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gem5
linux-kernel-module-cheat/gem5.md
Ciro Santilli 8ddefa940e gem5
2017-12-28 12:54:24 +00:00

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GEM5

Introduction

GEM5 is a system simulator, much like QEMU: http://gem5.org/

Vs QEMU:

  • advantage: simulates a generic more realistic CPU pipelined and optionally out of order CPU cycle by cycle, including a realistic DRAM memory access model with latencies, caches and page table manipulations. This allows us to:

    • do much more realistic performance benchmarking with it, which makes absolutely no sense in QEMU, which is purely functional
    • make functional cache observations, e.g. to use Linux kernel APIs that flush memory like DMA, which are crucial for driver development. In QEMU, the driver would still work even if we forget to flush caches.

    It is not of course truly cycle accurate, as that would require exposing proprietary information of the CPU designs: https://stackoverflow.com/questions/17454955/can-you-check-performance-of-a-program-running-with-qemu-simulator/33580850#33580850, but the approximation is reasonable.

    It is used mostly for research purposes: when you are making a new chip technology, you don't really need to specialize enormously to an existing microarchitecture, but rather develop something that will work with a wide range of future architectures.

  • disadvantage: slower than QEMU by TODO 10x? Which implies:

    • GEM5 is used only by chip makers, who keep everything that really works closed, and researchers, who can't version track or document code properly >:-). So the documentation is much more scarce.

    • the user base is much smaller (no Android devs!), and so it takes longer to support new hardware features, and reach newer kernel compatibility.

ARM

./configure
./build -a arm-gem5
./rungem5

On another shell:

./rungem5-shell

This is the best guide so far: http://www.gem5.org/ARM_Kernel

git checkout gem5-v4.9

Linux:

cd linux
git checkout 69973b830859bc6529a7a0468ba0d80ee5117826

Version found by: go down on branch gem5/v4.9 of https://gem5.googlesource.com/arm/linux until you find Linus :-) The patches there are just simple optimizations and instrumentation, but they are not needed to boot.

cd buildroot
git checkout 73b075737e23814a68c66e481230af662e1529cb

Version found by: search for the message of type "linux: bump default to version 4.9.6". This changes BR2_LINUX_KERNEL_LATEST_VERSION in /linux/Config.in.

Kernel command line arguments

TODO no matter what argument I pass to: --command-line, e.g. even an innocent --command-line='printk.time=y', it fails with:

**** REAL SIMULATION ****
warn: Existing EnergyCtrl, but no enabled DVFSHandler found.
info: Entering event queue @ 0.  Starting simulation...
warn: The csselr register isn't implemented.
warn: The ccsidr register isn't implemented and always reads as 0.
warn:   instruction 'mcr dcisw' unimplemented
warn: Not doing anything for miscreg ACTLR
warn: Not doing anything for write of miscreg ACTLR
warn:   instruction 'mcr icimvau' unimplemented
warn:   instruction 'mcr bpiallis' unimplemented
warn: Device system.membus.badaddr_responder accessed by write to address 0xefffe000 size=4 data=0
gem5.opt: build/ARM/cpu/simple/atomic.cc:492: virtual Fault AtomicSimpleCPU::writeMem(uint8_t*, unsigned int, Addr, Request::Flags, uint64_t*): Assertion `!pkt.isError()' failed.                                 Program aborted at tick 296677000
Aborted (core dumped)

QEMU with GEM5 kernel configuration

TODO:

./run -a arm

hangs at:

audio: Could not init `oss' audio driver

and the display shows " "

GEM5 with QEMU kernel configuration

TODO hangs at:

**** REAL SIMULATION ****
warn: Existing EnergyCtrl, but no enabled DVFSHandler found.
info: Entering event queue @ 0.  Starting simulation...
1614868500: system.terminal: attach terminal 0

and the telnet at:

2017-12-28-11-59-51@ciro@ciro-p51$ ./rungem5-shell
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
==== m5 slave terminal: Terminal 0 ====

x86

TODO didn't get it working yet.

