[PATCH][gdb/symtab] Recognize .gdb_index symbol table with empty entries as empty

[Tom de Vries <tdevries@suse.de>]

Hi,

When reading a .gdb_index that contains a non-empty symbol table with only
empty entries, gdb doesn't recognize it as empty.

Fix this by recognizing that the constant pool is empty, and then setting the
symbol table to empty.

Tested on x86_64-linux.

Any comments?

I don't see the need to propagate to gdb-11-branch, but perhaps I'm wrong there?

Thanks,
- Tom

[gdb/symtab] Recognize .gdb_index symbol table with empty entries as empty

gdb/ChangeLog:

2021-08-01  Tom de Vries  <tdevries@suse.de>

	PR symtab/28159
	* dwarf2/read.c (read_gdb_index_from_buffer): Handle symbol table
	filled with empty entries.

gdb/testsuite/ChangeLog:

2021-08-01  Tom de Vries  <tdevries@suse.de>

	PR symtab/28159
	* gdb.dwarf2/dw2-zero-range.exp: Remove kfail.

---
 gdb/dwarf2/read.c                           |  7 +++++++
 gdb/testsuite/gdb.dwarf2/dw2-zero-range.exp | 22 ++--------------------
 2 files changed, 9 insertions(+), 20 deletions(-)

diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index de84c47b626..a937fbef1cc 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -2777,6 +2777,13 @@ to use the section anyway."),
   ++i;
   map->constant_pool = buffer.slice (metadata[i]);
 
+  if (map->constant_pool.empty () && !map->symbol_table.empty ())
+    {
+      map->symbol_table
+	= offset_view (gdb::array_view<const gdb_byte> (symbol_table,
+							symbol_table));
+    }
+
   return 1;
 }
 
diff --git a/gdb/testsuite/gdb.dwarf2/dw2-zero-range.exp b/gdb/testsuite/gdb.dwarf2/dw2-zero-range.exp
index 7b46c93d9b5..c3ae7537346 100644
--- a/gdb/testsuite/gdb.dwarf2/dw2-zero-range.exp
+++ b/gdb/testsuite/gdb.dwarf2/dw2-zero-range.exp
@@ -148,16 +148,7 @@ foreach_with_prefix ranges_sect {ranges rnglists} {
 	    }
 	}
 
-	if { $have_complaint } {
-	    pass $test
-	} else {
-	    set index [have_index $lib1]
-	    if { $index == "gdb_index" } {
-		kfail symtab/28159 $test
-	    } else {
-		fail $test
-	    }
-	}
+	gdb_assert { $have_complaint } $test
     }
 
     if { ! $readnow_p } {
@@ -173,16 +164,7 @@ foreach_with_prefix ranges_sect {ranges rnglists} {
 	gdb_load $lib1
 	set test "Zero address complaint - unrelocated - psymtab"
 	set have_complaint [regexp $re.* $gdb_file_cmd_msg]
-	if { $have_complaint } {
-	    pass $test
-	} else {
-	    set index [have_index $lib1]
-	    if { $index == "gdb_index" } {
-		kfail symtab/28159 $test
-	    } else {
-		fail $test
-	    }
-	}
+	gdb_assert { $have_complaint } $test
     }
 
     if { ! $readnow_p } {