFIG_KALLSYMS*/
 
 static inline void print_ip_sym(const char *loglvl, unsigned long ip)
--- a/lib/vsprintf.c~kallsyms-print-module-name-in-%ps-s-case-when-kallsyms-is-disabled
+++ a/lib/vsprintf.c
@@ -984,9 +984,7 @@ char *symbol_string(char *buf, char *end
 		    struct printf_spec spec, const char *fmt)
 {
 	unsigned long value;
-#ifdef CONFIG_KALLSYMS
 	char sym[KSYM_SYMBOL_LEN];
-#endif
 
 	if (fmt[1] == 'R')
 		ptr = __builtin_extract_return_addr(ptr);
@@ -1006,6 +1004,9 @@ char *symbol_string(char *buf, char *end
 
 	return string_nocheck(buf, end, sym, spec);
 #else
+	if (fill_minimal_module_info(sym, KSYM_SYMBOL_LEN, value))
+		return string_nocheck(buf, end, sym, spec);
+
 	return special_hex_number(buf, end, value, sizeof(void *));
 #endif
 }
_