Messages in this thread | | | Date | Wed, 29 Sep 2021 15:54:33 -0700 | From | Lucas De Marchi <> | Subject | Re: [PATCH v2 2/3] drm/i915/utils: do not depend on config being defined |
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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.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,
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 */
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