Specifications

System Macros Invoked by Drivers

FIND_CPU_DATA

Locates the start of the per-CPU database area (CPU) for the current process.

Format

FIND_CPU_DATA reg [,amod=G^] [,istack=NO]

Parameters

reg

database structure (CPU)).

[amod=G^]

Addressing mode.

[istack=NO]

Mechanism to calculate the base address of the per-CPU database structure.

Use istack=YES only when it is certain that the processor is executing on the

interrupt stack. The mechanism used when istack=NO is somewhat slower, but

works whether the processor is executing on the interrupt stack or kernel stack.

Description

The FIND_CPU_DATA macro loads the starting virtual address of the current

processor’s per-CPU database (CPU) into the speciﬁed register. A driver generally

invokes the FIND_CPU_DATA macro in the process of determining the current

process of the current CPU when executing in system context.

Such a driver must adhere to the following rules:

• It must invoke the FIND_CPU_DATA macro in kernel mode at or above

IPL$_RESCHED.

• It must ensure that it will not be rescheduled after issuing the macro while it

is using the information returned by FIND_CPU_DATA. It typically does this

by remaining at IPL$_RESCHED or greater.

Example

FIND_CPU_DATA R0

MOVL CPU$L_CURPCB(R0),R1

The FIND_CPU_DATA macro returns the starting virtual address of the current

processor’s per-CPU database in R0. The subsequent MOVL instruction obtains

the address of the process currently active on that processor and places it in R1.

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