Re: [PATCH 7/7] bug: Move WARN_ON() "cut here" into exception handler

[Christophe Leroy]

Le 20/08/2019 à 12:06, Peter Zijlstra a écrit :
On Mon, Aug 19, 2019 at 04:41:11PM -0700, Kees Cook wrote:

diff --git a/include/asm-generic/bug.h b/include/asm-generic/bug.h
index 588dd59a5b72..da471fcc5487 100644
--- a/include/asm-generic/bug.h
+++ b/include/asm-generic/bug.h
@@ -10,6 +10,7 @@
  #define BUGFLAG_WARNING               (1 << 0)
  #define BUGFLAG_ONCE          (1 << 1)
  #define BUGFLAG_DONE          (1 << 2)
+#define BUGFLAG_PRINTK         (1 << 3)
  #define BUGFLAG_TAINT(taint)  ((taint) << 8)
  #define BUG_GET_TAINT(bug)    ((bug)->flags >> 8)
  #endif

diff --git a/lib/bug.c b/lib/bug.c
index 1077366f496b..6c22e8a6f9de 100644
--- a/lib/bug.c
+++ b/lib/bug.c
@@ -181,6 +181,15 @@ enum bug_trap_type report_bug(unsigned long bugaddr, 
struct pt_regs *regs)
                }
        }
  
+	/*
+        * BUG() and WARN_ON() families don't print a custom debug message
+        * before triggering the exception handler, so we must add the
+        * "cut here" line now. WARN() issues its own "cut here" before the
+        * extra debugging message it writes before triggering the handler.
+        */
+       if ((bug->flags & BUGFLAG_PRINTK) == 0)
+               printk(KERN_DEFAULT CUT_HERE);

I'm not loving that BUGFLAG_PRINTK name, BUGFLAG_CUT_HERE makes more
sense to me.


Actually it would be BUGFLAG_NO_CUT_HERE then, otherwise all arches not 
using the generic macros will have to add the flag to get the "cut here" 
line.

Christophe