On Fri, Apr 25, 2008 at 03:01:23PM +0530, sahlot arvind wrote: > >Now a new process is loaded to memory, which utilizes a .so already in > memory. How does ld.so know if the required .so is already in >memory and > what is its physical address? > > I think loader keeps track of which libraries are there in the memory and > their location. Execuatble file of the program contains dependency > information i.e. which libraries this exe depends upon. So while loading it > can check whether the required library is always there or not if not then > loader loads the lib into the memory. No, the loader doesn't need to know anything. It just maps the libraries the process needs into its address space. Because linux uses on-demand paging, nothing will happen at that point. Only when the process starts to access pages from the library the kernel will load those pages from disk. If the kernel figures out that particular page from that particular library was already mapped in another process, it will just create a map for that page into the current process and presto: shared mapping of a library. BTW this is not library specific, it happens with any file that gets mapped by two (or more) processes. That includes the binaries themselves, but also mmap()ed files. Erik -- Erik Mouw -- mouw@xxxxxxxxxxxx
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