[PATCHv3] gdb: Replace memcpy with std::copy to avoid some g++ warnings on sparc

  For some reason g++ 12.2.1 on sparc produces a spurious warnings for
stringop-overread and restrict in fbsd-tdep.c for some memcpy calls.
Use std::copy to avoid those.

In function ‘void* memcpy(void*, const void*, size_t)’,
    inlined from ‘gdb::optional<std::vector<unsigned char, gdb::default_init_allocator<unsigned char, std::allocator<unsigned char> > > > fbsd_make_note_desc(target_object, uint32_t)’ at ../../binutils-gdb/gdb/fbsd-tdep.c:666:10:
/usr/include/bits/string_fortified.h:29:33: error: ‘void* __builtin_memcpy(void*, const void*, long unsigned int)’ specified bound 18446744073709551612 exceeds maximum object size 9223372036854775807 [-Werror=stringop-overflow=]

In function ‘void* memcpy(void*, const void*, size_t)’,
    inlined from ‘gdb::optional<std::vector<unsigned char, gdb::default_init_allocator<unsigned char, std::allocator<unsigned char> > > > fbsd_make_note_desc(target_object, uint32_t)’ at ../../binutils-gdb/gdb/fbsd-tdep.c:673:10:
/usr/include/bits/string_fortified.h:29:33: error: ‘void* __builtin_memcpy(void*, const void*, long unsigned int)’ accessing 18446744073709551612 bytes at offsets 0 and 0 overlaps 9223372036854775801 bytes at offset -9223372036854775805 [-Werror=restrict]

gdb/ChangeLog:

	* fbsd-tdep.c (fbsd_make_note_desc): Use std::copy instead
	of memcpy.
---

V3: Drop diagnostic suppressions just use std::copy
V2: Fix typos and add example errors to commit messages

 gdb/fbsd-tdep.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)
  

On 1/24/23 15:16, Mark Wielaard wrote:
> For some reason g++ 12.2.1 on sparc produces a spurious warnings for
> stringop-overread and restrict in fbsd-tdep.c for some memcpy calls.
> Use std::copy to avoid those.
> 
> In function ‘void* memcpy(void*, const void*, size_t)’,
>     inlined from ‘gdb::optional<std::vector<unsigned char, gdb::default_init_allocator<unsigned char, std::allocator<unsigned char> > > > fbsd_make_note_desc(target_object, uint32_t)’ at ../../binutils-gdb/gdb/fbsd-tdep.c:666:10:
> /usr/include/bits/string_fortified.h:29:33: error: ‘void* __builtin_memcpy(void*, const void*, long unsigned int)’ specified bound 18446744073709551612 exceeds maximum object size 9223372036854775807 [-Werror=stringop-overflow=]
> 
> In function ‘void* memcpy(void*, const void*, size_t)’,
>     inlined from ‘gdb::optional<std::vector<unsigned char, gdb::default_init_allocator<unsigned char, std::allocator<unsigned char> > > > fbsd_make_note_desc(target_object, uint32_t)’ at ../../binutils-gdb/gdb/fbsd-tdep.c:673:10:
> /usr/include/bits/string_fortified.h:29:33: error: ‘void* __builtin_memcpy(void*, const void*, long unsigned int)’ accessing 18446744073709551612 bytes at offsets 0 and 0 overlaps 9223372036854775801 bytes at offset -9223372036854775805 [-Werror=restrict]
> 
> gdb/ChangeLog:
> 
> 	* fbsd-tdep.c (fbsd_make_note_desc): Use std::copy instead
> 	of memcpy.
> ---
> 
> V3: Drop diagnostic suppressions just use std::copy
> V2: Fix typos and add example errors to commit messages
> 
>  gdb/fbsd-tdep.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/gdb/fbsd-tdep.c b/gdb/fbsd-tdep.c
> index 203390d9880..ebc15543149 100644
> --- a/gdb/fbsd-tdep.c
> +++ b/gdb/fbsd-tdep.c
> @@ -662,8 +662,9 @@ fbsd_make_note_desc (enum target_object object, uint32_t structsize)
>      return buf;
>  
>    gdb::byte_vector desc (sizeof (structsize) + buf->size ());
> -  memcpy (desc.data (), &structsize, sizeof (structsize));
> -  memcpy (desc.data () + sizeof (structsize), buf->data (), buf->size ());
> +  std::copy (&structsize, &structsize + sizeof (structsize), desc.data ());
> +  std::copy (buf->data (), desc.data () + sizeof (structsize),
> +	     desc.data () + sizeof (structsize));

I think the second argument to the second std::copy call should have
`buf->data ()`, not `desc.data ().  Otherwise, LGTM.  However, it would
be nice to have the approval from John Baldwin.

Simon
  

Hi Simon,

On Tue, Jan 24, 2023 at 04:29:20PM -0500, Simon Marchi wrote:
> > diff --git a/gdb/fbsd-tdep.c b/gdb/fbsd-tdep.c
> > index 203390d9880..ebc15543149 100644
> > --- a/gdb/fbsd-tdep.c
> > +++ b/gdb/fbsd-tdep.c
> > @@ -662,8 +662,9 @@ fbsd_make_note_desc (enum target_object object, uint32_t structsize)
> >      return buf;
> >  
> >    gdb::byte_vector desc (sizeof (structsize) + buf->size ());
> > -  memcpy (desc.data (), &structsize, sizeof (structsize));
> > -  memcpy (desc.data () + sizeof (structsize), buf->data (), buf->size ());
> > +  std::copy (&structsize, &structsize + sizeof (structsize), desc.data ());
> > +  std::copy (buf->data (), desc.data () + sizeof (structsize),
> > +	     desc.data () + sizeof (structsize));
> 
> I think the second argument to the second std::copy call should have
> `buf->data ()`, not `desc.data ().  Otherwise, LGTM.  However, it would
> be nice to have the approval from John Baldwin.

Bah, what a stupid typo. You are right of course. Sorry. v4 coming up.

Thanks,

Mark