The entry code doesn't encode pt_regs for syscalls. But they're always
at the same location, so we can add a manual check for them.
Signed-off-by: Josh Poimboeuf <jpoim...@redhat.com>
---
arch/x86/kernel/unwind_frame.c | 35 +++++++++++++++++++++++++++++++++++
1 file changed, 35 insertions(+)
diff --git a/arch/x86/kernel/unwind_frame.c b/arch/x86/kernel/unwind_frame.c
index e02acec..d2480a3 100644
--- a/arch/x86/kernel/unwind_frame.c
+++ b/arch/x86/kernel/unwind_frame.c
@@ -24,6 +24,14 @@ unsigned long unwind_get_return_address(struct unwind_state
*state)
}
EXPORT_SYMBOL_GPL(unwind_get_return_address);
+static bool is_last_task_frame(struct unwind_state *state)
+{
+ unsigned long bp = (unsigned long)state->bp;
+ unsigned long regs = (unsigned long)task_pt_regs(state->task);
+
+ return bp == regs - FRAME_HEADER_SIZE;
+}
+
/*
* This determines if the frame pointer actually contains an encoded pointer to
* pt_regs on the stack. See ENCODE_FRAME_POINTER.
@@ -77,6 +85,33 @@ bool unwind_next_frame(struct unwind_state *state)
if (state->regs && user_mode(state->regs))
goto the_end;
+ if (is_last_task_frame(state)) {
+ regs = task_pt_regs(state->task);
+
+ /*
+ * kthreads (other than the boot CPU's idle thread) have some
+ * partial regs at the end of their stack which were placed
+ * there by copy_thread_tls(). But the regs don't have any
+ * useful information, so we can skip them.
+ *
+ * This user_mode() check is slightly broader than a PF_KTHREAD
+ * check because it also catches the awkward situation where a
+ * newly forked kthread transitions into a user task by calling
+ * do_execve(), which eventually clears PF_KTHREAD.
+ */
+ if (!user_mode(regs))
+ goto the_end;
+
+ /*
+ * We're almost at the end, but not quite: there's still the
+ * syscall regs frame. Entry code doesn't encode the regs
+ * pointer for syscalls, so we have to set it manually.
+ */
+ state->regs = regs;
+ state->bp = NULL;
+ return true;
+ }
+
/* get the next frame pointer */
if (state->regs)
next_bp = (unsigned long *)state->regs->bp;
--
2.7.4
