Compiling QEMU with different optimization levels & -Werror=maybe-uninitialized

Compiling QEMU with different optimization levels & -Werror=maybe-uninitialized

[Marc-André Lureau]

Hi,

Depending -Doptimization=<value>, I get different results (GCC 13.2.1)
- g: produces -Werror=maybe-uninitialized errors
- 0: clean build
- 1: produces -Werror=maybe-uninitialized errors
- 2: clean build
- 3: produces few -Werror=maybe-uninitialized errors
- s: produces -Werror=maybe-uninitialized errors

They are about 20, probably false-positives, although it's
understandable the compiler is confused as I am too sometime!

Is it a known issue? Are we willing to help the compiler in all those
optimization levels? I can send a patch series for review in this
case.

thanks

--
Marc-André Lureau

Re: Compiling QEMU with different optimization levels & -Werror=maybe-uninitialized

[Daniel P. Berrangé]

On Wed, Mar 27, 2024 at 03:28:08PM +0400, Marc-André Lureau wrote:
> Hi,
> 
> Depending -Doptimization=<value>, I get different results (GCC 13.2.1)
> - g: produces -Werror=maybe-uninitialized errors
> - 0: clean build
> - 1: produces -Werror=maybe-uninitialized errors
> - 2: clean build
> - 3: produces few -Werror=maybe-uninitialized errors
> - s: produces -Werror=maybe-uninitialized errors
> 
> They are about 20, probably false-positives, although it's
> understandable the compiler is confused as I am too sometime!

If any of those maybe-uninitialized warnings are genuine bugs, our
use of use of -ftrivial-auto-var-init provides a safety net that
protects us....

> 
> Is it a known issue? Are we willing to help the compiler in all those
> optimization levels? I can send a patch series for review in this
> case.

...none the less, IMHO, it is good practice to initialize all local stack
allocated variables at time of declaration no matter what. So if you have
patches to clear those false positives, I'd suggest  we just do it.

With regards,
Daniel
-- 
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