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[Qemu-devel] [PATCH v2 4/5] linux-user/uname: Fix GCC 9 build warnings

Alistair Francis posted 5 patches 6 years, 6 months ago
[Qemu-devel] [PATCH v2 4/5] linux-user/uname: Fix GCC 9 build warnings
Posted by Alistair Francis 6 years, 6 months ago 
Fix this warning when building with GCC9 on Fedora 30:
In function ‘strncpy’,
    inlined from ‘sys_uname’ at /home/alistair/qemu/linux-user/uname.c:94:3:
/usr/include/bits/string_fortified.h:106:10: error: ‘__builtin_strncpy’ output may be truncated copying 64 bytes from a string of length 64 [-Werror=stringop-truncation]
  106 |   return __builtin___strncpy_chk (__dest, __src, __len, __bos (__dest));
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
---
 linux-user/uname.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/linux-user/uname.c b/linux-user/uname.c
index 313b79dbad..2fc6096a5b 100644
--- a/linux-user/uname.c
+++ b/linux-user/uname.c
@@ -73,7 +73,7 @@ const char *cpu_to_uname_machine(void *cpu_env)
 #define COPY_UTSNAME_FIELD(dest, src) \
   do { \
       /* __NEW_UTS_LEN doesn't include terminating null */ \
-      (void) strncpy((dest), (src), __NEW_UTS_LEN); \
+      (void) memcpy((dest), (src), MIN(strlen(src), __NEW_UTS_LEN)); \
       (dest)[__NEW_UTS_LEN] = '\0'; \
   } while (0)
 
-- 
2.21.0
Re: [Qemu-devel] [PATCH v2 4/5] linux-user/uname: Fix GCC 9 build warnings
Posted by Laurent Vivier 6 years, 6 months ago 
On 01/05/2019 01:28, Alistair Francis wrote:
> Fix this warning when building with GCC9 on Fedora 30:
> In function ‘strncpy’,
>     inlined from ‘sys_uname’ at /home/alistair/qemu/linux-user/uname.c:94:3:
> /usr/include/bits/string_fortified.h:106:10: error: ‘__builtin_strncpy’ output may be truncated copying 64 bytes from a string of length 64 [-Werror=stringop-truncation]
>   106 |   return __builtin___strncpy_chk (__dest, __src, __len, __bos (__dest));
>       |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
> ---
>  linux-user/uname.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/linux-user/uname.c b/linux-user/uname.c
> index 313b79dbad..2fc6096a5b 100644
> --- a/linux-user/uname.c
> +++ b/linux-user/uname.c
> @@ -73,7 +73,7 @@ const char *cpu_to_uname_machine(void *cpu_env)
>  #define COPY_UTSNAME_FIELD(dest, src) \
>    do { \
>        /* __NEW_UTS_LEN doesn't include terminating null */ \
> -      (void) strncpy((dest), (src), __NEW_UTS_LEN); \
> +      (void) memcpy((dest), (src), MIN(strlen(src), __NEW_UTS_LEN)); \

You should use MIN(strlen(src) + 1, __NEW_UTS_LEN) to copy the NUL
character if it is present and fit in __NEW_UTS_LEN.

