Re: [PATCH] gdb: fix sparc memcpy fortify error

[Mark Kettenis <mark.kettenis@xs4all.nl>]

> From: Mike Frysinger <vapier@gentoo.org>
> Date: Thu, 18 Mar 2010 22:09:09 -0400
> 
> Building on an x86_64-linux system with --enable-targets=all fails on the
> sparc code with a fortify error:
> 
> cc1: warnings being treated as errors
> In file included from /usr/include/string.h:640,
>                  from gnulib/string.h:23,
>                  from ../../gdb/gdb_string.h:25,
>                  from ../../gdb/vec.h:25,
>                  from ../../gdb/memattr.h:24,
>                  from ../../gdb/target.h:60,
>                  from ../../gdb/exec.h:23,
>                  from ../../gdb/gdbcore.h:31,
>                  from ../../gdb/sparc-tdep.c:29:
> In function 'memcpy',
>     inlined from 'sparc32_store_return_value' at ../../gdb/sparc-tdep.c:1112,
>     inlined from 'sparc32_return_value' at ../../gdb/sparc-tdep.c:1170:
> /usr/include/bits/string3.h:52: error: call to __builtin___memcpy_chk will
> 	always overflow destination buffer
> make: *** [sparc-tdep.o] Error 1

That's a false positive I'm afraid.  I agree that it isn't trivial to
see that there is no buffer overflow here.  Unfortunately your
solution is a bit problematic:

> 2010-03-18  Mike Frysinger  <vapier@gentoo.org>
> 
> 	* gdb/sparc-tdep.c (sparc32_store_return_value): Declare the length
> 	of buf using the "len" variable.
> 
>  gdb/sparc-tdep.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/gdb/sparc-tdep.c b/gdb/sparc-tdep.c
> index f129a55..ea0cdd2 100644
> --- a/gdb/sparc-tdep.c
> +++ b/gdb/sparc-tdep.c
> @@ -1101,7 +1101,7 @@ sparc32_store_return_value (struct type *type, struct regcache *regcache,
>  			    const gdb_byte *valbuf)
>  {
>    int len = TYPE_LENGTH (type);
> -  gdb_byte buf[8];
> +  gdb_byte buf[max(len, 8)];

Sorry, but variable sized arrays aren't C90.

Does it help if you replace

>    gdb_assert (!(sparc_floating_p (type) && len == 16));

with

     gdb_assert (len <= 8);

?