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Re: [PATCH] migration: Silence compiler warning in global_state_store_ru
From: |
Thomas Huth |
Subject: |
Re: [PATCH] migration: Silence compiler warning in global_state_store_running() |
Date: |
Thu, 17 Sep 2020 09:29:32 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 |
On 17/09/2020 09.18, Paolo Bonzini wrote:
> On 17/09/20 08:30, Thomas Huth wrote:
>> On 16/09/2020 19.19, Thomas Huth wrote:
>>> GCC 9.3.0 on Ubuntu complains:
>>>
>>> In file included from /usr/include/string.h:495,
>>> from /home/travis/build/huth/qemu/include/qemu/osdep.h:87,
>>> from ../migration/global_state.c:13:
>>> In function ‘strncpy’,
>>> inlined from ‘global_state_store_running’ at
>>> ../migration/global_state.c:47:5:
>>> /usr/include/x86_64-linux-gnu/bits/string_fortified.h:106:10: error:
>>> ‘__builtin_strncpy’ specified bound 100 equals destination size
>>> [-Werror=stringop-truncation]
>>> 106 | return __builtin___strncpy_chk (__dest, __src, __len, __bos
>>> (__dest));
>>> |
>>> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>>
>>> ... but we apparently really want to do the strncpy here. Silence the
>>> warning with QEMU_NONSTRING.
>>>
>>> Signed-off-by: Thomas Huth <thuth@redhat.com>
>>> ---
>>> migration/global_state.c | 4 ++--
>>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/migration/global_state.c b/migration/global_state.c
>>> index 25311479a4..f1355d7d97 100644
>>> --- a/migration/global_state.c
>>> +++ b/migration/global_state.c
>>> @@ -43,9 +43,9 @@ int global_state_store(void)
>>> void global_state_store_running(void)
>>> {
>>> const char *state = RunState_str(RUN_STATE_RUNNING);
>>> + QEMU_NONSTRING char *dest = (char *)global_state.runstate;
>>> assert(strlen(state) < sizeof(global_state.runstate));
>>> - strncpy((char *)global_state.runstate,
>>> - state, sizeof(global_state.runstate));
>>> + strncpy(dest, state, sizeof(global_state.runstate));
>>> }
>>
>> Darn, I was sending too fast here, sorry, but seems like this does *not*
>> fix the issue with GCC 9.3:
>>
>> https://travis-ci.com/github/huth/qemu/jobs/385871010#L2930
>>
>> ... so maybe we should simply switch to strpadcpy() instead?
>
> Yes, and probably do so everywhere that strncpy is used.
I think the trick with QEMU_NONSTRING should work fine in all cases
where we have a real array, see e.g. buf[] in find_vdi_name() in
block/sheepdog.c. It just does not seem to work in case you have a char*
pointer instead of an array...
Thomas