ratheesh k wrote: > Suppose there are two executable elf . say A, B . And these two are > using libctest.so. > When A is executed libctest.so is loaded into RAM No, it is *mapped* into the process' address space (virtual memory). Data is loaded into physical RAM on demand by the kernel. > and linear address is correctly mapped. > > If we execute program B after A , will library will be loaded again ? It will be mapped into B's address space. > else, how OS know that libctest is already loaded into physical page ? > (so it can map linear address to it ) Mapping a file into a process' address space sets up structures within the kernel recording the fact that specific pages of the process' address space correspond to specific blocks of a specific device. Initially, the MMU will consider those pages as unmapped, so accessing those addresses will cause the CPU to generate an exception (page fault). The kernel handles the exception by ensuring that the appropriate disk block is loaded into physical RAM, updating the MMU so that the virtual memory page is mapped to the appropriate physical memory page, then restarting the instruction. When cached blocks are discarded from physical RAM, any the MMU mappings are removed so that a subsequent access will raise an exception. -- Glynn Clements <glynn@xxxxxxxxxxxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe linux-c-programming" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
