critical impact:

shmat - address space limitations (CrCh15)

Problem description

The HP-UX shmat function has limitations that do not exist on Tru64 UNIX. However, these limitations are resolved with the Adaptive Address Space (AAS) feature of HP-UX, which was added in HP-UX 11i v2.0.

The default address space layout on HP-UX places the following limitations on the value of the address parameter that Tru64 UNIX does not:

• If the shared memory segment has never been attached to by any process prior to the current shmat call, shmaddr must be specified as zero. The segment is attached at a location selected by the operating system.

• If this is not the first shmat call on the shared memory segment throughout the system, shmaddr must either be zero or contain a nonzero address that is identical to the one returned from previous shmat calls for that segment.

In summary, HP-UX does not allow a shared memory segment to occupy different virtual memory addresses in different processes; Tru64 UNIX allows this.

Identifiers

shmat

See also

• Background information on unclassified impacts
• shmat(2)

Solution description

The AAS feature of HP-UX provides a new address space layout, Mostly Private Address Space (MPAS), in which these limitations do not apply.

To make an executable use the MPAS layout, use the +as mpas option of ld or chatr. Note that MPAS might lower performance because it uses address aliasing and the default address space layout on HP-UX does not.

Review the AAS white paper for more information.

See also

• shmat(2)
• Adaptive Address Space white paper (PDF)

Problem summary