From 27c5d11d52192de8980dd179aa2721d2f6add9ea Mon Sep 17 00:00:00 2001
From: Sam Clegg <sbc@chromium.org>
Date: Wed, 23 Mar 2022 22:09:18 +0000
Subject: [PATCH] Allow binary reader to skip function bodies. NFC (#1871)

This is purely a performance optimization for wasm-objdump since it
doesn't always need to decode function bodies.

For a very large wasm file that I was testing this takes the time taken
for `wasm-objdump -h` from 8.6s to 1.5s.
---
 src/binary-reader-objdump.cc      |  2 ++
 src/binary-reader.cc              |  6 +++++-
 src/binary-reader.h               |  1 +
 test/binary/bad-opcode-prefix.txt | 12 ++----------
 test/binary/bad-opcode.txt        | 22 ++--------------------
 5 files changed, 12 insertions(+), 31 deletions(-)

diff --git a/src/binary-reader-objdump.cc b/src/binary-reader-objdump.cc
index 9c46f8782..dec861d7e 100644
--- a/src/binary-reader-objdump.cc
+++ b/src/binary-reader-objdump.cc
@@ -2354,6 +2354,7 @@ Result ReadBinaryObjdump(const uint8_t* data,
 
   switch (options->mode) {
     case ObjdumpMode::Prepass: {
+      read_options.skip_function_bodies = true;
       BinaryReaderObjdumpPrepass reader(data, size, options, state);
       return ReadBinary(data, size, &reader, read_options);
     }
@@ -2362,6 +2363,7 @@ Result ReadBinaryObjdump(const uint8_t* data,
       return ReadBinary(data, size, &reader, read_options);
     }
     default: {
+      read_options.skip_function_bodies = true;
       BinaryReaderObjdump reader(data, size, options, state);
       return ReadBinary(data, size, &reader, read_options);
     }
diff --git a/src/binary-reader.cc b/src/binary-reader.cc
index 28f47b649..7650486c0 100644
--- a/src/binary-reader.cc
+++ b/src/binary-reader.cc
@@ -2717,7 +2717,11 @@ Result BinaryReader::ReadCodeSection(Offset section_size) {
       CALLBACK(OnLocalDecl, k, num_local_types, local_type);
     }
 
-    CHECK_RESULT(ReadFunctionBody(end_offset));
+    if (options_.skip_function_bodies) {
+      state_.offset = end_offset;
+    } else {
+      CHECK_RESULT(ReadFunctionBody(end_offset));
+    }
 
     CALLBACK(EndFunctionBody, func_index);
   }
diff --git a/src/binary-reader.h b/src/binary-reader.h
index 4e068ecb4..521fe906a 100644
--- a/src/binary-reader.h
+++ b/src/binary-reader.h
@@ -49,6 +49,7 @@ struct ReadBinaryOptions {
   bool read_debug_names = false;
   bool stop_on_first_error = true;
   bool fail_on_custom_section_error = true;
+  bool skip_function_bodies = false;
 };
 
 // TODO: Move somewhere else?
diff --git a/test/binary/bad-opcode-prefix.txt b/test/binary/bad-opcode-prefix.txt
index 19ecfbcf8..b1d33c46d 100644
--- a/test/binary/bad-opcode-prefix.txt
+++ b/test/binary/bad-opcode-prefix.txt
@@ -1,5 +1,4 @@
-;;; TOOL: run-objdump-gen-wasm
-;;; ERROR: 1
+;;; TOOL: run-gen-wasm-bad
 magic
 version
 section(TYPE) { count[1] function params[0] results[1] i32 }
@@ -13,12 +12,5 @@ section(CODE) {
 }
 (;; STDERR ;;;
 000001a: error: unexpected opcode: 0xfe 0x7f
+000001a: error: unexpected opcode: 0xfe 0x7f
 ;;; STDERR ;;)
-(;; STDOUT ;;;
-
-bad-opcode-prefix.wasm:	file format wasm 0x1
-
-Code Disassembly:
-
-000017 func[0]:
-;;; STDOUT ;;)
diff --git a/test/binary/bad-opcode.txt b/test/binary/bad-opcode.txt
index ac1f6f945..d4f6a67d3 100644
--- a/test/binary/bad-opcode.txt
+++ b/test/binary/bad-opcode.txt
@@ -1,6 +1,4 @@
-;;; TOOL: run-objdump-gen-wasm
-;;; ARGS: -x
-;;; ERROR: 1
+;;; TOOL: run-gen-wasm-bad
 magic
 version
 section(TYPE) { count[1] function params[0] results[1] i32 }
@@ -14,21 +12,5 @@ section(CODE) {
 }
 (;; STDERR ;;;
 0000019: error: unexpected opcode: 0xff
+0000019: error: unexpected opcode: 0xff
 ;;; STDERR ;;)
-(;; STDOUT ;;;
-
-bad-opcode.wasm:	file format wasm 0x1
-
-Section Details:
-
-Type[1]:
- - type[0] () -> i32
-Function[1]:
- - func[0] sig=0
-Code[1]:
- - func[0] size=3
-
-Code Disassembly:
-
-000017 func[0]:
-;;; STDOUT ;;)