Date: Tue, 28 Aug 2012 18:02:22 +0400 From: Andrey Zonov <zont@FreeBSD.org> To: Warner Losh <imp@bsdimp.com> Cc: freebsd-arch@freebsd.org Subject: Re: warning: cast increases required alignment of target type Message-ID: <503CCF6E.7080208@FreeBSD.org> In-Reply-To: <CDF0AE44-1CB2-42F7-BE60-DD2E4697A374@bsdimp.com> References: <503C8809.3050507@FreeBSD.org> <CDF0AE44-1CB2-42F7-BE60-DD2E4697A374@bsdimp.com>
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On 8/28/12 5:12 PM, Warner Losh wrote:
>=20
> On Aug 28, 2012, at 2:57 AM, Andrey Zonov wrote:
>=20
>> Hi,
>>
>> Does anyone know how to correctly fix this warning for
>> arm/ia64/mips/sparc64?
>>
>> usr.bin/elf2aout/elf2aout.c: In function 'main':
>> usr.bin/elf2aout/elf2aout.c:129: warning: cast increases required
>> alignment of target type
>>
>> I found this explanation from bde, but still don't understand how to
>> correctly fix this issue.
>>
>> ----------------------------------------------------------------------=
--
>> r99799 | bde | 2002-07-11 22:06:09 +0400 (Thu, 11 Jul 2002) | 10 lines=
>>
>> Set NO_WERROR to ignore the following warning which is emitted on
>> alphas:
>> .../elf2aout.c:130: warning: cast increases required alignment of
>> target type
>> The warning is about casting ((char *)e + phoff) to a struct pointer,
>> where e is aligned but phoff might be garbage, so I think the warning
>> should be emitted on most machines (even on i386's, alignment checking=
>> might be on) and the correct fix would involve validation phoff before=
>> using it.
>>
>> Is this fix correct?
>=20
> No. You need to tell the compiler that e has the alignment you think i=
t has so that it can check to make sure that you are actually right. Jus=
t casting like this defeats the purpose of the check and will break on ot=
her architectures.
>=20
> Warner
>=20
What do you say about this one?
Index: usr.bin/elf2aout/elf2aout.c
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
--- usr.bin/elf2aout/elf2aout.c (revision 239611)
+++ usr.bin/elf2aout/elf2aout.c (working copy)
@@ -126,7 +126,7 @@
entry =3D xe64toh(e->e_entry);
phoff =3D xe64toh(e->e_phoff);
phnum =3D xe16toh(e->e_phnum);
- p =3D (Elf64_Phdr *)((char *)e + phoff);
+ p =3D (Elf64_Phdr *)(e + phoff);
bzero(&a, sizeof(a));
for (i =3D 0; i < phnum; i++) {
type =3D xe32toh(p[i].p_type);
I can build elf2aout without warnings on amd64 in 'buildenv' for all
targets.
>> Index: usr.bin/elf2aout/elf2aout.c
>> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
>> --- usr.bin/elf2aout/elf2aout.c (revision 239611)
>> +++ usr.bin/elf2aout/elf2aout.c (working copy)
>> @@ -126,7 +126,7 @@
>> entry =3D xe64toh(e->e_entry);
>> phoff =3D xe64toh(e->e_phoff);
>> phnum =3D xe16toh(e->e_phnum);
>> - p =3D (Elf64_Phdr *)((char *)e + phoff);
>> + p =3D (Elf64_Phdr *)(void *)((char *)e + phoff);
>> bzero(&a, sizeof(a));
>> for (i =3D 0; i < phnum; i++) {
>> type =3D xe32toh(p[i].p_type);
>>
>>
>> --=20
>> Andrey Zonov
>>
>=20
--=20
Andrey Zonov
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