mdavidsaver
4b03e97d7b
* Add GDB helper script
Pretty printing of some common argument types
Need to add a line to ~/.gdbinit
> add-auto-load-safe-path /path/to/base/checkout/
afterwards verify at GDB shell with
> info auto-load python-scripts
> info pretty-printer
Tested with GDB 16.3 circa Debian 13
Add $rcast(dbCommon) to up-cast
Add $record("name") to lookup record
Add $elln(ELLLIST,#) to index into list
115 lines
2.4 KiB
Markdown
115 lines
2.4 KiB
Markdown
# Debugging with GDB
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Starts a process in [GDB](https://sourceware.org/gdb/current/onlinedocs/gdb.html/):
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```sh
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gdb --args ../../bin/linux-x86_64-debug/myioc ./st.cmd
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```
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Attach to a running process by numeric PID:
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```sh
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gdb --pid=##
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```
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Shorthand if only one instance is running:
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```sh
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gdb --pid=`pgrep myioc`
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```
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## GDB shell Cheat sheet
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Print stack traces of all threads. Optionally with pagination disabled:
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```gdb
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(gdb) set pagination off
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(gdb) thread apply all backtrace
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(gdb) set pagination on
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```
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Note: consider sending or posting this very long output as an attachment file.
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Break when a certain record begins processing:
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```gdb
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(gdb) break dbProcess if $_streq(precord.name, "my:record")
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```
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Break when a `PACT` field changes:
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```gdb
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(gdb) watch -l $record("my:record").pact
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```
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Note: Uses custom `$record()` helper. See below.
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## Helpers
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If the bundled `epics-gdb-helper.py` is [enabled](#helper-enable),
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then a set of pretty printers are registered for some common database types.
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eg. `dbCommon*` will show the record name.
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`DBLINK*` will show the associated record name, and the link target.
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Also, several convenience are available.
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Use `$record()` to lookup a record by name:
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```gdb
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(gdb) print $record("my:record")
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$1 = (calcRecord*)(0x55555562f6f8, "my:record")
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```
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Note: `$record()` may only be called after record allocation during `iocInit()`.
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Use `$rcast()` to up-cast `dbCommon*` to the specific record type:
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```gdb
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(gdb) print precord
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$1 = (dbCommon*)(0x55555562f6f8, "my:record")
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(gdb) print $rcast(precord)
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$2 = (calcRecord*)(0x55555562f6f8, "my:record")
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```
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Use `$elln()` to index into `ELLLIST` linked lists.
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```gdb
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(gdb) print $elln(pdbbase.recordTypeList, 2)
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```
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### Enable (helper-enable)
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To automatically [enable](https://sourceware.org/gdb/current/onlinedocs/gdb.html/Auto_002dloading-safe-path.html),
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add a line to `~/.gdbinit`.
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```
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add-auto-load-safe-path /path/to/base/checkout/
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```
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Or each time run:
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```
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(gdb) source /path/to/base/checkout/modules/database/src/ioc/epics-gdb-helper.py
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```
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Note: Entries in the `safe-path` list may be files (`.so` or `.py`), or directories.
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When a directory is included, sub-directories are also trusted.
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eg. `add-auto-load-safe-path /opt/epics` would also trust a `/opt/epics/lib`.
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Afterwards verify at GDB shell by running:
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```gdb
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(gdb) info auto-load python-scripts
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Loaded Script
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...
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Yes epics-gdb-helper.py
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(gdb) info pretty-printer
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global pretty-printers:
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EPICS
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...
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```
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