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exc_add_pc_range(3) Library Functions Manual exc_add_pc_range(3) NAME exc_add_pc_range_table, exc_remove_pc_range_table, exc_lookup_func- tion_table, find_rpd, exc_lookup_function_entry, exc_re- mote_lookup_function_entry, exc_add_gp_range, exc_remove_gp_range, exc_lookup_gp - Routines to support mapping program counters to the data structures defined at run time LIBRARY Exception Handling Library (libexc.a) SYNOPSIS #include <excpt.h> void exc_add_pc_range_table( PRUNTIME_FUNCTION pbase, pdsc_count count); void exc_remove_pc_range_table( PRUNTIME_FUNCTION pbase); PRUNTIME_FUNCTION exc_lookup_function_table( exc_address pc); PRUNTIME_FUNCTION find_rpd( exc_address pc); PRUNTIME_FUNCTION exc_lookup_function_entry( exc_address pc); void exc_add_gp_range( exc_address begin_address, unsigned long length, exc_address gp); void exc_remove_gp_range( exc_address begin_address); exc_address exc_lookup_gp( exc_address pc); PRUNTIME_FUNCTION exc_remote_lookup_function_entry ( void *handle, int (*fetch_from_process) ( void *handle, void *addr, void *buffer, long size); exc_address pc exc_address crd_handle, PRUNTIME_FUNCTION *func_entry, PRUNTIME_FUNCTION *crd_base; PARAMETERS Pointer to the base of a code-range descriptor table. Number of code- range descriptors in the table pointed to by pbase. Address within a range of code for which the base of a code-range descriptor table is to be returned. First address for which the gp argument applies. Number of bytes from begin_address for which the gp argument applies. Address of the global pointer used to refer to the Global Offset Table and small data sections (see the Calling Standard for Alpha Systems and the Assembly Language Programmer's Guide). The following parameter descriptions apply to the exc_re- mote_lookup_function_entry routine. How these parameters are inter- preted depends on whether the process involved in the operation is lo- cal or remote. Remote lookup: A pointer to an arbitrary block of mem- ory, set up and managed by the user application and passed through the exception handling routines. This allows the author of fetch_from_process() to maintain any necessary state. The state main- tained here will most likely include the identity of the process to be unwound. Local lookup: This parameter is ignored. Remote lookup: An application-specific function contained in the user application that calls exc_remote_lookup_function_entry(). The handle para- meter is used by fetch_from_process(). If fetch_from_process() is NULL, the look up of the code-range descriptor takes place in the local process, not a remote process. The fetch_from_process function takes the following arguments: The handle parameter that was passed into exc_re- mote_lookup_function_entry. 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 mem- ory pointed to by buffer must be at least size bytes in length. Local lookup: Must be NULL (by definition). Remote lookup: The program counter (PC) value in the remote process for which code-range descriptor information is to be returned. Local lookup: The program counter (PC) value in the local process for which code-range descriptor information is to be re- turned. Remote lookup: The address of the cell exc_crd_list_head in the process whose function entry is being looked up. The means by which this address is communicated to the process calling exc_remote_lookup_function_entry is applica- tion specific. Remote lookup: The address of a PRUNTIME_FUNC- TION allocated by the caller, into which the appropriate code- range descriptor in the remote process is written. The PRUN- TIME_FUNCTION must point to struct pdsc_crd, which is also allo- cated by the caller. The code-range descriptor does not need to be initialized in any way. In the event of a lookup failure (that is, the function return value is zero), the contents of the structure pdsc_crd pointed to by this PRUNTIME_FUNCTION are unpredictable. Local lookup: The address of a PRUNTIME_FUNCTION. If a PRUN- TIME_FUNCTION is passed, the contents of the PRUNTIME_FUNCTION is written with the address of the appropriate pdsc_crd struc- ture. May be NULL. Remote lookup: The address of a PRUN- TIME_FUNCTION, where the base address of the code-range descrip- tor table is written. Note: this pointer is written with an ad- dress in the remote address space. Do not try to dereference this pointer. Local lookup: Same meaning as remote lookup case, except may be NULL. DESCRIPTION The exception system needs to access procedure-specific information at run time in order to perform unwinds and call handlers. You find this information by mapping a PC to a procedure and its structures. The PRUNTIME_FUNCTION typedef points to a code-range descriptor (pdsc(4)). A code-range descriptor represents a range of addresses. To support very high levels of optimization, one procedure can be rep- resented by many code-range descriptors (but a code-range descriptor belongs to only one procedure). The code-range descriptor provides the key to access all of the infor- mation that the exception system requires about a procedure (although some of it may be available only indirectly through the code-range de- scriptor). The assembler automatically generates code-range descriptors in the .pdata section of a relocatable object file that the linker merges into a single code-range descriptor table for each executable and shared ob- ject. The linker also generates code in the .init and .fini sections so that each executable and shared object will register (by calling exc_add_pc_range_table) and deregister (by calling exc_re- move_pc_range_table) their code-range descriptor tables at run time with the exception system (if present). You may need to call these routines manually if you are using the ex- ception system and generate or load code yourself without using stan- dard DIGITAL UNIX system libraries and services. The exception system maintains the list of registered code-range de- scriptor tables. The exc_lookup_function_table routine returns a pointer to the base of a code-range descriptor table containing a range of code that includes the address supplied in the pc argument. This routine returns a NULL (zero-value) pointer if an entry for the pc ar- gument is not found. The exc_lookup_function_entry and find_rpd routines each return a PRUN- TIME_FUNCTION for the address supplied by the pc argument. Note The find_rpd routine is an old ULTRIX libexc interface. It continues to work on DIGITAL UNIX systems if its callers treat its return argument as an opaque pointer. If they explicitly access fields in the returned structure, they will encounter incompatibilities. The exc_remote_lookup_function_entry routine can look up a code-range descriptor in either the local process or a remote process. When the correct code-range descriptor is located, it is copied into the local address space in storage indicated by the func_entry parameter. In normal remote unwinding use, exc_remote_lookup_function_entry is not called from the application, but is used as a utility routine by exc_remote_virtual_unwind(). In both cases (local and remote), exc_re- mote_lookup_function_entry returns the address of the code-range de- scriptor if successful and zero otherwise. Remote lookup of a code-range descriptor by the exc_remote_lookup_func- tion_entry function can involve either a local process or a remote process - unlike the other lookup and find functions that operate only on local processes. Remote lookup is controlled by the fetch_from_process parameter. This parameter is a pointer to (or han- dle for) an application-supplied function that knows how to access the memory of the process (local or remote) being acted on: If the user ap- plication passes a NULL value in the fetch_from_process parameter, the lookup operation is being performed on the local process. This allows the lookup 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 lookup routine is not allowed to assume anything about the process it is ac- cessing, and only the fetch routine is allowed to know the iden- tity of the process being acted on. 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 lookup is the capability to look up code-range de- scriptors in a process that is not necessarily the process doing the lookup. The unwind functions typically call some of these lookup and find func- tions to obtain enough information to virtually unwind procedure con- texts. The gp is not in the code-range or procedure descriptors (pdsc(4)) be- cause the same gp can be used for many routines and including the gp would waste space. Instead, the linker generates calls to exc_add_gp_range in the .init section of an executable or shared object and exc_remove_gp_range in the in their .init and .fini sections. The exc_lookup_gp routine returns a NULL (zero value) pointer if an en- try for the pc parameter is not found. 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), 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 exc_add_pc_range(3)