[Crash-utility] [PATCH] Fix x86 initialization for {hard, soft}irq_ctx

[OGAWA Hirofumi]

Current code is setting {hard,soft}irq_ctx[] to (irq_ctx **), because
per_cpu symbol itself is pointer of specified type (irq_ctx *).

But, I wonder how this works in past, the code is expecting
{hard,soft}_ctx[] are (irq_ctx *). This fixes by deref per_cpu in
initialization, and set expected pointers.

Tested on i386 v3.10.

---

 task.c |   28 ++++++++++++++++++++++++----
 1 file changed, 24 insertions(+), 4 deletions(-)

diff -puN task.c~ia32-irq-stack-fix task.c
--- crash-64/task.c~ia32-irq-stack-fix	2017-02-08 17:37:33.126367767 +0900
+++ crash-64-hirofumi/task.c	2017-02-08 17:46:06.900703326 +0900
@@ -570,10 +570,20 @@ irqstacks_init(void)
 	if ((hard_sp = per_cpu_symbol_search("per_cpu__hardirq_ctx"))) {
 		if ((kt->flags & SMP) && (kt->flags & PER_CPU_OFF)) {
 			for (i = 0; i < NR_CPUS; i++) {
+				ulong ptr;
+
 				if (!kt->__per_cpu_offset[i])
 					continue;
-				tt->hardirq_ctx[i] = hard_sp->value +
-					kt->__per_cpu_offset[i];
+				ptr = hard_sp->value + kt->__per_cpu_offset[i];
+
+				if (!readmem(ptr, KVADDR, &ptr,
+					     sizeof(void *), "hardirq ctx",
+					     RETURN_ON_ERROR)) {
+					error(INFO, "cannot read hardirq_ctx[%d] at %lx\n",
+					      i, ptr);
+					continue;
+				}
+				tt->hardirq_ctx[i] = ptr;
 			}
 		} else 
 			tt->hardirq_ctx[0] = hard_sp->value;
@@ -604,10 +614,20 @@ irqstacks_init(void)
 	if ((soft_sp = per_cpu_symbol_search("per_cpu__softirq_ctx"))) {
 		if ((kt->flags & SMP) && (kt->flags & PER_CPU_OFF)) {
 			for (i = 0; i < NR_CPUS; i++) {
+				ulong ptr;
+
 				if (!kt->__per_cpu_offset[i])
 					continue;
-				tt->softirq_ctx[i] = soft_sp->value +
-					kt->__per_cpu_offset[i];
+				ptr = soft_sp->value + kt->__per_cpu_offset[i];
+
+				if (!readmem(ptr, KVADDR, &ptr,
+					     sizeof(void *), "softirq ctx",
+					     RETURN_ON_ERROR)) {
+					error(INFO, "cannot read softirq_ctx[%d] at %lx\n",
+					      i, ptr);
+					continue;
+				}
+				tt->softirq_ctx[i] = ptr;
 			}
 		} else 
 			 tt->softirq_ctx[0] = soft_sp->value;

-- 
OGAWA Hirofumi <hirofumi at mail.parknet.co.jp>