CODEWITHSUNDEEP
clinuxshared-memory
Nuetrino
Nuetrino

Reputation: 1119

Shared memory segment shared between a 32 and 64 bit processes

Is it possible to create a shared memory segment that can be accessed by both 32 and 64 bit processes. The flag'TPF_IPC64' to support 64 bit addressing is as below

shmget(key,100,IPC_CREAT|TPF_IPC64);

Will this be accessible from a 32 bit Linux process?

Edit: It seems like the flag 'TPF_IPC64' is not supported in a normal Linux OS call to shmget. I think it is some proprietary to IBM ( my bad). I took it from this link

http://pic.dhe.ibm.com/infocenter/tpfhelp/current/index.jsp?topic=%2Fcom.ibm.ztpf-ztpfdf.doc_put.cur%2Fgtpc2%2Fcpp_shmget.html

Upvotes: 4

Views: 2158

Answers (2)

SSC
SSC

Reputation: 1331

From IBM's document

TPF_IPC64 Specifies that 64-bit addressing is supported. If you specify this flag, 64-bit system heap is used to satisfy the request if there is enough heap available. If there is no 64-bit system heap space available, 31-bit system heap will be used. Specify this flag only if all the users of this shared memory area can support 64-bit addresses.

The last sentence has mentioned that all the process has to support 64-bit address. So process with 32-bit address cannot access it.

However, I don't what is the behavior if you tried to access it with 32-bit process.

Upvotes: 0

David Ranieri
David Ranieri

Reputation: 41065

man shmget(2)

If IPC_CREAT is set in shmflg the shared memory segment created can only be shared by processes of the same executable type. That is, an application compiled as a 32-bit process will be able to share the same memory segment with other 32-bit processes, and an application compiled as a 64-bit process will be able to share the same memory segment with other 64-bit processes. If a 64-bit bit process want to create a shared memory segment which can also be shared with 32-bit processes, the 64-bit process must specify IPC_SHARE32 in addition to IPC_CREAT in shmflg . The 32-bit process does not need to specify IPC_SHARE32 .On Itanium(R)-based platforms, if the Adaptive Address Space feature is being used, then additional rules may apply. See the section below on Adaptive Address Space.

Upvotes: 4

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