[RFA] Avoid expect's buffer overflow in info-var.exp test.

[Philippe Waroquiers <philippe.waroquiers@skynet.be>]

Once the executable is started, info variables can show thousands
of variables belonging to glibc (see below).

This long list of variables then causes the test to fail, due
to expect's buffer overflow:
  Running /bd/home/philippe/gdb/git/build_binutils-gdb/gdb/testsuite/../../../binutils-gdb/gdb/testsuite/gdb.base/info-var.exp ...
  ERROR: internal buffer is full.
  ERROR: internal buffer is full.
  ERROR: internal buffer is full.

Fix this by running testing 'info variables' without running the
executable.

gdb ./info-var
...
Reading symbols from ./info-var...
(gdb) |info variables|wc
     27      54     971
(gdb) start
Temporary breakpoint 1 at 0x1129: file /bd/home/philippe/gdb/git/build_binutils-gdb/gdb/testsuite/../../../binutils-gdb/gdb/testsuite/gdb.base/info-var-f1.c, line 23.
Starting program: /bd/home/philippe/gdb/git/build_binutils-gdb/gdb/testsuite/outputs/gdb.base/info-var/info-var

Temporary breakpoint 1, main ()
    at /bd/home/philippe/gdb/git/build_binutils-gdb/gdb/testsuite/../../../binutils-gdb/gdb/testsuite/gdb.base/info-var-f1.c:23
23	  return global_var + get_offset() + f1_var;
(gdb) |info variables|wc
   4334   14581  130738
(gdb)

gdb/testsuite/ChangeLog
YYYY-MM-DD  Philippe Waroquiers  <philippe.waroquiers@skynet.be>

	* gdb.base/info-var.exp: Test info variables without running
	to main, to avoid expect's buffer overflow.
---
 gdb/testsuite/gdb.base/info-var.exp | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/gdb/testsuite/gdb.base/info-var.exp b/gdb/testsuite/gdb.base/info-var.exp
index 6dd896d8aa..c9b7485ffb 100644
--- a/gdb/testsuite/gdb.base/info-var.exp
+++ b/gdb/testsuite/gdb.base/info-var.exp
@@ -22,10 +22,9 @@ if {[prepare_for_testing "failed to prepare" \
     return -1
 }
 
-if ![runto_main] then {
-    fail "can't run to main"
-    return 0
-}
+# Note: we do not run to main, as otherwise, the output of info variables
+# can be very long, showing thousands of glibc variables.
+# This long output then causes expect's buffer to overflow.
 
 gdb_test "info variables" \
     [multi_line \
-- 
2.20.1