Avoid undefined behavior in expression dumping

-fsanitize=undefined pointed out undefined behavior in
dump_raw_expression like:

    runtime error: load of value 2887952, which is not a valid value for type 'exp_opcode'

dump_raw_expression will try to print the opcode for each element of
the expression, even when it is not valid.  To allow this, but have it
avoid undefined behavior, this patch sets the underlying type of enum
exp_opcode, and arranges for op_name to handle invalid opcodes more
nicely.

Before this patch, debug-expr.exp shows:

Dump of expression @ 0x60f000007750, before conversion to prefix form:
	Language c, 8 elements, 16 bytes each.
	Index                Opcode         Hex Value  String Value
	    0               OP_TYPE  89  Y...............
   <unknown 3851920>  107820862850704  ..:..b..........
	    2               OP_TYPE  89  Y...............
	    3          OP_VAR_VALUE  40  (...............
	    4     <unknown 2807568>  107820861806352  ..*..b..........
	    5     <unknown 2806368>  107820861805152  `.*..b..........
	    6          OP_VAR_VALUE  40  (...............
	    7      UNOP_MEMVAL_TYPE  57  9...............

Afterward, the output is:

Dump of expression @ 0x4820f90, before conversion to prefix form:
	Language c, 8 elements, 16 bytes each.
	Index                Opcode         Hex Value  String Value
	    0               OP_TYPE  89  Y...............
	    1   unknown opcode: 176  75444400  .0..............
	    2               OP_TYPE  89  Y...............
	    3          OP_VAR_VALUE  40  (...............
	    4               OP_BOOL  74616912  P.r.............
	    5   unknown opcode: 128  74615680  ..r.............
	    6          OP_VAR_VALUE  40  (...............
	    7      UNOP_MEMVAL_TYPE  57  9...............

gdb/ChangeLog
2018-10-03  Tom Tromey  <tom@tromey.com>

	* expression.h (enum exp_opcode): Use uint8_t as base type.
	* expprint.c (op_name): Handle invalid opcodes.

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 1a3cc6c30a2d443fe5f19aae31e7b71fcb586b03..8fd128ac6feb5a3e37a98d3076ef33c497dca93a 100644 (file)
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,8 @@
+2018-10-03  Tom Tromey  <tom@tromey.com>
+
+       * expression.h (enum exp_opcode): Use uint8_t as base type.
+       * expprint.c (op_name): Handle invalid opcodes.
+
 2018-10-03  Tom Tromey  <tom@tromey.com>
 
        * parse.c (prefixify_expression): Add assert.

diff --git a/gdb/expprint.c b/gdb/expprint.c
index d6ed41253ed86e6d9870142f7ea16ff51611f226..e87b3b709b90b79d0876c7305a01e3961a8f1e9b 100644 (file)
--- a/gdb/expprint.c
+++ b/gdb/expprint.c
@@ -687,6 +687,13 @@ static int dump_subexp_body (struct expression *exp, struct ui_file *, int);
 const char *
 op_name (struct expression *exp, enum exp_opcode opcode)
 {
+  if (opcode >= OP_UNUSED_LAST)
+    {
+      char *cell = get_print_cell ();
+      xsnprintf (cell, PRINT_CELL_SIZE, "unknown opcode: %u",
+                unsigned (opcode));
+      return cell;
+    }
   return exp->language_defn->la_exp_desc->op_name (opcode);
 }
 

diff --git a/gdb/expression.h b/gdb/expression.h
index bc7625f98427fb3168c2e00053ab947ef8303d55..a5cb4c678e73cbb897a84c83141ef28b5cc148ab 100644 (file)
--- a/gdb/expression.h
+++ b/gdb/expression.h
@@ -39,7 +39,7 @@
    and skip that many.  Strings, like numbers, are indicated
    by the preceding opcode.  */
 
-enum exp_opcode
+enum exp_opcode : uint8_t
   {
 #define OP(name) name ,