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[gdb] Don't set initial language if set manually

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Initially, gdb sets the language to auto/c:
...
$ gdb -q
(gdb) show language
The current source language is "auto; currently c".
...

And after loading a c++ executable, that changes to auto/c++:
...
(gdb) file a.out
Reading symbols from a.out...
(gdb) show language
The current source language is "auto; currently c++".
...

Now consider setting the language manually to c:
...
$ gdb -q
(gdb) show language
The current source language is "auto; currently c".
(gdb) set language c
(gdb) show language
The current source language is "c".
...
The resulting language is manual/c.

Surprisingly, a subsequent load of the c++ executable:
...
(gdb) file a.out
Reading symbols from a.out...
(gdb) show language
The current source language is "c++".
...
gets us language manual/c++.

Loading the file should get us either:
- auto/c++, or
- manual/c.
That is, either the manual setting should be reset by loading, or the manual
setting should persist.

Fix this in the manual/c fashion. [ Though we could make some gdb setting to
choose one or the other. ]

Build and reg-tested on x86_64-linux.

[ Note: In PR23710 comment 1 a cc1 binary is attached for which gdb is slow when
loading and settting a breakpoint on do_rpo_vn:
...
$ time.sh gdb cc1 -batch -ex "b do_rpo_vn"
Breakpoint 1 at 0xd40e30: do_rpo_vn. (2 locations)
maxmem: 1463496
real: 8.88
user: 8.59
system: 0.35
...

This fix enables a speedup by manually setting the language before
loading, reducing executing time with ~17%, due to not having to load the full
symtab containing main:
...
$ time.sh gdb -iex "set language c++" cc1 -batch -ex "b do_rpo_vn"
Breakpoint 1 at 0xd40e30: do_rpo_vn. (2 locations)
maxmem: 1067308
real: 7.36
user: 7.14
system: 0.28
... ]

gdb/ChangeLog:

2020-02-26  Tom de Vries  <tdevries@suse.de>

	PR gdb/25603
	* symfile.c (set_initial_language): Exit-early if
	language_mode == language_mode_manual.

gdb/testsuite/ChangeLog:

2020-02-26  Tom de Vries  <tdevries@suse.de>

	PR gdb/25603
	* gdb.base/persistent-lang.cc: New test.
	* gdb.base/persistent-lang.exp: New file.
This commit is contained in:
Tom de Vries 2020-02-26 14:52:00 +01:00
parent 3312f67c09
commit 0dce428051
5 changed files with 75 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
gdb/ChangeLog
View File

@ -1,3 +1,9 @@
2020-02-26 Tom de Vries <tdevries@suse.de>
PR gdb/25603
* symfile.c (set_initial_language): Exit-early if
language_mode == language_mode_manual.
2020-02-25 Simon Marchi <simon.marchi@polymtl.ca>
* dwarf2/loc.h (dwarf2_read_addr_index): Move...

2
gdb/symfile.c
View File

@ -1681,6 +1681,8 @@ symbol_file_command (const char *args, int from_tty)
void
set_initial_language (void)
{
if (language_mode == language_mode_manual)
return;
enum language lang = main_language ();
if (lang == language_unknown)

6
gdb/testsuite/ChangeLog
View File

@ -1,3 +1,9 @@
2020-02-26 Tom de Vries <tdevries@suse.de>
PR gdb/25603
* gdb.base/persistent-lang.cc: New test.
* gdb.base/persistent-lang.exp: New file.
2020-02-25 Andrew Burgess <andrew.burgess@embecosm.com>
* gdb.fortran/derived-type-striding.exp: Add a new test.

22
gdb/testsuite/gdb.base/persistent-lang.cc Normal file
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@ -0,0 +1,22 @@
/* This testcase is part of GDB, the GNU debugger.
Copyright 2020 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
int
main ()
{
return 0;
}

39
gdb/testsuite/gdb.base/persistent-lang.exp Normal file
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@ -0,0 +1,39 @@
# Copyright 2020 Free Software Foundation, Inc.
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
standard_testfile .cc
if {[build_executable "failed to prepare" $testfile $srcfile debug]} {
return -1
}
clean_restart
set auto_c \
"The current source language is \"auto; currently c\"\."
set manual_c \
"The current source language is \"c\"\."
gdb_test "show language" $auto_c \
"initial language is auto/c"
gdb_test_no_output "set language c"
gdb_test "show language" $manual_c \
"language updated to manual/c after set"
set binfile [standard_output_file ${testfile}]
gdb_load ${binfile}
gdb_test "show language" $manual_c \
"language still manual/c after load"