exc_resume(3) Library Functions Manual exc_resume(3)
NAME
exc_resume, exc_longjmp, exc_capture_context, exc_continue, exc_unwind, RtlUnwindRfp - entry points that support resuming execution of
user code.
LIBRARY
Exception Handling Library (libexc.a)
SYNOPSIS
#include <excpt.h> void exc_resume(
PCONTEXT contextRecord); void exc_longjmp(
PCONTEXT contextRecord,
long returnValue); unsigned long exc_capture_context(
PCONTEXT contextRecord); void exc_continue(
PCONTEXT contextRecord); void exc_unwind(
void TargetFrame,
void TargetIp,
system_exrec_type *exceptionRecord,
long returnValue); void RtlUnwindRfp(
void *TargetRealFrame,
void *TargetIp,
system_exrec_type *exceptionRecord,
long returnValue);
PARAMETERS
Pointer to a struct sigcontext (see signal(2)) used to represent a procedure's context. Value to be passed to the continuing code at the
completion of the unwind. If nonzero, virtual frame pointer of the target procedure invocation to which the unwind is to be done; if zero,
specifies that an exit unwind is to be initiated and causes the EXCEPTION_EXIT_UNWIND flag to be set in the exception record. If TargetRe-
alFrame is nonzero, address within the target invocation at which to continue execution; otherwise this parameter is ignored. Address of
primary exception record. If nonzero, real frame pointer of the target procedure invocation to which the unwind is to be done; if zero,
specifies that an exit unwind is to be initiated and causes the EXCEPTION_EXIT_UNWIND flag to be set in the exception record.
DESCRIPTION
exc_resume and exc_continue perform essentially the same operation as longjmp(3). The exc_resume function is a libexc entry point.
exc_capture_context saves the current procedure context in the struct sigcontext identified by contextRecord.
exc_longjmp restores the context that was saved by a previous call to exc_capture_context and calls exc_unwind, setting up its arguments
from information taken from the contextRecord argument. If the returnValue argument is 0 (zero), it is set to 1 (one) before the call.
exc_unwind initiates an unwind of procedure call frames. It sets the EXCEPTION_UNWINDING flag in the exception flags of the exception
record, which describes the machine state at the time of the exc_unwind call. If the TargetFrame argument is zero, then exc_unwind also
sets the EXCEPTION_EXIT_UNWIND flag. It then scans the procedure call frames towards the base of the call stack to find the target of the
unwind operation.
RtlUnwindRfp is similar to exc_unwind except that its first argument is a real frame pointer instead of a virtual frame pointer. Real frame
pointers point to the bottom of the statically allocated portion of a stack frame. Virtual frame pointers point to the top of the stack
frame.
As it encounters each frame, the unwind code determines the program counter where control left the corresponding function by looking at
exception handler information in the runtime function table built by the linker. If the respective routine has an exception handler, then
the unwind code calls it. This handler should perform cleanup code required for that activation. Programs written in the C programming
language, which supports structured exception handling, usually contain a try...finally block that implements a termination handler that
performs these chores (see c_excpt(4)). The unwind code also calls a handler when it reaches the TargetFrame so that any scope-oriented
cleanup code or termination handler can execute. In this case, it sets the EXCEPTION_TARGET_FRAME flag in the ExceptionFlags field of the
exception record.
Once it finds the TargetFrame (if specified) and calls its handler (if available), exc_unwind: sets the PC to the TargetIp sets the return
value to be the returnValue argument, if the returnValue argument is non-zero, sets the return value to be the ExceptionCode of the excep-
tion record if the returnValue argument is zero calls exc_continue
RETURN VALUES
The exc_capture_context function returns a value of 0 (zero), unless the return is from a call to the exc_longjmp function, in which case
exc_capture_context returns the non-zerovalue specified in the returnValue argument to exc_longjmp.
The exc_longjmp function cannot return 0 (zero) to the previous context. The value 0 is reserved to indicate the actual return from the
exc_capture_context function when first called by the program. If the exc_longjmp function is passed a returnValue parameter of 0, execu-
tion continues as if the corresponding call to the exc_capture_context function had returned a value of 1.
FILES
usr/ccs/lib/cmplrs/cc/libexc.a - exception handling library usr/include/excpt.h - include file usr/include/pdsc.h - include file
usr/include/signal.h - include file usr/include/machine/fpu.h - include file
RELATED INFORMATION
Functions: exception_intro(3), exception_dispatcher(3), exc_lookup_function_entry(3), signal(2), sigaction(2), __exc_last_chance(3),
ieee(3).
Files: excpt(4), c_excpt(4), signal(4), pdsc(4).
Assembly Language Programmer's Guide.
Calling Standard for Alpha Systems.
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