>        (dest)[__NEW_UTS_LEN] = '\0'; \
>    } while (0)
>  
>
Re: [Qemu-devel] [PATCH v2 4/5] linux-user/uname: Fix GCC 9 build warnings
Posted by Daniel P. Berrangé 6 years, 6 months ago 
On Wed, May 01, 2019 at 11:40:13AM +0200, Laurent Vivier wrote:
> On 01/05/2019 01:28, Alistair Francis wrote:
> > Fix this warning when building with GCC9 on Fedora 30:
> > In function ‘strncpy’,
> >     inlined from ‘sys_uname’ at /home/alistair/qemu/linux-user/uname.c:94:3:
> > /usr/include/bits/string_fortified.h:106:10: error: ‘__builtin_strncpy’ output may be truncated copying 64 bytes from a string of length 64 [-Werror=stringop-truncation]
> >   106 |   return __builtin___strncpy_chk (__dest, __src, __len, __bos (__dest));
> >       |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > 
> > Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
> > ---
> >  linux-user/uname.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/linux-user/uname.c b/linux-user/uname.c
> > index 313b79dbad..2fc6096a5b 100644
> > --- a/linux-user/uname.c
> > +++ b/linux-user/uname.c
> > @@ -73,7 +73,7 @@ const char *cpu_to_uname_machine(void *cpu_env)
> >  #define COPY_UTSNAME_FIELD(dest, src) \
> >    do { \
> >        /* __NEW_UTS_LEN doesn't include terminating null */ \
> > -      (void) strncpy((dest), (src), __NEW_UTS_LEN); \
> > +      (void) memcpy((dest), (src), MIN(strlen(src), __NEW_UTS_LEN)); \
> 
> You should use MIN(strlen(src) + 1, __NEW_UTS_LEN) to copy the NUL
> character if it is present and fit in __NEW_UTS_LEN.

IMHO we shouldn't use strlen at all. I proposed fixing it using sizeof()
instead here:

  https://lists.gnu.org/archive/html/qemu-devel/2019-04/msg02154.html

> 
> >        (dest)[__NEW_UTS_LEN] = '\0'; \
> >    } while (0)

Regards,
Daniel
-- 
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Re: [Qemu-devel] [PATCH v2 4/5] linux-user/uname: Fix GCC 9 build warnings
Posted by Laurent Vivier 6 years, 6 months ago 
On 01/05/2019 11:44, Daniel P. Berrangé wrote:
> On Wed, May 01, 2019 at 11:40:13AM +0200, Laurent Vivier wrote:
>> On 01/05/2019 01:28, Alistair Francis wrote:
>>> Fix this warning when building with GCC9 on Fedora 30:
>>> In function ‘strncpy’,
>>>     inlined from ‘sys_uname’ at /home/alistair/qemu/linux-user/uname.c:94:3:
>>> /usr/include/bits/string_fortified.h:106:10: error: ‘__builtin_strncpy’ output may be truncated copying 64 bytes from a string of length 64 [-Werror=stringop-truncation]
>>>   106 |   return __builtin___strncpy_chk (__dest, __src, __len, __bos (__dest));
>>>       |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>>
>>> Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
>>> ---
>>>  linux-user/uname.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/linux-user/uname.c b/linux-user/uname.c
>>> index 313b79dbad..2fc6096a5b 100644
>>> --- a/linux-user/uname.c
>>> +++ b/linux-user/uname.c
>>> @@ -73,7 +73,7 @@ const char *cpu_to_uname_machine(void *cpu_env)
>>>  #define COPY_UTSNAME_FIELD(dest, src) \
>>>    do { \
>>>        /* __NEW_UTS_LEN doesn't include terminating null */ \
>>> -      (void) strncpy((dest), (src), __NEW_UTS_LEN); \
>>> +      (void) memcpy((dest), (src), MIN(strlen(src), __NEW_UTS_LEN)); \
>>
>> You should use MIN(strlen(src) + 1, __NEW_UTS_LEN) to copy the NUL
>> character if it is present and fit in __NEW_UTS_LEN.
> 
> IMHO we shouldn't use strlen at all. I proposed fixing it using sizeof()
> instead here:
> 
>   https://lists.gnu.org/archive/html/qemu-devel/2019-04/msg02154.html
> 

Yes, it's better.

