emulate_branch.3

来自「<B>Digital的Unix操作系统VAX 4.2源码</B>」· 3 代码 · 共 63 行

.TH emulate_branch 3 RISC
.SH Name
emulate_branch, execute_branch \- branch emulation
.SH Syntax
.nf
.B #include <signal.h>
.PP
.B emulate_branch(\fIscp, branch_instruction\fP)
.B struct sigcontext *\fIscp\fP;
.B unsigned long \fIbranch_instruction\fP;
.PP
.B execute_branch(\fIbranch_instruction\fP)
.B unsigned long \fIbranch_instruction\fP;
.fi
.SH Description
The
.PN emulate_branch 
function is passed a signal context structure and a
branch instruction.  It emulates the branch based on the
register values in the signal context structure.  It
modifies the value of the program counter in the signal
context structure
.RI ( sc_pc )
to the target of the \fIbranch_instruction\fP.  
The program counter must initially be pointing
at the branch and the register values must be those at the
time of the branch.  If the branch is not taken the program
counter is advanced to point to the instruction after the
delay slot
.RI ( sc_pc
+= 8).
.PP
If the branch instruction is a 
`branch on coprocessor 2' or `branch on coprocessor 3'
instruction,
.PN emulate_branch
calls
.PN execute_branch 
to execute the branch in data space to
determine if it is taken or not.
.SH Return Values
The
.PN emulate_branch
function returns a 0 if the branch was emulated
successfully.  A non-zero value indicates the value passed
as a branch instruction was not a branch instruction.
.PP
The
.PN execute_branch
function returns non-zero on taken branches and zero
on non-taken branches.
.SH Restrictions
Since 
.PN execute_branch 
is only intended to be used by
.PN emulate_branch 
it does not check its parameter to see if in
fact it is a branch instruction.  It is really a stop gap in
case a coprocessor is added without the kernel fully
supporting it (which is unlikely).
.SH See Also
cacheflush(2), sigvec(2), signal(3)