RE: [PATCH] tools: hv: Fix a complier warning in the fcopy uio daemon

[Dexuan Cui]

> From: Saurabh Singh Sengar <ssengar@xxxxxxxxxxxxxxxxxxx>
> Sent: Friday, September 13, 2024 12:31 AM
> To: Dexuan Cui <decui@xxxxxxxxxxxxx>
> Cc: KY Srinivasan <kys@xxxxxxxxxxxxx>; Haiyang Zhang
> <haiyangz@xxxxxxxxxxxxx>; Wei Liu <wei.liu@xxxxxxxxxx>; Long Li
> <longli@xxxxxxxxxxxxx>; Greg Kroah-Hartman
> <gregkh@xxxxxxxxxxxxxxxxxxx>; open list:Hyper-V/Azure CORE AND DRIVERS
> <linux-hyperv@xxxxxxxxxxxxxxx>; open list <linux-kernel@xxxxxxxxxxxxxxx>;
> stable@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH] tools: hv: Fix a complier warning in the fcopy uio
> daemon
> 
> On Tue, Sep 10, 2024 at 12:44:32AM +0000, Dexuan Cui wrote:
> > hv_fcopy_uio_daemon.c:436:53: warning: '%s' directive output may be
> truncated
> > writing up to 14 bytes into a region of size 10 [-Wformat-truncation=]
> >   436 |  snprintf(uio_dev_path, sizeof(uio_dev_path), "/dev/%s",
> uio_name);
> 
> Makefile today doesn't have -Wformat-truncation flag enabled, I tried to add
> -Wformat-truncation=2 but I don't see any error in this file.
> 
> Do you mind sharing more details how you get this error ?
> 
> - Saurabh

This repros in a Ubuntu 20.04 VM:

root@decui-u2004-2024-0920:~/linux/tools/hv# cat /etc/os-release
NAME="Ubuntu"
VERSION="20.04.6 LTS (Focal Fossa)"
...

root@decui-u2004-2024-0920:~/linux/tools/hv# gcc --version
gcc (Ubuntu 9.4.0-1ubuntu1~20.04.2) 9.4.0
Copyright (C) 2019 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

root@decui-u2004-2024-0920:~/linux/tools/hv# make clean; make
...
make -f /root/linux/tools/build/Makefile.build dir=. obj=hv_fcopy_uio_daemon
make[1]: Entering directory '/root/linux/tools/hv'
  CC      hv_fcopy_uio_daemon.o
hv_fcopy_uio_daemon.c: In function 'main':
hv_fcopy_uio_daemon.c:443:53: warning: '%s' directive output may be truncated writing up to 14 bytes into a region of size 10 [-Wformat-truncation=]
  443 |  snprintf(uio_dev_path, sizeof(uio_dev_path), "/dev/%s", uio_name);
      |                                                     ^~   ~~~~~~~~
In file included from /usr/include/stdio.h:867,
                 from hv_fcopy_uio_daemon.c:20:
/usr/include/x86_64-linux-gnu/bits/stdio2.h:67:10: note: '__builtin___snprintf_chk' output between 6 and 20 bytes into a destination of size 15
   67 |   return __builtin___snprintf_chk (__s, __n, __USE_FORTIFY_LEVEL - 1,
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   68 |        __bos (__s), __fmt, __va_arg_pack ());
      |        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  CC      vmbus_bufring.o
  LD      hv_fcopy_uio_daemon-in.o
make[1]: Leaving directory '/root/linux/tools/hv'
  LINK    hv_fcopy_uio_daemon