RE: Kernel stack size

13 Apr 2005

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Thread-index: AcVAKKGC8AAkxdLDTZiLxBpKERH3PQABOCMQ
Thread-topic: Kernel stack size

Hey Thanks Nikita, I did not know about the M_ZERO flag.

I appreciate you taking the time to give us all that tip.

Carl

-----Original Message-----
From: darwin-kernel-bounces+csmith=fortresstech.com@lists.apple.com
[mailto:darwin-kernel-bounces+csmith=fortresstech.com@lists.apple.com]
On Behalf Of Nikita Danilov
Sent: Wednesday, April 13, 2005 8:59 AM
To: Carl Smith
Cc: darwin-kernel@lists.apple.com
Subject: Re: Kernel stack size

Carl Smith writes:
...
OK let me try it another way.
I have this structure declared as global:
Struct Frame_Data
{
  void *buff1;
  void *buff2;
  void *buff3;
}
Then I declare as a global:
Int g_Array_Cnt = 0;
struct Frame_Data my_data[50];
So in my kernel's init routine I do:
While(g_Array_Cnt < 50)
{
  if((my_data[g_Array_Cnt].buff1 = _MALLOC(1600, M_TEMP,
M_WAITOK)) != 0)
  {
      bzero(&my_data[g_Array_Cnt].buff1, 1600);
if((my_data[g_Array_Cnt].buff2 = _MALLOC(1600, M_TEMP,
M_WAITOK)) != 0)
      {
      	bzero(&my_data[g_Array_Cnt].buff2, 1600);
if((my_data[g_Array_Cnt].buff3 = _MALLOC(1600,
M_TEMP, M_WAITOK)) != 0)
      	{
      		bzero(&my_data[g_Array_Cnt].buff3,
1600);
      	}
      	else
      		// error handling
      }
      else
      	// error handling
  }
  else
      // error handling
This (after correcting obvious error pointed to by others in this
thread) can be simplified to

enum {
        FRAME_BUF_SIZE = 1600
};

my_data[g_Array_Cnt].buff1 = _MALLOC(FRAME_BUF_SIZE,
                                     M_TEMP, M_WAITOK | M_ZERO);
my_data[g_Array_Cnt].buff2 = _MALLOC(FRAME_BUF_SIZE,
                                     M_TEMP, M_WAITOK | M_ZERO);
my_data[g_Array_Cnt].buff3 = _MALLOC(FRAME_BUF_SIZE,
                                     M_TEMP, M_WAITOK | M_ZERO);

M_ZERO automatically zeroes allocated space, and M_WAITOK is guaranteed
to return non-NULL (or at least a _lot_ of places in core XNU code
assumes it is.). Identical calls to _MALLOC can be further factored into
special frame_alloc_buf() function.

Nikita.
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