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

[Stefan Weil <sw@weilnetz.de>]

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;
>>         }
>>
>>
>> gcc is too stupid to understand the control flow.  The initialization
>> shuts it up.
> Looks like most people's GCC is not that stupid, or I would have broken
> build for everyone, right?
>
> Paolo


Hi Paolo,

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]
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 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.

Regards
Stefan