Re: [PATCH] Handle encoding failures in Windows thread names

[Jon Turney <jon.turney@dronecode.org.uk>]

On 21/04/2022 15:39, Tom Tromey via Gdb-patches wrote:
> Internally at AdaCore, we noticed that the new Windows thread name
> code could fail.  First, it might return a zero-length string, but in
> gdb conventions it should return nullptr instead.  Second, an encoding
> failure could wind up showing replacement characters to the user; this
> is confusing and not useful; it's better to recognize such errors and
> simply discard the name.  This patch makes both of these changes.
> ---
>   gdb/nat/windows-nat.c | 17 ++++++++++++-----
>   1 file changed, 12 insertions(+), 5 deletions(-)
> 
> diff --git a/gdb/nat/windows-nat.c b/gdb/nat/windows-nat.c
> index bd1b9459145..7a4e804f891 100644
> --- a/gdb/nat/windows-nat.c
> +++ b/gdb/nat/windows-nat.c
> @@ -119,12 +119,19 @@ windows_thread_info::thread_name ()
>         HRESULT result = GetThreadDescription (h, &value);
>         if (SUCCEEDED (result))
>   	{
> -	  size_t needed = wcstombs (nullptr, value, 0);
> -	  if (needed != (size_t) -1)
> +	  int needed = WideCharToMultiByte (CP_ACP, 0, value, -1, nullptr, 0,
> +					    nullptr, nullptr);
> +	  if (needed != 0)
>   	    {
> -	      name.reset ((char *) xmalloc (needed));
> -	      if (wcstombs (name.get (), value, needed) == (size_t) -1)
> -		name.reset ();
> +	      BOOL used_default = FALSE;
> +	      gdb::unique_xmalloc_ptr<char> new_name
> +		((char *) xmalloc (needed));
> +	      if (WideCharToMultiByte (CP_ACP, 0, value, -1,
> +				       new_name.get (), needed,
> +				       nullptr, &used_default) == needed
> +		  && !used_default
> +		  && strlen (new_name.get ()) > 0)
> +		name = std::move (new_name);
>   	    }
>   	  LocalFree (value);
>   	}

This is probably wrong on Cygwin (as the target encoding should be 
Cygwin's conception of the locale, not the Windows codepage).