Re: [PATCH 2/2] util/compatfd.c: Replaced a malloc call with g_malloc.

[Philippe Mathieu-Daudé]

Hi Mahmoud,

On 3/15/21 11:58 AM, Mahmoud Mandour wrote:
> Replaced a call to malloc() and its respective call to free()
> with g_malloc() and g_free().
> 
> g_malloc() is preferred more than g_try_* functions, which
> return NULL on error, when the size of the requested
> allocation  is small. This is because allocating few
> bytes should not be a problem in a healthy system.
> Otherwise, the system is already in a critical state.
> 
> Subsequently, removed NULL-checking after g_malloc().
> 
> Signed-off-by: Mahmoud Mandour <ma.mandourr@gmail.com>
> ---
>  util/compatfd.c | 8 ++------
>  1 file changed, 2 insertions(+), 6 deletions(-)
> 
> diff --git a/util/compatfd.c b/util/compatfd.c
> index 174f394533..a8ec525c6c 100644
> --- a/util/compatfd.c
> +++ b/util/compatfd.c
> @@ -72,14 +72,10 @@ static int qemu_signalfd_compat(const sigset_t *mask)
>      QemuThread thread;
>      int fds[2];
>  
> -    info = malloc(sizeof(*info));
> -    if (info == NULL) {
> -        errno = ENOMEM;
> -        return -1;
> -    }
> +    info = g_malloc(sizeof(*info));

Watch out...

https://developer.gnome.org/glib/stable/glib-Memory-Allocation.html

  If any call to allocate memory using functions g_new(), g_new0(),
  g_renew(), g_malloc(), g_malloc0(), g_malloc0_n(), g_realloc(),
  and g_realloc_n() fails, the application is terminated.

So with your change instead of handling ENOMEM the QEMU process is
simply killed.

Don't you want to use g_try_new(struct sigfd_compat_info, 1) here
instead?

>  
>      if (pipe(fds) == -1) {
> -        free(info);
> +        g_free(info);
>          return -1;
>      }
>  
>