From 63e163f24fe80fe1509527e6ccfcfb9622f5e99e Mon Sep 17 00:00:00 2001 From: Andrew Burgess Date: Wed, 22 Jan 2020 18:21:58 +0000 Subject: gdb: Allow GDB to _not_ load a previous command history This commit aims to give a cleaner mechanism by which the user can prevent GDB from trying to load any previous command history. Currently the user can change the path to the history file, either using a command line flag, or by setting the GDBHISTFILE environment variable, and if the path is set to a non-existent file, then obviously GDB wont load any command history. However, this feels like a bit of a bodge, I'd like to add an official mechanism by which we can disable command history loading. Why would we want to prevent command history loading? The specific use case I have is GDB starting with a CWD that is a network mounted directory, and there is no command history present. Still GDB will access the network in order to check for the file. In my particular use case I'm actually starting a large number of GDB instances in parallel, all in the same network mounted directory, the large number of network accesses looking for this file introduces a noticeable delay at GDB startup. The approach I'm proposing here is a slight adjustment to the current rules for setting up the history filename. Currently, if a user does this, they see an error: (gdb) set history filename Argument required (filename to set it to.). However, if a user does this: $ GDBHISTFILE= gdb --quiet (gdb) set history save on (gdb) q warning: Could not rename -gdb18416~ to : No such file or directory So, we already have a bug in this area. My plan is to allow the empty filename to be accepted, and for this to mean, neither load, nor save the command history. This does mean that we now have two mechanisms to prevent saving the command history: (gdb) set history filename or (gdb) set history save off But the only way to prevent loading the command history is to set the filename to the empty string _before_ you get to a GDB prompt, either using a command line option, or the environment variable. I've updated some of the show commands, for example this session: (gdb) set history filename (gdb) show history filename There is no filename currently set for recording the command history in. (gdb) show history save Saving of the history record on exit is off. (gdb) set history save on (gdb) show history save Saving of the history is disabled due to the value of 'history filename'. (gdb) set history filename /tmp/hist (gdb) show history save Saving of the history record on exit is on. I've updated the manual, and added some tests. gdb/ChangeLog: * NEWS: Mention new behaviour of the history filename. * top.c (write_history_p): Add comment. (show_write_history_p): Add header comment, give a different message when history writing is on, but the history filename is empty. (history_filename): Add comment. (history_filename_empty): New function. (show_history_filename): Add header comment, give a different message when the filename is empty. (init_history): Compare history_filename against nullptr, and only read history if the filename is not empty. (set_history_filename): Add header comment, and only make non-empty filenames absolute. (init_main): Make the filename argument to 'set history filename' optional. gdb/doc/ChangeLog: * gdb.texinfo (Command History): Extend description for GDBHISTFILE and GDBHISTSIZE, add detail about the filename for 'set history filename' being optional. Describe the effect of an empty history filename on 'set history save on'. gdb/testsuite/ChangeLog: * gdb.base/default.exp: Remove test of 'set history filename'. * gdb.base/gdbinit-history.exp: Add tests for setting the history filename to the empty string. * lib/gdb.exp (gdb_init): Unset environment variables GDBHISTFILE and GDBHISTSIZE. Change-Id: Ia586e4311182fac99113b60f11ef8a11fbd5450b --- gdb/NEWS | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'gdb/NEWS') diff --git a/gdb/NEWS b/gdb/NEWS index d3a3605..cbdfcad 100644 --- a/gdb/NEWS +++ b/gdb/NEWS @@ -33,6 +33,12 @@ * TUI windows can now be arranged horizontally. +* The command history filename can now be set to the empty string + either using 'set history filename' or by setting 'GDBHISTFILE=' in + the environment. The effect of setting this filename to the empty + string is that GDB will not try to load any previous command + history. + * New commands set exec-file-mismatch -- Set exec-file-mismatch handling (ask|warn|off). -- cgit v1.1