[llvm-objcopy] Fix --section-add when section contain empty bytes

Implicit cast between char* and StringRef when writing sections.

Reproduce:
```
$> llvm-objcopy --dump-section=name=name.data out.wasm
$> llvm-objcopy --remove-section=name out.wasm out_no_name.wasm
$> llvm-objcopy --add-section=name=name.data out_no_name.wasm out_new_name.wasm

# With wasm-objdump -h we can see that the name section is not totally copied in the new wasm file (if it actually contain empty bytes)

```

Reviewed By: dschuff

Differential Revision: https://reviews.llvm.org/D139210

1 files changed, 4 insertions, 2 deletions

diff --git a/llvm/lib/ObjCopy/wasm/WasmObjcopy.cpp b/llvm/lib/ObjCopy/wasm/WasmObjcopy.cpp
index 6877cd6..19f10bf 100644
--- a/llvm/lib/ObjCopy/wasm/WasmObjcopy.cpp
+++ b/llvm/lib/ObjCopy/wasm/WasmObjcopy.cpp
@@ -126,9 +126,11 @@ static Error handleArgs(const CommonConfig &Config, Object &Obj) {
     Sec.SectionType = llvm::wasm::WASM_SEC_CUSTOM;
     Sec.Name = NewSection.SectionName;
 
+    llvm::StringRef InputData =
+        llvm::StringRef(NewSection.SectionData->getBufferStart(),
+                        NewSection.SectionData->getBufferSize());
     std::unique_ptr<MemoryBuffer> BufferCopy = MemoryBuffer::getMemBufferCopy(
-        NewSection.SectionData->getBufferStart(),
-        NewSection.SectionData->getBufferIdentifier());
+        InputData, NewSection.SectionData->getBufferIdentifier());
     Sec.Contents = makeArrayRef<uint8_t>(
         reinterpret_cast<const uint8_t *>(BufferCopy->getBufferStart()),
         BufferCopy->getBufferSize());