[gdb/symtab] Ignore DW_LNE_lo_user/DW_LNE_hi_user range

When reading an exec with a .debug_line section containing a vendor-specific
extended opcode, we get:
...
$ gdb -batch -iex "set complaints 10" dw2-vendor-extended-opcode
During symbol reading: mangled .debug_line section
...
and reading of the .debug_line section is abandoned.

The vendor-specific extended opcode should be ignored, as specified in the
DWARF standard (7.1 Vendor Extensibility).  [ FWIW, vendor-specific
standard opcodes are already ignored. ]

Fix this by ignoring all vendor-specific extended opcodes.

Build and tested on x86_64-linux.

gdb/ChangeLog:

2020-08-03  Tom de Vries  <tdevries@suse.de>

	PR symtab/26333
	* dwarf2/read.c (dwarf_decode_lines_1): Ignore
	DW_LNE_lo_user/DW_LNE_hi_user range.

gdb/testsuite/ChangeLog:

2020-08-03  Tom de Vries  <tdevries@suse.de>

	PR symtab/26333
	* lib/dwarf.exp (DW_LNE_user): New proc.
	* gdb.dwarf2/dw2-vendor-extended-opcode.c: New test.
	* gdb.dwarf2/dw2-vendor-extended-opcode.exp: New file.

2 files changed, 113 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.dwarf2/dw2-vendor-extended-opcode.c b/gdb/testsuite/gdb.dwarf2/dw2-vendor-extended-opcode.c
new file mode 100644
index 0000000..97e019b
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/dw2-vendor-extended-opcode.c
@@ -0,0 +1,32 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2020 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/>.  */
+
+void
+foo (void)
+{
+
+}
+
+int
+main()
+{
+  asm ("main_label: .globl main_label");
+  foo ();
+
+  asm ("main_label_2: .globl main_label_2");
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.dwarf2/dw2-vendor-extended-opcode.exp b/gdb/testsuite/gdb.dwarf2/dw2-vendor-extended-opcode.exp
new file mode 100644
index 0000000..92db7ea
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/dw2-vendor-extended-opcode.exp
@@ -0,0 +1,81 @@
+# Copyright 2020 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 and use gas.
+if {![dwarf2_support]} {
+    verbose "Skipping dw2-vendor-extended-opcode test."
+    return 0
+}
+
+# The .c files use __attribute__.
+if [get_compiler_info] {
+    return -1
+}
+if !$gcc_compiled {
+    verbose "Skipping dw2-vendor-extended-opcode test."
+    return 0
+}
+
+standard_testfile dw2-vendor-extended-opcode.c dw2-vendor-extended-opcode-dw.S
+
+set asm_file [standard_output_file $srcfile2]
+Dwarf::assemble $asm_file {
+    declare_labels Llines
+    global srcdir subdir srcfile
+
+    set DW_LNE_lo_usr 0x80
+    set DW_LNE_hi_usr 0xff
+
+    cu {} {
+	compile_unit {
+	    {language @DW_LANG_C}
+	    {name dw2-vendor-extended-opcode.c}
+	    {stmt_list $Llines DW_FORM_sec_offset}
+	} {
+	    subprogram {
+		{external 1 flag}
+		{MACRO_AT_func {main}}
+	    }
+	}
+    }
+
+    lines {version 2} Llines {
+	include_dir "${srcdir}/${subdir}"
+	file_name "$srcfile" 1
+
+	program {
+	    {DW_LNE_set_address main_label}
+	    {line 27}
+	    {DW_LNE_user 1 $DW_LNE_lo_usr}
+	    {DW_LNE_user 2 $DW_LNE_hi_usr}
+	    {DW_LNS_copy}
+
+	    {DW_LNE_set_address main_label_2}
+	    {DW_LNE_end_sequence}
+	}
+    }
+}
+
+if { [prepare_for_testing "failed to prepare" ${testfile} \
+	  [list $srcfile $asm_file] {nodebug}] } {
+    return -1
+}
+
+if ![runto_main] {
+    return -1
+}
+
+gdb_breakpoint "$srcfile:27" message