Determine if gem5 is running in a batch environment by checking if
STDIN is wired to a TTY or not. If the simulator is running in a batch
environment, disable all listeners by default. This behavior can be
overridden using the --enable-listeners option.
Change-Id: I404c709135339144216bf08a2769c016c543333c
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Sean McGoogan <sean.mcgoogan@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/2322
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Add a small Python script that uses Gerrit's Change-Id: tags to list
incoming and outgoing changes.
Change-Id: Iea1757b2d64a57a4c7b4e47718cfcaa725a99615
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Sascha Bischoff <sascha.bischoff@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/2329
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>
The clone system call added in 236719892 relies on header files
from Linux systems. Obviously, this prevents compilation for
anyone using FreeBSD or Mac to compile the simulator. This
changeset is meant as a temporary fix to allow builds on
non-Linux systems until a proper solution is found.
Change-Id: I404cc41c588ed193dd2c1ca0c1aea35b0786fe4e
Reviewed-on: https://gem5-review.googlesource.com/2420
Maintainer: Brandon Potter <Brandon.Potter@amd.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
This change adds the ability to print a message at intervals
of committed instruction count to indicate progress in the
trace replay.
Change-Id: I8363502354c42bfc52936d2627986598b63a5797
Reviewed-by: Rekai Gonzalez Alberquilla <rekai.gonzalezalberquilla@arm.com>
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/2321
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
With this change, the test script will output a warning when it reads
an incomplete (e.g., when a regression is still running) or corrupt
status file instead of throwing an exception. When the scipt is used
to show the results the corrupt file is skipped; when it is used to
test if all regressions run successfully it will return an error value
(2).
Change-Id: Ie7d9b457b200e3abc7ae6238e3efbf3d18cf4297
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/2320
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>
The Pl390::getAddrRanges() method should have been flagged using the
override keyword. Other methods in this class already use the override
keyword, so this results in a warning about inconsistent override
usage when compiling using clang.
Change-Id: I17449687a8e074262232562487b58c96466bd54e
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
The GIC model currently adds a delay to interrupts when posting them
to a target CPU. This means that an interrupt signal will be
represented by an event for a short period of time. We currently
ignore this when draining and serialize the tick when the interrupt
will fire. Upon loading the checkpoint, the simulated GIC reschedules
the pending events. This behaviour is undesirable when we implement
support for switching between in-kernel GIC emulation and gem5 GIC
emulation. In that case, the (kernel) GIC model gets a lot simpler if
we don't need to worry about in-flight interrupts from the gem5 GIC.
This changeset adds a draining check to force the GIC into a state
where all interrupts have been delivered prior to checkpointing/CPU
switching. It also removes the now redundant serialization of
interrupt events.
Change-Id: I8b8b080aa291ca029a3a7bdd1777f1fcd5b01179
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Curtis Dunham <curtis.dunham@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/2331
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Lots of minor cleaups:
* Make cached params const
* Don't serialize params
* Use AddrRange to represent the distributor and CPU address spaces
* Store a const AddrRangeList of all PIO ranges
Change-Id: I40a17bc3a38868fb3b8af247790e852cf99ddf1d
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Curtis Dunham <curtis.dunham@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/2330
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Change-Id: I02719f3572f6665cace1eb5681f297dcde9e71ce
Reviewed-on: https://gem5-review.googlesource.com/2271
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Michael LeBeane <Michael.Lebeane@amd.com>
Reviewed-by: Tony Gutierrez <anthony.gutierrez@amd.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>
This changeset sets the implementation policy for a subset of
system calls to the ignoreFunc implementation (for x86 only).
The ignored system calls likely will never be implemented and
this allows a warning to be issued instead of the simulation
exiting with a fatal.
Change-Id: I8d9741ad683151e88cc71156d3602e2d0ccb0acf
Reviewed-on: https://gem5-review.googlesource.com/2270
Maintainer: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Tony Gutierrez <anthony.gutierrez@amd.com>
Reviewed-by: Michael LeBeane <Michael.Lebeane@amd.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
The changeset does a major refactor on the exit, exit_group, and
futex system calls regarding exit functionality.
A FutexMap class and related structures are added into a new
file. This increases code clarity by encapsulating the futex
operations and the futex state into an object.
Several exit conditions were added to allow the simulator to end
processes under certain conditions. Also, the simulation only
exits now when all processes have finished executing.
Change-Id: I1ee244caa9b5586fe7375e5b9b50fd3959b9655e
Reviewed-on: https://gem5-review.googlesource.com/2269
Maintainer: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
This changeset adds support to kill a thread group by calling
the tgkill system call. The functionality is needed in some
pthread applications.
