On 13. 12. 22, 9:30, David Laight wrote:
From: Tejun Heo <htejun@xxxxxxxxx> On Behalf Of 'Tejun Heo'
Sent: 12 December 2022 21:47
To: Jiri Slaby <jirislaby@xxxxxxxxxx>
Cc: David Laight <David.Laight@xxxxxxxxxx>; Christoph Hellwig <hch@xxxxxxxxxxxxx>; linux-
kernel@xxxxxxxxxxxxxxx; Martin Liska <mliska@xxxxxxx>; Josef Bacik <josef@xxxxxxxxxxxxxx>; Jens Axboe
<axboe@xxxxxxxxx>; cgroups@xxxxxxxxxxxxxxx; linux-block@xxxxxxxxxxxxxxx
Subject: Re: [PATCH] block/blk-iocost (gcc13): cast enum members to int in prints
On Mon, Dec 12, 2022 at 01:14:31PM +0100, Jiri Slaby wrote:
If so, my suggestion is just sticking with the old behavior until we switch
to --std=g2x and then make one time adjustment at that point.
So is the enum split OK under these circumstances?
Oh man, it's kinda crazy that the compiler is changing in a way that the
same piece of code can't be compiled the same way across two adjoining
versions of the same compiler. But, yeah, if that's what gcc is gonna do and
splitting enums is the only way to be okay across the compiler versions,
there isn't any other choice we can make.
It is also a silent code-breaker.
Compile this for 32bit x86:
enum { a = 1, b = ~0ull};
But having ull in an enum is undefined anyway. C99 allows only int
constants. gnuC supports ulong expressions (IIRC).
extern int foo(int, ...);
int f(void)
{
return foo(0, a, 2);
}
gcc13 pushes an extra zero onto the stack between the 1 and 2.
So this is sort of "expected".
thanks,
--
js
suse labs
