[WebAssembly][libObject] Avoid re-use of Section object during parsing

The re-use of this struct across iterations of the loop was causing
fields (specifically Name) to be incorrectly shared between multiple
sections.

Differential Revision: https://reviews.llvm.org/D108984

llvm/lib/Object/WasmObjectFile.cpp

@@ -286,9 +286,9 @@ WasmObjectFile::WasmObjectFile(MemoryBufferRef Buffer, Error &Err)
     return;
   }
 
-  WasmSection Sec;
   WasmSectionOrderChecker Checker;
   while (Ctx.Ptr < Ctx.End) {
+    WasmSection Sec;
     if ((Err = readSection(Sec, Ctx, Checker)))
       return;
     if ((Err = parseSection(Sec)))

llvm/test/tools/llvm-objcopy/wasm/basic-only-section.test

@@ -1,32 +1,36 @@
 ## Test --only-section.
 # RUN: yaml2obj %s -o %t
-# RUN: llvm-objcopy --only-section=producers %t %t2
+# RUN: llvm-objcopy --only-section=foo %t %t2
 # RUN: obj2yaml %t2 | FileCheck --implicit-check-not TYPE --implicit-check-not linking %s
 
 ## Test that it's the same with only-section + keep-section (for the same section).
-# RUN: llvm-objcopy --only-section=producers --keep-section=producers %t %t2
+# RUN: llvm-objcopy --only-section=foo --keep-section=foo %t %t2
 # RUN: obj2yaml %t2 | FileCheck --implicit-check-not TYPE --implicit-check-not linking %s
 
 ## Also test that only-section overrides remove-section.
-# RUN: llvm-objcopy --only-section=producers --remove-section=producers %t %t2
+# RUN: llvm-objcopy --only-section=foo --remove-section=foo %t %t2
 # RUN: obj2yaml %t2 | FileCheck --implicit-check-not linking %s
 
-## This file has both known and custom sections. Check that only the producers section is left.
+## This file has both known and custom sections. Check that only the foo section is left.
 # CHECK:      Sections:
 # CHECK-NEXT:   - Type: CUSTOM
-# CHECK-NEXT:     Name: producers
-# CHECK-NEXT:     Tools:
+# CHECK-NEXT:     Name: foo
+# CHECK-NEXT:     Payload: DEADBEEF
+# CHECK-NEXT: ...
 
 ## Test that only-section + keep-section keeps both sections.
-# RUN: llvm-objcopy --only-section=producers --keep-section=linking %t %t2
+# RUN: llvm-objcopy --only-section=foo --keep-section=linking %t %t2
 # RUN: obj2yaml %t2 | FileCheck --implicit-check-not=TYPE --check-prefix=KEEP %s
+# KEEP: Name: foo
 # KEEP: Name: linking
-# KEEP: Name: producers
 
 --- !WASM
 FileHeader:
   Version: 0x00000001
 Sections:
+  - Type: CUSTOM
+    Name: foo
+    Payload: DEADBEEF
   - Type: TYPE
     Signatures:
       - Index: 0
@@ -37,8 +41,3 @@ Sections:
   - Type: CUSTOM
     Name: linking
     Version: 2
-  - Type: CUSTOM
-    Name: producers
-    Tools:
-      - Name:   clang
-        Version: 9.0.0