[PATCH] tools/xenmpd: Fix gcc10 snprintf warning

Bertrand Marquis posted 1 patch 2 weeks ago
Patches applied successfully (tree, apply log)
git fetch https://github.com/patchew-project/xen tags/patchew/0ade4264c537819c3dd45179fcea2723df66b045.1602672245.git.bertrand.marquis@arm.com
Maintainers: Wei Liu <wl@xen.org>, Ian Jackson <iwj@xenproject.org>
tools/xenpmd/xenpmd.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)

[PATCH] tools/xenmpd: Fix gcc10 snprintf warning

Posted by Bertrand Marquis 2 weeks ago
Add a check for snprintf return code and ignore the entry if we get an
error. This should in fact never happen and is more a trick to make gcc
happy and prevent compilation errors.

This is solving the gcc warning:
xenpmd.c:92:37: error: '%s' directive output may be truncated writing
between 4 and 2147483645 bytes into a region of size 271
[-Werror=format-truncation=]

Signed-off-by: Bertrand Marquis <bertrand.marquis@arm.com>
---
 tools/xenpmd/xenpmd.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/tools/xenpmd/xenpmd.c b/tools/xenpmd/xenpmd.c
index 35fd1c931a..12b82cf43e 100644
--- a/tools/xenpmd/xenpmd.c
+++ b/tools/xenpmd/xenpmd.c
@@ -102,6 +102,7 @@ FILE *get_next_battery_file(DIR *battery_dir,
     FILE *file = 0;
     struct dirent *dir_entries;
     char file_name[284];
+    int ret;
     
     do 
     {
@@ -111,11 +112,15 @@ FILE *get_next_battery_file(DIR *battery_dir,
         if ( strlen(dir_entries->d_name) < 4 )
             continue;
         if ( battery_info_type == BIF ) 
-            snprintf(file_name, sizeof(file_name), BATTERY_INFO_FILE_PATH,
+            ret = snprintf(file_name, sizeof(file_name), BATTERY_INFO_FILE_PATH,
                      dir_entries->d_name);
         else 
-            snprintf(file_name, sizeof(file_name), BATTERY_STATE_FILE_PATH,
+            ret = snprintf(file_name, sizeof(file_name), BATTERY_STATE_FILE_PATH,
                      dir_entries->d_name);
+        /* This should not happen but is needed to pass gcc checks */
+        if (ret < 0)
+            continue;
+        file_name[sizeof(file_name) - 1] = '\0';
         file = fopen(file_name, "r");
     } while ( !file );
 
-- 
2.17.1


Re: [PATCH] tools/xenmpd: Fix gcc10 snprintf warning

Posted by Julien Grall 2 weeks ago
Hi,

On 14/10/2020 11:47, Bertrand Marquis wrote:
> Add a check for snprintf return code and ignore the entry if we get an
> error. This should in fact never happen and is more a trick to make gcc
> happy and prevent compilation errors.
> 
> This is solving the gcc warning:
> xenpmd.c:92:37: error: '%s' directive output may be truncated writing
> between 4 and 2147483645 bytes into a region of size 271
> [-Werror=format-truncation=]

IIRC, this is only affecting GCC when building for Arm32 *and* when the 
optimizer is enabled. If so, it would be good to add more details in the 
commit message.

I would also suggest to link to the bug reported on Debian.

