• State Not Answered
  • Locked Locked
  • Replies 5 replies
  • Subscribers 21 subscribers
  • Views 1815 views
  • Users 0 members are here
2025 survey

We are running a survey to help us improve the experience for all of our members. If you see the survey appear, please take the time to tell us about your experience if you can.

Options
Related
How was your experience today?
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

How to malloc from the beginning of init_mempool.

Kan Deng

Hi, there,

The malloc always allocate memory at the tail of the memory initialized by init_mempool(). How to make "malloc()" allocate memory from the beginning of the initialized memory?

In details, suppose running following code fragment,

  byte xdata *M1;
  byte xdata *M2;
  init_mempool (&XBYTE [0x10], 0x1000);
  M1 = (byte xdata *) malloc (500);
  M2 = (byte xdata *) malloc (100);

The initialized memory starts from 0x10, ends at 0x1010. M1 starts from 0x0E1C to 0x1010, while M2 starts from 0x0DB4 to 0x0E18, with 4 bytes gaps from M1 and M2.

My question is how to allocate M1 so as to start from 0x0010, end with 0x0204? And then M2 starts with 0x0208 and ends with 0x026C?

thanks,
Kan

Parents
  • 0 in reply to Andy Neil

    Hi, there,

    Actually, my previous understanding was not correct. The codes don't have the erroneous assumption that the malloc must start from the beginning of the memory.

    What happened yesterday was that when I init_mempool(), I didn't assign an aligned value to be the size of initialized memory(0xFF00). Hence, M1 is not the expected 0xFD0C, instead it is 0xFD1C. And then M2 is not 0xFF00, but 0xFF10 which is out of the available memory.

    After I changed the init_mempool size to be 0xFE00, the problem is solved.

      init_mempool (&XBYTE [0x10], 0xFF00);
  M1 = (byte xdata *) malloc (500);
  M2 = M1 + 500;

    For the second question, the reason that we cannot get rid of all malloc() is that we are implementing a Java VM. We don't know what Java class that the users will use until runtime. Hence, we cannot statically malloc the java classes beforehand.

    Do I understand your suggestion clearly, Andy?

    many thanks,
    Kan

Reply
  • 0 in reply to Andy Neil

    Hi, there,

    Actually, my previous understanding was not correct. The codes don't have the erroneous assumption that the malloc must start from the beginning of the memory.

    What happened yesterday was that when I init_mempool(), I didn't assign an aligned value to be the size of initialized memory(0xFF00). Hence, M1 is not the expected 0xFD0C, instead it is 0xFD1C. And then M2 is not 0xFF00, but 0xFF10 which is out of the available memory.

    After I changed the init_mempool size to be 0xFE00, the problem is solved.

      init_mempool (&XBYTE [0x10], 0xFF00);
  M1 = (byte xdata *) malloc (500);
  M2 = M1 + 500;

    For the second question, the reason that we cannot get rid of all malloc() is that we are implementing a Java VM. We don't know what Java class that the users will use until runtime. Hence, we cannot statically malloc the java classes beforehand.

    Do I understand your suggestion clearly, Andy?

    many thanks,
    Kan

Children
No data