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Today's Topics:
1. Re: Fixing cast-align warning in ovdb (Julien ?LIE)
----------------------------------------------------------------------
Message: 1
Date: Sun, 2 Sep 2018 22:10:07 +0200
From: Julien ?LIE <[email protected]>
To: [email protected]
Subject: Re: Fixing cast-align warning in ovdb
Message-ID: <[email protected]>
Content-Type: text/plain; charset=utf-8; format=flowed
Hi Russ,
>> ovdb/ovdb.c: In function 'ovdb_add':
>> ovdb/ovdb.c:1951:6: error: cast increases required alignment of target type
>> [-Werror=cast-align]
>> ((struct ovdata *)databuf)->token = token;
>> ^
>> ovdb/ovdb.c:1952:6: error: cast increases required alignment of target type
>> [-Werror=cast-align]
>> ((struct ovdata *)databuf)->arrived = arrived;
>> ^
>> ovdb/ovdb.c:1953:6: error: cast increases required alignment of target type
>> [-Werror=cast-align]
>> ((struct ovdata *)databuf)->expires = expires;
>> ^
>
> I suspect it will work to change the type of databuf to void *, and then
> cast it to (struct ovdata *) when writing into that header and later to
> assign it to a variable of type char * when doing pointer math on it.
- ((struct ovdata *)databuf)->token = token;
- ((struct ovdata *)databuf)->arrived = arrived;
- ((struct ovdata *)databuf)->expires = expires;
+ ((struct ovdata *)(void *)databuf)->token = token;
+ ((struct ovdata *)(void *)databuf)->arrived = arrived;
+ ((struct ovdata *)(void *)databuf)->expires = expires;
gcc indeed no longer complains with the above change.
> The pointer is aligned, since the pointer is returned from malloc(), which is
> guaranteed to return a pointer with suitable alignment for any built-in
> type, so I think the warnings are just because it's immediately assigned
> to a char * variable, which has no required alignment, and the compiler
> isn't smart enough to keep track of this.
OK, thanks!
>> ovdb_stat.c: In function 'print_value':
>> ovdb_stat.c:157:7: warning: cast increases required alignment of target type
>> [-Werror=cast-align]
>> dl = (DB_LSN *)(cp + tab[i].a);
>> ^
>
> This is a similar problem, but the pointer math immediately before use of
> the pointer makes it a bit more complicated. If you replace cp in that
> expression with (char *) p, I wonder if having all the casts in the same
> expression would let the compiler figure it out?
Still the same cast-align error with either
dl = (DB_LSN *)((char *)cp + tab[i].a);
or
dl = (DB_LSN *)((char *)p + tab[i].a);
Note that
dl = (DB_LSN *)(void *)(cp + tab[i].a);
suppresses the warning. I can commit that change too so that the
warning is suppressed.
--
Julien ?LIE
??Vti, non abuti.??
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