libdrgn: dwarf_info: expand unknown DWARF expression opcode

Include the opcode name if known, and add the bug report link like we do
for unknown relocation types. This might give us some idea of how to
prioritize #321.

Signed-off-by: Omar Sandoval <[email protected]>

libdrgn/dwarf_constants.c

@@ -8,6 +8,13 @@
 
 #define X(name, _) if (value == name) return #name;
 
+const char *dw_op_str(int value, char buf[static DW_OP_STR_BUF_LEN])
+{
+	DW_OP_DEFINITIONS
+	snprintf(buf, DW_OP_STR_BUF_LEN, DW_OP_STR_UNKNOWN_FORMAT, value);
+	return buf;
+}
+
 const char *dw_tag_str(int value, char buf[static DW_TAG_STR_BUF_LEN])
 {
 	DW_TAG_DEFINITIONS

libdrgn/dwarf_constants.h

@@ -963,6 +963,15 @@ enum { DW_MACRO_DEFINITIONS };
 	X(DW_OP_PGI_omp_thread_num, 0xf8) \
 	X(DW_OP_hi_user, 0xff)
 enum { DW_OP_DEFINITIONS };
+#define DW_OP_STR_UNKNOWN_FORMAT "DW_OP_<0x%x>"
+#define DW_OP_STR_BUF_LEN (sizeof(DW_OP_STR_UNKNOWN_FORMAT) - 2 + 2 * sizeof(int))
+/**
+ * Get the name of a `DW_OP` value.
+ *
+ * @return Static string if the value is known or @p buf if the value is
+ * unknown.
+ */
+const char *dw_op_str(int value, char buf[static DW_OP_STR_BUF_LEN]);
 
 #define DW_ORD_DEFINITIONS \
 	X(DW_ORD_row_major, 0x0) \

libdrgn/dwarf_info.c

@@ -3774,9 +3774,14 @@ drgn_eval_dwarf_expression(struct drgn_dwarf_expression_context *ctx,
 		 *   DW_OP_xderef_size, DW_OP_xderef_type.
 		 */
 		default:
+		{
+			char op_buf[DW_OP_STR_BUF_LEN];
 			return binary_buffer_error(&ctx->bb,
-						   "unknown DWARF expression opcode %#" PRIx8,
-						   opcode);
+						   "unknown DWARF expression opcode %s; "
+						   "please report this to %s",
+						   dw_op_str(opcode, op_buf),
+						   PACKAGE_BUGREPORT);
+		}
 		}
 	}
 

scripts/gen_dwarf_constants.py

@@ -121,7 +121,7 @@ def insert_after(
     return result
 
 
-_DWARF_CONSTANTS_WANT_STR = {"DW_TAG"}
+_DWARF_CONSTANTS_WANT_STR = {"DW_OP", "DW_TAG"}
 
 
 def gen_dwarf_constants_h(