ftrace: handle archs that do not support irqs_disabled_flags

Impact: build fix on non-lockdep architectures

Some architectures do not support a way to read the irq flags that
is set from "local_irq_save(flags)" to determine if interrupts were
disabled or enabled. Ftrace uses this information to display to the user
if the trace occurred with interrupts enabled or disabled.

Besides the fact that those archs that do not support this will fail to
compile, unless they fix it, we do not want to have the trace simply
say interrupts were not disabled or they were enabled, without knowing
the real answer.

This patch adds a 'X' in the output to let the user know that the
architecture they are running on does not support a way for the tracer
to determine if interrupts were enabled or disabled. It also lets those
same archs compile with tracing enabled.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 3 insertions, 0 deletions

diff --git a/Documentation/ftrace.txt b/Documentation/ftrace.txt
index d330fe3103da..ea5a827395dd 100644
--- a/Documentation/ftrace.txt
+++ b/Documentation/ftrace.txt
@@ -291,6 +291,9 @@ explains which is which.
   CPU#: The CPU which the process was running on.
 
   irqs-off: 'd' interrupts are disabled. '.' otherwise.
+            Note: If the architecture does not support a way to
+                  read the irq flags variable, an 'X' will always
+                  be printed here.
 
   need-resched: 'N' task need_resched is set, '.' otherwise.