Thanks,
Laurent
Re: [Qemu-devel] [PATCH v2 4/5] linux-user/uname: Fix GCC 9 build warnings
Posted by Eric Blake 6 years, 6 months ago 
On 5/1/19 4:40 AM, Laurent Vivier wrote:
> On 01/05/2019 01:28, Alistair Francis wrote:
>> Fix this warning when building with GCC9 on Fedora 30:
>> In function ‘strncpy’,
>>     inlined from ‘sys_uname’ at /home/alistair/qemu/linux-user/uname.c:94:3:
>> /usr/include/bits/string_fortified.h:106:10: error: ‘__builtin_strncpy’ output may be truncated copying 64 bytes from a string of length 64 [-Werror=stringop-truncation]
>>   106 |   return __builtin___strncpy_chk (__dest, __src, __len, __bos (__dest));
>>       |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>
>> Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
>> ---
>>  linux-user/uname.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/linux-user/uname.c b/linux-user/uname.c
>> index 313b79dbad..2fc6096a5b 100644
>> --- a/linux-user/uname.c
>> +++ b/linux-user/uname.c
>> @@ -73,7 +73,7 @@ const char *cpu_to_uname_machine(void *cpu_env)
>>  #define COPY_UTSNAME_FIELD(dest, src) \
>>    do { \
>>        /* __NEW_UTS_LEN doesn't include terminating null */ \
>> -      (void) strncpy((dest), (src), __NEW_UTS_LEN); \
>> +      (void) memcpy((dest), (src), MIN(strlen(src), __NEW_UTS_LEN)); \
> 
> You should use MIN(strlen(src) + 1, __NEW_UTS_LEN) to copy the NUL
> character if it is present and fit in __NEW_UTS_LEN.

No, the NUL character is already present, due to the memset() prior to
any use of COPY_UTSNAME_FIELD().  However, the commit message should
call that out, as it is not part of the default 3-line diff.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org
Re: [Qemu-devel] [PATCH v2 4/5] linux-user/uname: Fix GCC 9 build warnings
Posted by Alistair Francis 6 years, 6 months ago 
On Wed, May 1, 2019 at 5:00 AM Eric Blake <eblake@redhat.com> wrote:
>
> On 5/1/19 4:40 AM, Laurent Vivier wrote:
> > On 01/05/2019 01:28, Alistair Francis wrote:
> >> Fix this warning when building with GCC9 on Fedora 30:
> >> In function ‘strncpy’,
> >>     inlined from ‘sys_uname’ at /home/alistair/qemu/linux-user/uname.c:94:3:
> >> /usr/include/bits/string_fortified.h:106:10: error: ‘__builtin_strncpy’ output may be truncated copying 64 bytes from a string of length 64 [-Werror=stringop-truncation]
> >>   106 |   return __builtin___strncpy_chk (__dest, __src, __len, __bos (__dest));
> >>       |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >>
> >> Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

I'm dropping this patch in favour of the other one.

Alistair

> >> ---
> >>  linux-user/uname.c | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/linux-user/uname.c b/linux-user/uname.c
> >> index 313b79dbad..2fc6096a5b 100644
> >> --- a/linux-user/uname.c
> >> +++ b/linux-user/uname.c
> >> @@ -73,7 +73,7 @@ const char *cpu_to_uname_machine(void *cpu_env)
> >>  #define COPY_UTSNAME_FIELD(dest, src) \
> >>    do { \
> >>        /* __NEW_UTS_LEN doesn't include terminating null */ \
> >> -      (void) strncpy((dest), (src), __NEW_UTS_LEN); \
> >> +      (void) memcpy((dest), (src), MIN(strlen(src), __NEW_UTS_LEN)); \
> >
> > You should use MIN(strlen(src) + 1, __NEW_UTS_LEN) to copy the NUL
> > character if it is present and fit in __NEW_UTS_LEN.
>
> No, the NUL character is already present, due to the memset() prior to
> any use of COPY_UTSNAME_FIELD().  However, the commit message should
> call that out, as it is not part of the default 3-line diff.
>
> --
> Eric Blake, Principal Software Engineer
> Red Hat, Inc.           +1-919-301-3226
> Virtualization:  qemu.org | libvirt.org
>

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