From: Ingo Molnar <[email protected]>
document stack frame nesting internals some more.
Signed-off-by: Ingo Molnar <[email protected]>
Signed-off-by: Arjan van de Ven <[email protected]>
---
arch/x86_64/kernel/traps.c | 64 +++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 62 insertions(+), 2 deletions(-)
Index: linux/arch/x86_64/kernel/traps.c
===================================================================
--- linux.orig/arch/x86_64/kernel/traps.c
+++ linux/arch/x86_64/kernel/traps.c
@@ -134,8 +134,9 @@ void printk_address(unsigned long addres
}
#endif
-static unsigned long *in_exception_stack(unsigned cpu, unsigned long stack,
- unsigned *usedp, const char **idp)
+unsigned long *
+in_exception_stack(unsigned cpu, unsigned long stack, unsigned *usedp,
+ const char **idp)
{
static char ids[][8] = {
[DEBUG_STACK - 1] = "#DB",
@@ -149,10 +150,22 @@ static unsigned long *in_exception_stack
};
unsigned k;
+ /*
+ * Iterate over all exception stacks, and figure out whether
+ * 'stack' is in one of them:
+ */
for (k = 0; k < N_EXCEPTION_STACKS; k++) {
unsigned long end;
+ /*
+ * set 'end' to the end of the exception stack.
+ */
switch (k + 1) {
+ /*
+ * TODO: this block is not needed i think, because
+ * setup64.c:cpu_init() sets up t->ist[DEBUG_STACK]
+ * properly too.
+ */
#if DEBUG_STKSZ > EXCEPTION_STKSZ
case DEBUG_STACK:
end = cpu_pda(cpu)->debugstack + DEBUG_STKSZ;
@@ -162,19 +175,43 @@ static unsigned long *in_exception_stack
end = per_cpu(init_tss, cpu).ist[k];
break;
}
+ /*
+ * Is 'stack' above this exception frame's end?
+ * If yes then skip to the next frame.
+ */
if (stack >= end)
continue;
+ /*
+ * Is 'stack' above this exception frame's start address?
+ * If yes then we found the right frame.
+ */
if (stack >= end - EXCEPTION_STKSZ) {
+ /*
+ * Make sure we only iterate through an exception
+ * stack once. If it comes up for the second time
+ * then there's something wrong going on - just
+ * break out and return NULL:
+ */
if (*usedp & (1U << k))
break;
*usedp |= 1U << k;
*idp = ids[k];
return (unsigned long *)end;
}
+ /*
+ * If this is a debug stack, and if it has a larger size than
+ * the usual exception stacks, then 'stack' might still
+ * be within the lower portion of the debug stack:
+ */
#if DEBUG_STKSZ > EXCEPTION_STKSZ
if (k == DEBUG_STACK - 1 && stack >= end - DEBUG_STKSZ) {
unsigned j = N_EXCEPTION_STACKS - 1;
+ /*
+ * Black magic. A large debug stack is composed of
+ * multiple exception stack entries, which we
+ * iterate through now. Dont look:
+ */
do {
++j;
end -= EXCEPTION_STKSZ;
@@ -206,6 +243,11 @@ void show_trace(unsigned long *stack)
printk("\nCall Trace:\n");
+ /*
+ * Print function call entries within a stack. 'cond' is the
+ * "end of stackframe" condition, that the 'stack++'
+ * iteration will eventually trigger.
+ */
#define HANDLE_STACK(cond) \
do while (cond) { \
unsigned long addr = *stack++; \
@@ -223,6 +265,11 @@ void show_trace(unsigned long *stack)
} \
} while (0)
+ /*
+ * Print function call entries in all stacks, starting at the
+ * current stack address. If the stacks consist of nested
+ * exceptions
+ */
for ( ; ; ) {
const char *id;
unsigned long *estack_end;
@@ -233,6 +280,11 @@ void show_trace(unsigned long *stack)
printk(" <%s>", id);
HANDLE_STACK (stack < estack_end);
printk(" <EOE>");
+ /*
+ * We link to the next stack via the
+ * second-to-last pointer (index -2 to end) in the
+ * exception stack:
+ */
stack = (unsigned long *) estack_end[-2];
continue;
}
@@ -244,6 +296,11 @@ void show_trace(unsigned long *stack)
if (stack >= irqstack && stack < irqstack_end) {
printk(" <IRQ>");
HANDLE_STACK (stack < irqstack_end);
+ /*
+ * We link to the next stack (which would be
+ * the process stack normally) the last
+ * pointer (index -1 to end) in the IRQ stack:
+ */
stack = (unsigned long *) (irqstack_end[-1]);
irqstack_end = NULL;
printk(" <EOI>");
@@ -253,6 +310,9 @@ void show_trace(unsigned long *stack)
break;
}
+ /*
+ * This prints the process stack:
+ */
HANDLE_STACK (((long) stack & (THREAD_SIZE-1)) != 0);
#undef HANDLE_STACK
-
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