diff options
Diffstat (limited to 'subx_debugging.md')
| -rw-r--r-- | subx_debugging.md | 36 |
1 files changed, 17 insertions, 19 deletions
diff --git a/subx_debugging.md b/subx_debugging.md index 27b98774..acd6f88d 100644 --- a/subx_debugging.md +++ b/subx_debugging.md @@ -27,28 +27,16 @@ rudimentary but hopefully still workable toolkit: mode (`bootstrap run`): ``` - $ ./bootstrap translate input.subx -o binary - $ ./bootstrap --trace run binary arg1 arg2 2>trace + $ ./translate_subx_debug file1.subx file2.subx ... # generating a.elf + $ ./bootstrap --trace run a.elf arg1 arg2 + saving trace to 'last_run' ``` The ability to generate a trace is the essential reason for the existence of `bootstrap run` mode. It gives far better visibility into program internals than running natively. -- As a further refinement, it is possible to render label names in the trace - by adding a second flag to the `bootstrap translate` command: - - ``` - $ ./bootstrap --debug translate input.subx -o binary - $ ./bootstrap --trace run binary arg1 arg2 2>trace - ``` - - `bootstrap --debug translate` emits a mapping from label to address in a file - called `labels`. `bootstrap --trace run` reads in the `labels` file if - it exists and prints out any matching label name as it traces each instruction - executed. - - Here's a sample of what a trace looks like, with a few boxes highlighted: + Here's a sample of the contents of `last_run`, with a few boxes highlighted: <img alt='trace example' src='html/trace.png'> @@ -60,10 +48,10 @@ rudimentary but hopefully still workable toolkit: address `0x0900005e` maps to label `$loop` and presumably marks the start of some loop. Function names get similar `run: == label` lines. -- One trick when emitting traces with labels: +- One quick trick when scanning a trace for the first time: ``` - $ grep label trace + $ grep label last_run ``` This is useful for quickly showing you the control flow for the run, and the @@ -115,11 +103,21 @@ rudimentary but hopefully still workable toolkit: `./translate_subx_debug`, and then running: ``` - ./bootstrap --trace --dump run a.elf test 2>&1 |grep 'label test' + grep 'label test-' |tail ``` Just read out the last test printed out before the segfault. + Even outside of tests, I can often quickly debug an error just by scanning + the end of a trace for labels: + + ``` + $ grep label last_run |tail + ``` + + Knowing _where_ the error occurred is often enough to put me on the right + track to debugging an error. + Hopefully these hints are enough to get you started. The main thing to remember is to not be afraid of modifying the sources. A good debugging session gets into a nice rhythm of generating a trace, staring at it for a |