Avoid buffer overflow in value_x_unop

Commit 6b1747cd1 ("invoke_xmethod & array_view") contains this change:

-  argvec = (struct value **) alloca (sizeof (struct value *) * 4);
+  value *argvec_storage[3];
+  gdb::array_view<value *> argvec = argvec_storage;

However, value_x_unop still does:

      argvec[2] = value_from_longest (builtin_type (gdbarch)->builtin_int, 0);
      argvec[3] = 0;

This triggers an error with -fsanitize=address from userdef.exp:

ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7ffdcf185068 at pc 0x000000e4f912 bp 0x7ffdcf184d80 sp 0x7ffdcf184d70
WRITE of size 8 at 0x7ffdcf185068 thread T0
    #0 0xe4f911 in value_x_unop(value*, exp_opcode, noside) ../../binutils-gdb/gdb/valarith.c:557
[...]

I think the two assignments to argvec[3] should just be removed, and
that this was intended in the earlier patch but just missed.

This passes userdef.exp with -fsanitize=address.

gdb/ChangeLog
2018-11-29  Tom Tromey  <tom@tromey.com>

	* valarith.c (value_x_unop): Don't set argvec[3].

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 1c714dd..70d4c06 100644 (file)
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,7 @@
+2018-11-29  Tom Tromey  <tom@tromey.com>
+
+       * valarith.c (value_x_unop): Don't set argvec[3].
+
 2018-11-26  Simon Marchi  <simon.marchi@ericsson.com>
 
        PR gdb/23917

diff --git a/gdb/valarith.c b/gdb/valarith.c
index 3a59ada..66cd904 100644 (file)
--- a/gdb/valarith.c
+++ b/gdb/valarith.c
@@ -554,13 +554,11 @@ value_x_unop (struct value *arg1, enum exp_opcode op, enum noside noside)
     case UNOP_POSTINCREMENT:
       strcpy (ptr, "++");
       argvec[2] = value_from_longest (builtin_type (gdbarch)->builtin_int, 0);
-      argvec[3] = 0;
       nargs ++;
       break;
     case UNOP_POSTDECREMENT:
       strcpy (ptr, "--");
       argvec[2] = value_from_longest (builtin_type (gdbarch)->builtin_int, 0);
-      argvec[3] = 0;
       nargs ++;
       break;
     case UNOP_LOGICAL_NOT: