02-01-2002
Ok. Apparently I understood you correctly in the first post. First of all, when you create an object containing a virtual function, you do not create a virtual function table. At compile time, a pointer to the virtual function is created and placed into a module wide virtual function table which is a table of pointers to virtual functions defined within the compiled object. If you can get the value of the pointer pointing to the virtual function table, it will only have meaning in the executable that contains the instantiation of Class1, in this case object Obj1.
Secondly, if you create a shared memory segment and place a pointer to the virtual function, the virtual function table, or a pointer to anything inside the address space of ProcessA, you are NOT "sharing the object". You are passing a virtual memory address with meaning in ProcessA, to ProcessB where it has no meaning. When ProcessB dereferences the pointer, you will more than likely get a SIGSEGV.
Shared memory is used for passing DATA objects, not executable text (i.e. a virtual function) or a pointer.
Obviously, I don't know why ProcessB needs to access the Obj1 object defined in ProcessA. If the Class1 template (with virtual functions and all) is declared inside both source modules (or more likely in a header file and included in the source), then you could have separate instantiations of the template in both processes. If you need to share data values between the instantiated objects, then you could pass the data values using shared memory, but you cannot pass a pointer to the executable text of the virtual function. You don't need to as you would have the same executable text in each process.
Now, that said, you should look at the load() system call in AIX. I've used this to dynamically create modules and load them into the process address space of a running process. Realize that this is a non-portable system call. Since I don't know what your ultimate goal is here, this is the only possible option I can come up with.
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LEARN ABOUT REDHAT
mremap
MREMAP(2) Linux Programmer's Manual MREMAP(2)
NAME
mremap - re-map a virtual memory address
SYNOPSIS
#include <unistd.h>
#include <sys/mman.h>
void * mremap(void *old_address, size_t old_size , size_t new_size, unsigned long flags);
DESCRIPTION
mremap expands (or shrinks) an existing memory mapping, potentially moving it at the same time (controlled by the flags argument and the
available virtual address space).
old_address is the old address of the virtual memory block that you want to expand (or shrink). Note that old_address has to be page
aligned. old_size is the old size of the virtual memory block. new_size is the requested size of the virtual memory block after the
resize.
The flags argument is a bitmap of flags.
In Linux the memory is divided into pages. A user process has (one or) several linear virtual memory segments. Each virtual memory seg-
ment has one or more mappings to real memory pages (in the page table). Each virtual memory segment has its own protection (access
rights), which may cause a segmentation violation if the memory is accessed incorrectly (e.g., writing to a read-only segment). Accessing
virtual memory outside of the segments will also cause a segmentation violation.
mremap uses the Linux page table scheme. mremap changes the mapping between virtual addresses and memory pages. This can be used to
implement a very efficient realloc.
FLAGS
MREMAP_MAYMOVE
indicates if the operation should fail, or change the virtual address if the resize cannot be done at the current virtual address.
RETURN VALUE
On success mremap returns a pointer to the new virtual memory area. On error, -1 is returned, and errno is set appropriately.
ERRORS
EINVAL An invalid argument was given. Most likely old_address was not page aligned.
EFAULT "Segmentation fault." Some address in the range old_address to old_address+old_size is an invalid virtual memory address for this
process. You can also get EFAULT even if there exist mappings that cover the whole address space requested, but those mappings are
of different types.
EAGAIN The memory segment is locked and cannot be re-mapped.
ENOMEM The memory area cannot be expanded at the current virtual address, and the MREMAP_MAYMOVE flag is not set in flags. Or, there is
not enough (virtual) memory available.
NOTES
With current glibc includes, in order to get the definition of MREMAP_MAYMOVE, you need to define _GNU_SOURCE before including
<sys/mman.h>.
CONFORMING TO
This call is Linux-specific, and should not be used in programs intended to be portable. 4.2BSD had a (never actually implemented)
mremap(2) call with completely different semantics.
SEE ALSO
getpagesize(2), realloc(3), malloc(3), brk(2), sbrk(2), mmap(2)
Your favorite OS text book for more information on paged memory. (Modern Operating Systems by Andrew S. Tannenbaum, Inside Linux by Ran-
dolf Bentson, The Design of the UNIX Operating System by Maurice J. Bach.)
Linux 1.3.87 1996-04-12 MREMAP(2)