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.Dd April 8, 2011 .Dt STACK 9 .Os .Sh NAME .Nm STACK .Nd stack macros .Sh SYNOPSIS n sys/param.h .Ft type .Fn STACK_ALLOC "sp" "size" .Ft type .Fn STACK_MAX "sp" "size" .Ft type .Fn STACK_ALIGN "sp" "bytes" .Ft type .Fn STACK_GROW "sp" "size" .Ft type .Fn STACK_SHRINK "sp" "size" .Sh DESCRIPTION A stack is an area of memory with a fixed origin but with a variable size. A stack pointer points to the most recently referenced location on the stack. Initially, when the stack has a size of zero, the stack pointer points to the origin of the stack. When data items are added to the stack, the stack pointer moves away from the origin.
p The .Fn STACK_ALLOC macro returns a pointer to allocated stack space of some .Fa size . Given the returned pointer .Fa sp and .Fa size , .Fn STACK_MAX returns the maximum stack address of the allocated stack space. The .Fn STACK_ALIGN macro can be used to align the stack pointer .Fa sp by the specified amount of .Fa bytes .
p Two basic operations are common to all stacks: a data item is added
q Dq push to the location pointed by .Fa sp or a data item is removed
q Dq pop from the stack. The stack pointer must be subsequently adjusted by the size of the data item. The .Fn STACK_GROW and .Fn STACK_SHRINK macros adjust the stack pointer .Fa sp by given .Fa size .
p A stack may grow either up or down. The described macros take this into account by using the .Dv __MACHINE_STACK_GROWS_UP preprocessor define. .Sh SEE ALSO .Xr param 3 , .Xr queue 3