Related threads:

Working baseline

Working x86 with the pre-built magic image with an ancient 2.6.22.9 kernel starting point:

sudo mkdir -p /dist/m5/system
sudo chmod 777 /dist/m5/system
cd /dist/m5/system
# Backed up at:
# https://github.com/cirosantilli/media/releases/tag/gem5
wget http://www.gem5.org/dist/current/x86/x86-system.tar.bz2
tar xvf x86-system.tar.bz2
cd x86-system
dd if=/dev/zero of=disks/linux-bigswap2.img bs=1024 count=65536
mkswap disks/linux-bigswap2.img
cd ..

git clone https://gem5.googlesource.com/public/gem5
cd gem5
git checkout da79d6c6cde0fbe5473ce868c9be4771160a003b
scons -j$(nproc) build/X86/gem5.opt
# That old blob has wrong filenames.
./build/X86/gem5.opt \
    -d /tmp/output \
    --disk-image=/dist/m5/system/disks/linux-x86.img \
    --kernel=/dist/m5/system/binaries/x86_64-vmlinux-2.6.22.9 \
    configs/example/fs.py

On another shell:

telnet localhost 3456

Unmodified Buildroot images

bzImage fails, so we always try with vmlinux obtained from inside build/.

rootfs.ext2 and vmlinux from 670366caaded57d318b6dbef34e863e3b30f7f29ails as:

Fails as:

Global frequency set at 1000000000000 ticks per second
warn: DRAM device capacity (8192 Mbytes) does not match the address range assigned (512 Mbytes)
info: kernel located at: /data/git/linux-kernel-module-cheat/buildroot/output.x86_64~/build/linux-custom/vmlinux
Listening for com_1 connection on port 3456
    0: rtc: Real-time clock set to Sun Jan  1 00:00:00 2012
0: system.remote_gdb.listener: listening for remote gdb #0 on port 7000
warn: Reading current count from inactive timer.
**** REAL SIMULATION ****
info: Entering event queue @ 0.  Starting simulation...
warn: instruction 'fninit' unimplemented
warn: Don't know what interrupt to clear for console.
12516923000: system.pc.com_1.terminal: attach terminal 0
warn: i8042 "Write output port" command not implemented.
warn: i8042 "Write keyboard output buffer" command not implemented.
warn: Write to unknown i8042 (keyboard controller) command port.
hack: Assuming logical destinations are 1 << id.
panic: Resetting mouse wrap mode unimplemented.
Memory Usage: 1003456 KBytes
Program aborted at tick 632745027500
--- BEGIN LIBC BACKTRACE ---
./build/X86/gem5.opt(_Z15print_backtracev+0x15)[0x12b8165]
./build/X86/gem5.opt(_Z12abortHandleri+0x39)[0x12c32f9]
/lib/x86_64-linux-gnu/libpthread.so.0(+0x11390)[0x7fe047a71390]
/lib/x86_64-linux-gnu/libc.so.6(gsignal+0x38)[0x7fe046601428]
