linux-kernel - GCC fails to spot uninitialized variable

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Message-ID: <YtHJbckxy1FJ3ts7@carbon.gago.life>
Date:   Fri, 15 Jul 2022 23:09:17 +0300
From:   Petko Manolov <petko.manolov@...sulko.com>
To:     linux-kernel@...r.kernel.org
Subject: GCC fails to spot uninitialized variable

	Guys,

Today i was bitten by a stupid bug that i introduced myself while writing some
v4l2 code.  Looking at it a bit more carefully i was surprised that GCC didn't
catch this one, as it was something that should definitely emit a warning.

When included into the driver, this particular code:

int blah(int a, int *b)
{
	int ret;

	switch (a) {
	case 0:
		ret = a;
		break;
	case 1:
		ret = *b;
		break;
	case 2:
		*b = a;
		break;
	default:
		ret = 0;
	}

	return ret;
}

somehow managed to defeat GCC checks.  Compiling it as a standalone .c file
with:

	gcc -Wall -O2 -c t.c

gives me nice:

t.c:19:16: warning: 'ret' may be used uninitialized in this function [-Wmaybe-uninitialized]
   19 |         return ret;
      |                ^~~

Any idea what might have gone wrong?

cheers,
Petko