[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, 15 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.fortran/function-calls.exp b/gdb/testsuite/gdb.fortran/function-calls.exp
index a14cfae..00036d9 100644
--- a/gdb/testsuite/gdb.fortran/function-calls.exp
+++ b/gdb/testsuite/gdb.fortran/function-calls.exp
@@ -24,6 +24,21 @@ if {[prepare_for_testing ${testfile}.exp ${testfile} ${srcfile} {debug f90}]} {
     return -1
 }
 
+with_complaints 5 {
+    set cmd "maint expand-symtabs $srcfile"
+    set cmd_regexp [string_to_regexp $cmd]
+    set re_kfail [concat "During symbol reading:" \
+		      " unable to find array range"]
+    gdb_test_multiple $cmd "no complaints in srcfile" {
+	-re -wrap "$re_kfail.*" {
+	    kfail symtab/27388 $gdb_test_name
+	}
+        -re "^$cmd_regexp\r\n$gdb_prompt $" {
+	    pass $gdb_test_name
+	}
+    }
+}
+
 if {![runto [gdb_get_line_number "post_init"]]} then {
     perror "couldn't run to breakpoint post_init"
     continue