ARM: reduce the information printed in call traces

A while back, Linus complained about the numeric values printed by the
ARM backtracing code. Printing these values does not make sense if one
does not have access to the kernel ELF image (as is normally the case
when helping a third party on a mailing list), but if one does, they
can be very useful to find the code, rather than searching for the
function name, and then doing hex math to work out where the backtrace
entry is referring to.

Provide an option to control whether this information is included,
which will only be visible if EXPERT is enabled.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

arch/arm/Kconfig.debug

@@ -81,6 +81,17 @@ endchoice
 config ARM_UNWIND
 	bool
 
+config BACKTRACE_VERBOSE
+	bool "Verbose backtrace"
+	depends on EXPERT
+	help
+	  When the kernel produces a warning or oops, the kernel prints a
+	  trace of the call chain. This option controls whether we include
+	  the numeric addresses or only include the symbolic information.
+
+	  In most cases, say N here, unless you are intending to debug the
+	  kernel and have access to the kernel binary image.
+
 config FRAME_POINTER
 	bool
 

arch/arm/kernel/traps.c

@@ -67,12 +67,14 @@ void dump_backtrace_entry(unsigned long where, unsigned long from,
 {
 	unsigned long end = frame + 4 + sizeof(struct pt_regs);
 
-#ifdef CONFIG_KALLSYMS
+#ifndef CONFIG_KALLSYMS
+	printk("%sFunction entered at [<%08lx>] from [<%08lx>]\n",
+		loglvl, where, from);
+#elif defined CONFIG_BACKTRACE_VERBOSE
 	printk("%s[<%08lx>] (%ps) from [<%08lx>] (%pS)\n",
 		loglvl, where, (void *)where, from, (void *)from);
 #else
-	printk("%sFunction entered at [<%08lx>] from [<%08lx>]\n",
-		loglvl, where, from);
+	printk("%s %ps from %pS\n", loglvl, (void *)where, (void *)from);
 #endif
 
 	if (in_entry_text(from) && end <= ALIGN(frame, THREAD_SIZE))