Debugging

Disabling the JIT

Sometimes it is useful to completely disable the JIT to verify that a problem is JIT-related. You can do this with the YK_JITC environment variable (see run-time configuration for details).

Trace optimisation

Trace optimisation can make it difficult to understand why a yk interpreter has behaved in the way it does. It is worth trying to run your code with the optimiser turned off. You can do this with the YKD_OPT environment variable, which takes the following values:

• 1: turn the optimiser on. Default if not otherwise specified.
• 0: turn the optimiser off.

Debugging JITted code

Often you will find the need to inspect JITted code with a debugger. If the problem trace comes from a C test (i.e. one of the test cases under tests/c), then you can use bin/rr_c_test or bin/gdb_c_test.

Run these tools with no arguments for help on how to use them.

Note that because these tools don’t run tests under lang_tester, environment variables usually set by env-var in the test file will not be applied. If need be, you can set them manually, e.g. YKD_SERAIALISE_COMPILATION=1 ./bin/rr_c_test ....

GDB plugin

Yk comes with a GDB plugin that allows the debugger to show higher-level information in the source view window.

The plugin is built by default and put in target/yk_gdb_plugin.so.

To use it, put this line in ~/.gdbinit:

jit-reader-load /path/to/yk/target/yk_gdb_plugin.so

Then when you run GDB, you should see:

Yk JIT support loaded.

When you are inside JITted code, the source view will show higher-level debugging information. You can show the assembler and source views on one GDB screen using the “split” layout. Type:

la spl