[DragonFlyBSD - Bug #2910] Rethinking __printflike in the context of drm's __printf

bugtracker-admin at leaf.dragonflybsd.org bugtracker-admin at leaf.dragonflybsd.org
Sat May 7 08:44:42 PDT 2016

Issue #2910 has been updated by swildner.

If Linux understands __printf as NULL being allowed for the format, defining __printf as __printf0like instead sounds reasonable. I'll leave that to whoever brings in such code in the future.

Regarding the second question about having both __printflike and __printf0like, I'm not sure I understand. As long as __printflike implies __nonnull, we need an extra macro for cases where a NULL format shall be allowed. If we removed __nonnull__ from __printflike, we'd have to add __nonnull to all prototypes that have __printflike right now, in order to not lose these checks.

Bug #2910: Rethinking __printflike in the context of drm's __printf

* Author: davshao
* Status: New
* Priority: Normal
* Assignee: 
* Category: 
* Target version: 
Currently DragonFly drm defines __printf to be __printflike.  It seems likely to me that Linux drm actually expects behavior __printf0like, without the __nonnull__(fmtarg) attribute.  

For example, more recent versions of Linux drm want to define a function like this:

extern __printf(6, 7)
int drm_crtc_init_with_planes(struct drm_device *dev,
			      struct drm_crtc *crtc,
			      struct drm_plane *primary,
			      struct drm_plane *cursor,
			      const struct drm_crtc_funcs *funcs,
			      const char *name, ...);

and call it sometimes (well strangely enough, so far all of the time) with name == NULL.
Then inside the newer versions of the function is something like this:

	if (name) {
		__va_list ap;

		__va_start(ap, name);
		crtc->name = kvasprintf(GFP_KERNEL, name, ap);
	} else {
		crtc->name = kasprintf(GFP_KERNEL, "crtc-%d",

The obvious fix is in sys/dev/drm/include/linux/compiler.h
to redefine __printf as __printf0like.

For curiosity's sake, given the gcc 4+ series of compilers now used for DragonFly in 2015
as opposed to 2004 when the __printflike and __printf0like distinction was made, is it
still necessary to have both __printflike and printf0like?

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