[Objcopy][Wasm] Allow selecting known sections by name

Currently, only custom sections can be selected by operations that use section
names, because only custom sections have explicit names (whereas known sections
have names defined by the spec and only use their indices in the binary format).
This CL makes objdopy use the spec-defined names for these sections, allowing
them to be used in operations such as dumping and removal.

This is a prerequisite for fixing
https://github.com/emscripten-core/emscripten/issues/13084

Differential Revision: https://reviews.llvm.org/D126509

llvm/lib/ObjCopy/wasm/WasmReader.cpp

@@ -24,6 +24,15 @@ Expected<std::unique_ptr<Object>> Reader::create() const {
     const WasmSection &WS = WasmObj.getWasmSection(Sec);
     Obj->Sections.push_back(
         {static_cast<uint8_t>(WS.Type), WS.Name, WS.Content});
+    // Give known sections standard names to allow them to be selected.
+    Section &ReaderSec = Obj->Sections.back();
+    if (ReaderSec.SectionType > WASM_SEC_CUSTOM &&
+        ReaderSec.SectionType <= WASM_SEC_TAG)
+      ReaderSec.Name = sectionTypeToString(ReaderSec.SectionType);
+    // If the section type is CUSTOM, it has a name already. If it's a new type
+    // of section that we don't explicitly handle here, it will have an empty
+    // name and objcopy won't be able to select it by name (e.g. for removal
+    // or dumping) but it will still be valid and able to be copied.
   }
   return std::move(Obj);
 }

llvm/test/tools/llvm-objcopy/wasm/dump-section.test

@@ -13,6 +13,14 @@
 # NONEXISTENT: section 'nonexistent' not found
 # DIROUT: error: {{.*}}/bar': [[MSG]]
 
+## Test dumping the type section (a known section).
+# RUN: llvm-objcopy --dump-section=TYPE=%t.sec %t
+# RUN: od -t x1 %t.sec | FileCheck %s --check-prefix=TYPESEC
+
+## Raw contents of the type section.
+# TYPESEC: 000000 01 60 01 7f 01 7d
+# TYPESEC: 000006
+
 ## Check that dumping and removing a section works in the same invocation
 # RUN: llvm-objcopy --dump-section=producers=%t.sec --remove-section=producers %t %t2
 # RUN: od -t x1 %t.sec | FileCheck %s

llvm/test/tools/llvm-objcopy/wasm/only-keep-debug.test

@@ -8,7 +8,13 @@
 # RUN: llvm-strip --only-keep-debug --keep-section=foo %t
 # RUN: obj2yaml %t | FileCheck --implicit-check-not=Name --check-prefix=CHECK --check-prefix=KEEP %s
 
+## Test that keep-section overrides only-keep-debug, even for known sections.
+# RUN: yaml2obj %s -o %t
+# RUN: llvm-strip --only-keep-debug --keep-section=TYPE %t
+# RUN: obj2yaml %t | FileCheck --implicit-check-not=Name --check-prefix=CHECK --check-prefix=KEEPTYPE %s
+
 # CHECK:      Sections:
+# KEEPTYPE:       Type: TYPE
 # CHECK:        - Type: CUSTOM
 # CHECK-NEXT:     Name: .debug_info
 # CHECK:        - Type: CUSTOM

llvm/test/tools/llvm-objcopy/wasm/remove-section.test

@@ -8,6 +8,12 @@
 ## Requests to remove nonexistent sections are silently ignored.
 # RUN: llvm-objcopy --remove-section=nonexistent=%t.sec %t 2>&1 | count 0
 
+## Remove the type section.
+# RUN: llvm-objcopy -R TYPE %t %t3
+# RUN: obj2yaml %t3 | FileCheck --check-prefix=REMOVETYPE --implicit-check-not=TYPE %s
+## Check that the producers section is still there.
+# REMOVETYPE: producers
+
 --- !WASM
 FileHeader:
   Version: 0x00000001