On Wed, Sep 29, 2021 at 11:08:18PM +0200, Andrzej Hajda wrote:
W dniu 29.09.2021 o 20:33, Lucas De Marchi pisze:
Like the IS_ENABLED() counterpart, we can make IS_CONFIG_NONZERO() to
return the right thing when the config is not defined rather than a
build error, with the limitation that it can't be used on preprocessor
context.
The trick here is that macro names can't start with a number or dash, so
we stringify the argument and check that the first char is a number != 0
(or starting with a dash to cover negative numbers). Except for -O0
builds the strings are all eliminated.
Taking CONFIG_DRM_I915_REQUEST_TIMEOUT in
drivers/gpu/drm/i915/gem/i915_gem_context.c as example, we have the
following output of the preprocessor:
old:
if (((20000) != 0) &&
new:
if (( ("20000"[0] > '0' && "20000"[0] < '9') || "20000"[0] == '-' ) &&
New one looks worse, but is also eliminated from the object:
$ size drivers/gpu/drm/i915/gem/i915_gem_context.o.*
text data bss dec hex filename
52021 1070 232 53323 d04b
drivers/gpu/drm/i915/gem/i915_gem_context.o.new
52021 1070 232 53323 d04b
drivers/gpu/drm/i915/gem/i915_gem_context.o.old
Signed-off-by: Lucas De Marchi <lucas.demar...@intel.com>
---
drivers/gpu/drm/i915/i915_utils.h | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/i915/i915_utils.h
b/drivers/gpu/drm/i915/i915_utils.h
index 02bbfa4d68d3..436ce612c46a 100644
--- a/drivers/gpu/drm/i915/i915_utils.h
+++ b/drivers/gpu/drm/i915/i915_utils.h
@@ -28,6 +28,7 @@
#include <linux/list.h>
#include <linux/overflow.h>
#include <linux/sched.h>
+#include <linux/stringify.h>
#include <linux/types.h>
#include <linux/workqueue.h>
@@ -469,6 +470,9 @@ static inline bool timer_expired(const struct timer_list *t)
*
* Returns 0 if @config is 0, 1 if set to any value.
*/
-#define IS_CONFIG_NONZERO(config) ((config) != 0)
+#define IS_CONFIG_NONZERO(config) (
\
+ (__stringify_1(config)[0] > '0' && __stringify_1(config)[0] < '9') ||
\
+ __stringify_1(config)[0] == '-'
\
+)
Quite clever trick, but I see two issues:
- gcc < 8.1 treats expressions with string indices (ex. "abc"[0]) as
non-constant expressions, so they cannot be used everywhere, for example
in global variable initializations,
ugh, that would kill the idea - having the strings and additional
runtime checks would not be good. Maybe if we check with
__builtin_constant_p() and do the simpler expansion if it's not
constant?
- it does not work with hex (0x1) or octal values (01)
indeed, but I guess that would be fixable by checking (s[0] == '0' && s[1] ==
'\0')?
However, it seems kconfig doesn't support setting int options to hex or
octal.
If I try an hex value in menuconfig it says "You have made an invalid entry."
If I try editing .config or setting via scripts/config --set-val, it
just gets reset when trying to generate include/generated/autoconf.h
Lucas De Marchi
It is probably OK for private macro, but it can hurt in kconfig.h,
especially the 2nd issue
Regards
Andrzej
#endif /* !__I915_UTILS_H */
