[PATCHv5] gdb: Replace memcpy with std::copy to avoid some g++ warnings on sparc

  For some reason g++ 12.2.1 on sparc produces 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.
---

 V5: Use buf->begin (), buf->end () in second std::copy
 V4: Fix std::copy argument typo
 V3: Drop diagnostic suppressions just use std::copy
 V2: Fix typos and add example errors to commit messages

 gdb/fbsd-tdep.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
  

Am Mittwoch, 25. Januar 2023 um 09:56:03 MEZ hat Mark Wielaard <mark@klomp.org> Folgendes geschrieben:

> For some reason g++ 12.2.1 on sparc produces 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.
> ---
>
> V5: Use buf->begin (), buf->end () in second std::copy
> V4: Fix std::copy argument typo
> V3: Drop diagnostic suppressions just use std::copy
> V2: Fix typos and add example errors to commit messages
>
> gdb/fbsd-tdep.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/gdb/fbsd-tdep.c b/gdb/fbsd-tdep.c
> index 203390d9880..d03ea419aa8 100644
> --- a/gdb/fbsd-tdep.c
> +++ b/gdb/fbsd-tdep.c
> @@ -662,8 +662,8 @@ 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 ());

structsize is of type uint32_t, so wouldn't that effectively copy 4*4 bytes, instead of just 4?

Shouldn't it rather look like this?:

  std::copy (&structsize, &structsize + 1, desc.data ());


> +  std::copy (buf->begin (), buf->end (), desc.data () + sizeof (structsize));
>   return desc;
> }
>
> --
> 2.31.1


Hannes
  

Hi Hannes,

On Wed, Jan 25, 2023 at 12:00:05PM +0000, Hannes Domani wrote:
>  Am Mittwoch, 25. Januar 2023 um 09:56:03 MEZ hat Mark Wielaard <mark@klomp.org> Folgendes geschrieben:
> 
> >   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 ());
> 
> structsize is of type uint32_t, so wouldn't that effectively copy 4*4 bytes, instead of just 4?
> 
> Shouldn't it rather look like this?:
> 
>   std::copy (&structsize, &structsize + 1, desc.data ());

Aha, yeah, std::copy acts on the whole elements of the input. Maybe
less confusing to just keep using memcpy here. It is only the second
memcpy that produces the issue on sparc. That also brings down the fix
to a simple oneliner. Will sent a v6.

Thanks,

Mark