[PATCH -resend 1/1] dumpstack: fix printk_address for direct addresses

From: Jiri Slaby
Date: Fri Oct 25 2013 - 09:31:38 EST

Consider modules like this:
static int my_init(void)
char *map = (void *)0x5;
*map = 3;
return 0;

When we turn off FRAME_POINTERs, the very first instruction in that
function causes a BUG. The problem is that we print IP in the BUG
report using %pB (from printk_address). And %pB decrements the pointer
by one to fix printing addresses of functions with tail calls. This
was added in commit 71f9e59800e5ad4e6b683348424c9fe54306cd43 (x86,
dumpstack: Use %pB format specifier for stack trace) to fix the call
stack printouts.

So instead of correct output:
BUG: unable to handle kernel NULL pointer dereference at 0000000000000005
IP: [<ffffffffa01ac000>] my_init+0x0/0x10 [pb173]

We get:
BUG: unable to handle kernel NULL pointer dereference at 0000000000000005
IP: [<ffffffffa0152000>] 0xffffffffa0151fff

To fix that, we use %pS only for stack addresses printouts (via newly
added printk_stack_address) and %pB for regs->ip (via printk_address).
I.e. we revert to the old behaviour for all except call stacks. And
since from all those reliable is 1, we remove that parameter from

Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxx>
Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: joe@xxxxxxxxxxx

I sent this patch 2 weeks ago. Only Joe commented that the prints
should be done inline instead. But I don't agree as prining the output
from one point is better IMHO.

So after discussing what to do with this patch with Ingo, I am


arch/x86/include/asm/kdebug.h | 2 +-
arch/x86/kernel/dumpstack.c | 11 ++++++++---
arch/x86/kernel/process_64.c | 2 +-
arch/x86/mm/fault.c | 2 +-
arch/x86/platform/uv/uv_nmi.c | 2 +-
5 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/arch/x86/include/asm/kdebug.h b/arch/x86/include/asm/kdebug.h
index 2c37aad..32ce713 100644
--- a/arch/x86/include/asm/kdebug.h
+++ b/arch/x86/include/asm/kdebug.h
@@ -21,7 +21,7 @@ enum die_val {

-extern void printk_address(unsigned long address, int reliable);
+extern void printk_address(unsigned long address);
extern void die(const char *, struct pt_regs *,long);
extern int __must_check __die(const char *, struct pt_regs *, long);
extern void show_trace(struct task_struct *t, struct pt_regs *regs,
diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
index deb6421..d9c12d3 100644
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -25,12 +25,17 @@ unsigned int code_bytes = 64;
int kstack_depth_to_print = 3 * STACKSLOTS_PER_LINE;
static int die_counter;

-void printk_address(unsigned long address, int reliable)
+static void printk_stack_address(unsigned long address, int reliable)
pr_cont(" [<%p>] %s%pB\n",
(void *)address, reliable ? "" : "? ", (void *)address);

+void printk_address(unsigned long address)
+ pr_cont(" [<%p>] %pS\n", (void *)address, (void *)address);
static void
print_ftrace_graph_addr(unsigned long addr, void *data,
@@ -151,7 +156,7 @@ static void print_trace_address(void *data, unsigned long addr, int reliable)
- printk_address(addr, reliable);
+ printk_stack_address(addr, reliable);

static const struct stacktrace_ops print_trace_ops = {
@@ -281,7 +286,7 @@ int __kprobes __die(const char *str, struct pt_regs *regs, long err)
/* Executive summary in case the oops scrolled away */
printk(KERN_ALERT "RIP ");
- printk_address(regs->ip, 1);
+ printk_address(regs->ip);
printk(" RSP <%016lx>\n", regs->sp);
return 0;
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 45ab4d6..176ad94 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -63,7 +63,7 @@ void __show_regs(struct pt_regs *regs, int all)
unsigned int ds, cs, es;

printk(KERN_DEFAULT "RIP: %04lx:[<%016lx>] ", regs->cs & 0xffff, regs->ip);
- printk_address(regs->ip, 1);
+ printk_address(regs->ip);
printk(KERN_DEFAULT "RSP: %04lx:%016lx EFLAGS: %08lx\n", regs->ss,
regs->sp, regs->flags);
printk(KERN_DEFAULT "RAX: %016lx RBX: %016lx RCX: %016lx\n",
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 3aaeffc..18feeb3 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -596,7 +596,7 @@ show_fault_oops(struct pt_regs *regs, unsigned long error_code,

printk(KERN_CONT " at %p\n", (void *) address);
printk(KERN_ALERT "IP:");
- printk_address(regs->ip, 1);
+ printk_address(regs->ip);

diff --git a/arch/x86/platform/uv/uv_nmi.c b/arch/x86/platform/uv/uv_nmi.c
index 9126dfb..019b6ec 100644
--- a/arch/x86/platform/uv/uv_nmi.c
+++ b/arch/x86/platform/uv/uv_nmi.c
@@ -402,7 +402,7 @@ static void uv_nmi_dump_cpu_ip(int cpu, struct pt_regs *regs)
printk(KERN_DEFAULT "UV: %4d %6d %-32.32s ",
cpu, current->pid, current->comm);

- printk_address(regs->ip, 1);
+ printk_address(regs->ip);

/* Dump this cpu's state */

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/