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SubjectRe: [RFC] Smarter stack traces using the frame pointer
On 04 Nov 2003 14:13:49 -0800 Adam Litke <agl@us.ibm.com> wrote:
>
> I was working on this for the mjb tree but I thought I'd throw it out
> here in case anyone else finds it interesting. This simple change to
> the stack trace code uses the frame pointer to do the trace instead of
> assuming any kernel address on the stack is a return address. It makes
> for much more readable stack traces.

I was asked by a colleague to do the same thing and came up with this
alternative version which, I think, gets it mostly right - I am not
sure about the stack trace from an OOPS.

Don't bother to tell me this is a bit of a hack - I know :-)

Patch relative to 2.6.0-test9.
--
Cheers,
Stephen Rothwell sfr@canb.auug.org.au
http://www.canb.auug.org.au/~sfr/

diff -ruN 2.6.0-test9/arch/i386/kernel/process.c 2.6.0-test9-sfr.1/arch/i386/kernel/process.c
--- 2.6.0-test9/arch/i386/kernel/process.c 2003-10-09 10:22:41.000000000 +1000
+++ 2.6.0-test9-sfr.1/arch/i386/kernel/process.c 2003-10-28 17:00:40.000000000 +1100
@@ -243,7 +243,7 @@
".previous \n"
: "=r" (cr4): "0" (0));
printk("CR0: %08lx CR2: %08lx CR3: %08lx CR4: %08lx\n", cr0, cr2, cr3, cr4);
- show_trace(NULL, &regs->esp);
+ show_trace(&regs->esp, (unsigned long *)regs->ebp);
}

/*
diff -ruN 2.6.0-test9/arch/i386/kernel/traps.c 2.6.0-test9-sfr.1/arch/i386/kernel/traps.c
--- 2.6.0-test9/arch/i386/kernel/traps.c 2003-10-20 11:35:54.000000000 +1000
+++ 2.6.0-test9-sfr.1/arch/i386/kernel/traps.c 2003-10-29 15:45:50.000000000 +1100
@@ -91,9 +91,11 @@
asmlinkage void spurious_interrupt_bug(void);
asmlinkage void machine_check(void);

+#define DECLARE_EBP register unsigned long *ebp asm("ebp")
+
static int kstack_depth_to_print = 24;

-void show_trace(struct task_struct *task, unsigned long * stack)
+void show_trace(unsigned long *stack, unsigned long *frame)
{
unsigned long addr;

@@ -106,10 +108,24 @@
#endif
while (!kstack_end(stack)) {
addr = *stack++;
- if (kernel_text_address(addr)) {
+ if (
+#ifdef CONFIG_FRAME_POINTER
+ /*
+ * The plus 2 is because the return address
+ * is immediately above where the frame pointer
+ * points and we incremented the stack pointer
+ * above ...
+ */
+ (!frame || (stack == (frame + 2))) &&
+#endif
+ kernel_text_address(addr)) {
printk(" [<%08lx>] ", addr);
print_symbol("%s\n", addr);
}
+#ifdef CONFIG_FRAME_POINTER
+ if (frame && (stack == (frame + 2)))
+ frame = (unsigned long *)*frame;
+#endif
}
printk("\n");
}
@@ -121,19 +137,45 @@
/* User space on another CPU? */
if ((esp ^ (unsigned long)tsk->thread_info) & (PAGE_MASK<<1))
return;
- show_trace(tsk, (unsigned long *)esp);
+ /*
+ * switch_to pushes the frame pointer just before saving
+ * the stack pointer.
+ */
+ show_trace((unsigned long *)esp, (unsigned long *)*(unsigned long *)esp);
}

void show_stack(struct task_struct *task, unsigned long *esp)
{
unsigned long *stack;
int i;
+ DECLARE_EBP;
+ unsigned long *frame;

if (esp == NULL) {
- if (task)
+ if (task && (task != current)) {
esp = (unsigned long*)task->thread.esp;
- else
+ /*
+ * switch_to pushes the frame pointer just before
+ * saving the stack pointer.
+ */
+ frame = (unsigned long *)*esp;
+ } else {
esp = (unsigned long *)&esp;
+ frame = ebp;
+#ifdef CONFIG_FRAME_POINTER
+ /* we want the enclosing frame ... */
+ frame = (unsigned long *)*ebp;
+#endif
+ }
+ } else {
+ /*
+ * The only place that calls show_stack with task == NULL
+ * and esp != NULL is show_registers below, where esp
+ * points at the esp field of a pt_regs structure on the
+ * stack. So this gets us the saved ebp value.
+ */
+ frame = ((struct pt_regs *)((unsigned char *)esp -
+ offsetof(struct pt_regs, esp)))->ebp;
}

stack = esp;
@@ -145,7 +187,7 @@
printk("%08lx ", *stack++);
}
printk("\n");
- show_trace(task, esp);
+ show_trace(esp, frame);
}

/*
@@ -154,8 +196,9 @@
void dump_stack(void)
{
unsigned long stack;
+ DECLARE_EBP;

- show_trace(current, &stack);
+ show_trace(&stack, ebp);
}

EXPORT_SYMBOL(dump_stack);
diff -ruN 2.6.0-test9/include/asm-i386/processor.h 2.6.0-test9-sfr.1/include/asm-i386/processor.h
--- 2.6.0-test9/include/asm-i386/processor.h 2003-10-20 11:36:07.000000000 +1000
+++ 2.6.0-test9-sfr.1/include/asm-i386/processor.h 2003-10-28 16:57:42.000000000 +1100
@@ -492,7 +492,7 @@
extern int kernel_thread(int (*fn)(void *), void * arg, unsigned long flags);

extern unsigned long thread_saved_pc(struct task_struct *tsk);
-void show_trace(struct task_struct *task, unsigned long *stack);
+void show_trace(unsigned long *stack, unsigned long *frame);

unsigned long get_wchan(struct task_struct *p);
#define KSTK_EIP(tsk) (((unsigned long *)(4096+(unsigned long)(tsk)->thread_info))[1019])
-
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