[PATCH] Don't crash if parse_definition_macro's 'body' is NULL

[Sergio Durigan Junior <sergiodj@redhat.com>]

Hi,

Ref.: https://bugzilla.redhat.com/show_bug.cgi?id=1708192
      https://bugzilla.redhat.com/show_bug.cgi?id=1708786

Fedora's rpm-build's "debugedit" program will silently corrupt
.debug_macro strings when a binary is compiled with -g3.  Later in the
build phase, gdb-add-index is invoked to extract the DWARF index from
the binary, and GDB will segfault because
dwarf2read.c:parse_definition_macro's 'body' variable is NULL.

This very simple patch is just a safeguard against this scenario; it
is not a fix for the problem (which actually happens on "debugedit",
and which Mark Wielaard is already working on), but at least it makes
GDB not crash on invalid DWARF, which is a plus IMO.

OK for master?

gdb/ChangeLog:
2019-05-10  Sergio Durigan Junior  <sergiodj@redhat.com>

	Ref.: https://bugzilla.redhat.com/show_bug.cgi?id=1708192
	* dwarf2read.c (parse_macro_definition): Check whether 'body' is
	NULL, and complain/return if that's the case.
---
 gdb/ChangeLog    | 6 ++++++
 gdb/dwarf2read.c | 7 +++++++
 2 files changed, 13 insertions(+)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 4da409633a..53a4721cb3 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,9 @@
+2019-05-10  Sergio Durigan Junior  <sergiodj@redhat.com>
+
+	Ref.: https://bugzilla.redhat.com/show_bug.cgi?id=1708192
+	* dwarf2read.c (parse_macro_definition): Check whether 'body' is
+	NULL, and complain/return if that's the case.
+
 2019-05-10  Simon Marchi  <simon.marchi@efficios.com>
 
 	* contrib/cc-with-tweaks.sh: Validate dwz's work.
diff --git a/gdb/dwarf2read.c b/gdb/dwarf2read.c
index b29c089606..e270e7cef3 100644
--- a/gdb/dwarf2read.c
+++ b/gdb/dwarf2read.c
@@ -24161,6 +24161,13 @@ parse_macro_definition (struct macro_source_file *file, int line,
 {
   const char *p;
 
+  if (body == NULL)
+    {
+      complaint (_("macro debug info contains a malformed "
+		   "(null) macro definition"));
+      return;
+    }
+
   /* The body string takes one of two forms.  For object-like macro
      definitions, it should be:
 
-- 
2.17.2