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[debug] Allow debug messages to be initially disabled at runtime

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Extend the DEBUG=... syntax to allow debug messages to be compiled in
but disabled by default.  For example:

  make bin/undionly.kpxe DEBUG=netdevice:3:1

would compile in the messages as for DEBUG=netdevice:3, but would set
the debug level mask so that only the DEBUG=netdevice:1 messages would
be displayed.

This allows for external code to selectively enable the additional
debug messages at runtime, without being overwhelmed by unwanted
initial noise.  For example, a developer of a new protocol may want to
temporarily enable tracing of all packets received: this can be done
by building with DEBUG=netdevice:3:1 and using

  // temporarily enable per-packet messages
  DBG_ENABLE_OBJECT ( netdevice, DBGLVL_EXTRA );
  ...
  // disable per-packet messages
  DBG_DISABLE_OBJECT ( netdevice, DBGLVL_EXTRA );

Note that unlike the usual DBG_ENABLE() and DBG_DISABLE() macros,
DBG_ENABLE_OBJECT() and DBG_DISABLE_OBJECT() will not be removed via
dead code elimination if debugging is disabled in the specified
object.  In particular, this means that using either of these macros
will always result in a symbol reference to the specified object.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
This commit is contained in:
Michael Brown
2016-07-05 10:19:36 +01:00
parent e2c0a20d60
commit 6e1ce52d14
2 changed files with 19 additions and 7 deletions
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6
src/include/compiler.h
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@@ -270,6 +270,10 @@ PROVIDE_SYMBOL ( OBJECT_SYMBOL );
#define DBGLVL_MAX 0
#endif
#ifndef DBGLVL_DFLT
#define DBGLVL_DFLT DBGLVL_MAX
#endif
#ifndef ASSEMBLY
/** printf() for debugging */
@@ -286,7 +290,7 @@ extern void dbg_more ( void );
/* Allow for selective disabling of enabled debug levels */
#define __debug_disable( object ) _C2 ( __debug_disable_, object )
char __debug_disable(OBJECT);
char __debug_disable(OBJECT) = ( DBGLVL_MAX & ~DBGLVL_DFLT );
#define DBG_DISABLE_OBJECT( object, level ) do { \
extern char __debug_disable(object); \
__debug_disable(object) |= (level); \