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path: root/src/sim/syscall_desc.hh
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2017-02-27syscall_emul: [PATCH 15/22] add clone/execve for threading and multiprocess ↵Brandon Potter
simulations Modifies the clone system call and adds execve system call. Requires allowing processes to steal thread contexts from other processes in the same system object and the ability to detach pieces of process state (such as MemState) to allow dynamic sharing.
2015-07-20syscall_emul: [patch 13/22] add system call retry capabilityBrandon Potter
This changeset adds functionality that allows system calls to retry without affecting thread context state such as the program counter or register values for the associated thread context (when system calls return with a retry fault). This functionality is needed to solve problems with blocking system calls in multi-process or multi-threaded simulations where information is passed between processes/threads. Blocking system calls can cause deadlock because the simulator itself is single threaded. There is only a single thread servicing the event queue which can cause deadlock if the thread hits a blocking system call instruction. To illustrate the problem, consider two processes using the producer/consumer sharing model. The processes can use file descriptors and the read and write calls to pass information to one another. If the consumer calls the blocking read system call before the producer has produced anything, the call will block the event queue (while executing the system call instruction) and deadlock the simulation. The solution implemented in this changeset is to recognize that the system calls will block and then generate a special retry fault. The fault will be sent back up through the function call chain until it is exposed to the cpu model's pipeline where the fault becomes visible. The fault will trigger the cpu model to replay the instruction at a future tick where the call has a chance to succeed without actually going into a blocking state. In subsequent patches, we recognize that a syscall will block by calling a non-blocking poll (from inside the system call implementation) and checking for events. When events show up during the poll, it signifies that the call would not have blocked and the syscall is allowed to proceed (calling an underlying host system call if necessary). If no events are returned from the poll, we generate the fault and try the instruction for the thread context at a distant tick. Note that retrying every tick is not efficient. As an aside, the simulator has some multi-threading support for the event queue, but it is not used by default and needs work. Even if the event queue was completely multi-threaded, meaning that there is a hardware thread on the host servicing a single simulator thread contexts with a 1:1 mapping between them, it's still possible to run into deadlock due to the event queue barriers on quantum boundaries. The solution of replaying at a later tick is the simplest solution and solves the problem generally.
2016-11-09syscall_emul: [patch 5/22] remove LiveProcess class and use Process insteadBrandon Potter
The EIOProcess class was removed recently and it was the only other class which derived from Process. Since every Process invocation is also a LiveProcess invocation, it makes sense to simplify the organization by combining the fields from LiveProcess into Process.
2016-11-09syscall_emul: [patch 2/22] move SyscallDesc into its own .hh and .ccBrandon Potter
The class was crammed into syscall_emul.hh which has tons of forward declarations and template definitions. To clean it up a bit, moved the class into separate files and commented the class with doxygen style comments. Also, provided some encapsulation by adding some accessors and a mutator. The syscallreturn.hh file was renamed syscall_return.hh to make it consistent with other similarly named files in the src/sim directory. The DPRINTF_SYSCALL macro was moved into its own header file with the include the Base and Verbose flags as well. --HG-- rename : src/sim/syscallreturn.hh => src/sim/syscall_return.hh