[PATCH] Make gdb.base/corefile.exp work on terminals with few rows

[Simon Marchi <simon.marchi@polymtl.ca>]

When creating a pty to spawn a subprocess (such as gdb), Expect
copies the settings of its own controlling terminal, including the
number of rows and columns.  If you "make check" on a terminal with just
a few rows (e.g. 4), GDB will paginate before reaching the initial
prompt.  In default_gdb_start, used by most tests, this is already
handled: if we see the pagination prompt, we sent \n to continue.

Philippe reported that gdb.base/corefile.exp didn't work in terminals
with just a few rows.  This test spawns GDB by hand, because it needs to
check things before the initial prompt, which it couldn't do if it used
default_gdb_start.

In this case I think it's not safe to use the same technique as in
default_gdb_start.  Even if we could send a \n if we see a pagination
prompt, we match some multiline regexes in there.  So if a pagination
slips in there, it might make the regexes not match and fail the test.

It's also not possible to use -ex "set height 0" or -iex "set height 0",
it is handled after the introduction text is shown.

The simplest way I found to avoid showing the pagination completely is
to set stty_init (documented in expect's man page) to initialize gdb's
pty with a fixed number of rows.

gdb/testsuite/ChangeLog:

	* gdb.base/corefile.exp: Set stty_init.
---
 gdb/testsuite/gdb.base/corefile.exp | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/gdb/testsuite/gdb.base/corefile.exp b/gdb/testsuite/gdb.base/corefile.exp
index 0053f0594586..c494a875bd31 100644
--- a/gdb/testsuite/gdb.base/corefile.exp
+++ b/gdb/testsuite/gdb.base/corefile.exp
@@ -39,6 +39,10 @@ if {$corefile == ""} {
     return 0
 }
 
+# Initialize GDB's pty with a fixed size, to make sure we avoid pagination
+# during startup.  See "man expect" for details about stty_init.
+set stty_init "rows 25 cols 80"
+
 # Test that we can simply startup with a "-core=$corefile" command line arg
 # and recognize that the core file is a valid, usable core file.
 # To do this, we must shutdown the currently running gdb and restart
-- 
2.20.1