Re: [Xen-devel] [PATCH v3] tools: fix several "format-truncation" warnings with GCC 7

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Tue, Jun 20, 2017 at 11:58:53AM +0100, Julien Grall wrote:
> Hi Wei,
> 
> On 06/19/2017 12:39 PM, Wei Liu wrote:
> > On Wed, Jun 14, 2017 at 09:11:48AM +0800, Zhongze Liu wrote:
> > > GCC 7.1.1 complains that several buffers passed to snprintf() in xenpmd
> > > and tools/ocmal/xc are too small to hold the largest possible resulting 
> > > string,
> > > which is calculated by adding up the maximum length of all the substrings.
> > > 
> > > The warnings are treated as errors by -Werror, and goes like this 
> > > (abbreviated):
> > > 
> > > xenpmd.c:94:36: error: ‘%s’ directive output may be truncated writing up 
> > > to
> > > 255 bytes into a region of size 13 [-Werror=format-truncation=]
> > >       #define BATTERY_INFO_FILE_PATH "/proc/acpi/battery/%s/info"
> > >                                      ^
> > > xenpmd.c:113:13: note: ‘snprintf’ output between 25 and 280 bytes into a
> > > destination of size 32
> > > 
> > > xenpmd.c:95:37: error: ‘%s’ directive output may be truncated writing up 
> > > to
> > > 255 bytes into a region of size 13 [-Werror=format-truncation=]
> > >       #define BATTERY_STATE_FILE_PATH "/proc/acpi/battery/%s/state"
> > >                                       ^
> > > xenpmd.c:116:13: note: ‘snprintf’ output between 26 and 281 bytes into a
> > > destination of size 32
> > > 
> > > xenctrl_stubs.c:65:15: error: ‘%s’ directive output may be truncated 
> > > writing
> > > up to 1023 bytes into a region of size 252 [-Werror=format-truncation=]
> > >        "%d: %s: %s", error->code,
> > >                 ^~
> > > xenctrl_stubs.c:64:4: note: ‘snprintf’ output 5 or more bytes (assuming 
> > > 1028)
> > > into a destination of size 256
> > > 
> > > Enlarge the size of these buffers as suggested by the complier
> > > (and slightly rounded) to fix the warnings.
> > > 
> > > No functional changes.
> > > 
> > > Signed-off-by: Zhongze Liu <blackskygg@xxxxxxxxx>
> > > Acked-by: Wei Liu <wei.liu2@xxxxxxxxxx>
> > 
> > Applied.
> > 
> > Julien, consider this for 4.9?
> 
> Looking quickly at the patch, it sounds a bit strange to allocate 1028 bytes
> on the stack. It is more than 1/8 of default stack in Linux (8K). Are we
> sure the stack will never explode?
> 

The default stack size is 8M, not 8K so we it be fine.

> Cheers,
> 
> -- 
> Julien Grall

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