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.demarchi@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,
- it does not work with hex (0x1) or octal values (01)
It is probably OK for private macro, but it can hurt in kconfig.h, especially the 2nd issue
Regards
Andrzej
#endif /* !__I915_UTILS_H */