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Old 08-22-2008, 06:40 PM   #1
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Registered: Aug 2008
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Linux shared memory segment access problem and x86 Virtual Memory layout.

Hi all,

I have been trying to attach a shared memory segment in a 32-bit x86 machine in the virtual address range ( 0xff80 0000 to 0xffff ffff ) with no luck.

  0xffff ffff+-----------------+  (4096 MB) 4 GB
             |   Problem :(    |
  0xff80 0000+-----------------+  (4088 MB)  
             |                 |
             |                 |
             |                 |
  0x7fff ffff+-----------------+
             |                 |
             |                 |
             |                 |
  0x7f80 0000+-----------------+
             |                 |
             |                 |
             |                 |
  0x0000 0000+-----------------+
This definitely falls in the upper 1 GB address space which belongs to the Kernel.

Is there any way by which I can attach a shared memory segment to one of those addresses in that zone ???

I tried increasing the SHMMAX value to as high as 4 GB. Din't help.

Eventually I will have to attach similarly for an x86_64 architecture. Please let me know if my problem has a solution and the same approach can be applied for a x86_64 architecture that uses canonical form of virtual addresses.

Old 08-23-2008, 01:11 AM   #2
Valery Reznic
ELF Statifier author
Registered: Oct 2007
Posts: 676

Rep: Reputation: 137Reputation: 137
Could you explain what you are trying to achieve ?


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