Re: [PATCH 08/26] gdbserver: convert free_register_cache into a destructor of regcache

Simon Marchi
2023-12-21T20:57:57Z

On 2/28/23 06:28, Tankut Baris Aktemur via Gdb-patches wrote:
> Convert the `free_register_cache` function into a destructor of the
> regcache struct. In one place, we completely remove the call to free
> the regcache object by stack-allocating the object.
>
> We also delete the copy constructor explicitly to prevent the risk of
> copying regcaches and then double-freeing buffers when they are
> destructed.
> ---
> gdbserver/gdbthread.h | 2 +-
> gdbserver/regcache.cc | 15 +++++----------
> gdbserver/regcache.h | 9 +++++----
> gdbserver/server.cc | 8 +++-----
> 4 files changed, 14 insertions(+), 20 deletions(-)
>
> diff --git a/gdbserver/gdbthread.h b/gdbserver/gdbthread.h
> index 493e1dbf6cb..cfd81870af9 100644
> --- a/gdbserver/gdbthread.h
> +++ b/gdbserver/gdbthread.h
> @@ -35,7 +35,7 @@ struct thread_info
>
> ~thread_info ()
> {
> - free_register_cache (this->regcache_data);
> + delete this->regcache_data;

Perhaps in another patch, but you could make regcache_data a unique_ptr
(I quickly skimmed the subjects of the rest of the series and didn't see
a patch that would do that).

> }
>
> /* The id of this thread. */
> diff --git a/gdbserver/regcache.cc b/gdbserver/regcache.cc
> index be01df342bb..7b6337166ad 100644
> --- a/gdbserver/regcache.cc
> +++ b/gdbserver/regcache.cc
> @@ -165,16 +165,11 @@ regcache::regcache (const target_desc *tdesc)
> initialize (tdesc, nullptr);
> }
>
> -void
> -free_register_cache (struct regcache *regcache)
> +regcache::~regcache ()
> {
> - if (regcache)
> - {
> - if (regcache->registers_owned)
> - free (regcache->registers);
> - free (regcache->register_status);
> - delete regcache;
> - }
> + if (registers_owned)
> + free (registers);
> + free (register_status);
> }
>
> #endif
> @@ -280,7 +275,7 @@ free_register_cache_thread (struct thread_info *thread)
> if (regcache != NULL)
> {
> regcache_invalidate_thread (thread);
> - free_register_cache (regcache);
> + delete regcache;
> set_thread_regcache_data (thread, NULL);
> }
> }
> diff --git a/gdbserver/regcache.h b/gdbserver/regcache.h
> index 32b3a8dccfc..614d5a2561f 100644
> --- a/gdbserver/regcache.h
> +++ b/gdbserver/regcache.h
> @@ -51,6 +51,11 @@ struct regcache : public reg_buffer_common
> /* Constructors. */
> regcache () = default;
> regcache (const target_desc *tdesc);
> + regcache (const regcache &rhs) = delete;
> + regcache &operator= (const regcache &rhs) = delete;

Use DISALLOW_COPY_AND_ASSIGN. And I think it wouldn't hurt to put it
outside of the `#ifndef IN_PROCESS_AGENT`. If you follow my previous
suggestions, the constructor with 2 arguments would also need to be
outside the ifndef.

> +
> + /* Deconstructor. */
> + virtual ~regcache ();

Deconstructor -> Destructor :)

But really, I don't think it's necessary, anybody slightly familiar with
C++ will know this is the destructor... as you wish.

I guess you might need in the rest of the series, but as of now the
destructor doesn't need to be virtual, so I wouldn't make it virtual
in this patch.

Simon