From 29e59b5c73d779cd7cce6923f8ff97a5c9ac5479 Mon Sep 17 00:00:00 2001
From: Omar Sandoval <osandov@osandov.com>
Date: Thu, 28 Sep 2023 10:45:09 -0700
Subject: [PATCH] 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 <osandov@osandov.com>
---
 libdrgn/dwarf_constants.c      | 7 +++++++
 libdrgn/dwarf_constants.h      | 9 +++++++++
 libdrgn/dwarf_info.c           | 9 +++++++--
 scripts/gen_dwarf_constants.py | 2 +-
 4 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/libdrgn/dwarf_constants.c b/libdrgn/dwarf_constants.c
index 170bb1fa0..85744b32c 100644
--- a/libdrgn/dwarf_constants.c
+++ b/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
diff --git a/libdrgn/dwarf_constants.h b/libdrgn/dwarf_constants.h
index 83a0abed2..64011f182 100644
--- a/libdrgn/dwarf_constants.h
+++ b/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) \
diff --git a/libdrgn/dwarf_info.c b/libdrgn/dwarf_info.c
index 0afbc43ae..56ab93b99 100644
--- a/libdrgn/dwarf_info.c
+++ b/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);
+		}
 		}
 	}
 
diff --git a/scripts/gen_dwarf_constants.py b/scripts/gen_dwarf_constants.py
index c63b036fc..2fcca21ad 100755
--- a/scripts/gen_dwarf_constants.py
+++ b/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(