On Tue, Oct 18, 2016 at 04:10:51PM -0700, Sagar Borikar wrote:
> I tried these patches but still don't get correct bt output.
I think I see the problem now. Your EPC is 0 so we hit the if
(!IS_KVADDR(current.pc)) condition on the first iteration of the
backtrace loop and exit without trying futher.
Could you please try the following patch? Please include a log with
debugging enabled ("set debug 8") if it still doesn't work. Thanks.
8<------------------
>From 4ae6ab8d181deea53ece847007d27d228166370d Mon Sep 17 00:00:00 2001
From: Rabin Vincent <rabinv@xxxxxxxx>
Date: Thu, 20 Oct 2016 00:19:33 +0200
Subject: [PATCH] mips: allow one invalid PC at start or after exception
Before:
PID: 2810 TASK: 835e41a8 CPU: 1 COMMAND: "sh"
#0 [8315bb00] crash_kexec at 800b26a4
#1 [8315bbe0] panic at 800dc0fc
#2 [8315bc20] die at 8001fa74
#3 [8315bc50] __do_page_fault at 8002de74
#4 [8315bd28] ret_from_irq at 80019624
$ 0 : 00000000 00000001 80690000 00000000
$ 4 : 00000063 812972dc 81297db8 000000c2
$ 8 : 00004b38 00000001 80680000 80620000
$12 : 00000104 00000002 00000000 00000000
$16 : 80622530 80620000 00000063 80620000
$20 : 80622470 00000001 00000000 00b9f322
$24 : 00000003 00000000 00440000 800dca80
$28 : 8315a000 8315bde0 00000000 80313b30
Hi : 00000046
Lo : 0f5c2a0e
epc : 00000000
ra : 80313b30 __handle_sysrq+0x144
Status: 1100fc03
Cause : 10800008
BadVA : 00000000
After:
crash> bt
PID: 2810 TASK: 835e41a8 CPU: 1 COMMAND: "sh"
#0 [8315bb00] crash_kexec at 800b26a4
#1 [8315bbe0] panic at 800dc0fc
#2 [8315bc20] die at 8001fa74
#3 [8315bc50] __do_page_fault at 8002de74
#4 [8315bd28] ret_from_irq at 80019624
$ 0 : 00000000 00000001 80690000 00000000
$ 4 : 00000063 812972dc 81297db8 000000c2
$ 8 : 00004b38 00000001 80680000 80620000
$12 : 00000104 00000002 00000000 00000000
$16 : 80622530 80620000 00000063 80620000
$20 : 80622470 00000001 00000000 00b9f322
$24 : 00000003 00000000 00440000 800dca80
$28 : 8315a000 8315bde0 00000000 80313b30
Hi : 00000046
Lo : 0f5c2a0e
epc : 00000000
ra : 80313b30 __handle_sysrq+0x144
Status: 1100fc03
Cause : 10800008
BadVA : 00000000
#5 [8315bde0] (invalid) at 0
#6 [8315bde0] __handle_sysrq at 80313b30
#7 [8315be18] write_sysrq_trigger at 80313c24
#8 [8315be38] proc_reg_write at 80178074
#9 [8315be58] __vfs_write at 8011ea78
#10 [8315bec0] vfs_write at 8011fe7c
#11 [8315bef0] sys_write at 801201e8
#12 [8315bf28] syscall_common at 800275c8
---
mips.c | 35 +++++++++++++++++++++++++----------
1 file changed, 25 insertions(+), 10 deletions(-)
diff --git a/mips.c b/mips.c
index 6cd8d1f..1bb4d27 100644
--- a/mips.c
+++ b/mips.c
@@ -413,7 +413,7 @@ mips_dump_backtrace_entry(struct bt_info *bt, struct syment *sym,
struct mips_unwind_frame *current,
struct mips_unwind_frame *previous, int level)
{
- const char *name = sym->name;
+ const char *name = sym ? sym->name : "(invalid)";
struct load_module *lm;
char *name_plus_offset;
char buf[BUFSIZE];
@@ -447,7 +447,7 @@ mips_dump_backtrace_entry(struct bt_info *bt, struct syment *sym,
fprintf(fp, " %s\n", buf);
}
- if (mips_is_exception_entry(sym)) {
+ if (sym && mips_is_exception_entry(sym)) {
char pt_regs[SIZE(pt_regs)];
GET_STACK_DATA(current->sp, &pt_regs, SIZE(pt_regs));
@@ -533,6 +533,7 @@ mips_back_trace_cmd(struct bt_info *bt)
{
struct mips_unwind_frame current, previous;
int level = 0;
+ int invalid_ok = 1;
if (bt->flags & BT_REGS_NOT_FOUND)
return;
@@ -549,22 +550,24 @@ mips_back_trace_cmd(struct bt_info *bt)
}
while (INSTACK(current.sp, bt)) {
- struct syment *symbol;
+ struct syment *symbol = NULL;
ulong offset;
if (CRASHDEBUG(8))
fprintf(fp, "level %d pc %#lx ra %#lx sp %lx\n",
level, current.pc, current.ra, current.sp);
- if (!IS_KVADDR(current.pc))
+ if (!IS_KVADDR(current.pc) && !invalid_ok)
return;
symbol = value_search(current.pc, &offset);
- if (!symbol) {
+ if (!symbol && !invalid_ok) {
error(FATAL, "PC is unknown symbol (%lx)", current.pc);
return;
}
+ invalid_ok = 0;
+
/*
* If we get an address which points to the start of a
* function, then it could one of the following:
@@ -586,7 +589,7 @@ mips_back_trace_cmd(struct bt_info *bt)
* * ret_from_fork
* * ret_from_kernel_thread
*/
- if (!current.ra && !offset && !STRNEQ(symbol->name, "ret_from")) {
+ if (!current.ra && !offset && symbol && !STRNEQ(symbol->name, "ret_from")) {
if (CRASHDEBUG(8))
fprintf(fp, "zero offset at %s, try previous symbol\n",
symbol->name);
@@ -598,7 +601,7 @@ mips_back_trace_cmd(struct bt_info *bt)
}
}
- if (mips_is_exception_entry(symbol)) {
+ if (symbol && mips_is_exception_entry(symbol)) {
struct mips_pt_regs_main *mains;
struct mips_pt_regs_cp0 *cp0;
char pt_regs[SIZE(pt_regs)];
@@ -617,18 +620,30 @@ mips_back_trace_cmd(struct bt_info *bt)
if (CRASHDEBUG(8))
fprintf(fp, "exception pc %#lx ra %#lx sp %lx\n",
previous.pc, previous.ra, previous.sp);
- } else {
+
+ /* The PC causing the exception may have been invalid */
+ invalid_ok = 1;
+ } else if (symbol) {
mips_analyze_function(symbol->value, offset, ¤t, &previous);
+ } else {
+ /*
+ * The current PC is invalid. Assume that the code
+ * jumped through a invalid pointer and that the SP has
+ * not been adjusted.
+ */
+ previous.sp = current.sp;
}
mips_dump_backtrace_entry(bt, symbol, ¤t, &previous, level++);
- if (!current.ra)
- break;
current.pc = current.ra;
current.sp = previous.sp;
current.ra = previous.ra;
+ if (CRASHDEBUG(8))
+ fprintf(fp, "next %d pc %#lx ra %#lx sp %lx\n",
+ level, current.pc, current.ra, current.sp);
+
previous.sp = previous.pc = previous.ra = 0;
}
}
--
2.1.4
--
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