schedBreak(<tick>) gdb debugging function not working - gdb

Question

I am trying to create breakpoints and debug gem5 using gdb. I referred to http://www.gem5.org/Debugger_Based_Debugging.
As in the official documentation in the above link, I tried `call schedBreak() but it doesn't work. the following are the full commands:
➜ test-gem5-x86 git:(master) ✗ gdb --args ./build/X86/gem5.opt configs/learning_gem5/part1/simple.py
GNU gdb (Ubuntu 8.1-0ubuntu3) 8.1.0.20180409-git
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This GDB was configured as "x86_64-linux-gnu".
Type "show configuration" for configuration details.
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Reading symbols from ./build/X86/gem5.opt...done.
(gdb) b main
Breakpoint 1 at 0x4b0d20: main. (4 locations)
(gdb) run
Starting program: /home/hari/test-gem5-x86/build/X86/gem5.opt configs/learning_gem5/part1/simple.py
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Breakpoint 1, main (argc=2, argv=0x7fffffffdef8) at build/X86/sim/main.cc:42
42 {
(gdb) call schedBreak(10000)
warn: need to stop all queues
(gdb) c
Continuing.
gem5 Simulator System. http://gem5.org
gem5 is copyrighted software; use the --copyright option for details.
gem5 compiled Aug 26 2019 20:59:02
gem5 started Sep 8 2019 15:17:55
gem5 executing on nirmal-cadsl2, pid 30158
command line: /home/hari/test-gem5-x86/build/X86/gem5.opt configs/learning_gem5/part1/simple.py
Global frequency set at 1000000000000 ticks per second
warn: DRAM device capacity (8192 Mbytes) does not match the address range assigned (512 Mbytes)
0: system.remote_gdb: listening for remote gdb on port 7001
Beginning simulation!
info: Entering event queue # 0. Starting simulation...
Hello world!
Exiting # tick 501393000 because exiting with last active thread context
[Inferior 1 (process 30158) exited normally]
(gdb)
While this other tutorial http://gem5.org/wiki/images/0/0e/ASPLOS2017_gem5_tutorial.pdf (assuming the debug function is not particular to ISA) tells me that the function is actually schedBreakCycle(), it gives me this No symbol "schedBreakCycle" in current context. The full commands shown below.
➜ test-gem5-x86 git:(master) ✗ gdb --args ./build/X86/gem5.opt configs/learning_gem5/part1/simple.py
GNU gdb (Ubuntu 8.1-0ubuntu3) 8.1.0.20180409-git
Copyright (C) 2018 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from ./build/X86/gem5.opt...done.
(gdb) b main
Breakpoint 1 at 0x4b0d20: main. (4 locations)
(gdb) run
Starting program: /home/hari/test-gem5-x86/build/X86/gem5.opt configs/learning_gem5/part1/simple.py
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Breakpoint 1, main (argc=2, argv=0x7fffffffdef8) at build/X86/sim/main.cc:42
42 {
(gdb) call schedBreakCycle(10000)
No symbol "schedBreakCycle" in current context.
(gdb)
gem5 version: ea8c435b6c6c092d72047eee50f125f5ae7347c3
gdb version: GNU gdb (Ubuntu 8.1-0ubuntu3) 8.1.0.20180409-git
Also, if I want to debug ALPHA or ARM full system on my ubuntu 18.04(x86), do I have to use any cross-compiled gdb versions or would native gdb suffice?

Answer 1

The tutorial is correct, you have to pass --debug-break to gem5:
gdb --args gem5.debug --debug-break=1000 ...
and then without breaking at main:
run
call schedBreak(5000)
continue
--debug-break generates a break at time 1000 and makes GDB stop there after main, and from that point, schedBreak does work.
Or alternatively first go to:
tbreak doSimLoop
run
call schedBreak(5000)
continue
schedBreak schedules an event in the event queue, which cannot be ready at main.
The breaks work by raising a signal, which GDB stops at by default.
ALPHA and ARM won't make a difference since schedBreak is a tiny helper to debug the host emulator itself, which is likely an x86 program. To debug the guest code, which is what most people want, see e.g. this tutorial.
Tested gem5 master at e87a293d1ffa6da38ba8fa145e7dc5128138ab77 in an X86 debug build.