[PR gdb/27614] gdb-add-index fails on symlinks.

PR 27614 shows that gdb-add-index fails to generate the index when its
argument is a symlink.

The following one liner illustrates the reported problem:

        $ echo 'int main(){}'|gcc -g -x c -;ln -s a.out symlink;gdb-add-index symlink
        gdb-add-index: No index was created for symlink
        gdb-add-index: [Was there no debuginfo? Was there already an index?]
        $ ls -l
        -rwxr-xr-x 1 25712 Mar 19 23:05 a.out*
        -rw------- 1  8277 Mar 19 23:05 a.out.gdb-index
        lrwxrwxrwx 1     5 Mar 19 23:05 symlink -> a.out*

GDB generates the .gdb-index file with a name that matches the name of
the actual program (a.out.gdb-index here), not the symlink that
references it.  The remaining of the script is looking for a file named
after the provided argument (would be 'symlink.gdb-index' in our
example).

gdb/ChangeLog:

	PR gdb/27614
	* contrib/gdb-add-index.sh: Fix when called with a symlink as an
	argument.

gdb/testsuite/ChangeLog:

	PR gdb/27614
	* gdb.dwarf2/gdb-add-index-symlink.exp: New test.

gdb/ChangeLog

@@ -1,3 +1,9 @@
+2021-05-10  Lancelot Six  <lsix@lancelotsix.com>
+
+	PR gdb/27614
+	* contrib/gdb-add-index.sh: Fix when called with a symlink as an
+	argument.
+
 2021-05-10  Simon Marchi  <simon.marchi@polymtl.ca>
 
 	* nat/linux-waitpid.c (status_to_str): Show signal name.

gdb/contrib/gdb-add-index.sh

@@ -37,6 +37,34 @@ fi
 
 file="$1"
 
+if test -L "$file"; then
+    if ! command -v readlink >/dev/null 2>&1; then
+	echo "$myname: 'readlink' missing.  Failed to follow symlink $1." 1>&2
+	exit 1
+    fi
+
+    # Count number of links followed in order to detect loops.
+    count=0
+    while test -L "$file"; do
+	target=$(readlink "$file")
+
+	case "$target" in
+	    /*)
+		file="$target"
+		;;
+	    *)
+		file="$(dirname "$file")/$target"
+		;;
+	esac
+
+	count="$((count + 1))"
+	if test "$count" -gt 10; then
+	    echo "$myname: Detected loop while following link $file"
+	    exit 1
+	fi
+    done
+fi
+
 if test ! -r "$file"; then
     echo "$myname: unable to access: $file" 1>&2
     exit 1

gdb/testsuite/ChangeLog

@@ -1,3 +1,8 @@
+2021-05-10  Lancelot Six  <lsix@lancelotsix.com>
+
+	PR gdb/27614
+	* gdb.dwarf2/gdb-add-index-symlink.exp: New test.
+
 2021-05-10  Andrew Burgess  <andrew.burgess@embecosm.com>
 
 	* gdb.guile/guile.exp: Don't use the source directory as a

gdb/testsuite/gdb.dwarf2/gdb-add-index-symlink.exp

@@ -0,0 +1,47 @@
+# Copyright 2021 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/>.
+
+load_lib dwarf.exp
+
+# This test can only be run on targets which support DWARF-2.
+if {![dwarf2_support]} {
+    return 0
+}
+
+standard_testfile main.c
+
+if { [prepare_for_testing "failed to prepare" "${testfile}" \
+	  [list ${srcfile}]] } {
+    return -1
+}
+
+set symlink [file dirname $binfile]/symlink
+
+if { ![file exists $symlink] } {
+    file link -symbolic $symlink $binfile
+}
+
+if { [ensure_gdb_index $symlink] == -1 } {
+    fail "Unable to call gdb-add-index with a symlink to a symfile"
+    return -1
+}
+
+# Ok, we have a copy of $binfile with an index.
+# Restart gdb and verify the index was used.
+
+clean_restart $symlink
+gdb_test "mt print objfiles ${testfile}" \
+    "(gdb_index|debug_names).*" \
+    "index used"