Commit 5f01c988 authored by Jiri Slaby's avatar Jiri Slaby Committed by Ingo Molnar
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x86/dumpstack: Fix printk_address for direct addresses

Consider a kernel crash in a module, simulated the following way:

 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 71f9e598

 ("x86, dumpstack: Use
%pB format specifier for stack trace") to fix the call stack

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 printk_address.
Signed-off-by: default avatarJiri Slaby <>
Cc: Namhyung Kim <>
Cc: Frederic Weisbecker <>
Cc: Ingo Molnar <>
Cc: "H. Peter Anvin" <>

Signed-off-by: default avatarIngo Molnar <>
parent 9b66bfb2
......@@ -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,
......@@ -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(" RSP <%016lx>\n", regs->sp);
return 0;
......@@ -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(KERN_DEFAULT "RSP: %04lx:%016lx EFLAGS: %08lx\n", regs->ss,
regs->sp, regs->flags);
printk(KERN_DEFAULT "RAX: %016lx RBX: %016lx RCX: %016lx\n",
......@@ -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);
......@@ -399,7 +399,7 @@ 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);
/* Dump this cpu's state */
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