Change-Id: I0413a3331be69b74dfab30de95384113ec4efb63
Reviewed-on: https://gem5-review.googlesource.com/2268
Maintainer: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Tony Gutierrez <anthony.gutierrez@amd.com>
Reviewed-by: Michael LeBeane <Michael.Lebeane@amd.com>
This changeset adds a simple class definition and a member
in the System object to track signals sent between processes.
The implementation cannot support all signals that might be
sent between processes, but it can support some of the simple
use cases like SIGCHLD.
Change-Id: Id5f95aa60e7f49da1c5b5596fbfa26e729453ac7
Reviewed-on: https://gem5-review.googlesource.com/2267
Reviewed-by: Michael LeBeane <Michael.Lebeane@amd.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>
This changeset extends the pipe system call to work with
architectures other than Alpha (and enables the syscall for
x86). For the dup system call, it sets the clone-on-exec
flag by default. For the dup2 system call, the changeset
adds an implementation (and enables it for x86).
Change-Id: I00ddb416744ee7dd61a5cd02c4c3d97f30543878
Reviewed-on: https://gem5-review.googlesource.com/2266
Maintainer: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Tony Gutierrez <anthony.gutierrez@amd.com>
Reviewed-by: Michael LeBeane <Michael.Lebeane@amd.com>
This changeset adds refactors the existing open system call,
adds the openat variant (enabled for x86 builds), and adds
additional "special file" test cases for /proc/meminfo and
/etc/passwd.
Change-Id: I6f429db65bbf2a28ffa3fd12df518c2d0de49663
Reviewed-on: https://gem5-review.googlesource.com/2265
Maintainer: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Tony Gutierrez <anthony.gutierrez@amd.com>
Reviewed-by: Michael LeBeane <Michael.Lebeane@amd.com>
This changeset fixes line alignment issues, spacing, spelling,
etc. for files that are used during SE Mode.
Change-Id: Ie61b8d0eb4ebb5af554d72f1297808027833616e
Reviewed-on: https://gem5-review.googlesource.com/2264
Maintainer: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Tony Gutierrez <anthony.gutierrez@amd.com>
Reviewed-by: Michael LeBeane <Michael.Lebeane@amd.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Pierre-Yves Péneau <pierre-yves.peneau@lirmm.fr>
The Process class is full of implementation details and
structures related to SE Mode. This changeset factors out an
internal class from Process and moves it into a separate file.
The purpose behind doing this is to clean up the code and make
it a bit more modular.
Change-Id: Ic6941a1657751e8d51d5b6b1dcc04f1195884280
Reviewed-on: https://gem5-review.googlesource.com/2263
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
See a06a46f and a854373.
Change-Id: Id66427db22b7d7764c218b9cd78d95db929f4127
Signed-off-by: Pierre-Yves Péneau <pierre-yves.peneau@lirmm.fr>
Reviewed-on: https://gem5-review.googlesource.com/2224
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>
The MOESI_hammer directory assumes a contiguous address space, but X86
has an IO gap from 3-4GB. This patch allows the directory to work with
more than 3GB of memory on X86.
Assumptions: the physical address space (range of possible physical
addresses) is 0-XGB when X <= 3GB, and 0-(X+1)GB when X > 3GB. If there
is no IO gap this patch should still work.
Change-Id: I5453a09e953643cada2c096a91d339a3676f55ee
Reviewed-on: https://gem5-review.googlesource.com/2169
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>
The slicc compiler currently treats && and || with the same precedence.
This is highly non-intuitive to people used to C, and was probably an
error. This patch makes && bind tighter than ||.
For example, previously:
if (A || B && C)
compiled to:
if ((A || B) && C)
With this patch, it compiles to:
if (A || (B && C))
Change-Id: Idbbd5b50cc86a8d6601045adc14a253284d7b791
Signed-off-by: Lena Olson (leolson@google.com)
Reviewed-on: https://gem5-review.googlesource.com/2168
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Joe Gross <criusx@gmail.com>
Reviewed-by: Sooraj Puthoor <puthoorsooraj@gmail.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>
Conflicts:
COPYING
This document details how to contribute to gem5 based on our new
contribution flow with git and gerrit.
Change-Id: I0a7e15fd83a3ee3ab6c85c1192f46f1e1d33b7c2
Signed-off-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-on: http://reviews.gem5.org/r/3814/
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Tony Gutierrez <anthony.gutierrez@amd.com>
Reviewed-by: Pierre-Yves Peneau <pierre-yves.peneau@lirmm.fr>
Reviewed-by: Andreas Hansson <andreas.hansson@arm.com>
Reviewed-by: Brad Beckmann <brad.beckmann@amd.com>
Reviewed-by: Ali Saidi <Ali.Saidi@ARM.com>
The GPUCoalescer and the Shader classes have different base classes in
C++ and Python. This causes subtle bugs in SWIG and compilation errors
for PyBind.
