[WebAssembly] libObject: Don't include the name the size of custom sections

[sbc100]

Summary

lld change: https://reviews.llvm.org/D45580

[yurydelendik]

Looks good to me. I would also add error check to ensure that name fits into the section.

lib/Object/WasmObjectFile.cpp

184

It will be nice to add an error check to see if Size < Ptr - NameStart

[sbc100]

lib/Object/WasmObjectFile.cpp

184

I generaly we don't yes handle that kind of malformedness gracefully. Probably we could want to change all the uses of Ptr (such as the argument to readString) to contain the end ptr too. That is probably separate change.

[sbc100]

• update tests

lib/Object/WasmObjectFile.cpp

static Error readSection(WasmSection &Section, const uint8_t *&Ptr,
   Section.Type = readUint8(Ptr);
   uint32_t Size = readVaruint32(Ptr);
   if (Size == 0)
     return make_error<StringError>("Zero length section",
                                    object_error::parse_failed);
   if (Ptr + Size > Eof)
     return make_error<StringError>("Section too large",
                                    object_error::parse_failed);
+  if (Section.Type == wasm::WASM_SEC_CUSTOM) {
+    const uint8_t *NameStart = Ptr;
+    Section.Name = readString(Ptr);
+    Size -= Ptr - NameStart;
+  }
   Section.Content = ArrayRef<uint8_t>(Ptr, Size);
   Ptr += Size;
   return Error::success();
 }
 
 WasmObjectFile::WasmObjectFile(MemoryBufferRef Buffer, Error &Err)
     : ObjectFile(Binary::ID_Wasm, Buffer) {
   ErrorAsOutParameter ErrAsOutParam(&Err);
Error WasmObjectFile::parseRelocSection(StringRef Name, const uint8_t *Ptr,
   if (Ptr != End)
     return make_error<GenericBinaryError>("Reloc section ended prematurely",
                                           object_error::parse_failed);
   return Error::success();
 }
 
 Error WasmObjectFile::parseCustomSection(WasmSection &Sec,
                                          const uint8_t *Ptr, const uint8_t *End) {
-  Sec.Name = readString(Ptr);
   if (Sec.Name == "name") {
     if (Error Err = parseNameSection(Ptr, End))
       return Err;
   } else if (Sec.Name == "linking") {
     if (Error Err = parseLinkingSection(Ptr, End))
       return Err;
   } else if (Sec.Name.startswith("reloc.")) {
     if (Error Err = parseRelocSection(Sec.Name, Ptr, End))

test/MC/WebAssembly/custom-sections.ll

 ; RUN: llc -filetype=obj %s -o - | llvm-readobj -s | FileCheck %s
 
 ; Test the mechanism for defining user custom sections.
 
 target triple = "wasm32-unknown-unknown-wasm"
 
 !0 = !{ !"red", !"foo" }
 !1 = !{ !"green", !"bar" }
 !2 = !{ !"green", !"qux" }
 !wasm.custom_sections = !{ !0, !1, !2 }
 
 ; CHECK:  Section {
 ; CHECK:    Type: CUSTOM (0x0)
-; CHECK:    Size: 7
+; CHECK:    Size: 3
 ; CHECK:    Offset: 72
 ; CHECK:    Name: red
 ; CHECK:  }
 ; CHECK:  Section {
 ; CHECK:    Type: CUSTOM (0x0)
-; CHECK:    Size: 12
+; CHECK:    Size: 6
 ; CHECK:    Offset: 85
 ; CHECK:    Name: green
 ; CHECK:  }

test/ObjectYAML/wasm/custom_section.yaml

 # RUN: yaml2obj %s | obj2yaml | FileCheck %s
 --- !WASM
 FileHeader:
   Version:         0x00000001
 Sections:
   - Type:            CUSTOM
     Name:            foo
-    Payload:         03666F6F0401020304
+    Payload:         '0401020304'
 ...
 # CHECK: --- !WASM
 # CHECK: FileHeader:
 # CHECK:   Version:           0x00000001
 # CHECK: Sections:
 # CHECK:  - Type:            CUSTOM
 # CHECK:    Name:            foo
-# CHECK:    Payload:         03666F6F0401020304
+# CHECK:    Payload:         '0401020304'
 # CHECK: ...

test/tools/llvm-objdump/wasm.txt

 # RUN: llvm-objdump -h %p/Inputs/trivial.obj.wasm | FileCheck %s
 
 # CHECK:      Sections:
 # CHECK-NEXT: Idx Name          Size      Address          Type
 # CHECK-NEXT:  0 TYPE          0000000e 0000000000000000
 # CHECK-NEXT:  1 IMPORT        0000005d 0000000000000000
 # CHECK-NEXT:  2 FUNCTION      00000002 0000000000000000
 # CHECK-NEXT:  3 CODE          00000019 0000000000000000 TEXT
 # CHECK-NEXT:  4 DATA          0000001c 0000000000000000 DATA
-# CHECK-NEXT:  5 linking       00000055 0000000000000000
-# CHECK-NEXT:  6 reloc.CODE    00000017 0000000000000000
+# CHECK-NEXT:  5 linking       0000004d 0000000000000000
+# CHECK-NEXT:  6 reloc.CODE    0000000c 0000000000000000
 
 # RUN: llvm-objdump -p %p/Inputs/trivial.obj.wasm | FileCheck %s -check-prefix CHECK-HEADER
 
 # CHECK-HEADER: Program Header:
 # CHECK-HEADER: Version: 0x1
 
 # RUN: llvm-objdump -s --section=CODE %p/Inputs/trivial.obj.wasm | FileCheck %s -check-prefix CHECK-SECTIONS
 
 # CHECK-SECTIONS: Contents of section CODE:
 # CHECK-SECTIONS: 0000 01170041 80808080 00108080 8080001a  ...A............
 # CHECK-SECTIONS: 0010 10818080 80004100 0b                 ......A..

test/tools/llvm-readobj/sections.test

 WASM-NEXT:         Name: .rodata..L.str
 WASM-NEXT:         Size: 13
 WASM-NEXT:         Offset: 0
 WASM-NEXT:       }
 WASM-NEXT:     ]
 WASM-NEXT:   }
 WASM-NEXT:   Section {
 WASM-NEXT:     Type: CUSTOM (0x0)
-WASM-NEXT:     Size: 65
+WASM-NEXT:     Size: 57
 WASM-NEXT:     Offset: 191
 WASM-NEXT:     Name: linking
 WASM-NEXT:   }
 WASM-NEXT:   Section {
 WASM-NEXT:     Type: CUSTOM (0x0)
-WASM-NEXT:     Size: 23
+WASM-NEXT:     Size: 12
 WASM-NEXT:     Offset: 262
 WASM-NEXT:     Name: reloc.CODE
 WASM-NEXT:   }
 WASM-NEXT: ]

tools/yaml2obj/yaml2wasm.cpp

int WasmWriter::writeSectionContent(raw_ostream &OS,
                                     WasmYAML::CustomSection &Section) {
   if (auto S = dyn_cast<WasmYAML::NameSection>(&Section)) {
     if (auto Err = writeSectionContent(OS, *S))
       return Err;
   } else if (auto S = dyn_cast<WasmYAML::LinkingSection>(&Section)) {
     if (auto Err = writeSectionContent(OS, *S))
       return Err;
   } else {
+    writeStringRef(Section.Name, OS);
     Section.Payload.writeAsBinary(OS);
   }
   return 0;
 }
 
 int WasmWriter::writeSectionContent(raw_ostream &OS,
                                     WasmYAML::TypeSection &Section) {
   encodeULEB128(Section.Signatures.size(), OS);