Re: [Xen-devel] Re: c/s 23253:a3db6b91f32d causes build failure with gcc 4.4.3-4ubuntu5

[Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>]

On Fri, 2011-05-06 at 13:50 +0100, George Dunlap wrote:
> Unfortunately not.
> 
> Looks like we could either make libxl__domain_bios() a #define (not
> tested), or make the argument "%s" (which seems to work, patch
> attached).
> 
> Adding a format string of just a string seems kind of dumb, but I
> don't think this is a really hot path...

It's actually sensible to use "%s" when the string might be untrusted
but in this case it's really just a string literal, I guess the
laundering through a function is enough to hide that from gcc. Using %s
is the best fix, I think.

Ian. 

> 
>  -George
> 
> 
> On Fri, May 6, 2011 at 1:33 PM, Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx> 
> wrote:
> > On Fri, 2011-05-06 at 12:14 +0100, George Dunlap wrote:
> >
> >> The line in question is:
> >>     libxl__xs_write(gc, XBT_NULL, libxl__sprintf(gc, "%s/bios", path),
> >>                     libxl__domain_bios(gc, info));
> >>
> >> Looks like libxl__xs_write() is expecting the 4th argument to be a
> >> format string...?
> >
> > Yes, and hence it needs to be a const char * not a char *, so we should
> > change both libxl__domain_bios and libxl__xs_write I think.
> >
> > Does this help? It works for me, but my compiler doesn't appear to
> > complain in this way...
> >
> > Ian.
> >
> > 8<-------------------------------------------
> >
> > # HG changeset patch
> > # User Ian Campbell <ian.campbell@xxxxxxxxxx>
> > # Date 1304685175 -3600
> > # Node ID 4e5487962178e7affd7d7d0341a90dde8c60915e
> > # Parent  faca1c90188e536eb0f02992c766d06759be376f
> > libxl: libxl__xs_write format string should be const.
> >
> > George Dunlap reports that gcc 4.4.3 complains:
> >        libxl_dm.c: In function libxl__create_device_mode:
> >        libxl_dm.c:776: error: format not a string literal and no format 
> > arguments
> > And indeed the format argument here is a char * from libxl__domain_bios().
> >
> > Make the argument to libxl__xs_write a const char * and change
> > libxl__domain_bios to return a const char too.
> >
> > Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> >
> > diff -r faca1c90188e -r 4e5487962178 tools/libxl/libxl_dm.c
> > --- a/tools/libxl/libxl_dm.c    Fri May 06 13:14:24 2011 +0100
> > +++ b/tools/libxl/libxl_dm.c    Fri May 06 13:32:55 2011 +0100
> > @@ -68,12 +68,12 @@ const char *libxl__domain_device_model(l
> >     return dm;
> >  }
> >
> > -static char *libxl__domain_bios(libxl__gc *gc,
> > +static const char *libxl__domain_bios(libxl__gc *gc,
> >                                 libxl_device_model_info *info)
> >  {
> >     switch (info->device_model_version) {
> > -    case 1: return libxl__strdup(gc, "rombios");
> > -    case 2: return libxl__strdup(gc, "seabios");
> > +    case 1: return "rombios";
> > +    case 2: return "seabios";
> >     default:return NULL;
> >     }
> >  }
> > diff -r faca1c90188e -r 4e5487962178 tools/libxl/libxl_internal.h
> > --- a/tools/libxl/libxl_internal.h      Fri May 06 13:14:24 2011 +0100
> > +++ b/tools/libxl/libxl_internal.h      Fri May 06 13:32:55 2011 +0100
> > @@ -153,7 +153,7 @@ _hidden char **libxl__xs_kvs_of_flexarra
> >  _hidden int libxl__xs_writev(libxl__gc *gc, xs_transaction_t t,
> >                     char *dir, char **kvs);
> >  _hidden int libxl__xs_write(libxl__gc *gc, xs_transaction_t t,
> > -                   char *path, char *fmt, ...) PRINTF_ATTRIBUTE(4, 5);
> > +                   char *path, const char *fmt, ...) PRINTF_ATTRIBUTE(4, 
> > 5);
> >    /* Each fn returns 0 on success.
> >     * On error: returns -1, sets errno (no logging) */
> >
> > diff -r faca1c90188e -r 4e5487962178 tools/libxl/libxl_xshelp.c
> > --- a/tools/libxl/libxl_xshelp.c        Fri May 06 13:14:24 2011 +0100
> > +++ b/tools/libxl/libxl_xshelp.c        Fri May 06 13:32:55 2011 +0100
> > @@ -69,7 +69,7 @@ int libxl__xs_writev(libxl__gc *gc, xs_t
> >  }
> >
> >  int libxl__xs_write(libxl__gc *gc, xs_transaction_t t,
> > -                   char *path, char *fmt, ...)
> > +                   char *path, const char *fmt, ...)
> >  {
> >     libxl_ctx *ctx = libxl__gc_owner(gc);
> >     char *s;
> >
> >
> >
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@xxxxxxxxxxxxxxxxxxx
> > http://lists.xensource.com/xen-devel
> >



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