Re: [PATCH 0/4] Fix the x86 defconfig build with GCC 17

[Vineet Gupta <vineet.gupta@linux.dev>]

+CC Jakub

On 11/4/26 8:27 AM, Borislav Petkov wrote:
> On Wed, Nov 04, 2026 at 08:07:17AM -0800, Vineet Gupta wrote:
>> Fix build warnings and failures (CONFIG_WERROR=y) with a GCC 17 build.
>> GCC 17 adds -Wconstant-logical-operand which is strict about operands
>> of && or || that fold to a constant other than 0 or 1.
> Just from looking at it, my initial reaction would be to disable that option.
>
> Because, frankly, I don't see the point.

Here's my 2 cents:

I wondered if this brings any codegen improvements, since we are telling 
the compiler that something is 0 or 1 vs. some other range before. And 
it doesn't, because of the way it is used. So focusing on just 1/4.

- Constant bit: __builtin_constant_p(bit) && MASK_BIT_SET(bit) folds at 
compile time to the same truth value, with or without the !! bool 
conversion.
- Variable bit: __builtin_constant_p(bit) is 0, so && short-circuits and 
the mask is never evaluated.

Basically, the masked value never reaches generated code, so compiler 
gets nothing new to work with.

So I did some digging, and turns out that it can be helpful to catch 
bugs in the source code itself. In fact GCC implemented the toggle at 
all, when Jakub spotted an issue with a typo: (data->flags && 
ff_genericize) vs. (data->flags & ff_genericize).

In kernel, the predicate like *_BIT_SET() not returning a bool is not 
clean IMO and it used to return 0/1 before anyway so its not like we are 
going out of the way here.

I'm mildly in the favor of keeping the warning, but ultimately your 
call, I can respin with it disabled.

Thx,
-Vineet