Change-Id: I1ddd2a8ea43f083470538ddfea891347b21d14d8
Reviewed-by: Andreas Hansson <andreas.hansson@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/2228
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Tony Gutierrez <anthony.gutierrez@amd.com>
Reviewed-by: Pierre-Yves Péneau <pierre-yves.peneau@lirmm.fr>
Reviewed-by: Bradford Beckmann <brad.beckmann@amd.com>
The Python wrappers get confused by the forward declarations in the
power framework. This changeset restructures the code slightly to
avoid the troublesome forward declarations.
Change-Id: Id8c93224f1988edb5fdf9d3abc6237f2f688c02d
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Andreas Hansson <andreas.hansson@arm.com>
Reviewed-by: Curtis Dunham <curtis.dunham@arm.com>
Reviewed-by: Sascha Bischoff <sascha.bischoff@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/2227
Reviewed-by: Pierre-Yves Péneau <pierre-yves.peneau@lirmm.fr>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>
Use the new fast scan-out API in the PixelPump to render frames at a
fixed frame rate in KVM mode. The refresh rate when running in KVM can
be controlled by the virt_refresh_rate parameter.
Change-Id: Ib3c78f174e3f8f4ca8a9b723c4e5d311a433b8aa
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/2242
Reviewed-by: Rahul Thakur <rjthakur@google.com>
Add a helper function to scan out an entire frame in one time
step. This requires the public PixelPump to be changed somewhat to
separate timing updates from general PixelPump control. Instead of
calling PixelPump::start(timings), timings now need to be updated
using a separate call to PixelPump::updateTimings(timings) before
calling PixelPump::start().
Display controllers that don't need accurate timing (e.g., in KVM
mode), can use the new PixelPump::renderFrame() API to render an
entire frame in one step. This call results in the same callbacks
(e.g., calls to nextPixel()) as the timing calls, but they all happen
in immediately. Unlike the timing counterpart, renderFrame() doesn't
support buffer underruns and will panic if nextPixle() indicates an
underrun.
Change-Id: I76c84db04249b02d4207c5281d82aa693d0881be
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/2241
Reviewed-by: Rahul Thakur <rjthakur@google.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Use a fast, functional, read operations keep the DMA FIFO full when
running in KVM mode.
Change-Id: I5b378c2fb6a1d3e687cef15e807e63a0a53a60e2
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/2226
Reviewed-by: Rahul Thakur <rjthakur@google.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>
Added functionality to check and clear interrupts for KMI
devices. This fixes a boot bug when using KVM and in-kernel GIC
emulation.
Change-Id: Ia3e91d07567b7faf3f82b0adfda4a165a502a339
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/2225
Reviewed-by: Rahul Thakur <rjthakur@google.com>
The WaitRec structure in the Process class is unnecessary. There
is a member declaration inside of the Process class, waitList,
that uses the WaitRec definition. However, waitList is unused so
they are both dead bits of code. This changeset removes both the
WaitRec struct and waitList member from Process.
Change-Id: Ia6ee7488b9f47fd0f0ae29c818fba6ea0710699c
Reviewed-on: https://gem5-review.googlesource.com/2262
Reviewed-by: Tony Gutierrez <anthony.gutierrez@amd.com>
Reviewed-by: Michael LeBeane <Michael.Lebeane@amd.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>
blkAlign was defined as a separate function in the base associative
and fully-associative tags classes although both functions implemented
identical functionality. This patch moves the blkAlign in the base
tags class.
Change-Id: I3d415d0e62bddeec7ce0d559667e40a8c5fdc2d4
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Andreas Hansson <andreas.hansson@arm.com>
Change-Id: I0ed4e528cb750a323facdc811dde7f0ed1ff228e
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Andreas Hansson <andreas.hansson@arm.com>
The gem5 stores flags separately from other fields CPSR, so we need to
split them out and recombine on trips to/from KVM.
Change-Id: I28ed00eb6f0e2a1436adfbc51b6ccf056958afeb
Reviewed-on: https://gem5-review.googlesource.com/2260
Reviewed-by: Rahul Thakur <rjthakur@google.com>
Maintainer: Rahul Thakur <rjthakur@google.com>
If output redirection is activated, the error message is printed in
simout. This change ensure it will be printed in simerr.
