[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.

1 files changed, 28 insertions, 0 deletions

diff --git a/gdb/contrib/gdb-add-index.sh b/gdb/contrib/gdb-add-index.sh
index 2ac3fdd..734110c 100755
--- a/gdb/contrib/gdb-add-index.sh
+++ b/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