[gdb/testsuite] Add REMOTE_TARGET_USERNAME in remote-gdbserver-on-localhost.exp

As reported here
( https://sourceware.org/pipermail/gdb-patches/2022-October/193147.html ) a
number of test-cases fails with a remote target setup, for instance test-case
gdb.base/print-file-var.exp.

So, why don't we see these fails with our remote target boards in
gdb/testsuite/boards, say remote-gdbserver-on-localhost.exp?

The problem is that the target board uses the same machine and user for
both (by-definition-local) build and remote target, and when using absolute
pathnames to refer to files on build, we can access those files on target,
which in a real remote target setup wouldn't be the case: we'd have to
download them to target first, and then the filename would also be different.

For aforementioned test-case, this happens when the name of a shared library is
passed as absolute file name to gcc:
...
gcc ...  -DSHLIB_NAME="$outputs/gdb.base/print-file-var/\
  print-file-var-lib2-hidden0-dlopen1-version_id_main0_c.so"
...

Make these problems visible with remote-gdbserver-on-localhost.exp by
adding an option to specify a test account (still on the same machine)
using REMOTE_TARGET_USERNAME.

We make sure by restricting file permissions, that the test account cannot see
the build files on the $USER account, and that the $USER account cannot see
the target files on the test account.

And so we can reproduce the reported fails:
...
$ cd build/gdb
$ tc="gdb.base/print-file-var.exp"
$ tb="--target_board remote-gdbserver-on-localhost"
$ tbu="REMOTE_TARGET_USERNAME=remote-target"
$ make check RUNTESTFLAGS="$tb $tbu $tc"
   ...
FAIL: gdb.base/print-file-var.exp: lang=c: hidden=0: dlopen=1: \
  version_id_main=0: continue to STOP marker
...

Tested on x86_64-linux.

Reported-by: Ivan Tetyushkin <ivan.tetyushkin@syntacore.com>

1 files changed, 27 insertions, 2 deletions

diff --git a/gdb/testsuite/boards/remote-gdbserver-on-localhost.exp b/gdb/testsuite/boards/remote-gdbserver-on-localhost.exp
index dacbbfb..931fba7 100644
--- a/gdb/testsuite/boards/remote-gdbserver-on-localhost.exp
+++ b/gdb/testsuite/boards/remote-gdbserver-on-localhost.exp
@@ -18,7 +18,8 @@
 #
 # To use this file:
 # bash$ cd ${build_dir}/gdb
-# bash$ make check RUNTESTFLAGS="--target_board=remote-gdbserver-on-localhost"
+# bash$ make check RUNTESTFLAGS="--target_board=remote-gdbserver-on-localhost
+#   [ REMOTE_TARGET_USERNAME=<remote_target_username> ]"
 
 load_generic_config "gdbserver"
 load_board_description "gdbserver-base"
@@ -29,9 +30,33 @@ load_board_description "gdbserver-base"
 set_board_info rcp_prog "/usr/bin/scp"
 set_board_info rsh_prog "/usr/bin/ssh"
 set_board_info protocol standard
-set_board_info username $env(USER)
+if { [info exists REMOTE_TARGET_USERNAME] } {
+    set_board_info username $REMOTE_TARGET_USERNAME
+} else {
+    set_board_info username $env(USER)
+}
 set_board_info hostname localhost
 
+# Handle separate test account.
+if { [board_info $board username] != $env(USER) } {
+    # We're pretending that some local user account is remote target.
+    # Make things a bit more realistic by restricting file permissions.
+
+    # Make sure remote target can't see files on build.  Note that we're
+    # currently using $objdir/output instead of $objdir because of gdbserver
+    # being accessed on the target using $objdir/../../gdbserver/gdbserver.
+    remote_exec build "chmod go-rx $objdir/outputs"
+
+    # Make sure build can't see files on remote target.  We can't use
+    # remote_exec target, because we're in the middle of parsing the
+    # target board.
+    remote_exec build \
+	"[board_info $board rsh_prog] \
+		     -l [board_info $board username] \
+			[board_info $board hostname] \
+	chmod go-rx ."
+}
+
 proc ${board}_spawn { board cmd } {
     global board_info