Change-Id: Ie661ac6b6978bf2e4aaaccdf23134795d764d459
Signed-off-by: Pierre-Yves Péneau <pierre-yves.peneau@lirmm.fr>
Reviewed-on: https://gem5-review.googlesource.com/2221
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
The slicc compiler currently treats && and || with the same precedence.
This is highly non-intuitive to people used to C, and was probably an
error. This patch makes && bind tighter than ||.
For example, previously:
if (A || B && C)
compiled to:
if ((A || B) && C)
With this patch, it compiles to:
if (A || (B && C))
Change-Id: Idbbd5b50cc86a8d6601045adc14a253284d7b791
Signed-off-by: Lena Olson (leolson@google.com)
Reviewed-on: https://gem5-review.googlesource.com/2168
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Joe Gross <criusx@gmail.com>
Reviewed-by: Sooraj Puthoor <puthoorsooraj@gmail.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>
[ Rebased onto master ]
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Gerrit requires that all commit messages have a Change-Id tag. This
tag is added automatically by a commit message hook in Git. Include
the default Gerrit commit message hook and add it automatically using
scons to make life easier for everyone.
Change-Id: I1270fbaaadf6ed151bddf14521a38e0c1a02d131
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/2166
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
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.
The clang compiler complains that the wavefront member in
the GpuISA class is unused. This changeset removes the member,
because it does not appear serve a purpose.
The clang compiler is more stringent than the recent versions of
GCC when dealing with overrides. This changeset adds the specifier
to the methods which need it to silence the compiler.
The generated decoder header defines macros that represent bit fields
within instructions. These fields typically have short names that
conflict with names in other header files. Include the generated
header after all normal header to avoid this issue.
Change-Id: I53d149b75432c20abdbf651e32c3c785d897973b
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Curtis Dunham <curtis.dunham@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
It's currently possible to change the log level in gem5 by tweaking a
set of global variables. These variables are currently exposed to
Python using SWIG. This mechanism is far from ideal for two reasons:
First, changing the log level requires that the Python world enables
or disables individual levels. Ideally, this should be a single call
where a log level is selected. Second, exporting global variables is
poorly supported by most Python frameworks. SWIG puts variables in
their own namespace and PyBind doesn't seem to support it at all.
This changeset refactors the logging code to create a more abstract
interface. Each log level is associated with an instance of a Logger
class. This class contains common functionality, an enable flag, and a
verbose flag.
Available LogLevels are described by the LogLevel class. Lower log
levels are used for more critical messages (PANIC being level 0) and
higher levels for less critical messages. The highest log level that
is printed is controlled by calling Logger:setLevel().
Change-Id: I31e44299d242d953197a8e62679250c91d6ef776
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Gabor Dozsa <gabor.dozsa@arm.com>
Reviewed-by: Curtis Dunham <curtis.dunham@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Don't output verbose text descriptions in stat files when running
tests. This saves a lot of space when storing reference data.
Change-Id: I2a7ead4843586e800ecf83846694b73f0c356373
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Sascha Bischoff <sascha.bischoff@arm.com>
Reviewed-by: Curtis Dunham <curtis.dunham@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Tony Gutierrez <anthony.gutierrez@amd.com>
Add a mechanism to configure the stat output format using a URL-like
syntax. This makes it possible to specify both an output format
(currently, only text is supported) and override default
parameters.
On the Python-side, this is implemented using a helper function
(m5.stats.addStatVisitor) that adds a visitor to the list of active
stat visitors. The helper function parses a URL-like stat
specification to determine the stat output type. Optional parameters
can be specified to change how stat visitors behave.
For example, to output stats in text format without stat descriptions:
m5.stats.addStatVisitor("text://stats.txt?desc=False")
From the command line:
gem5.opt --stats-file="text://stats.txt?desc=False"
Internally, the stat framework uses the _url_factory decorator
to wrap a Python function with the fn(path, **kwargs) signature in a
function that takes a parsed URL as its only argument. The path and
keyword arguments are automatically derived from the URL in the
wrapper function.
New output formats can be registered in the m5.stats.factories
dictionary. This dictionary contains a mapping between format names
(URL schemes) and factory methods.
To retain backwards compatibility, the code automatically assumes that
the user wants text output if no format has been specified (i.e., when
specifying a plain path).
Change-Id: Ic4dce93ab4ead07ffdf71e55a22ba0ae5a143061
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Curtis Dunham <curtis.dunham@arm.com>
Reviewed-by: Sascha Bischoff <sascha.bischoff@arm.com>
Reviewed-by: Ilias Vougioukas <ilias.vougioukas@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Tony Gutierrez <anthony.gutierrez@amd.com>
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.