Cheers,

> 
> Signed-off-by: Bertrand Marquis <bertrand.marquis@arm.com>
> ---
>   tools/xenpmd/xenpmd.c | 9 +++++++--
>   1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/xenpmd/xenpmd.c b/tools/xenpmd/xenpmd.c
> index 35fd1c931a..12b82cf43e 100644
> --- a/tools/xenpmd/xenpmd.c
> +++ b/tools/xenpmd/xenpmd.c
> @@ -102,6 +102,7 @@ FILE *get_next_battery_file(DIR *battery_dir,
>       FILE *file = 0;
>       struct dirent *dir_entries;
>       char file_name[284];
> +    int ret;
>       
>       do
>       {
> @@ -111,11 +112,15 @@ FILE *get_next_battery_file(DIR *battery_dir,
>           if ( strlen(dir_entries->d_name) < 4 )
>               continue;
>           if ( battery_info_type == BIF )
> -            snprintf(file_name, sizeof(file_name), BATTERY_INFO_FILE_PATH,
> +            ret = snprintf(file_name, sizeof(file_name), BATTERY_INFO_FILE_PATH,
>                        dir_entries->d_name);
>           else
> -            snprintf(file_name, sizeof(file_name), BATTERY_STATE_FILE_PATH,
> +            ret = snprintf(file_name, sizeof(file_name), BATTERY_STATE_FILE_PATH,
>                        dir_entries->d_name);
> +        /* This should not happen but is needed to pass gcc checks */
> +        if (ret < 0)
> +            continue;
> +        file_name[sizeof(file_name) - 1] = '\0';
>           file = fopen(file_name, "r");
>       } while ( !file );
>   
> 

Cheers,

-- 
Julien Grall

Re: [PATCH] tools/xenmpd: Fix gcc10 snprintf warning

Posted by Bertrand Marquis 2 weeks ago
Hi Julien,

> On 14 Oct 2020, at 12:04, Julien Grall <julien@xen.org> wrote:
> 
> Hi,
> 
> On 14/10/2020 11:47, Bertrand Marquis wrote:
>> Add a check for snprintf return code and ignore the entry if we get an
>> error. This should in fact never happen and is more a trick to make gcc
>> happy and prevent compilation errors.
>> This is solving the gcc warning:
>> xenpmd.c:92:37: error: '%s' directive output may be truncated writing
>> between 4 and 2147483645 bytes into a region of size 271
>> [-Werror=format-truncation=]
> 
> IIRC, this is only affecting GCC when building for Arm32 *and* when the optimizer is enabled. If so, it would be good to add more details in the commit message.

I can confirm this is the only build catching it on my side.

I will modify the commit message to say that the problem was encountered on arm32 build with the optimizer enabled.

> 
> I would also suggest to link to the bug reported on Debian.

I will add it to the commit message.

Cheers
Bertrand

> 
> Cheers,
> 
>> Signed-off-by: Bertrand Marquis <bertrand.marquis@arm.com>
>> ---
>>  tools/xenpmd/xenpmd.c | 9 +++++++--
>>  1 file changed, 7 insertions(+), 2 deletions(-)
>> diff --git a/tools/xenpmd/xenpmd.c b/tools/xenpmd/xenpmd.c
>> index 35fd1c931a..12b82cf43e 100644
>> --- a/tools/xenpmd/xenpmd.c
>> +++ b/tools/xenpmd/xenpmd.c
>> @@ -102,6 +102,7 @@ FILE *get_next_battery_file(DIR *battery_dir,
>>      FILE *file = 0;
>>      struct dirent *dir_entries;
>>      char file_name[284];
>> +    int ret;
>>            do
>>      {
>> @@ -111,11 +112,15 @@ FILE *get_next_battery_file(DIR *battery_dir,
>>          if ( strlen(dir_entries->d_name) < 4 )
>>              continue;
>>          if ( battery_info_type == BIF )
>> -            snprintf(file_name, sizeof(file_name), BATTERY_INFO_FILE_PATH,
>> +            ret = snprintf(file_name, sizeof(file_name), BATTERY_INFO_FILE_PATH,
>>                       dir_entries->d_name);
>>          else
>> -            snprintf(file_name, sizeof(file_name), BATTERY_STATE_FILE_PATH,
>> +            ret = snprintf(file_name, sizeof(file_name), BATTERY_STATE_FILE_PATH,
>>                       dir_entries->d_name);
>> +        /* This should not happen but is needed to pass gcc checks */
>> +        if (ret < 0)
>> +            continue;
>> +        file_name[sizeof(file_name) - 1] = '\0';
>>          file = fopen(file_name, "r");
>>      } while ( !file );
>>  
> 
> Cheers,
> 
> -- 
> Julien Grall