Re: [Qemu-devel] [PATCH V2] build: remove compile warning

[Wenchao Xia <xiawenc@linux.vnet.ibm.com>]

于 2013-6-24 22:44, Paolo Bonzini 写道:
> Il 22/06/2013 12:03, Stefan Weil ha scritto:
>> Am 18.06.2013 12:13, schrieb Paolo Bonzini:
>>> Il 07/06/2013 14:17, Markus Armbruster ha scritto:
>>>>> diff --git a/util/iov.c b/util/iov.c
>>>>> index cc6e837..b91cfb9 100644
>>>>> --- a/util/iov.c
>>>>> +++ b/util/iov.c
>>>>> @@ -146,7 +146,7 @@ ssize_t iov_send_recv(int sockfd, struct iovec *iov, unsigned iov_cnt,
>>>>>   {
>>>>>       ssize_t total = 0;
>>>>>       ssize_t ret;
>>>>> -    size_t orig_len, tail;
>>>>> +    size_t orig_len = 0, tail;
>>>>>       unsigned niov;
>>>>>
>>>>>       while (bytes > 0) {
>>>> Here are the uses of orig_len:
>>>>
>>>>          if (tail) {
>>>>              /* second, fixup the last element, and remember the original
>>>>               * length */
>>>>              assert(niov < iov_cnt);
>>>>              assert(iov[niov].iov_len > tail);
>>>>              orig_len = iov[niov].iov_len;
>>>>              iov[niov++].iov_len = tail;
>>>>          }
>>>>
>>>>          ret = do_send_recv(sockfd, iov, niov, do_send);
>>>>
>>>>          /* Undo the changes above before checking for errors */
>>>>          if (tail) {
>>>>              iov[niov-1].iov_len = orig_len;
>>>>          }
>>>>
>>>>
>>
>> I get this warning, too, when I run a normal cross compilation with
>> MinGW-w64:
>>
>> util/iov.c:190:33: warning: ‘orig_len’ may be used uninitialized in this
>> function [-Wuninitialized]
>>
>> My build environment:
>>
>> Debian wheezy with packages gcc-mingw-w64-i686, gcc-mingw-w64-x86-64
>> (4.6.3-14+8).
>>
>> A complete build results in 5 warnings. Here are the other 4 of them:
>>
>> hw/arm/spitz.c:280:0: warning: "MOD_SHIFT" redefined [enabled by default]
>> hw/ppc/spapr.c:673:26: warning: cast from pointer to integer of
>> different size [-Wpointer-to-int-cast]
>
> Isn't this one a Win64 bug?
>
>> hw/ppc/spapr_hcall.c:188:1: warning: control reaches end of non-void
>> function [-Wreturn-type]
>> hw/ppc/spapr_pci.c:454:1: warning: control reaches end of non-void
>> function [-Wreturn-type]
>
> I think you could report this to mingw.  GCC should handle "if (!0)
> foo()" just fine if foo is noreturn, perhaps the "assertion failure"
> runtime function is not noreturn in mingw.
>
>> I already sent a patch for the MOD_SHIFT issue.
>>
>> The remaining 3 warnings are also caused by code which makes it difficult
>> for the compiler to detect that it is correct.
>
> Not as hard as this one, though.
>
> Anyway, I would be okay a fix that makes the code easier to follow for
> compilers (and doesn't have too much duplication so that humans are also
> happy).  But adding "= 0" is the worst, because smart compilers will not
> detect a human's mistakes anymore.
>
> Paolo
>

Hi Palo,
   There is V3 remove uninitlized warning without adding "= 0", could
u take a look for it?

http://lists.nongnu.org/archive/html/qemu-devel/2013-06/msg02348.html

-- 
Best Regards

Wenchao Xia