Re: [Qemu-devel] [PATCH] ui: Use g_new() & friends where that makes obvious sense

[Markus Armbruster <armbru@redhat.com>]

Eric Blake <eblake@redhat.com> writes:

> On 09/14/2015 05:03 AM, Markus Armbruster wrote:
>> g_new(T, n) is neater than g_malloc(sizeof(T) * n).  It's also safer,
>> for two reasons.  One, it catches multiplication overflowing size_t.
>> Two, it returns T * rather than void *, which lets the compiler catch
>> more type errors.
>> 
>> This commit only touches allocations with size arguments of the form
>> sizeof(T).  Same Coccinelle semantic patch as in commit b45c03f.
>> 
>> Signed-off-by: Markus Armbruster <armbru@redhat.com>
>> ---
>>  ui/console.c      | 2 +-
>>  ui/curses.c       | 2 +-
>>  ui/input-legacy.c | 4 ++--
>>  ui/keymaps.c      | 2 +-
>>  ui/sdl.c          | 2 +-
>>  ui/vnc-jobs.c     | 6 +++---
>>  ui/vnc.c          | 6 +++---
>>  7 files changed, 12 insertions(+), 12 deletions(-)
>
> Reviewed-by: Eric Blake <eblake@redhat.com>
>
>> 
>> diff --git a/ui/console.c b/ui/console.c
>> index 75fc492..6edda1e 100644
>> --- a/ui/console.c
>> +++ b/ui/console.c
>> @@ -449,7 +449,7 @@ static void text_console_resize(QemuConsole *s)
>>      if (s->width < w1)
>>          w1 = s->width;
>>  
>> -    cells = g_malloc(s->width * s->total_height * sizeof(TextCell));
>> +    cells = g_new(TextCell, s->width * s->total_height);
>
> Hopefully s->width * s->total_height can't overflow.

Two billion is a helluva lot of character cells :)

>> @@ -3025,7 +3025,7 @@ static void vnc_connect(VncDisplay *vd, int csock,
>>  
>>      vs->lossy_rect = g_malloc0(VNC_STAT_ROWS * sizeof (*vs->lossy_rect));
>>      for (i = 0; i < VNC_STAT_ROWS; ++i) {
>> -        vs->lossy_rect[i] = g_malloc0(VNC_STAT_COLS * sizeof (uint8_t));
>> +        vs->lossy_rect[i] = g_new0(uint8_t, VNC_STAT_COLS);
>
> sizeof(uint8_t) == 1, according to POSIX.  This could be further
> simplified to g_malloc0(VNC_STAT_COLS). But if someone wants to do that
> simplification, it should be a separate patch.

g_new0(uint8_t, VNC_STAT_COLS) returns uint8_t *.

g_malloc0(VNC_STAT_COLS) returns void *.

Transforming the former to the latter loses a bit of type checking.