088c8a224c
Inside the code of cloneFunc(…) //syscall_emul.hh
cp->initState(); //line 1483
p->clone(tc, ctc, cp, flags); //line 1484
…
ctc->clearArchRegs(); //line 1503
OS::archClone(flags, p, cp, tc, ctc, newStack, tlsPtr); //line 1505
…
At line 1483, initState() is called and the activateContext() of the
corresponding MinorCPU is eventually called. The actual architecture
clone happens at line 1505 where PC of the new thread could have a
correct value.
In the existing implementation of MinorCPU::activateContext(ThreadID
thread_id), the below line 275 is called
pipeline->wakeupFetch(thread_id);
to start fetching instruction with current value of PC, which is 0x0,
leading to panic “Page table fault when accessing virtual address 0”.
This is because the OS::archClone() is not yet called. So, the below bug
fix handles the wakeup fetch for a thread for two scenarios:
...
if (!threads[thread_id]->getUseForClone())
{ //the thread is not cloned
pipeline->wakeupFetch(thread_id);
} else {//the thread from clone
if (fetchEventWrapper != NULL)
delete fetchEventWrapper;
fetchEventWrapper = new EventFunctionWrapper([this, thread_id]
{pipeline->wakeupFetch(thread_id);}, "wakeupFetch");
schedule(*fetchEventWrapper, clockEdge(Cycles(0)));
}
...
If a thread is not cloned, pipeline->wakeupFetch() is called
immediately.
For the cloned thread, the above bug fix delays the execution of
pipeline->wakeupFetch()
after the OS::archClone is done. ThreadContext::getUseForClone() return
true if a thread is cloned.
A member variable fetchEventWrapper is added to MinorCPU class for
delayed fetch event.
A member variable useForClone and its corresponding get/set methods are
added to ThreadContext class. This approach allows future reuse of this
useForClone variable by other CPU models if needed and also avoid lots
of changes resulted by modifying parameters of activateContext () and
activate() which are defined as override.
Inside the syscall cloneFunc, the useForClone member of a ThreadContext
object is set via its set method right before Process's initState() is
called, shown as below.
ctc->setUseForClone(true);
cp->initState();
p->clone(tc, ctc, cp, flags);
A few previously failed RISC-V ASM tests have been open in tests.py file
after the bug fix works.
JIRA issue: https://gem5.atlassian.net/browse/GEM5-374
Change-Id: Ibffe46522e2617443d29f49df180692c54830f14
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/37315
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>
This is the gem5 simulator. The main website can be found at http://www.gem5.org A good starting point is http://www.gem5.org/about, and for more information about building the simulator and getting started please see http://www.gem5.org/documentation and http://www.gem5.org/documentation/learning_gem5/introduction. To build gem5, you will need the following software: g++ or clang, Python (gem5 links in the Python interpreter), SCons, SWIG, zlib, m4, and lastly protobuf if you want trace capture and playback support. Please see http://www.gem5.org/documentation/general_docs/building for more details concerning the minimum versions of the aforementioned tools. Once you have all dependencies resolved, type 'scons build/<ARCH>/gem5.opt' where ARCH is one of ARM, NULL, MIPS, POWER, SPARC, or X86. This will build an optimized version of the gem5 binary (gem5.opt) for the the specified architecture. See http://www.gem5.org/documentation/general_docs/building for more details and options. The basic source release includes these subdirectories: - configs: example simulation configuration scripts - ext: less-common external packages needed to build gem5 - src: source code of the gem5 simulator - system: source for some optional system software for simulated systems - tests: regression tests - util: useful utility programs and files To run full-system simulations, you will need compiled system firmware (console and PALcode for Alpha), kernel binaries and one or more disk images. If you have questions, please send mail to gem5-users@gem5.org Enjoy using gem5 and please share your modifications and extensions.