/lib/x86_64-linux-gnu/libc.so.6(abort+0x16a)[0x7fe04660302a]
./build/X86/gem5.opt(_ZN6X86ISA8PS2Mouse11processDataEh+0xf5)[0x1391095]
./build/X86/gem5.opt(_ZN6X86ISA5I80425writeEP6Packet+0x51c)[0x13927ec]
./build/X86/gem5.opt(_ZN7PioPort10recvAtomicEP6Packet+0x66)[0x139f7b6]
./build/X86/gem5.opt(_ZN15NoncoherentXBar10recvAtomicEP6Packets+0x200)[0x1434af0]
./build/X86/gem5.opt(_ZN6Bridge15BridgeSlavePort10recvAtomicEP6Packet+0x5d)[0x140ee9d]
./build/X86/gem5.opt(_ZN12CoherentXBar10recvAtomicEP6Packets+0x3e7)[0x1415b77]
./build/X86/gem5.opt(_ZN15AtomicSimpleCPU8writeMemEPhjm5FlagsIjEPm+0x327)[0xa790a7]
./build/X86/gem5.opt(_ZN17SimpleExecContext8writeMemEPhjm5FlagsIjEPm+0x19)[0xa856b9]
./build/X86/gem5.opt(_ZNK10X86ISAInst2St7executeEP11ExecContextPN5Trace10InstRecordE+0x235)[0xfb9e65]
./build/X86/gem5.opt(_ZN15AtomicSimpleCPU4tickEv+0x23c)[0xa784fc]
./build/X86/gem5.opt(_ZN10EventQueue10serviceOneEv+0xc5)[0x12be0d5]
./build/X86/gem5.opt(_Z9doSimLoopP10EventQueue+0x38)[0x12cd558]
./build/X86/gem5.opt(_Z8simulatem+0x2eb)[0x12cdbdb]
./build/X86/gem5.opt(_ZZN8pybind1112cpp_function10initializeIRPFP22GlobalSimLoopExitEventmES3_ImEINS_4nameENS_5scopeENS_7siblingENS_5arg_vEEEEvOT_PFT0_DpT1_EDpRKT2_ENUlRNS_6detail13function_callEE1_4_FUNESO_+0x41)[0x13fca11]
./build/X86/gem5.opt(_ZN8pybind1112cpp_function10dispatcherEP7_objectS2_S2_+0x8d8)[0xfc7398]
/usr/lib/x86_64-linux-gnu/libpython2.7.so.1.0(PyEval_EvalFrameEx+0x7852)[0x7fe047d3b552]
/usr/lib/x86_64-linux-gnu/libpython2.7.so.1.0(PyEval_EvalCodeEx+0x85c)[0x7fe047e6501c]
/usr/lib/x86_64-linux-gnu/libpython2.7.so.1.0(PyEval_EvalFrameEx+0x6ffd)[0x7fe047d3acfd]
/usr/lib/x86_64-linux-gnu/libpython2.7.so.1.0(PyEval_EvalFrameEx+0x7124)[0x7fe047d3ae24]
/usr/lib/x86_64-linux-gnu/libpython2.7.so.1.0(PyEval_EvalFrameEx+0x7124)[0x7fe047d3ae24]
/usr/lib/x86_64-linux-gnu/libpython2.7.so.1.0(PyEval_EvalCodeEx+0x85c)[0x7fe047e6501c]
/usr/lib/x86_64-linux-gnu/libpython2.7.so.1.0(PyEval_EvalCode+0x19)[0x7fe047d33b89]
/usr/lib/x86_64-linux-gnu/libpython2.7.so.1.0(PyEval_EvalFrameEx+0x613b)[0x7fe047d39e3b]
/usr/lib/x86_64-linux-gnu/libpython2.7.so.1.0(PyEval_EvalCodeEx+0x85c)[0x7fe047e6501c]
/usr/lib/x86_64-linux-gnu/libpython2.7.so.1.0(PyEval_EvalFrameEx+0x6ffd)[0x7fe047d3acfd]
/usr/lib/x86_64-linux-gnu/libpython2.7.so.1.0(PyEval_EvalCodeEx+0x85c)[0x7fe047e6501c]
/usr/lib/x86_64-linux-gnu/libpython2.7.so.1.0(PyEval_EvalCode+0x19)[0x7fe047d33b89]
--- END LIBC BACKTRACE ---
Aborted (core dumped)

