Interactive simulation with GDB

Motivation

GDB provides a lot of facilities to control execution in interactive mode: read and write memory, fetch and store register values, redirect execution flow. However, "bare metal" is not the only option — simulators can be controlled as well, and MIPT-MIPS is not an exception. Instead of writing our own driver of interactive simulation, we are fully utilizing GDB, obtaining its well-know CLI interfaces and GUI frontends.

Build

Firstly, you have to get GDB 8.3 sources and build MIPS GDB:

wget http://ftp.gnu.org/gnu/gdb/gdb-8.3.tar.gz
tar -xzf gdb-8.3.tar.gz
cd gdb-8.3

Create a build directory somewhere:

mkdir build
cd buid
/path/to/gdb-8.3/configure --target=mipsel-unknown-linux
make

NB: target must match the target of binutils/gcc you use to build binaries!

First build may take a long time, because external libraries are being built. Additionally, you have libsim.a built with default simulator (not MIPT-MIPS). You have to build libsim.a, which contains MIPT-MIPS simulator and GDB interfaces and linked to GDB, from our repository

mkdir mipt-mips/cmake-build
cd mipt-mips/cmake-build
cmake ../simulator -DGDB_SOURCE_PATH=/path/to/gdb/sources -DGDB_BUILD_PATH=/path/to/gdb/build/directory
make

After that, you may link GDB with MIPT-MIPS and get gdb executable in gdb/ directory

cd /path/to/gdb/build/directory/gdb
make gdb

Getting started

Unlike usual debugging with GDB, some additional steps are required to use the simulator. So, you launch GDB with some executable file:

./gdb -q /path/to/file
target sim [simulator-args, e.g. --mars]
load

target sim tells GDB that we are going to execute program via built-in simulator (in our case it's MIPT-MIPS). You may pass arguments to simulator as well if needed. load loads program to simulator memory. If target sim fails with "Undefined target command: sim", make sure you are running the GDB you built with simulator, not the system installed one.

Workflows

Workflow is perfectly described in this manual for the case of ARM simulation; however, there is no much difference for the MIPS case.