Re: [PATCH v3] tftp.h: rework layout to work with fortification

[Mike Frysinger <vapier at gentoo dot org>]

On Monday 07 May 2012 11:52:18 Carlos O'Donell wrote:
> On Mon, May 7, 2012 at 11:51 AM, Joseph S. Myers wrote:
> > On Mon, 7 May 2012, Carlos O'Donell wrote:
> >> On Mon, May 7, 2012 at 10:38 AM, Joseph S. Myers wrote:
> >> > On Mon, 7 May 2012, Carlos O'Donell wrote:
> >> >> It still doesn't work with -Wall -Werror -pedantic because zero sized
> >> >> arrays are not allowed in ISO C.
> >> > 
> >> > This should not give errors in system headers.  Have you found such an
> >> > error with the header installed in a system header directory?  If so,
> >> > that would be a GCC bug.
> >> 
> >> No, I haven't tried installing this and testing.
> >> 
> >> I didn't know that GCC had special handling for system headers.
> >> 
> >> How does that work?
> > 
> > Most warnings are not emitted for locations in system headers (those
> > found in system header directories, with -isystem or marked with #pragma
> > GCC system_header), unless -Wsystem-headers.  This applies before
> > pedwarns are turned into errors.
> 
> Thanks, I wasn't aware of this special handling.
> 
> In that case if Mike can show that the installed header works with
> -Werror -Wall -pedantic then I'm happy with the final version.

$ echo '#include <arpa/tftp.h>' | gcc -x c -c - -Werror -Wall -pedantic
$ echo $?
0
$ echo '#include <arpa/tftp.h>' | gcc -E -dD - | sed -n '/^struct tftphdr/,/^}/p'
struct tftphdr {
 short th_opcode;
 union {
  char tu_padding[3];
  struct {
   union {
    unsigned short tu_block;
    short tu_code;
   } __attribute__ ((__packed__)) th_u3;
   char tu_data[0];
  } __attribute__ ((__packed__)) th_u2;
  char tu_stuff[0];
 } __attribute__ ((__packed__)) th_u1;
} __attribute__ ((__packed__));

i would have used flexible arrays but gcc doesn't allow those in unions:
tftp.h:60:8: error: flexible array member in union
-mike

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