parisc: Report trap type as human readable string

When faulting on some trap, the kernel currently reports in dmesg:

 do_page_fault() command='perl' type=6 address=0xbe400403 in libcrypt-2.24.so[f9086000+9000]
 vm_start = 0x00922000, vm_end = 0x00aed000

With this change the trap type additionally gets reported as human readable
string which makes it simpler to recognize the type of problem:

 do_page_fault() command='perl' type=6 address=0xbe400403 in libcrypt-2.24.so[f9086000+9000]
 trap #6: Instruction TLB miss fault, vm_start = 0x00922000, vm_end = 0x00aed000
Signed-off-by: Helge Deller <deller@gmx.de>

arch/parisc/mm/fault.c

@@ -167,6 +167,43 @@ int fixup_exception(struct pt_regs *regs)
 	return 0;
 }
 
+/*
+ * parisc hardware trap list
+ *
+ * Documented in section 3 "Addressing and Access Control" of the
+ * "PA-RISC 1.1 Architecture and Instruction Set Reference Manual"
+ * https://parisc.wiki.kernel.org/index.php/File:Pa11_acd.pdf
+ *
+ * For implementation see handle_interruption() in traps.c
+ */
+static const char * const trap_description[] = {
+	[1] "High-priority machine check (HPMC)",
+	[2] "Power failure interrupt",
+	[3] "Recovery counter trap",
+	[5] "Low-priority machine check",
+	[6] "Instruction TLB miss fault",
+	[7] "Instruction access rights / protection trap",
+	[8] "Illegal instruction trap",
+	[9] "Break instruction trap",
+	[10] "Privileged operation trap",
+	[11] "Privileged register trap",
+	[12] "Overflow trap",
+	[13] "Conditional trap",
+	[14] "FP Assist Exception trap",
+	[15] "Data TLB miss fault",
+	[16] "Non-access ITLB miss fault",
+	[17] "Non-access DTLB miss fault",
+	[18] "Data memory protection/unaligned access trap",
+	[19] "Data memory break trap",
+	[20] "TLB dirty bit trap",
+	[21] "Page reference trap",
+	[22] "Assist emulation trap",
+	[25] "Taken branch trap",
+	[26] "Data memory access rights trap",
+	[27] "Data memory protection ID trap",
+	[28] "Unaligned data reference trap",
+};
+
 /*
  * Print out info about fatal segfaults, if the show_unhandled_signals
  * sysctl is set:
@@ -176,6 +213,8 @@ show_signal_msg(struct pt_regs *regs, unsigned long code,
 		unsigned long address, struct task_struct *tsk,
 		struct vm_area_struct *vma)
 {
+	const char *trap_name = NULL;
+
 	if (!unhandled_signal(tsk, SIGSEGV))
 		return;
 
@@ -186,8 +225,15 @@ show_signal_msg(struct pt_regs *regs, unsigned long code,
 	pr_warn("do_page_fault() command='%s' type=%lu address=0x%08lx",
 	    tsk->comm, code, address);
 	print_vma_addr(KERN_CONT " in ", regs->iaoq[0]);
+
+	if (code < ARRAY_SIZE(trap_description))
+		trap_name = trap_description[code];
+	pr_warn(KERN_CONT " trap #%lu: %s%c", code,
+		trap_name ? trap_name : "unknown",
+		vma ? ',':'\n');
+
 	if (vma)
-		pr_warn(" vm_start = 0x%08lx, vm_end = 0x%08lx\n",
+		pr_warn(KERN_CONT " vm_start = 0x%08lx, vm_end = 0x%08lx\n",
 				vma->vm_start, vma->vm_end);
 
 	show_regs(regs);