[PATCH] Don't crash if dwarf_decode_macro_bytes'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

During the Fedora RPM build process, 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.

The underlying problem is that Fedora's rpm-build's "debugedit"
program will silently corrupt .debug_macro strings when a binary is
compiled with -g3.  This is being taken care of by Mark Wielaard,
here:

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

However, I still feel it's important to make GDB more resilient
against invalid DWARF input, so I'm proposing this rather simple patch
to catch the situation when "body == NULL" (i.e., it's probably been
corrupted) and issue a complaint.  This is not a real fix to the
problem, of course, but at least GDB is able to finish without
segfaulting.

OK for master?

gdb/ChangeLog:
2019-05-14  Sergio Durigan Junior  <sergiodj@redhat.com>

	Ref.: https://bugzilla.redhat.com/show_bug.cgi?id=1708192
	* dwarf2read.c (dwarf_decode_macro_bytes): Check whether 'body' is
	NULL, and complain if that's the case.
---
 gdb/ChangeLog    |  6 ++++++
 gdb/dwarf2read.c | 18 +++++++++++++++++-
 2 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 19458ccc72..d64ed7df04 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,9 @@
+2019-05-14  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.
+
 2019-05-12  Paul Naert  <paul.naert@polymtl.ca>
 
 	* language.c (language_sniff_from_mangled_name): Fix "langauge"
diff --git a/gdb/dwarf2read.c b/gdb/dwarf2read.c
index b29c089606..63622ba76f 100644
--- a/gdb/dwarf2read.c
+++ b/gdb/dwarf2read.c
@@ -24609,7 +24609,23 @@ dwarf_decode_macro_bytes (struct dwarf2_cu *cu,
 			 line == 0 ? _("zero") : _("non-zero"), line, body);
 
 	    if (is_define)
-	      parse_macro_definition (current_file, line, body);
+	      {
+		if (body != NULL)
+		  parse_macro_definition (current_file, line, body);
+		else
+		  {
+		    /* Fedora's rpm-build's "debugedit" binary
+		       corrupted .debug_macro sections.
+
+		       For more info, see
+		       https://bugzilla.redhat.com/show_bug.cgi?id=1708786 */
+		    complaint (_("debug info gives %s invalid macro definition "
+				 "without body (corrupted?) at line %d"),
+			       at_commandline ? _("command-line")
+			       : _("in-file"),
+			       line == 0 ? _("zero") : _("non-zero"), line);
+		  }
+	      }
 	    else
 	      {
 		gdb_assert (macinfo_type == DW_MACRO_undef
-- 
2.17.2