Boot goes quite far, on telnet:

ALSA device list:
  No soundcards found.

So just looks like we have to disable some Linux configs which GEM5 does not support... so fragile.

Copy upstream 2.6 configs on 4.9 kernel

The magic image provides its kernel configurations, so let's try that.

The configs are present at:

wget http://www.gem5.org/dist/current/x86/config-x86.tar.bz2

backed up at: https://github.com/cirosantilli/media/releases/tag/gem5

Copy linux-2.6.22.9 into the kernel tree as .config, git checkout v4.9.6, make olddefconfig, make, then use the Buildroot filesystem as above, failure:

panic: Invalid IDE control register offset: 0
Memory Usage: 931272 KBytes
Program aborted at tick 382834812000
--- BEGIN LIBC BACKTRACE ---
./build/X86/gem5.opt(_Z15print_backtracev+0x15)[0x12b8165]
./build/X86/gem5.opt(_Z12abortHandleri+0x39)[0x12c32f9]
/lib/x86_64-linux-gnu/libpthread.so.0(+0x11390)[0x7fc2081c6390]
/lib/x86_64-linux-gnu/libc.so.6(gsignal+0x38)[0x7fc206d56428]
/lib/x86_64-linux-gnu/libc.so.6(abort+0x16a)[0x7fc206d5802a]
./build/X86/gem5.opt(_ZN7IdeDisk11readControlEmiPh+0xd9)[0xa96989]
./build/X86/gem5.opt(_ZN13IdeController14dispatchAccessEP6Packetb+0x53e)[0xa947ae]
./build/X86/gem5.opt(_ZN13IdeController4readEP6Packet+0xe)[0xa94a5e]
./build/X86/gem5.opt(_ZN7PioPort10recvAtomicEP6Packet+0x3f)[0x139f78f]
./build/X86/gem5.opt(_ZN15NoncoherentXBar10recvAtomicEP6Packets+0x200)[0x1434af0]
./build/X86/gem5.opt(_ZN6Bridge15BridgeSlavePort10recvAtomicEP6Packet+0x5d)[0x140ee9d]
./build/X86/gem5.opt(_ZN12CoherentXBar10recvAtomicEP6Packets+0x3e7)[0x1415b77]
./build/X86/gem5.opt(_ZN15AtomicSimpleCPU7readMemEmPhj5FlagsIjE+0x3ef)[0xa780ef]
./build/X86/gem5.opt(_ZN17SimpleExecContext7readMemEmPhj5FlagsIjE+0x11)[0xa85671]
./build/X86/gem5.opt(_ZNK10X86ISAInst2Ld7executeEP11ExecContextPN5Trace10InstRecordE+0x130)[0xfb6c00]
./build/X86/gem5.opt(_ZN15AtomicSimpleCPU4tickEv+0x23c)[0xa784fc]
./build/X86/gem5.opt(_ZN10EventQueue10serviceOneEv+0xc5)[0x12be0d5]
./build/X86/gem5.opt(_Z9doSimLoopP10EventQueue+0x38)[0x12cd558]
./build/X86/gem5.opt(_Z8simulatem+0x2eb)[0x12cdbdb]
./build/X86/gem5.opt(_ZZN8pybind1112cpp_function10initializeIRPFP22GlobalSimLoopExitEventmES3_ImEINS_4nameENS_5scopeENS_7siblingENS_5arg_vEEEEvOT_PFT0_DpT1_EDpRKT2_ENUlRNS_6detail13function_callEE1_4_FUNESO_+0x41)[0x13fca11]
./build/X86/gem5.opt(_ZN8pybind1112cpp_function10dispatcherEP7_objectS2_S2_+0x8d8)[0xfc7398]
/usr/lib/x86_64-linux-gnu/libpython2.7.so.1.0(PyEval_EvalFrameEx+0x7852)[0x7fc208490552]
/usr/lib/x86_64-linux-gnu/libpython2.7.so.1.0(PyEval_EvalCodeEx+0x85c)[0x7fc2085ba01c]
/usr/lib/x86_64-linux-gnu/libpython2.7.so.1.0(PyEval_EvalFrameEx+0x6ffd)[0x7fc20848fcfd]
/usr/lib/x86_64-linux-gnu/libpython2.7.so.1.0(PyEval_EvalFrameEx+0x7124)[0x7fc20848fe24]
/usr/lib/x86_64-linux-gnu/libpython2.7.so.1.0(PyEval_EvalFrameEx+0x7124)[0x7fc20848fe24]
/usr/lib/x86_64-linux-gnu/libpython2.7.so.1.0(PyEval_EvalCodeEx+0x85c)[0x7fc2085ba01c]
/usr/lib/x86_64-linux-gnu/libpython2.7.so.1.0(PyEval_EvalCode+0x19)[0x7fc208488b89]
/usr/lib/x86_64-linux-gnu/libpython2.7.so.1.0(PyEval_EvalFrameEx+0x613b)[0x7fc20848ee3b]
/usr/lib/x86_64-linux-gnu/libpython2.7.so.1.0(PyEval_EvalCodeEx+0x85c)[0x7fc2085ba01c]
/usr/lib/x86_64-linux-gnu/libpython2.7.so.1.0(PyEval_EvalFrameEx+0x6ffd)[0x7fc20848fcfd]
/usr/lib/x86_64-linux-gnu/libpython2.7.so.1.0(PyEval_EvalCodeEx+0x85c)[0x7fc2085ba01c]
--- END LIBC BACKTRACE ---
Aborted (core dumped)

Use upstream 2.6 configs and 2.6 kernel

If we checkout to the ancient kernel v2.6.22.9, it fails to compile with modern GNU make 4.1: https://stackoverflow.com/questions/35002691/makefile-make-clean-why-getting-mixed-implicit-and-normal-rules-deprecated-s lol