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.

Signed-off-by: Omar Sandoval <osandov@osandov.com>

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(