[gdb/symtab] Fix element type modification in read_array_type

When running test-case gdb.fortran/function-calls.exp with target board
unix/gdb:debug_flags=-gdwarf-5, I run into:
...
(gdb) PASS: gdb.fortran/function-calls.exp: \
  p derived_types_and_module_calls::pass_cart(c)
p derived_types_and_module_calls::pass_cart_nd(c_nd)^M
^M
Program received signal SIGSEGV, Segmentation fault.^M
0x0000000000400f73 in derived_types_and_module_calls::pass_cart_nd \
  (c=<error reading variable: Cannot access memory at address 0xc>) at \
  function-calls.f90:130^M
130             pass_cart_nd = ubound(c%d,1,4)^M
The program being debugged was signaled while in a function called from GDB.^M
GDB has restored the context to what it was before the call.^M
To change this behavior use "set unwindonsignal off".^M
Evaluation of the expression containing the function^M
(derived_types_and_module_calls::pass_cart_nd) will be abandoned.^M
(gdb) FAIL: gdb.fortran/function-calls.exp: p
...

The problem originates in read_array_type, when reading a DW_TAG_array_type
with a dwarf-5 DW_TAG_generic_subrange child.  This is not supported, and the
fallout of this is that rather than constructing a new array type, the code
proceeds to modify the element type.

Fix this conservatively by issuing a complaint and bailing out in
read_array_type when not being able to construct an array type, such that we
have:
...
(gdb) maint expand-symtabs function-calls.f90^M
During symbol reading: unable to find array range \
  - DIE at 0xe1e [in module function-calls]^M
During symbol reading: unable to find array range \
  - DIE at 0xe1e [in module function-calls]^M
(gdb) KFAIL: gdb.fortran/function-calls.exp: no complaints in srcfile \
  (PRMS: symtab/27388)
...

Tested on x86_64-linux.

gdb/ChangeLog:

2021-02-09  Tom de Vries  <tdevries@suse.de>

	PR symtab/27341
	* dwarf2/read.c (read_array_type): Return NULL when not being able to
	construct an array type.  Add assert to ensure that element_type is
	not being modified.

gdb/testsuite/ChangeLog:

2021-02-09  Tom de Vries  <tdevries@suse.de>

	PR symtab/27341
	* lib/gdb.exp (with_complaints): New proc, factored out of ...
	(gdb_load_no_complaints): ... here.
	* gdb.fortran/function-calls.exp: Add test-case.

1 files changed, 33 insertions, 10 deletions

diff --git a/gdb/testsuite/lib/gdb.exp b/gdb/testsuite/lib/gdb.exp
index 53ac9f1..1406b91 100644
--- a/gdb/testsuite/lib/gdb.exp
+++ b/gdb/testsuite/lib/gdb.exp
@@ -5096,11 +5096,11 @@ proc gdb_load { arg } {
 }
 
 #
-# gdb_load_no_complaints -- As gdb_load, but in addition verifies that
-# loading caused no symbol reading complaints.
+# with_complaints -- Execute BODY and set complaints temporary to N for the
+# duration.
 #
-proc gdb_load_no_complaints { arg } {
-    global gdb_prompt gdb_file_cmd_msg decimal
+proc with_complaints { n body } {
+    global decimal
 
     # Save current setting of complaints.
     set save ""
@@ -5112,16 +5112,39 @@ proc gdb_load_no_complaints { arg } {
 	}
     }
 
-    # Fall back to regular gdb_load if we couldn't get the current setting
-    # of complaints.
     if { $save == "" } {
-	return gdb_load $arg
+	perror "Did not manage to set complaints"
+    } else {
+	# Set complaints.
+	gdb_test_no_output "set complaints $n" ""
     }
 
-    # Temporarily set complaint to a small non-zero number.
-    gdb_test_no_output "set complaints 5" ""
+    set code [catch {uplevel 1 $body} result]
+
+    # Restore saved setting of complaints.
+    if { $save != "" } {
+	gdb_test_no_output "set complaints $save" ""
+    }
+
+    if {$code == 1} {
+	global errorInfo errorCode
+	return -code $code -errorinfo $errorInfo -errorcode $errorCode $result
+    } else {
+	return -code $code $result
+    }
+}
+
+#
+# gdb_load_no_complaints -- As gdb_load, but in addition verifies that
+# loading caused no symbol reading complaints.
+#
+proc gdb_load_no_complaints { arg } {
+    global gdb_prompt gdb_file_cmd_msg decimal
 
-    gdb_load $arg
+    # Temporarily set complaint to a small non-zero number.
+    with_complaints 5 {
+	gdb_load $arg
+    }
 
     # Verify that there were no complaints.
     set re "^Reading symbols from \[^\r\n\]*\r\n$gdb_prompt $"