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.\" Copyright 2015 Joyent, Inc.
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.Dd May 11, 2016
.Dt PSTACK_ITER 3PROC
.Os
.Sh NAME
.Nm Pstack_iter
.Nd iterate process stack frames
.Sh SYNOPSIS
.Lb libproc
.In libproc.h
.Ft int
.Fo Pstack_iter
.Fa "struct ps_prochandle *P"
.Fa "const prgregset_t regs"
.Fa "proc_stack_f *func"
.Fa "void *data"
.Fc
.Sh DESCRIPTION
The
.Fn Pstack_iter
function iterates over the stack frames in the process
.Fa P
starting at the point defined by
.Fa regs .
.Pp
For each valid stack frame encountered, the callback function
.Fa func
is invoked with
.Fa data
passed as argument.
The full signature of
.Ft proc_stack_f
is defined in
.Xr libproc 3LIB .
With each callback, a register set, argument set, and argument count
will be provided.
In that register set, only a subset of the registers will be valid, which
include the frame pointer, program counter, and on SPARC systems, the next
program counter.
These registers can be accessed with the constants
.Sy R_FP ,
.Sy R_PC ,
and
.Sy R_nPC
respectively.
These correspond to the registers
.Em %ebp
and
.Em %eip
on i386,
.Em %rbp
and
.Em %rip
on amd64,
.Em %fp ,
.Em %pc ,
and
.Em %npc
on both SPARC and SPARCv9.
.Pp
Callers will receive a callback for the first stack frame indicated by
.Fa regs
and then will receive a subsequent callback for each caller of that
frame until no such frame can be found.
Stack frames that logically come after the frame indicated by
.Fa regs
will not receive callbacks.
.Pp
The compiler can either facilitate or stymie the iteration of the stack.
Programs that have been compiled in such a way as to omit the frame pointer will
result in truncated stacks.
Similarly, if the initial set of registers passed in via
.Fa regs
is invalid, then the ability to iterate the stack will be limited.
The return value of
.Fa func
controls whether or not iteration continues.
If
.Fa func
returns
.Sy 0
then iteration continues.
However, if
.Fa func
returns non-zero, then iteration will halt and that value will be used
as the return value of the
.Fn Pstack_iter
function.
Because
.Fn Pstack_iter
returns
.Sy -1
on internal failure it is recommended the callback function not return
.Sy -1
to indicate an error.
Thus the caller may distinguish between the failure of the callback function and
the failure of the
.Fn Pstack_iter
function.
.Sh RETURN VALUES
Upon successful completion, the
.Fn Pstack_iter
function returns
.Sy 0.
If there was an internal error then
.Sy -1
is returned.
Otherwise, if the callback function
.Fa func
returns non-zero, then its return value will be returned instead.
.Sh INTERFACE STABILITY
.Sy Uncommitted
.Sh MT-LEVEL
See
.Sy LOCKING
in
.Xr libproc 3LIB .
.Sh SEE ALSO
.Xr libproc 3LIB ,
.Xr proc 4