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unwind(3) Library Functions Manual unwind(3) NAME unwind, exc_virtual_unwind, RtlVirtualUnwind, exc_find_frame_ptr, exc_remote_virtual_unwind - Routines to unwind a context SYNOPSIS #include <excpt.h> void unwind( PCONTEXT pcontext, PRUNTIME_FUNCTION prf); void exc_virtual_unwind( PRUNTIME_FUNCTION prf, PCONTEXT pcontext); exc_address RtlVirtualUnwind( exc_address controlpc, PRUNTIME_FUNCTION prf, PCONTEXT pcontext, PCONTEXT_POINTERS ppointers); exc_address exc_find_frame_ptr( PRUNTIME_FUNCTION prf, PCONTEXT pcontext); PCONTEXT pnext_context); unsigned long exc_remote_virtual_unwind ( void *handle, int (*fetch_from_process) ( void *handle, void *addr, void *buffer, long *size), exc_address crd_handle, PRUNTIME_FUNCTION pcrd, PCONTEXT pcontext); PARAMETERS Pointer to a struct sigcontext (see signal(2)) used to represent a pro- cedure's context. Pointer to a struct sigcontext (see signal(2)) used to represent the context of a procedure's caller. If you specify a non-zero pnext_context argument, the pcontext argument is ignored. Pointer to run-time function (code-range descriptor) for the PC stored in the sc_pc field of the activation context record; a call to exc_lookup_function_entry(3) returns this value. Although this argu- ment can be zero, by providing this argument, a caller already having this information would save an extra search for the run-time function. Copy of the sc_pc field of the activation context record. Pointer to structure containing addresses corresponding to the locations that were used to restore registers; if zero, this argument is ignored. The following descriptions apply to parameters for the exc_remote_vir- tual_unwind routine. How these parameters are interpreted depends on whether the process involved in the operation is local or remote. Re- mote unwind: A pointer to an arbitrary block of memory, set up and man- aged by the user application, and passed throught the exception han- dling routines. This allows the author of fetch_from_process() to maintain any necessary state. The state maintained here will most likely include the identity of the process to be unwound. Local unwind: This parameter is ignored. Remote unwind: An application-specific function, written by the author of the ap- plication that calls exc_remote_virtual_unwind(). The handle parameter is used by fetch_from_process(). If fetch_from_process() is NULL, the unwind takes place in the lo- cal process, not a remote process. The fetch_from_process function takes the following arguments: The handle parameter that was passed into exc_remote_virtual_un- wind. The starting address in the remote process from which to copy memory. A buffer in the local process into which data from the remote process is copied. The number of bytes to copy from addr to buffer. The region of memory pointed to by buffer must be at least size bytes in length. Local unwind: The fetch_from_process parameter is ignored. Re- mote unwind: The address of the cell exc_crd_list_head in the remote process. The means by which this address is communicated to the local (tracing) process is application specific. Local unwind: This parameter is ignored. Remote unwind: This parameter is ignored. Local unwind: The address of a code-range descriptor describing the context from which to begin the unwind. If NULL, the code- range descriptor is looked up based on the PC contained in the pcontext parameter. This is often passed as NULL for the ini- tial invocation of exc_remote_virtual_unwind() and is always passed as NULL for iterated invocations during the stack walk. A pointer to a struct sigcontext representing the context of the procedure (local or remote) that is to be unwound. At a minimum, this context structure must contain the following context for the routine to be unwound: FP register ($15), SP register ($30), RA register ($26 in a standard call), and the PC. Additionally, the context may contain the preserved regis- ters. This argument needs to be set up only once; consecutive calls to exc_remote_virtual_unwind() manipulate this structure to repre- sent the state of successively earlier procedures in the call chain. DESCRIPTION All of the unwind routines perform a virtual unwind. Unlike the rou- tines described in exc_resume(3), these routines do not actually unwind a procedure call by modifying the real registers and other machine state. Instead, these routines modify the structure pointed to by the pcontext argument so that it represents the previous procedure in the call stack. The routines use procedure information supplied in the structure pointed to by the prf argument to decide how to virtually un- wind the context (for instance, how to modify the registers and other machine state). This information is placed in the object by the assem- bler and linker and conforms to the calling standard for Alpha systems. If the specify a procedure's context in pcontext and the pnext_context argument is non-zero, exc_find_frame_ptr generates a copy of the pcon- text argument. The original copy of the context is not modified. If you supply a pointer to the context of the caller in the pnext_context argument, exc_find_frame_ptr returns the stack pointer associated with that context as the frame pointer of the current context. The other unwind routines modify the structure pointed to by the pcon- text argument in order to represent the context of the caller. Remote unwinding by the exc_remote_virtual_unwind function can involve a local or remote process - unlike the unwind, exc_virtual_unwind, and RtlVirtualUnwind functions that operate only on local processes. Remote unwinding is controlled by the fetch_from_process parameter. This pa- rameter is a pointer to (or handle for) an application-supplied func- tion that knows how to access the memory of the process (local or re- mote) being acted on: If the user application passes a NULL value in the fetch_from_process parameter, the local process is performing an unwind on its own stack. This allows the unwind routine to make certain optimizations in its processing. If the user application passes the address of a routine in the fetch_from_process parameter, the unwind routine is not allowed to assume anything about the process it is ac- cessing, and only the fetch routine is allowed to know the identity of the process being unwound. It might be the local process, it might be another process in the system, it might be a process on another system on the network, or it might be a corefile from a long-deceased process. To summarize, remote unwinding is the capability to unwind the stack of a process that is not necessarily the process doing the unwind. All of the unwind routines typically use masks and stack offsets found in procedure related data structures (described in the Calling Standard for Alpha Systems) to restore registers. Those data structures also can contain enough information for these routines to adequately deal with prologues, epilogues, and signal frames. Users writing assembly language routines should consult the Assembly Language Programmer's Guide to determine which directives are required to provide enough information for these routines to correctly unwind through them. Note The origins of the various unwind routines are as follows: unwind orig- inated in the ULTRIX libexc and has an interface compatible with the original one, as long as the ULTRIX caller treated the prf argument as an opaque pointer. The prf structure has been changed to conform to the calling standard for Alpha systems, and any callers that explicitly access its fields will encounter incompatibilities. exc_virtual_unwind originated in libexc. RtlVirtualUnwind is a Microsoft Windows NT run- time library interface. It returns a copy of the updated sc_pc field of the sigcontext when leaving the routine. The routine also updates the structure pointed to by the ppointers argument. FILES usr/ccs/lib/cmplrs/cc/libexc.a - exception handling library usr/in- clude/excpt.h - include file usr/include/pdsc.h - include file usr/in- clude/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), setjmp(3), exc_unwind(3), __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. delim off unwind(3)